Research Article |
Corresponding author: Arthur Georges ( georges@aerg.canberra.edu.au ) Academic editor: Uwe Fritz
© 2023 Scott A. Thomson, Natália R. Friol, Arthur White, Dion Wedd, Arthur Georges.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Thomson SA, Friol NR, White A, Wedd D, Georges A (2023) The Australian gulf snapping turtle Elseya lavarackorum (Testudines: Chelidae) revisited—Is the late Pleistocene fossil species extant? Vertebrate Zoology 73: 237-256. https://doi.org/10.3897/vz.73.e99495
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Disagreement exists on the taxonomic identity of the extant populations of the Australian Elseya referred to in 1992 as the gulf Elseya (= Elseya sp. aff. dentata [Nicholson]). The extant form has since 1997 been considered conspecific with the late Pleistocene fossil Elseya lavarackorum (White and Archer, 1994). Recently it has been considered a new species, Elseya oneiros
Chelonia, chelid, chronospecies, fossil, Lazarus turtle
In May 1984, exploration of eroded fluviatile deposits exposed in the catchment of the Gregory River on Riversleigh Station, north-western Queensland, revealed several sites that produced fossil vertebrates. One of these, known as Terrace Site (
Referring to the recessed nuchal region,
In a recent paper,
Characterization of morphological variation in the shells of extant Elseya can provide a baseline for interpretation of the character states of fossil specimens. However, other studies of this type serve to highlight the difficulties inherent in recognizing and accommodating intraspecific diversity in the fossil record (
In this paper, we confirm that the affinities of Elseya lavarackorum lie with the subgenus Pelocomastes, not with the subgenus Elseya (
We examined the fossil holotype (
Carapace of the fossil holotype of Elseya lavarackorum (White and Archer, 1994) (QMF24121). A Dorsal view; B ventral view; C dorsal view with sulci marked where they can reliably be discerned (solid lines). Note the points of most anterior extent establishing the existence of a nuchal bay.
Incomplete plastron of the fossil referred to Elseya lavarackorum (White and Archer, 1994) by
We also examined high quality photographs of extant specimens provided to us by the co-authors of
A total of 106 characters scored for 24 taxa were used for phylogenetic analysis using Maximum Parsimony as implemented in PAUP Version 4.0a (build 169) for 32-bit Microsoft Windows (built on Feb 10 2021 at 22: 12: 44). A heuristic search was undertaken, with MAXTREES set to 40,000. A consensus of 10,236 equally parsimonious trees (length 153) was obtained using Majority Rule (> 0.5), and consensus for nodes is indicated on the Fig.
Shell terminology follows that of
The Anterior Bridge Strut Suture, or axillary hyoplastral buttress suture of
The anterior bridge strut suture between the plastral bridge element and the carapace in the holotype of Elseya lavarackorum (QMF24121). A Ventral (internal) view of the carapace showing the strong angle of the anterior bridge strut suture against the rib element of pleural bone 2, and the prominent anterior bridge strut elements still embedded in the suture; B an enlarged view of the region of the suture showing more clearly the breaks that were formed when the carapace was separated from the plastron and the resultant overhangs (labelled (c) and (e) in A above); C the boundary of the anterior bridge suture as interpreted by
Fragments of the hyoplastron of
The other two fossils from the Riversleigh Terrace Site (QMF30317, QMF30318) contemporary with the Elseya lavarackorum fossil are represented by plastral material only (Figs
A second character of relevance to the assignment to subgenus of
Characterisation of shell shape in species of Elseya (Pelocomastes). A Ovoid shell of Elseya (Elseya) branderhorsti (
The fossil holotype of Elseya lavarackorum (
The other two fossils from the Riversleigh Terrace Site (QMF30317, QMF30318) contemporary with the Elseya lavarackorum fossil are represented by plastral material only (Figs
The fossils of the Riversleigh Terrace Site are unusual in that the scutes of the shell appear to have remained incorporated into the fossils. As a consequence, the bony sutures of the carapace and plastron are less prominent on the surfaces external to the shell, and the sulci are evident as scute junctions rather than indentations in the underlying bone.
Variation in the humeral-pectoral sulcus in extant Elseya lavarackorum from the Roper River, NT. A Specimen A112 shows the character state represented by the fossil holotype Elseya lavarackorum (sinusiodal sulcus sensu
As an example of variation in a meristic character, the sulci between the first vertebral scute V1 and the first costal scute C1 join to marginal scutes M3 in the E. oneiros holotype (
Furthermore, many of the scute characters of
A phylogeny (Majority Rule Consensus Tree, length 153) of 24 extant and fossil species of chelid turtle based on 106 morphological characters (Tables S1 and S2). Pelomedusoid Podocnemis sextuberculata was the outgroup taxon. Note that the clades representing subgenera Elseya and Pelocomastes have high consensus (first value on nodes) and strong bootstrap support (second value on nodes). The fossil material from the Riversleigh Terrace Site and the extant Elseya sp. aff. dentata [Nicholson] fall in the Pelocomastes clade.
Generating a robust phylogeny using a combination of fossil and extant taxa is challenging because the fossils are often partial whereby the matrix of character states (Table S1) is sparse, with many characters unable to be scored. Nevertheless, we were able to generate a phylogeny (Fig.
Although not directly relevant to the questions posed in this paper, the phylogeny provides information of broader relevance to chelid phylogeny. Caution is required in the interpretation of the topology, particularly where the support values are low. The three clades of Elseya represented as the subgenera are well supported by allozymes (
The lectotype of Pelocomastes ampla, type species for Pelocomastes is partial and its synonymy with Chelymys uberrima (
Chelymys dentata Gray, 1863 (= Elseya (Elseya) dentata [Gray, 1863] sensu
Elseya (Elseya) branderhorsti (Ouwens, 1911) sensu
Platemys novaeguineae Meyer, 1874 (= Elseya (Hanwarachelys) novaeguineae [Meyer, 1874: 128] sensu
Elseya (Hanwarachelys) caelatus Joseph-Ouni & McCord, 2019: 25 sensu Joseph-Ouni and McCord (2019), Elseya (Hanwarachelys) orestiad Joseph-Ouni & McCord, 2019: 47 sensu Joseph-Ouni and McCord (2019), Elseya (Hanwarachelys) schultzei (Vogt, 1911: 410) sensu
Pelocomastes ampla (= Elseya [Pelocomastes] uberrima de Vis, 1897 sensu
Elseya (Pelocomastes) albagula Thomson, Georges & Limpus, 2006 sensu
Although many of the external characters are highly variable and thus not diagnostic when considered individually, it is possible to provide guidance for the identification of extant Elseya (Elseya) dentata and Elseya (Pelocomastes) lavarackorum. This is particularly important where they occur in sympatry (e.g. the Roper River, NT,
We re-examined the fossil material relevant to Elseya (Pelocomastes) lavarackorum (White and Archer, 1994) and considered the interpretation of characters by
The analysis of
We are not arguing that scute characters are of no value taxonomically. Clearly, the contact or lack of contact of the gular scutes anterior to the intergular is an important diagnostic character at the level of genus in the Australian Chelidae. The numbers of costal and vertebral scutes are important taxonomic characters for the species identification of marine turtles (
Even given the above caveats, scutellation characters may be informative and form part of the description of the Type material, but not in a diagnostic sense. Scutellation characters can be used to capture differences in the pattern of interindividual variation between putative species that overlap to varying degrees in different putative species using Principal Components Analysis (PCA) or Discriminant Analysis (DFA). This requires capturing a good representation of that interindividual variation for all taxa under consideration and of course, that is very seldom possible when examining fossil forms; it is certainly not possible to capture interindividual variation in the population from which the fossil Elseya lavarackorum (
Marrying the procedures for defining species based on extant and fossil taxa is challenging (
The two perspectives come together when considering species delineation of very young fossils and sub-fossils. The fossil material, usually represented by a single specimen or a few specimens, is compared to living forms for which there are abundant data to capture inter-individual variability. Under this framework, there are two ways to argue that the fossil Elseya lavarackorum and the extant Elseya sp. aff. dentata [Nicholson] (
The second way to make a case that the fossil Elseya lavarackorum and the extant Elseya sp. aff. dentata [Nicholson] are different species is to argue that they are chronospecies, that is, that they are on the same evolutionary lineage, with the more recent individuals having diverged sufficiently from the earlier individuals to warrant them being considered as separate species. It is a significant challenge to demonstrate that variations seen between a single ancient fossil and modern-day individuals of the same species are not just a result of natural adaptations within the same species. The fossil that is from late Pleistocene sediments, aged by carbon dating (and companion fossils) at 23.9 Ka BP (+4100–2700) (
We argue that
We note that
Based upon our reanalysis of the fossils and associated characters in the extant forms, including those of subgenus Pelocomastes, we find that the differences between the fossil Elseya lavarackorum (White and Archer, 1994) and Elseya sp. aff. dentata [Nicholson] (
DW collected and photographed the specimens of Elseya lavarackorum and Elseya dentata from the Roper River drainage; AG and AW examined, photographed and measured the fossil specimens lodged with the
We thank Mike Archer and Anna Gillespie (
Abbreviations:
Elseya (Pelocomastes) lavarackorum (Holotype) Riversleigh, Queensland: registered
Elseya (Pelocomastes) sp. inc. ced. – Riversleigh, Queensland: Registered
Elseya (Pelocomastes) uberrima – Darling Downs, Qld. QMF 9040 (Lectotype;
Elseya (Pelocomastes) nadibajagu – Bluff Downs, Qld.: QMF30576 (Holotype), QMF30577
Elseya dentata – NHM 1947.3.6.2 (Paratype), NHM 1947.3.6.3 (Paratype) – Australia. King Edward River – WA 28119,
Elseya flaviventralis (voucher Label Elseya sp. aff. dentata [Sth Alligator]
Elseya branderhorsti –
Elseya albagula – Fitzroy-Dawson Drainage –
Elseya irwini (voucher label Elseya sp. aff. dentata [Johnstone]
Elseya lavarackorum – Roper River – NTM 16328–30 Red Lilly Lagoon, Roper River (14°42’ S, 134°05’ E);
Elseya rhodini – PNGM R25203 (Paratype), R25204 (Holotype), Rue Creek (tributary of Wau Creek), Gulf Province, Papua New Guinea (07°11’67.3” S, 144°37’13.8” E) MCZ134421 MCZ134422 MCZ134423 MCZ134424 MCZ134425 MCZ134426 MCZ134429 MCZ134430 MCZ134431
Elseya schultzei –
Elseya novaeguineae – MTKD 8222 (Holotype), Passim, Barbussi River, Papua, Indonesia, (1°41’S, 134°05’E), CRI 3133, CRI 6545–49, CRI 6586–88, CRI 6597, Indonesia: Irian Jaya, CRI 3397, captive hatched Germany, CRI 3787 no data ex Calif. Acad. Sci., CRI 4487, 7027, no data.
Myuchelys latisternum –
Myuchelys bellii – AM123028–29,
Myuchelys georgesi – CRI 5391–92, CRI 5449–50, Bellinger River, N.S.W. UM 02016–17, Bellinger River;
Myuchelys purvisi – CRI 2196, no data, CRI 2391, CRI 5390, CRI 5393–94, CRI 5447, Manning River, N.S.W., Australia, QM59289–90, Barnard River;
Figures S1–S4
Data type: .pdf
Explanation notes: Supplementary figures as referred to in the main text.
Tables S1–S4
Data type: .pdf
Explanation notes: Supplementary tables as referred to in the main text.
PAUP output
Data type: .pdf
Explanation notes: Output of the PAUP analysis, including the majority consensus and bootstrap consensus trees.