We sequenced fragments of two mitochondrial genes (12S and 16S ribosomal RNA) and one nuclear gene (c-mos). These genes were primarily selected because they are the most widely used in phylogenetic studies of Dipsadinae yielding successful results (e.g., Zaher et al. 2009). Consequently, they are the genes with the largest number of available sequences in GenBank for Philodryas and related genera. We generated sequences of these genes from three species of Philodryas: two individuals of P. aestiva, nine of P. trilineata, and 37 of P. patagoniensis. To enrich our dataset, we included sequences of eight additional Philodryas species available on GenBank: P. aestiva (n = 1), P. agassizii (n = 1), P. baroni (n = 1), P. mattogrossensis (n = 1), P. nattereri (n = 1), P. olfersii (n = 1), P. patagoniensis from Brazil (n = 1), and P. psammophidea (n = 1). We also included the same gene fragments of Chlorosoma viridissima and Xenoxybelis argenteus as outgroups (see Table SS1 for voucher information, GenBank accession numbers, and collection localities). Unfortunately, we were unable to include new sequences of species currently unavailable in GenBank (P. arnaldoi, P. erlandi, P. livida, and P. varia), despite their inclusion in two recent phylogenies (Zaher et al. 2019; Arredondo et al. 2020), including new sequences of P. agassizii.

Total genomic DNA was extracted from tissue samples using a saline DNA extraction method based on lithium chloride, following the protocol of Gemmell and Akiyama (1996). Fragments of the 12S rRNA, 16S rRNA, and c-mos genes were amplified independently via polymerase chain reactions (PCR) using the following primers (see Zaher et al. 2009 for details): (1) for 12S rRNA, L1091mod (5’ CAA ACT AGG ATT AGATAC CCT ACT AT 3’) and H1557 (5’ GTA CRC TTA CCWTGT TAC GAC TT 3’); (2) for 16S rRNA, L2510 (5’ CCG ACT GTT TAM CAAAAA CA 3’) and H3056 (5’ CTC CGG TCT GAA CTC AGA TCA CGTRGG 3’); and (3) for c-mos, S77 (5’ CAT GGA CTG GGA TCAGTT ATG 3’) and S78 (5’ CCT TGG GTG TGATTT TCT CAC CT 3’).

The PCR was performed using a Bio-Rad T-1000 thermal cycler. The annealing temperature was 54 °C for the 12S and 16S gene fragments and 56 °C for the c-mos fragment. Amplified products were sequenced in Macrogen Inc. (Seoul, South Korea).

Most specimens used in the morphological analysis are currently housed in the herpetological collections of the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (MACN, Buenos Aires, Argentina) and Museo de La Plata (MLP.JW and MLP.R, Buenos Aires, Argentina). In addition, we examined photographs of key specimens from Natural History Museum (BMNH, London, United Kingdom), Museu de Ciências e Tecnologia da Pontifícia Universidade Católica do Rio Grande do Sul (MCP, Rio Grande do Sul, Brazil) and United States National Museum, Smithsonian Institution (USNM, Washington, United States: lectotype of P. patagoniensis) (File S1). The sampling used for study of morphological characters (such as scale counts, body measurements, and colouration) was substantially larger than that used for other analyses (genetic, hemipenial, cranial osteology, and other morphology traits), resulting in various degrees of freedom among character types (File S1, Table SS2). Morphological comparisons and analyses within Philodryas patagoniensis were based on morphotypes that were highly consistent with different genetic types (haplogroups). Juvenile specimens were identified following Fowler and Salomão (1995), who established the critical snout-vent length thresholds marking the transition to adulthood in males and females of six Philodryas species; in the case of P. patagoniensis, these thresholds are 420 mm in males and 470 mm in females. Sex was determined by making a small incision to check for the presence of hemipenes. Juveniles were sexed when possible, included in scale count and body colouration analyses, and excluded from body measurements. External morphology was assessed through the following body measurement characters: head length (HL) measured to the nearest 0.1 mm, using a digital calliper; snout-vent length (SVL), tail length (TL), and total length (TTL), all measured to the nearest 1 mm by carefully extending the specimens along a fixed ruler. Cephalic and body scale counts followed Dowling (1951) and Giraudo (2001), including formulae for dorsal, infralabial, supralabial, and temporal scales, as well as the number of postocular, preocular, subcaudal, and ventral scales. The raw data collected from scale counts, scale formulae, and external measurements are presented in Table SS2. The colour pattern was described using the 39-colour chart proposed by Yu et al. (2018). The statistical comparison of body measurements was conducted using proportions of each measurement relative to total length, rather than comparing the raw data alone, in order to account for effect of size caused by age of specimens that may exist among individuals in our sample (for details on these widely used morphometric procedures: Baur and Leuenberger 2011). Thus, this procedure was applied to the proportional variables HL/TTL, SVL/TTL, and TL/TTL. Ventral and subcaudal scale numbers, unaffected by total length, were statistically compared as raw data. All comparisons were performed for each combination of morphotype and sex using the Mann-Whitney U-test, implemented in the software PAST v3.04 (Hammer et al. 2001).

Cranial osteology was analysed based on the limited descriptions available for skulls of the genus (Bonino et al. 1987; Lobo and Scrocchi 1994; Di Pietro et al. 2014). Skulls of five specimens of P. patagoniensis and two of P. agassizii used for comparison were prepared following the protocol of Taylor and Van Dyke (1985) (File S1). Bone terminology follows Cundall and Irish (2008). Hemipenes of 10 specimens were prepared using the technique described by Zaher and Prudente (2003), and descriptions follow the terminology proposed by Zaher (1999) (File S1). For genera, species, and higher clade taxonomy, we follow Uetz et al. (2025).

The geographic distribution map of the morphotypes of P. patagoniensis was constructed using QGIS v3.28 software (QGIS Development Team 2024), incorporating the aforementioned museum specimens and supplemented with locality data from citizen science platforms such as iNaturalist (https://www.inaturalist.org; last accessed 26 November 2024) and Ecoregistros (https://www.ecoregistros.org; last accessed 26 November 2024). In the case of citizen science platforms, we only considered records with photographs that allowed for unequivocal classification of the species and morphotype. File S1 provided the complete list of specimens employed for the distribution analysis.

Sequences were aligned using the MUSCLE algorithm in MEGA7 v7.0 (Kumar et al. 2016) and concatenated with SequenceMatrix v1.7.8 (Vaidya et al. 2011). The final matrix comprised 58 terminals and 1161 base pairs (12S with 289 bp, 16S with 379 bp, and c-mos with 493 bp). A haplotype network based on parsimony analysis was constructed using the TCS algorithm (Clement et al. 2000) implemented in PopArt, with each gene alignment of Philodryas patagoniensis analysed separately. The network illustrated geographic relationships among haplotypes, considering their frequencies and geographic origins. Ambiguous connections (loops) in the network were resolved following the method of Crandall and Templeton (1993). Uncorrected genetic p distances between species/linages were calculated using MEGA7 v7.0 (Kumar et al. 2016), excluding positions with gaps and missing data.

We conducted a phylogenetic analysis of Philodryas using a concatenated matrix of the three genes, comprising our sequences and those retrieved from GenBank (1161 bp, 58 terminals). We coded seven external morphological characters related to body measurements and scutellation (four binary and three multistate), five characters concerning the shape and pattern of cephalic scales (three binary and two multistate), and four colour pattern characters (one binary and three multistate), totalling 16 external morphological characters. The states of continuous scutellation characters (i.e., ventrals, subcaudals) were delimited and coded on the basis of the observed discontinuities within the overall variation of a given character. Following this procedure, we selected midpoints within these gaps and defined them as boundaries separating each character state. These were coded following Thomas (1976), Di Pietro et al. (2013), Cacciali et al. (2016a), Rivas et al. (2024), and our observations. Additionally, we included 10 cranial osteological characters involving the nasal, palatine, parabasisphenoid, parietal, prefrontal, premaxilla, and quadrate bones (one multistate and nine binary), coded according to Bonino (1987), Lobo and Scrocchi (1994), and our observations. One binary character concerning hemipenial size was coded following Thomas (1976), Zaher (1999), Cacciali et al. (2016a), and our observations. Furthermore, one biochemical character (toxin type in the venom composition) was included as a multistate character, entirely coded from Tioyama et al. (2023). Detailed descriptions of the morphological characters are provided in File S2, while File S1 contains a list of specimens coded based on personal examination. The 28 morphological characters were combined with the molecular data, and this matrix was used in a total evidence phylogenetic analysis based on the principle of maximum parsimony, as implemented in the software TNT v1.6 (Goloboff et al. 2008; Goloboff and Morales 2023).

The total evidence analysis (1161 base pairs plus 28 morphological characters, and 58 terminals; see matrix in File S3) was performed using the traditional search option, beginning with 100 rounds of Wagner trees. Tree Bisection and Reconnection (TBR) was used as the swapping algorithm, with 10 trees saved per round and trees replaced. Chlorosoma viridissima was designated as outgroup. A strict consensus tree, the absolute Bootstrap support (100 replicates) and Jackknife support (removal probability of 40%, 100 replicates), and the list of synapomorphies for each clade, were obtained using the specific tools of the TNT software. The resulting consensus tree was exported as a tree in which the number of synapomorphies on each branch is represented by varying branch lengths, similar to, but distinct from a phylogram. For this purpose, we used the following script: “ttag = ; blength* n; export > filename;” (where n refers to the number of the tree to be exported, using a filename with the .nex extension). For further details on this and other TNT commands, see Goloboff et al. (2008) and the general software documentation referenced therein.

The parsimony analysis implemented in TCS for each gene alignment separately identified two haplogroups within Philodryas patagoniensis, referred to here as A- and B-haplogroups, each comprising several haplotypes (Fig. 1). Thus, the haplogroups stand out in the networks due to the genetic distances involved (i.e., haplotypes within each group differ by only one or two variable sites, while the haplogroups themselves are separated by more variable sites). Interestingly, the c-mos gene also reveals two haplogroups, although the differences are much less marked than those observed in the mitochondrial genes. Each haplogroup corresponded to a distinctive morphological pattern; thus, we refer to them as morphotypes A and B, respectively. The following sections enumerate and describe the distinguishing characteristics between the two morphotypes to avoid redundancy. Specimens assigned to A-haplogroup (n = 16) are from northern samples (Córdoba, Corrientes, Entre Ríos, and Santa Fe provinces, Argentina; and Rio Grande do Sul, Brazil: northern populations), whereas those in B-haplogroup (n = 22) represent the southernmost samples (Chubut, Buenos Aires, and Rio Negro provinces, Argentina: southern populations). As shown in Figure 1, mitochondrial gene sequences revealed substantial divergence between haplogroups (10 mutational steps in both 12S and 16S), while the nuclear c-mos gene exhibited lower divergence (two mutational steps). The number of haplotypes within A-haplogroup ranged from three (mitochondrial genes) to six (c-mos), while in B-haplogroup it varied from four (12S) to six (16S and c-mos). The uncorrected p distance between both haplogroups was 4% ± 1% for 12S, 3% ± 1% for 16S, and 1% ± 0% for c-mos. Although these values were lower than the mean divergence observed among all species pairs used for comparison (12S: 7.7% ± 1.9%; 16S: 5.2% ± 1.3%; c-mos: 1.1% ± 0.4%), they were equivalent to or exceeded those observed in some species pairs (Table 1).

We analysed the morphological characters based on the assignment of specimens to the two haplogroups/morphotypes. For external morphology, we measured 142 specimens representing both morphotypes (A-morphotype = 42; B-morphotype = 100; see Table 2 for variation in body measurements and scale counts). We found significant differences between morphotypes and between sexes within each morphotype for all body proportions and the number of ventral and subcaudal scales, except HL/TTL, which did not differ between males and females of the A-morphotype (Fig. 2). These results indicate that A-morphotype specimens possess proportionally longer heads, bodies, and tails, as well as higher counts of ventral and subcaudal scales compared to B-morphotype specimens. Statistical significance for these comparisons is detailed in Figure 2.

Figure 2. 

Box-plots comparing body proportions (%) and scale counts between both morphotypes (A and B), stratified by sex, and globally. Asterisks denote significant differences at p < 0.05. In the plot, black squares represent the mean, white squares denote the mean ± standard error, lines reflect the mean ± 2standard deviation.

Although cephalic scales and dorsal scale counts showed considerable variation, we identified a dominant pattern for each scale type within each morphotype (e.g., dorsal scale formula 19–19–15 vs. other less represented combinations, see Table 3), with no differences between sexes. Thus, the dominant patterns, when potentially informative, were used in the phylogenetic analysis. The colouration pattern indicates a general tendency towards increased dark pigmentation in specimens of B-morphotype (e.g., maculated pattern on dorsal scales, presence of black dots on the lateral margins of each ventral scale, and irregular dark blotches on the dorsal head scales; see Figs 3, 4, 5, 6). The configuration and shape of certain cephalic scales also differed between morphotypes, with a general tendency for specimens of A-morphotype to exhibit more enlarged scales (e.g., rectangular loreal scale, larger first temporal scale; Fig. 3). In summary, we found nine external morphology characters that varied between morphotypes (characters 1–3 and 10–15 in File S2). This number increased to 16 external characters by incorporating additional external traits potentially informative for Philodryas systematics (see character descriptions in File S2), which were subsequently used for phylogenetic analysis (see below).

Figure 3. 

Lateral (A–C), dorsal (D–F), and ventral (G–I) views of the heads of representative specimens from both morphotypes. The left column (A, D, G) shows a B-morphotype specimen from the Monte of Plains and Plateaus (Rio Negro province, MLP.R 5313). The middle column (B, E, H) features a B-morphotype specimen from the Pampa (Buenos Aires province, MLP.R 6039). The right column (C, F, I) presents an A-morphotype specimen from the Humid Chaco (Corrientes province, MLP.R 5449, holotype). Arrows and asterisks highlight character states (see File S2). Photographs A–F include a line-drawing diagram highlighting in grey the scales involved in each character state, as indicated by arrows and asterisks in the corresponding images. Scale bars = 5 mm.

Figure 4. 

Lateral views at midbody of the same specimens described in Figure 3: A B-morphotype, MLP.R 5313; B B-morphotype, MLP.R 6039; and C A-morphotype, MLP.R 5449, holotype. Asterisks highlight character states (see File S2). To improve clarity, each photograph is paired with a corresponding line drawing on the right. Scale bars = 5 mm.

Figure 5. 

Dorsal views at midbody of the same specimens described in Figure 3: A B-morphotype, MLP.R 5313; B B-morphotype, MLP.R 6039; and C A-morphotype, MLP.R 5449, holotype. Asterisks highlight character states (see File S2). To improve clarity, each photograph is accompanied by a corresponding line drawing on the right. Scale bars = 5 mm.

Figure 6. 

Ventral views at midbody of the same specimens described in Figure 3: A B-morphotype, MLP.R 5313; B B-morphotype, MLP.R 6039; and C A-morphotype, MLP.R 5449, holotype. Asterisks highlight character states (see File S2). To clarify the characters, each photograph includes a corresponding line drawing on the right. Scale bars = 5 mm.

The hemipenes of both morphotypes were found to be extremely similar (Fig. 7). We were only able to detect one relevant character for use in the cladistic analysis, primarily related to the variation observed in the outgroup (see character 27 in File S2: relative size of the hemipenes). Additional hemipenial features will be described in the context of the forthcoming taxonomic revision of P. patagoniensis (see below).

Figure 7. 

Sulcate (A, C, E) and asulcate (B, D, F) faces of the hemipenes from both morphotypes: (A, B) B-morphotype specimen from the Monte of Plains and Plateaus (Neuquén province, MLP.JW 1821); (C, D) B-morphotype specimen from Pampa (Buenos Aires province, MLP.R 6039); and (E, F) A-morphotype specimen from Humid Chaco (Corrientes province, MLP.R 5449, holotype). Scale bars = 5 mm.

The cranial osteological analysis revealed variations in four bones between the two morphotypes: shape of the vomerine process of the premaxilla (rectangular in A-morphotype, square in B-morphotype, character 17), orientation of the vomerine processes of the premaxilla (divergent in A-morphotype, sub-parallel in B-morphotype, character 18), general appearance of the horizontal dorsal nasal lamina (slender in A-morphotype, robust in B-morphotype, character 20), posterior edge of the horizontal dorsal nasal lamina (notched in A-morphoptype, smooth in B-morphotype, character 21), configuration of the parabasisphenoid rostrum (bidentate in A-morphotype, tridentate in B-morphotype, character 22), and shape of the maxillary process of the palatine (pointed in A-morphotype, rounded in B-morphotype, character 24); see Figure 8 and File S2. These traits were included in the phylogenetic analysis alongside eight of the ten cranial characters previously used by Lobo and Scrocchi (1994); see File S2 for character description.

Figure 8. 

Osteological characters of the A-morphotype (right side drawings: B, D, F, H) and B-morphotype (left side drawings: A, C, E, G): (A, B) ventral view of the premaxilla; (C, D) dorsal view of nasals; (E, F) ventral view of the parabasisphenoid; and (G, H) dorsal view of the left palatine. Arrows highlight character states (see File S2). Scale bars = 1 mm.

We obtained 70 equally parsimonious trees (374 steps), in which both clades of Philodryas patagoniensis (A- and B-morphotypes) were consistently recovered with high support (each with Bootstrap 100 and Jackknife 100). As consequence, the consensus tree retained the clades described in the next paragraphs (Fig. 9). The species P. agassizii invariably formed a sister group to the clade comprising all terminals of the B-morphotype (Bootstrap 83; Jackknife 80). In contrast, the clade containing all terminals of the A-morphotype was recovered as sister to the P. agassizii + B-morphotype clade (Bootstrap 85; Jackknife 86). Similarly, the consensus recovered a clade comprising P. baroni and P. trilineata (Bootstrap 100; Jackknife 100), with P. mattogrossensis as their sister taxon, although with low support (Bootstrap and Jackknife < 60). Another clade was identified in which P. psammophidea was nested within P. aestiva (Bootstrap 95; Jackknife 97). These clades exhibited a comparable number of synapomorphies. The nine terminals of P. trilineata formed a clade supported by five morphological (23 anterior dorsal scales, dorsal head scales with black spots, ventral scales with dark spots in a random pattern, marbled dorsal and lateral colouration at midbody, and pointed maxillary process of the palatine) and eight molecular synapomorphies. This clade and a single terminal of P. baroni were grouped based on three morphological (23 dorsal scales at midbody, 17 dorsal scales at the posterior body, and simple, undivided cloacal scale) and 11 molecular synapomorphies. Meanwhile, the three terminals of P. aestiva and the single terminal of P. psammophidea were grouped together based on one morphological (immaculate dorsal pattern at midbody, reversed to stripped pattern in P. psammophidea) and nine molecular synapomorphies. The clade comprising P. aestiva + P. psammophidea was further recovered as sister to the clade here referred to as the patagoniensis group (including both morphotypes of P. patagoniensis and P. agassizii), supported based on one morphological (cloacal scale divided) and four molecular synapomorphies.

Figure 9. 

Strict consensus tree constructed from a parsimony analysis using total evidence. Bootstrap and jackknife support values for each major clade are shown below the grey circles, in that order and separated by a slash. The number of synapomorphies supporting each clade of interest is indicated in rectangles, with the number before the plus sign referring to morphological synapomorphies and the number after to molecular ones.

The patagoniensis group was defined by three morphological synapomorphies (supralabial formula 7(3,4)*; infralabial formula 9(5); anterior border of the optic foramen positioned anterior to the midline that bisects the orbit*) and six molecular synapomorphies (asterisks indicate unambiguous synapomorphies). Within this group, we found two distinct clades: one corresponding to the A-morphotype and the other to the B-morphotype + P. agassizii. The A-morphotype clade was strongly supported by five morphological (head proportionally long with HL/TTL<3%; lateral edge of the supraocular scale straight in a dorsal view; long first temporal scale with height <45% of the length; ventral scales at midbody with consistently transverse lines and lacking lateral spots*; and dorsal scales at midbody in adults exhibiting a dotted pattern) and 11 molecular synapomorphies. The clade comprising B-morphotype + P. agassizii is supported by six morphological synapomorphies (mean number of ventral scales<178*; mean number of subcaudal scales<87*; dorsal head scales bearing noticeable black spots centrally and occasionally along the margins; sub-parallel vomerine processes of the premaxilla; a robust horizontal dorsal nasal lamina; and a rounded maxillary process of the palatine), but we did not recover molecular synapomorphies. The species P. agassizii exhibited four morphological autapomorphies (13 dorsal scale rows at the anterior body*; 13 dorsal scale rows at midbody*; 13 dorsal scale rows at the posterior body; and an infralabial formula 8(5)*), and 12 molecular synapomorphies. All terminals of the B-morphotype formed a clade supported by two morphological synapomorphies (midbody ventral scales in adults exhibiting a transverse line that may be complete, incomplete, or absent with a lateral black spot always present; and a maculated dorsal and lateral colour pattern at midbody in adults*) in addition to 11 molecular synapomorphies. See File S2 for the details of each character state.

The recovered topology and levels of support enabled the recognition of two distinct taxa within the nominal P. patagoniensis. Notably, one of these was grouped in a clade that included all specimens of P. patagoniensis (Girard, 1858) sensu stricto. In contrast, the other clade comprises all A-haplogroup specimens (A-morphotype), representing a new species that has remained cryptic due to the extensive morphological variability within P. patagoniensis sensu lato. The only specimen of P. agassizii genetically analysed in this study corresponds to the sole available sequence in the GenBank, and (except Zaher et al. 2019 and Arredondo et al. 2020) used in all phylogenetic treatments of this taxon since Zaher et al. (2009). As P. agassizii is represented by a single terminal, it must necessarily group with one clade or another; in our study, it was recovered as sister to the clade formed by all terminals of the B-morphotype (see Discussion). In any case, our phylogenetic analysis further reveals that P. agassizii is more closely related to the terminal taxa of the B-morphotype than to the other Philodryas species analysed, supporting the conclusion that P. agassizii, together with the A- and B-morphotype clades, constitutes one of the three primary forms within the patagoniensis species group. Additionally, accumulating autapomorphies within P. agassizii reinforces its classification as a distinct and well-defined species.

To formally re-describe P. patagoniensis (Girard, 1858) and encompass the full spectrum of morphological variation, we will focus on key aspects and distinctive features that differentiate it (B-haplogroup, B-morphotype, southern populations: see above for the list of characters) from the A-morphotype (A-haplogroup, northern populations), which will be designated as a new species.

Philodryas patagoniensis (Girard, 1858)

Figures 3A, 3B, 3D, 3E, 3G, 3H, 4A, 4B, 5A, 5B, 6A, 6B, 7A–D, 9A, 9C, 9E, 9G, 10, 11A, 11B

Callirhinus patagoniensis Girard, 1858: 182

Euophrys modestus Günther, 1858: 139

Pseudophis patagoniensis – Cope (1862: 348)

Liophis poecilostictus Jan, 1863a: 289

Dirrhox patagoniensis – Cope (1887: 58)

Philodryas schottii (not Schlegel, 1837) – Boulenger (1896: 130, in part), Koslowsky (1898: 196, in part), Nágera (1915: 28), Devincenzi (1925: 47, in part)

Chlorosoma schottii – Amaral (1929: 214, in part), Serié (1936: 51, in part)

Philodryas patagoniensis – Hoge (1964: 67, in part), Peters and Orejas-Miranda (1970: 244, in part), Thomas (1976: 172, in part), Vega and Bellagamba (1990: 12), Williams and Francini (1991: 75, in part), Cei (1993: 639, in part), Vega and Bellagamba (1994: 143), Tiranti and Avila (1997: 111), Achaval (2001: 7, in part), Carreira (2002: 36, in part), Giraudo and Scrocchi (2002: 32, in part), Carreira et al. (2005: 372, in part), Scolaro (2005: 66), (2006: 92), Scrocchi et al. (2010: 218), Wallach et al. (2014: 551, in part), Harrington et al. (2018: 71, in part), Nogueira et al. (2019: 221, in part), Di Pietro et al. (2020a: 3), (2020b: 7), Williams et al. (2021: 73, in part), Chuliver and Scanferla (2024: 10, in part)

Common name.

We propose changing the common name “Patagonia green racer” used for P. patagoniensis sensu lato to “Patagonia maculated racer” to better reflect the characteristics (i.e., distinctive maculation pattern) of P. patagoniensis sensu stricto.

Figure 10. 

Lectotype of P. patagoniensis (USNM 5536): dorsal (A) and ventral (B) views of the body; lateral (C), dorsal (D) and ventral (E) views of the head. Scale bars = 5 mm. Photo credits: Teresa Hsu and Esther M. Langan.

Figure 11. 

In-life colouration of A a Monte of Plains and Plateaus specimen of P. patagoniensis (Rio Negro, Chipauquil, Meseta de Somuncura), B a Pampa specimen of P. patagoniensis (Buenos Aires, Sierra de Curamalal), and C a Humid Chaco specimen of P. pseudomamba sp. nov. (Chaco, Tres Isletas). Photos are not to scale. Photo credits: David Vera (A), Eduardo Schaeffer (B).

Lectotype.

USNM 5536, an adult female from the mouth of the Río Negro, border of Río Negro and Buenos Aires provinces, Argentina (41.0241°S, 62.7896°W; elevation 0 m), collected by the U.S. Exploring Expedition under the command of Captain Charles Wilkes during 1838–1842.

Referred specimens.

We examined 213 museum specimens (see File S1) from Argentina and Uruguay, corresponding to the B-morphotype. This collection included photographs of the lectotype, and also of the two syntypes of E. modestus, which were entirely consistent with our re-description of P. patagoniensis (see below), thereby confirming that name as a junior synonym of P. patagoniensis sensu stricto. Additionally, numerous photographs from citizen science platforms were analysed to enhance the distribution dataset, bringing the total number of B-morphotype specimens considered for this purpose to 322 (File S1).

Emended diagnosis.

Philodryas patagoniensis differs from all other species of the genus by the following combination of characters: (1) dorsal scale rows 19–19–15, (2) HL/TTL between 2.3 and 4.6%, (3) SVL/TTL between 68.2 and 88.8%, (4) TL/TTL between 11.2 and 31.8%, (5) ventral scales between 159 and 193, (6) subcaudal scales between 57 and 109, (7) loreal markedly quadrate, (8) dorsal half of the preocular barely exceeds the posterior margin of the loreal, (9) supralabials 7 (3,4), (10) lateral border of the supraocular concave in dorsal view, (11) first temporal scale short (height >45% of the length), (12) dorsal scales of the head brown, irregularly spotted with black, and bordered with wide black margins, (13) dorsal body design with maculated pattern, and (14) ventral scales exhibiting lateral black spots.

Re-description of the lectotype.

See Fig. 10. We examined photographs of the lectotype (USNM 5536) and found it to be entirely consistent with the Girard (1858) description and the Thomas (1976) enriched account. Additionally, we enriched the earlier descriptions as follows: (1) loreal supernumerary (2/2) and not 1/1 as is typical for the species, (2) dominant loreal (ventral) square-shaped with no dominant axis; (3) preoculars 1/1 with the dorsal half barely exceeding the posterior margin of the loreal; (4) postocular 2/2; (5) external border of the supraocular concave in dorsal view; (6) temporals 1+2, first temporal short (height representing 46% of the scale length); (7) supralabials 7(3,4)/7(3,4); (8) infralabials 9(5)/10(6); (9) dorsal head scales (parietals, frontal, supraoculars) exhibit dark irregular areas and wide black scale borders; (10) dorsal scales with single apical pits; (11) uniform dorsal and head colouration; (12) lateral black spots present between successive ventral scales (a pattern blurred in the subcaudals); (13) 19–19–15 dorsal scales; (14) 182 ventral scales; (15) 69 subcaudal scales; and (16) tail short (TL/TTL = 17.6%; calculated based on the measurements provided by Thomas in the description of the lectotype).

Variation.

In adult males, TTL ranges from 605 to 976 mm (mean: 747.2 ± 95.6 mm), HL from 18.5 to 30.6 mm (mean: 24.4 ± 2.9 mm), SVL from 425 to 752 mm (mean: 545.5 ± 73.1 mm), and TL from 161 to 259 mm (mean: 205.5 ± 25.8 mm); in adult females, TTL ranges from 622 to 1415 mm (mean: 981.1 ± 180 mm), HL from 20.3 to 39.4 mm (mean: 30.2 ± 4.7 mm), SVL from 471 to 1130 mm (mean: 765.8 ± 147.4 mm), and TL from 128 to 285 mm (mean: 218.5 ± 41.5 mm). Tables 2 and 3 summarise variations in pholidosis and measurements.

In life, the colouration of P. patagoniensis (Fig. 11A, B) exhibits two distinct patterns of dorsal and lateral head and body colouration, characterised by varying shades of brown and the presence of dorsal and lateral body maculation. It is important to note that maculation may not be uniformly expressed across the entire series of dorsal scales. The dorsal head scales (parietals, frontal, and supraoculars) typically display dark irregular areas with broad black scale borders. One of the two distinct patterns occurs in specimens from the Monte of Plains and Plateaus, Patagonian Forests, Steppe, southeast Espinal, and south Pampa ecoregions (Chubut, La Pampa, Mendoza, Neuquén, Rio Negro, southern San Luis, and southern Buenos Aires provinces). These specimens range from brown or black-brown on the dorsal and lateral head and maculated body areas, to pale brown in the non-maculated regions (Fig. 11 A). The point at which the lateral head colour transitions from dorsal brown to ventral pale yellow colour is variable, typically occurring near the supralabials. The second pattern is observed in specimens from the northern parts of the Pampa (mainly Buenos Aires province), Espinal (southern Santa Fe province), south-eastern Dry Chaco (Córdoba province), and the Pampa of south and central Uruguay (Fig. 11B). These specimens exhibit a more homogeneous colouration across the dorsal head scales and the dorsal and lateral parts of the body, characterised by a pronounced brown (sometimes olive-brown) hue in the non-maculated areas, which renders the macula on the scales difficult to distinguish.

Some specimens from both patterns exhibit paravertebral lines on the dorsal scales. The lateral areas of the head (the ventral half of the supralabials and infralabials), the gular region, and all ventral and subcaudal scales are pale yellow. The caudal edge of each supralabial is bordered in black. The pale-yellow ventral colouration is interrupted by black pigmentation on the ventral scales (less distinct on the subcaudals). This pigmentation forms lateral spots along adjacent scales’ anterior and posterior margins, sometimes producing a black line between them, which may be complete, incomplete, or absent. The tongue is bicoloured, with a red base and a black fork.

The colouration in preservative remains similar to that observed in life, except in poorly preserved specimens or those fixed with aggressive concentrations of formalin, which tend to exhibit a general darkening of the scales (e.g., obscuring maculae and other scale patterns). Specimens that have been properly fixed and well preserved exhibit a slightly attenuated pattern compared to live individuals; for example, the ventral scales shift from pale yellow to beige or white. The contrast between the head and dorsal body colouration remains evident, although in slightly muted tones. Loss of the outermost scale layer can result in a lighter appearance (pale lavender; see Fig. 5B). The overall head and body colouration could not be confirmed in specimens that were partially (one adult male from Neuquén province; MACN 30463) or fully melanistic (two adult males from Buenos Aires and Santa Fe provinces; MACN 48145 and MACN 27957, respectively). Notably, we observed an unusual body colouration in a single P. patagoniensis female (MACN 48160; Córdoba province), whose dorsal skin exhibited a black ring surrounding each scale, a pattern commonly seen in the new species described below.

The hemipenes of P. patagoniensis are long and bilobed, with the maximum width occurring at the level of the lobes (width 2.8 to 3.5 times the length of the hemipenis). The lobes comprise approximately one-third of the total hemipenis length. On the sulcate face, the spermatic groove is bifurcated near the base, with both branches running parallel and close to each other before diverging approximately halfway along the hemipenis. The sulcate and asulcate faces exhibit longitudinal rows of elongated spines that increase in length distally. Among the eight hemipenes examined, the sulcate face displayed various spine configurations: 4/4, 4/6, 5/5 (n = 3), 5/6 (n = 2), and 7/7 (Fig. 7A, C). The spines on the asulcate face showed configurations of 5/4, 5/5 (n = 5), 6/4, and 6/6 (Fig. 7B, D). The asulcate face presents two longitudinal rows of large calyces extending over the body’s middle and distal portions and lobes. Additionally, the general reticulation of the lobes and the scattered distribution of the spinule patches resemble the descriptions of P. patagoniensis sensu lato provided by Thomas (1976; without specifying the origin of the specimens), Zaher (1999), Melo-Sampaio et al. (2021: fig. 2C), and Scrocchi et al. (2024). Notably, the latter three studies based their descriptions on specimens from the distribution area of the species we describe below.

Distribution (Fig. 1).

Based on current knowledge, the distribution of Philodryas patagoniensis should be considered restricted to Argentina and Uruguay, with most records concentrated in Argentina. In Argentina, the species occurs across nine provinces: Buenos Aires, Chubut, Córdoba, La Pampa, Mendoza, Neuquén, Río Negro, San Luis, and Santa Fe. Its range encompasses six ecoregions (Patagonian Forests, Dry Chaco, Espinal, Steppe, the Monte of Plains and Plateaus, and the Pampa) and 22 regional sub-complexes sensu Morello et al. (2012).

Finally, the species has also been recorded in 14 departments of Uruguay: Canelones, Colonia, Durazno, Florida, Lavalleja, Maldonado, Montevideo, Paysandú, Río Negro, Rocha, Salto, San José, Soriano, and Tacuarembó. These localities span seven ecozones sensu Brazeiro et al. (2012): South and West Sedimentary Basins, Basaltic Slope, Crystalline Shield, Merín Lagoon Graben, Santa Lucía Graben, and the Eastern Hills.

Taxonomic and nomenclatural remarks.

The species was initially described as Callirhinus patagoniensis by Girard (1858), based on two syntypes collected from the mouth of the Río Negro, between the Argentine provinces of Buenos Aires and Río Negro. One of these specimens is currently lost, while the other (USNM 5536) was designated as the lectotype of the species (Thomas 1976). Some decades earlier, Fitzinger (1826) examined snakes in the collection of the Imperial and Royal Zoological Museum (Vienna) and listed a specimen from “Ex-America, Brasilia” (his original words) as Coluber schottii. The following year, Boie (1827) referred to the same specimen as Xenodon schottii, a species that was formally described a decade later by Schlegel (1837). Subsequent reclassifications included transfers to the genera Pseudophis by Fitzinger (1843) and Dryophilax by Duméril (1853). Duméril et al. (1854) maintained the transfer of X. schottii to D. schottii and accompanied this change with a description based on specimens that clearly correspond to what is currently recognised as P. patagoniensis. They highlighted the opisthoglyphous dentition of these specimens and provided vague locality data, without referencing collection acronyms, although they did mention that the specimens were housed in the Paris Museum. The description was accompanied by the term “Nobis” (Latin for “us”) indicating that the genus transfer was of their own authorship. Late, Günther (1858) published a catalogue of specimens housed in the British Museum (London). On page 125 of this catalogue, he examined three specimens of a rear-fanged snake from Brazil, placing them in the genus Philodryas under the specific name P. schottii, and associating them with the Coluber schottii specimens listed by Fitzinger (1826). Furthermore, on page 139, Günther (1858) described Euophrys modestus, a species that was traditionally included in the synonymy of P. patagoniensis (Peters and Orejas-Miranda 1970; Thomas 1976). It was formally described based on two syntypes, one lacking a specific locality and the other reportedly from “Canton”, China, likely an error (currently catalogued as BMNH 1946.1.2.84 and 1946.1.8.40). Similarly, Jan (1863a) described Liophis poecilostictus from southern Uruguay; with the type specimens now lost, this species has traditionally been considered a synonym of P. patagoniensis (Peters and Orejas-Miranda 1970). In subsequent years, the only taxonomic changes involved generic reassignments. Cope (1862) grouped Callirhinus patagoniensis and Philodryas schottii back into Pseudophis and later Cope (1887) transferred C. patagoniensis to the genus Dirrhox. Boulenger (1896) compiled a catalogue of snakes in the British Museum, in which he classified several specimens under Philodryas schottii, following the erroneous usage of the name introduced by Duméril et al. (1854) and later perpetuated by Günther (1858). Boulenger (1896) provided descriptions and listed multiple individuals, including the type specimens of E. modestus described by Günther (1858). Years later, Amaral (1929), based on the Principle of Priority, assigned all Philodryas species known at that time to the genus Chlorosoma, an action that did not gain acceptance, largely due to the arguments presented by Parker (1932). Finally, controversies regarding the name schottii were resolved by Hoge (1964), who reviewed the material used by Schlegel (1837) in the original description of X. schottii, and concluded that the name schottii should refer to what is currently recognised as Erythrolamprus poecilogyrus schottii (Schlegel, 1837), a non-rear-fanged snake that, according to Entiauspe-Neto et al. (2021), is distributed throughout Paraguay, Brazil, and Argentina. Thomas (1976) criticised and ultimately rejected the action taken by Duméril et al. (1854), who had erroneously assigned the epithet schottii to opisthoglyphous snakes. This subsequent misapplication of the species name, later perpetuated by Günther (1858) and Boulenger (1896), persisted until the publication of Hoge’s work in 1964. According to Article 49 of the ICZN (1999), such a misapplication of a species name does not constitute an available name and, for this reason, we have assigned a new name for the northern populations of P. patagoniensis sensu lato (see below).

Philodryas pseudomamba sp. nov.

https://zoobank.org/2B06036E-8122-4542-8179-EBBE27576145

Figures 3C, 3F, 3I, 4C, 5C, 6C, 7E, 7F, 9B, 9D, 9F, 9H, 11C, 12

Dryophilax schottii (not Schlegel, 1837) – Duméril (1853: 112), Duméril et al. (1854: 1118)

Philodryas schottii (not Schlegel, 1837) – Günther (1858: 125), Jan (1863b: 83), Hensel (1868: 332), Boettger (1885: 235), Boulenger (1886: 434), Cope (1895: 218), Peracca (1895: 18), Boulenger (1896: 130, in part), Koslowsky (1898: 196, in part), Devincenzi (1925: 46, in part), Ábalos et al. (1964: 264)

Pseudophis schottii – Cope (1862: 348)

Chlorosoma schottii – Amaral (1929: 214, in part), Amaral (1932: 101), Serié (1936: 51, in part)

Philodryas patagoniensis – Hoge (1964: 67, in part), Peters and Orejas-Miranda (1970: 244, in part), Thomas (1976: 172, in part), Williams and Francini (1991: 75, in part), Cei (1993: 639, in part), Lobo and Scrocchi (1994: 105), Fowler and Salomão (1995: 150), Leynaud and Bucher (1999: 30), Zaher (1999: 67), Achaval (2001: 7, in part), Giraudo (2001: 155), Carreira (2002: 36, in part), Giraudo and Scrocchi (2002: 32, in part), Carreira et al. (2005: 372, in part), Hartmann and Marques (2005: 25), López and Giraudo (2008: 474), Zaher et al. (2009: 121), Vidal et al. (2010: 53), Pyron et al. (2011: 337), Grazziotin et al. (2012: 443), Wallach et al. (2014: 551, in part), Cabral and Bueno-Villafañe (2015: 13), Cacciali et al. (2016b: 240), Gouveia et al. (2017: 6), Harrington et al. (2018: 71, in part), Nogueira et al. (2019: 221, in part), Quintela and Loebmann (2019: 12), Zaher et al. (2019: 28), Arredondo et al. (2020: 6), Williams et al. (2021: 73, in part), Tioyama et al. (2023: 14), Chuliver and Scanferla (2024: 10, in part)

Pseudablabes patagoniensis – Melo-Sampaio et al. (2021: 37), Dubeux et al. (2022: 6)

Suggested common name.

South American dotted racer.

Holotype.

MLP.R 5449, an adult male from Colonia Carlos Pellegrini, San Martin department (28.5333°S, 57.1712°W; elevation 67 m), Corrientes Province, Argentina; collected by Cátedra de Herpetología, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata between 11 and 15 November 2008.

Paratypes (n = 14).

Argentina. Chaco Province: MLP.JW 1949 (adult female) from Juan José Castelli, General Güemes department, collected by I. Berkunsky in January 2001; MACN 38710 (adult female) from Resistencia, San Fernando department, collected by C. Schlinger on 19 November 1956. Corrientes Province: MACN 50189 (adult female) from Provincial Road 5 between San Luis del Palmar and Laguna Brava, San Cosme department, collected by B. Cajade and E. Nenda on 30 July 2017; MACN 48195 (adult male) from Yapeyú, San Martín department, collected by Ayudantía Marítima Yapeyú on 6 September 1965. Entre Ríos Province: MACN 48165 (adult female) from the surroundings of La Paz, La Paz department, collected by M. Baldi on 7 November 1975; MACN 48163 (adult female) from Pronunciamiento, Uruguay department, collected on 30 October 1967. Formosa Province: MACN 48134 (adult male) from Bartolomé de Las Casas, Patiño department. Misiones Province: MACN 48166 (adult female) from Posadas, Capital department, collected on 24 April 1966. Santa Fe Province: MLP.R 6445 (adult male) from 4 km NE of Aguará Grande, San Cristóbal department, collected by L. Alcalde, M. J. Cassano and M. B. Semeñiuk on 29 October 2016; MLP.R 6434 (adult male) from Provincial Road 3 in Los Tábanos, Vera department, collected by L. Alcalde, M. J. Cassano and M. B. Semeñiuk on 21 October 2016; MLP.R 6450 (adult female) from Provincial Road 3 near Vera, Vera department, collected by L. Alcalde, M. J. Cassano and M. B. Semeñiuk on 25 October 2016; MLP.R 6455 (adult male) from road cross between Provincial Road 3 and National Road 11 near Vera, Vera department, collected by L. Alcalde, M. J. Cassano and M. B. Semeñiuk on 25 October 2016. Santiago del Estero Province: MACN 4325 (adult male) form Malbrán, Aguirre department, collected by Cazale and Peyrade. — Brazil: São Pablo State: MACN 36703 (adult female) from the surroundings of Ibiúna, Ibiúna municipality, collected by Instituto Butantán in April 1996.

Referred specimens.

For the species description, 178 museum specimens corresponding to the A-morphotype were examined (File S1), including those from the type series. In addition, numerous photographs from citizen science platforms were analysed to enhance the distribution dataset, bringing the total number of A-morphotype specimens considered to 403 (File S1).

Etymology.

The prefix pseudo of the epithet derives from Greek, meaning “falseness” or “falsehood”. Mamba refers to the term “imamba” used in the Bantú language (spoken by various African ethnic groups) to designate snakes of the genus Dendroaspis, commonly known in English and other languages as “mambas”. The species name was explicitly inspired by D. polylepis (the black mamba), due to the general physical resemblance and notably aggressive behaviour shared by both species.

Diagnosis.

Philodryas pseudomamba sp. nov. differs from all other species of the genus by the following combination of characters: (1) dorsal scale rows 19–19–15, (2) HL/TTL between 2 and 3.4%, (3) SVL/TTL between 68 and 77.7%, (4) TL/TTL between 22.2 and 32%, (5) ventral scales between 166 and 199, (6) subcaudal scales between 81 and 124, (7) loreal scale rectangular, longer than tall, (8) dorsal half of the preocular markedly exceeding the posterior margin of the loreal, (9) supralabials 7 (3,4), (10) lateral border of the supraocular straight in dorsal view, (11) first temporal scale large (height being less than 40% of the length), (12) dorsal scales of the head with completely immaculate olive colouration featuring tiny black scale margins, (13) dorsal body design dotted, not maculated, and (14) ventral scales lacking lateral black spots.

Description of the holotype.

See Figs 3C, 3F, 3I, 4C, 5C, 6C, 12. Adult male, TTL of 910 mm, HL of 27.3 mm, SVL of 645 mm, and TL of 265 mm; proportions, HL/TTL = 3%, SVL/TTL = 70.8%, and TL/TTL = 29.2%.

Figure 12. 

Holotype of P. pseudomamba sp. nov. (MLP 5449): dorsal (A) and ventral (B) views of the body. Scale bars = 10 mm.

Morphological features include: loreals 1/1 (square-shaped with a dominant cranial-caudal axis, longer than tall), preoculars 1/1 (with the dorsal half markedly exceeding the half of the loreal), postoculars 2/2, temporals 1+2/1+2 (the first temporal is long, with the height representing 35% of the scale length), supralabials 7(3,4)/7(3,4) with the 5^th and 6^th being larger than the others (Fig. 3C), infralabials 9(5)/9(5) (Figs 3C, 3I), and external border of the supraocular straight or slightly expanded laterally in dorsal view (Fig. 3F). Dorsal scales 19–19–15, smooth, with single apical pits (Figs 4C, 5C). There are 176 ventral scales and 104 subcaudal scales, anal and subcaudals are divided.

In preservative, the dorsal surfaces of the head and neck are olive brown, closely matching the colouration of the dorsal body (Fig. 12). The ventral surface of the head is beige-white, with the dorsal-ventral colour transition occurring at the midpoint of the supralabials (Fig. 3C). The dorsal head scales lack dark markings and exhibit fine black interscale sutures (Fig. 3F). Paravertebral lines evident, the dorsal scales display dark spots at their anterior and posterior ends, which converge between adjacent scales to form a single dot (Figs 4C, 5C, 12). Many dorsal scales have lost their outermost layer, resulting in a lighter, pale lavender appearance (Fig. 12). Ventral scales are beige-white, each separated by a continuous black interscale line (Fig. 6C), which becomes blurred along the subcaudal region (Fig. 12).

The hemipenes of the holotype of P. pseudomamba sp. nov. are long and bilobed, with the lobes comprising approximately one-third of the total hemipenial length. The maximum width occurs at the level of the lobes and corresponds to 3.1 times the hemipenial length. The branches of the spermatic groove bifurcate near the base of the hemipenis and run in close parallel before diverging at approximately the midpoint of the organ. The sulcate and asulcate faces bear longitudinal rows of enlarged spines that increase in height distally. On the asulcate face, the spine configuration is 5/6, and on the sulcate face, 6/6 (Fig. 7 E, F). The counts of the sulcate face begin at the bifurcation point of the spermatic groove toward the distal end (i.e., spines posterior to this point were considered spinules). Two longitudinal rows of large calyces are on the asulcate surface, covering the middle and distal portions of the body and lobes. These calyces are associated with a profuse reticulation of the lobes and randomly distributed patches of spinules. Overall, the hemipenial morphology of the holotype resembles that described by Zaher (1999), Melo-Sampaio et al. (2021: fig. 2C), and Scrocchi et al. (2024) for specimens whose geographic distribution corresponds to P. pseudomamba sp. nov.

Variation.

In adult males, TTL ranges from 618 to 1207 mm (mean: 954.3 ± 138.8 mm), HL from 21.1 to 33.1 mm (mean: 28 ± 3.1 mm), SVL from 435 to 871 mm (mean: 678.5 ± 104.5 mm), and TL from 183 to 343 mm (mean: 275.7 ± 43.3 mm); in adult females, TTL ranges from 672 to 1552 mm (mean: 1135 ± 191.9 mm), HL from 22.9 to 39.4 mm (mean: 32 ± 4.3 mm), SVL from 497 to 1170 mm (mean: 849.7 ± 142.9 mm), and TL from 175 to 382 mm (mean: 285.2 ± 52.1 mm). Tables 2 and 3 summarise variations in pholidosis and measurements.

The colouration in life (Fig. 11C) is less variable than that observed in P. patagoniensis. A consistent difference in colouration exists between the head and neck compared to the rest of the body. Depending on the individual, the dorsum and laterals of the head and neck range from ochre to orange. The body dorsum is typically olive but may also appear as mint green or olive green. Each dorsal scale bears a subtle dark spot at its anterior and posterior ends, with the anterior spot being less pronounced than in P. patagoniensis. These spots on adjacent scales converge to form a single dot, rather than a maculation as seen in P. patagoniensis, except in juveniles. The aggregation of these dots along the same dorsal scale row forms oblique lines oriented ventro-dorsally and cranially-caudally. In both dorsal and lateral views, these oblique lines give the dorsal scales a pectinated appearance on either side of the mid-vertebral line. Continuous paravertebral lines formed between subsequent scales are more frequently observed than in P. patagoniensis.

The ventral colouration of the head and body is pale yellow. The boundary between the dorsal ochre and the ventral pale-yellow lies below the midpoint of the supralabials. The black pigmentation along the sutures of the head scales is more delicate than in P. patagoniensis, particularly in the parietals, frontal, and supraoculars, which also lack the irregular dark markings characteristic of P. patagoniensis. The pale yellow ventral colouration is occasionally interrupted by black lines between successive ventral scales. Each of these lines is typically continuous, although they may less frequently be interrupted at the mid-ventral region. In the subcaudal region, this pattern becomes progressively blurred. The tongue is bicoloured, displaying a red base and a black fork.

In preservative, the colouration resembles that observed in life, except in poorly preserved specimens. Adequately fixed and well-preserved specimens appear pale compared to live specimens. For example, the ventral scales often fade from pale yellow to beige or white, and the contrast between the head and dorsal body colouration becomes less distinct. Although melanistic specimens are frequently found in collections (e.g., MACN 10228 or MACN 39619), we did not encounter melanism during our fieldwork. Typical head and body patterns are entirely or partially obscured in these melanistic specimens. Furthermore, black rings surrounding dorsal scales are present in some specimens and appear more frequently than in P. patagoniensis (e.g., MACN 7841, MACN 48179).

The other specimen examined for hemipenial morphology differed from the holotype in a single aspect: it exhibited a 5/5 configuration of the elongated spines on the sulcate and asulcate faces.

Comparison.

The dorsal scale rows distinguish Philodryas pseudomamba sp. nov. (19–19–15) from P. agassizii (13–13–13), P. varia (17–17–13 to 19–17–13; Thomas 1976), P. livida (17–17–15), P. boliviana (15–17–13 to 17–17–13; Thomas 1976), P. baroni (ranging from 21–21–17 to 23–23–17; Thomas 1976), P. nattereri (from 21–21–15 to 21–22–17; Thomas 1976), and P. trilineata (21–23–17 to 26–23–17; Thomas 1976). The absence of a dorsal colour that shifts from green in the anterior half of the body to brown in the posterior part distinguishes P. pseudomamba sp. nov. from P. erlandi and P. mattogrossensis, which exhibit a dorsal colour shift between the mid and posterior body. The lack of well-defined broad stripes on the body distinguishes P. pseudomamba sp. nov. from P. chamissonis and P. psammophidea, both of which possess stripes. Both P. aestiva and P. olfersii display a uniform green colouration on the dorsum and flanges of the body and tail, which is absent in P. pseudomamba sp. nov. Additionally, P. aestiva differs in having keeled dorsal scales (smooth dorsal scales in P. pseudomamba sp. nov.), while P. olfersii typically features a black ocular stripe, which is always absent in P. pseudomamba sp. nov. The rare P. cordata can be distinguished from P. pseudomamba sp. nov. by its entirely black tongue (bicoloured in P. pseudomamba sp. nov., with a red base and black fork), and its hemipenial features, which are markedly divergent from those described in all Philodryas species. Certain body proportions are useful to distinguish between P. pseudomamba sp. nov. and P. arnaldoi (Amaral 1932). In P. pseudomamba sp. nov., the tail is shorter (mean TL/TTL < 27% for both sexes) than in P. arnaldoi (> 46%).

Lastly, P. pseudomamba sp. nov. differs from P. patagoniensis by (character states of the former in parenthesis): (1) head and body shorter (larger), (2) short tail (large), (3) subcaudal scales 57–109 and ventral scales 159–193 (high number in both cases: 81–124 subcaudal scales and 166–199 ventral scales), (4) loreal scale markedly quadrate with no dominant axis, and the dorsal half of the preocular barely exceeds the posterior margin of the loreal (loreal scale is rectangular, longer than tall, with the dorsal half of the preocular markedly exceeding the posterior margin of the loreal), (5) external border of the supraocular concave in dorsal view (straight in dorsal view), (6) first temporal scale shorter, with the height representing more than 45% of the length (longer than it is tall, with the height being less than 40% of the length), (7) parietal, frontal, and supraocular scales brown, irregularly spotted with black, and bordered with wide black margins (completely immaculate olive colouration featuring tiny black scale margins), (8) dorsal scales exhibit a maculated pattern (not maculated), (9) lateral black spots present in the ventral scales (absent), (10) vomerine processes of the premaxilla sub-parallel (slightly divergent), (11) dorsal lamina of the nasal robust with non-concave posterolateral flange (dorsal lamina of the nasal slender with concave posterolateral flange), (12) three pointed and double-notched anterior ends of the parabasisphenoid (two pointed and single median-notched), and (13) rounded maxillary process of the palatine (triangular).

Distribution.

See Fig. 1. Philodryas pseudomamba sp. nov. is distributed across five countries: Argentina, Bolivia, Brazil, Paraguay, and Uruguay. In Argentina, the species occurs in 12 provinces: Buenos Aires, Chaco, Córdoba, Corrientes, Entre Ríos, Formosa, Misiones, San Luis, Santa Fe, Santiago del Estero, Tucumán, and Jujuy. It inhabits nine ecoregions (Delta and Islands of the Paraná and Uruguay Rivers, Dry Chaco, Espinal, Fields and Weeds, Humid Chaco, Ibera’s Marshlands, Pampa, Paranaense Forest, and Yungas Forest), and 33 regional complexes (sensu Morello et al. 2012).

In Uruguay, P. pseudomamba has been recorded in seven departments: Artigas, Cerro Largo, Paysandú, Río Negro, Rivera, Salto, and Tacuarembó. It occurs in four ecozones: Western Sedimentary Basin, Basaltic Slope, Gondwanic Sedimentary Basin, and Eastern Hills (Brazeiro et al. 2012). In Paraguay, this species occurs in six departments: Alto Paraná, Central, Misiones, Ñeembucú, Paraguari, and Presidente Hayes. It inhabits two ecoregions: Alto Paraná and the Atlantic Forest, and the Humid Chaco (Ávila Torres et al. 2018). In Bolivia, the species has been recorded in the Santa Cruz department, and the Gran Chaco and Chiquitano Dry Forest ecoregions (Ibisch et al. 2003). In Brazil, P. pseudomamba sp. nov. occurs in 14 states: Bahia, Distrito Federal, Goiás, Mato Grosso, Minas Gerais, Paraíba, Paraná, Rio de Janeiro, Rio Grande do Norte, Rio Grande do Sul, São Paulo, Santa Catarina, Sergipe, and Espírito Santo. Its distribution spans five major Brazilian biomes: Atlantic Forest, Caatinga, Cerrado, Pampa, and Pantanal (IBGE 2019).

In this study we identified two distinct taxa, P. patagoniensis sensu stricto (hereafter referred to as such unless otherwise specified) and P. pseudomamba sp. nov., based on variation in two mitochondrial genes (12S and 16S ribosomal RNA) and one nuclear gene (c-mos). The p distance values observed between P. patagoniensis and P. pseudomamba sp. nov. exceeded those found between other well-differentiated species pairs within the genus (e.g., P. aestiva–P. psammophidea for 12S, P. aestiva–P. agassizii for c-mos, and P. trilineata–P. baroni for all three genes; see Table 1). Moreover, the genetic distances between P. patagoniensis and P. pseudomamba sp. nov. were greater than those reported between closely related species within Dipsadinae. For instance, Lehr et al. (2023) reported a 2.1% genetic divergence in the 12S between Tachymenoides affinis and T. harrisonfordi, while Carvalho et al. (2020) found a 0.43% divergence in the 16S gene between Hydrodynastes gigas and H. bicinctus. More strikingly, several closely related species of Atractus, such as A. iridescens–A. dunni (0%), A. typhon–A. gigas (1%), and A. resplendens–A. duboisi (2%), exhibit very low genetic distances for the 16S gene (Araújo De Oliveira and Hernández Ruz 2016). A similar pattern is observed in Apostolepis albicollaris and A. dimidiata, which show only 1% divergence for the 12S gene and 0% for c-mos (Entiauspe-Neto et al. 2022). Concerning the c-mos sequences, Entiauspe-Neto et al. (2022) have argued that this gene is not particularly informative for phylogenetic reconstruction due to its low number of variable sites at the species level, a limitation also noted in squamate phylogenies (Saint et al. 1998). However, despite its limited variability, the c-mos gene remains valuable for delimitation and corroborating candidate species initially identified through mitochondrial markers (Wüster et al. 2024; present study).

Our objective was to establish a phylogenetic framework to assess the position of the new species relative to P. patagoniensis and other species of Philodryas, rather than to perform a comprehensive phylogenetic analysis of the genus’ internal and external relationships. Accordingly, we do not provide a detailed discussion of the phylogenetic relationships recovered. Nevertheless, we note that, in broad terms, our results are consistent with clades and relationships previously reported in the literature. For instance, our results support the clade formed by P. trilineata + P. baroni (Lobo and Scrocchi 1994; Arredondo et al. 2020; Melo-Sampaio et al. 2021) and the close relationship between P. aestiva and P. psammophidea (Grazziotin et al. 2012; Melo-Sampaio et al. 2021), with the latter consistently exhibiting some degree of association with the patagoniensis clade. The sequences we used for P. psammophidea correspond to two mitochondrial fragments (12S and 16S) originally uploaded to GenBank by Vidal et al. (2010). In this study, P. psammophidea forms a clade with P. aestiva, a pattern also observed in other studies that employed the same sequences (Grazziotin et al. 2012; Figueroa et al. 2016; Melo-Sampaio et al. 2021). This finding did not attract attention, as those studies used a single terminal for each species. Zaher et al. (2019) and Arredondo et al. (2020) used own P. psammophidea sequences (never uploaded to GenBank) and excluded, without explanation, the sequence from Vidal et al. (2010). Consequently, in their analyses, P. psammophidea was placed within the patagoniensis group, whereas P. aestiva appeared as sister to that group, showing no direct relationship with P. psammophidea. These findings are consistent with the clear morphological distinctiveness of both species and their largely disjunct geographic distributions (Giraudo 2001; Nogueira et al. 2019). We therefore believe that the sequence attributed to P. psammophidea by Vidal et al. (2010) actually corresponds to P. aestiva, as supported by our phylogenetic results, in which this sequence nests within the P. aestiva terminals.

Except for Zaher et al. (2019) and Arredondo et al. (2020), who used different terminal taxa, other molecular phylogenetic analyses have placed P. agassizii within a clade with P. patagoniensis sensu lato (Zaher et al. 2009; Grazziotin et al. 2012; Melo-Sampaio et al. 2021). However, these analyses included specimens of P. patagoniensis sensu lato that correspond to P. pseudomamba sp. nov., specifically MCP 5753 (which, based on requested photographs, undoubtedly exhibits the A-morphotype; see File S1), and a second voucher specimen from Santa Fe, Argentina, represented only by a tail fragment (MACN 47276), for which sequence data are no longer available in GenBank (the latter generated by Arredondo et al. 2020). Philodryas agassizii, P. patagoniensis, and P. pseudomamba sp. nov. formed a clade with moderate support (the patagoniensis group), with P. pseudomamba sp. nov. recovered as sister to P. patagoniensis + P. agassizii, and strongly supported by morphological and molecular synapomorphies (see Results section). Zaher et al. (2019) and Arredondo et al. (2020) found subtle differences in the positioning of certain species within the patagoniensis group. In the study by Arredondo et al. (2020), P. agassizii was recovered as sister to P. livida, while the individuals they referred to as P. patagoniensis (now identified as P. pseudomamba sp. nov.) form a clade with P. varia. Zaher et al. (2019) found P. agassizii to be sister to the patagoniensis group clade, whereas P. patagoniensis (now identified as P. pseudomamba sp. nov.) forms a clade with P. varia. This discrepancy between their results and ours may be attributed to two factors, or even an interaction between both. One possible factor is that Zaher et al. (2019) and Arredondo et al. (2020) used two new sequences of P. agassizii that differ from the one we employed in our study, which has also been used in all phylogenetic analyses involving this species (from Zaher et al. 2009 to Melo-Sampaio et al. 2021). In this regard, we assessed the sequence of P. agassizii used in our study across the three genes (c-mos, 12S, and 16S) by running it through the BLAST+ suite (Camacho et al. 2009), and found no evidence of anomalies. Furthermore, this sequence is the only one available for the species (see Materials and Methods) since the P. agassizii sequences used by Zaher et al. (2019) and Arredondo et al. (2020) were never uploaded to GenBank. Alternatively, the discordance between these studies and ours likely arises from their use of a different (and uncheckable) taxonomic sampling. None of the relevant sequences they used were uploaded to GenBank (their sampling included P. arnaldoi, two new sequences of P. agassizii, P. erlandi, P. livida, and P. varia). For the reasons already explained, none of these species were included in our analysis. Additionally, we used sequences from P. patagoniensis sensu stricto, a species for which no sequences were available to Zaher et al. (2019) and Arredondo et al. (2020). In fact, all the sequences of the species employed in various phylogenies actually correspond to P. pseudomamba sp. nov. (e.g., Zaher et al. 2009; Grazziotin et al. 2012). In summary, it is important to highlight that Zaher et al. (2019) and Arredondo et al. (2020) did not use the P. agassizii GenBank sequence we used (the only available), nor did they address its exclusion. The supplementary material table S6 in Zaher et al. (2019) explained the exclusion of several GenBank sequences from their analysis, listing the species whose sequences were chimeras or contained various types of errors, with no mention or justification for the exclusion of the P. agassizii we used in our work. We believe that the most appropriate way to evaluate the status of this P. agassizii sequence would be to include it alongside the new sequences analysed by Zaher et al. (2019) and Arredondo et al. (2020) in a joint phylogenetic assessment to verify its true position within the genus.

Many of the synapomorphies we identified were first discussed by earlier authors, who highlighted several of them in their studies on the variation of external morphology within P. patagoniensis sensu lato. For example, Thomas (1976) noted geographical variation in the number of ventral and subcaudal scales, with counts decreasing from north to south, a pattern that strongly supports the recognition of a northern species (P. pseudomamba sp. nov.) and a more southern species (P. patagoniensis) (characters 2 and 3 in the present study, see File S2). Similarly, the same author noted that P. patagoniensis sensu lato from Brazil and adjacent areas of Paraguay exhibit dark pigmentation on the posterior part of each ventral and subcaudal scale, a feature absent in specimens from Argentina and Uruguay (character 14 of our work, File S2). Additional synapomorphies supporting clades in our analysis, including within the internal group, are osteological. Although cranial osteology in snakes is seldom used for species diagnoses due to presumed low variability between closely related taxa (Di Pietro et al. 2014), we employed several osteological characters from Lobo and Scrocchi (1994), along with other characters verified explicitly for this study (characters 17–26 in File S2). The three most parsimonious cladograms recovered by Lobo and Scrocchi’s (1994) displayed numerous polytomies and exhibited limited resolution of clades. In contrast, our total evidence analysis revealed that many osteological characters functioned as synapomorphies for clades or autapomorphies for individual species, underscoring their value when evaluated with molecular data, enhancing the overall resolution of phylogenetic trees. Our analysis recovered that the patagoniensis species group clade was supported by one osteological character (anterior border of the optic foramen positioned anterior to the vertical midline that bisects the orbit), while the clade P. agassizii + P. patagoniensis is supported by three (a sub-parallel vomerine processes of the premaxilla; a robust horizontal dorsal nasal lamina; and a rounded maxillary process of the palatine). Although we counted the teeth, we chose not to use this character source because our counts for both species showed high variability and completely overlapped with the ranges reported in the literature for P. patagoniensis sensu lato (Thomas 1976) and P. pseudomamba sp. nov. (Lobo and Scrocchi 1994). Therefore, these characters, and other minor hemipenial traits, did not prove helpful in distinguishing between the two species.

The geographical distribution of P. pseudomamba sp. nov. and P. patagoniensis reveals a clear correlation with forested and open habitats, respectively (FAO 2020), with an area of overlap in central Argentina and central Uruguay (Fig. 1).

Philodryas pseudomamba sp. nov. exhibits greater snout-vent length (SVL) and tail length (TL), and higher counts of ventral and subcaudal scales than P. patagoniensis. These traits are strongly associated with arboreal habits in snakes (e.g., Harrington et al. 2018). Hartmann and Marques (2005) documented habitat use in specimens corresponding to P. pseudomamba sp. nov. from southern Brazil, finding that one-third was located in forested areas and two-thirds in open areas. Similarly, Harrington et al. (2018) reviewed the ecology and traits of arboreal snakes and classified P. patagoniensis sensu lato as semi-arboreal. However, habitat use studies in P. patagoniensis sensu stricto suggest a clear preference for open environments (e.g., Vega and Bellagamba 1990; Di Pietro et al. 2020b). In contrast, the regions inhabited by P. pseudomamba sp. nov. offer more potential arboreal niches compared to those occupied by P. patagoniensis, where trees are scarce or absent (Morello et al. 2012). Moreover, differential habitat use in snakes is often associated with variation in food resource utilisation (Luiselli 2006; Goodyear and Pianka 2008).

In the context outlined above, the previously observed geographical variation in the diet of P. patagoniensis sensu lato may offer valuable ecological insight into the morphological differences between P. patagoniensis and P. pseudomamba sp. nov. Both species exhibit a broad diet that includes anurans, lizards, snakes (including instances of cannibalism), small birds and mammals (primarily rodents), and even fish and a wide range of arthropods (e.g., ants, coleopterans) (Carreira 2002; Lopez and Giraudo 2008; Quintela and Loebmann 2019; Di Pietro et al. 2020b). The latter prey should be considered secondary, i.e., organisms included in the diet as prey of the actual target prey (e.g., Di Pietro et al. 2020b). However, a notable difference exists in the diet of the species analysed: the consumption of Lycosa spiders as primary prey. This is evidenced by the high frequency of spiders in the stomachs of P. patagoniensis from southern Uruguay and central Argentina (Carreira 2002; Di Pietro et al. 2020b; Chuliver and Scanferla 2024), in contrast to their absence in P. pseudomamba sp. nov. from Brazil, northern Uruguay and northern Argentina (Carreira 2002; Hartmann and Marques 2005; López and Giraudo 2008; Quintela and Loebmann 2019). The preference of P. patagoniensis for open areas seems to be linked to its consumption of Lycosa spiders, a genus widely recognised as typical grassland dwellers (Jocqué and Alderweireldt 2005). Accordingly, a diet rich in Lycosa spiders and a predominantly terrestrial lifestyle, are distinguishing traits of P. patagoniensis + P. agassizii compared to P. pseudomamba sp. nov. The terrestrial habits of P. patagoniensis and P. agassizii may be partially a result of the scarcity of large forested areas within their range, a factor especially relevant for P. patagoniensis. However, the consumption of Lycosa spiders may also reflect additional ecological or behavioural drivers. Notably, the first reports of spider consumption in the diet of P. patagoniensis were provided by Carreira (2002) and Di Pietro et al. (2020b). The most interesting aspect of the latter study is the significant correlation between prey volume and snake size and the fact that larger individuals continue consuming small prey, particularly Lycosa spiders. In other words, larger specimens of P. patagoniensis tend to consume larger prey while still including Lycosa spiders in their diet. This pattern may reflect the retention of juvenile dietary preferences into adulthood, an idea recently revisited by Chulliver and Scanferla (2024) through a comparative analysis of the morphology and diet of P. patagoniensis sensu lato and P. agassizii. They conclude that P. agassizii is a paedomorphic species whose adults differ from P. patagoniensis by retaining juvenile cranial traits and maintaining a diet rich in spiders, in clear contrast with evidence showing that adult P. patagoniensis never cease to consume Lycosa spiders (Carreira 2002; Di Pietro et al. 2020b).

Finally, this study re-describes P. patagoniensis and formally describes P. pseudomamba sp. nov., reflecting the molecular and morphological variation previously observed within P. patagoniensis sensu lato. Distinct patterns of colouration, cranial osteology, scale morphology (shape and counts), body proportions, and aspects of natural history, such as diet and habitat use, allow clear differentiation between the two species.