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. 2019 Feb 18:7:e6280.
doi: 10.7717/peerj.6280. eCollection 2019.

A new testudinoid turtle from the middle to late Eocene of Vietnam

Rafaella C Garbin  1 , Madelaine Böhme  2   3 , Walter G Joyce  1
Affiliations

A new testudinoid turtle from the middle to late Eocene of Vietnam

Rafaella C Garbin et al. PeerJ. .

Abstract

Background: Testudinoidea is a major clade of turtles that has colonized different ecological environments across the globe throughout the Tertiary. Aquatic testudinoids have a particularly rich fossil record in the Tertiary of the northern hemisphere, but little is known about the evolutionary history of the group, as the phylogenetic relationships of most fossils have not been established with confidence, in part due to high levels of homoplasy and polymorphism.

Methods: We here focus on describing a sample of 30 testudinoid shells, belonging to a single population that was collected from lake sediments from the middle to late Eocene (35-39 Ma) Na Duong Formation in Vietnam. The phylogenetic placement of this new material is investigated by integrating it and 11 other species of putative geoemydids from the Eocene and Oligocene to a recently published matrix of geoemydid turtles, that embraces the use of polymorphic characters, and then running a total-evidence analysis.

Results: The new material is highly polymorphic, but can be inferred with confidence to be a new taxon, Banhxeochelys trani gen. et sp. nov. It shares morphological similarities with other southeastern Asian testudinoids, Isometremys lacuna and Guangdongemys pingi, but is placed phylogenetically at the base of Pan-Testuguria when fossils are included in the analysis, or as a stem geoemydid when other fossils are deactivated from the matrix. The vast majority of other putative fossil geoemydids are placed at the base of Pan-Testuguria as well.

Discussion: The phylogenetic placement of fossil testudinoids used in the analysis is discussed individually and each species compared to Banhxeochelys trani gen. et sp. nov. The high levels of polymorphism observed in the new taxon is discussed in terms of ontogenetic and random variability. This is the first time that a large sample of fossil testudinoids has its morphological variation described in detail.

Keywords: Geoemydidae; Intraspecific variation; Paleontology; Polymorphism; Testudinoidea.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1. Map of Southeast Asia showing Paleogene localities that yielded geoemydid turtles.
Stars: Maoming basin, China (eate Eocene); Krabi basin, Thailand (late Eocene—early Oligocene); Na Duong basin, Vietnam (middle to late Eocene). Based on UN map No. 4365.
Figure 2
Figure 2. GPIT/RE/09760, Banhxeochelys trani gen. et sp. nov., holotype, subadult, middle to late Eocene (Priabonian) of Vietnam.
(A) Photograph of carapace. (B) Illustration of carapace. (C) Photograph of plastron. (D) Illustration of plastron. Abbreviations: An, anal scute; co, costal; epi, epiplastron; Gu, gular scute; Hu, humeral scute; hyo, hyoplastron; Ma, marginal scute; mdf, musk duct foramen; ne, neural; nu, nuchal; per, peripheral; spy, suprapygal; Ve, vertebral scute; xi, xiphiplastron.
Figure 3
Figure 3. GPIT/RE/09735, Banhxeochelys trani gen. et sp. nov., adult, middle to late Eocene of Vietnam.
(A) Photograph of carapace. (B) Illustration of carapace. (C) Photograph of plastron. (D) Illustration of plastron. Abbreviations: An, anal scute; co, costal; ent, entoplastron; epi, epiplastron; Gu, gular scute; Hu, humeral scute; hyo, hyoplastron; Ma, marginal scute; ne, neural; nu, nuchal; per, peripheral; spy, suprapygal; Ve, vertebral scute.
Figure 4
Figure 4. GPIT/RE/09747, Banhxeochelys trani gen. et sp. nov., subadult, middle to late Eocene of Vietnam.
(A) Photograph of carapace. (B) Illustration of carapace. (C) Photograph of plastron. (D) Illustration of plastron. Abbreviations: Ab, abdominal scute; An, anal scute; Ma, marginal scute; ne, neural; per, peripheral; Pl, pleural scute; py, pygal; Ve, vertebral scute; xi, xiphiplastron.
Figure 5
Figure 5. GPIT/RE/09733, Banhxeochelys trani gen. et sp. nov., adult, middle to late Eocene of Vietnam.
(A) Photograph of carapace. (B) Illustration of carapace. (C) Photograph of plastron. (D) Illustration of plastron. Abbreviations: Ab, abdominal scute; An, anal scute; Ce, cervical scute; co, costal; ent, entoplastron; epi, epiplastron; Gu, gular scute; Hu, humeral scute; ne, neural; nu, nuchal; per, peripheral; Pl, pleural scute; Ve, vertebral scute; xi, xiphiplastron.
Figure 6
Figure 6. GPIT/RE/09749, Banhxeochelys trani gen. et sp. nov., subadult, middle to late Eocene of Vietnam.
(A) Photograph of carapace. (B) Illustration of carapace. Abbreviations: Ce, cervical scute; co, costal; epi, epiplastron; Gu, gular scute; ne, neural; per, peripheral; Pl, pleural scute; Ve, vertebral scute.
Figure 7
Figure 7. GPIT/RE/09731, Banhxeochelys trani gen. et sp. nov., adult, middle to late Eocene of Vietnam.
(A) Photograph of carapace. (B) Illustration of carapace. (C) Photograph of plastron. (D) Illustration of plastron. Abbreviations: Ab, abdominal scute; An, anal scute; Ce, cervical scute; co, costal; epi, epiplastron; Hu, humeral scute; hyo, hyoplastron; ne, neural; nu, nuchal; per, peripheral; Pl, pleural scute; py, pygal; xi, xiphiplastron.
Figure 8
Figure 8. GPIT/RE/09732, Banhxeochelys trani gen. et sp. nov., adult, middle to late Eocene of Vietnam.
(A) Photograph of carapace. (B) Illustration of carapace. (C) Photograph of plastron. (D) Illustration of plastron. Abbreviations: co, costal; epi, epiplastron; Hu, humeral scute; hypo, hypoplastron; ne, neural; nu, nuchal; Pl, pleural scute; Ve, vertebral scute; xi, xiphiplastron.
Figure 9
Figure 9. GPIT/RE/09738, Banhxeochelys trani gen. et sp. nov., adult, middle to late Eocene of Vietnam.
(A) Photograph of carapace. (B) Illustration of carapace. (C) Photograph of plastron. (D) Illustration of plastron. Abbreviations: co, costal; ent, entoplastron; epi, epiplastron; Fe, femoral scute; Gu, gular scute; Ma, marginal scute; ne, neural; nu, nuchal; Pe, pectoral scute; per, peripheral; Pl, pleural scute; Ve, vertebral scute; sp, suprapygal; xi, xiphiplastron.
Figure 10
Figure 10. GPIT/RE/09759, Banhxeochelys trani gen. et sp. nov., juvenile, middle to late Eocene of Vietnam.
(A) Photograph of carapace. (B) Illustration of carapace. (C) Photograph of plastron. (D) Illustration of plastron. Abbreviations: Hu, humeral scute; hyo, hyoplastron; Ma, marginal scute; ne, neural; nu, nuchal; per, peripheral; Pl, pleural scute; spy, suprapygal; xi, xiphiplastron.
Figure 11
Figure 11. GPIT/RE/09743, Banhxeochelys trani gen. et sp. nov., juvenile, middle to late Eocene of Vietnam.
(A) Photograph of carapace. (B) Illustration of carapace. (C) Photograph of plastron. (D) Illustration of plastron. Abbreviations: An, anal scute; co, costal; ent, entoplastron; epi, epiplastron; Hu, humeral scute; hyo, hyoplastron; ne, neural; nu, nuchal; per, peripheral; Ve, vertebral scute; xi, xiphiplastron.
Figure 12
Figure 12. Median length of the hypoplastron (HypoML) in a sample of 18 specimens of Banhxeochelys train.
The trend in the measurements show the presence of three size groups. Adults have a hypoplastron with 70 mm in length or more. Subadults have an average HypoML of 60 mm. Juveniles have a hypoplastron median length average of 40 mm.
Figure 13
Figure 13. Strict consensus of 133,736 most parsimonious trees including all extant and fossil species on our matrix.
Fossil species are shown in bold. Major extant clades of Geoemydidae retrieved as monophyletic are marked in colors.
Figure 14
Figure 14. Strict consensus of 133,736 MPTs after pruning all extinct species with exception of Guangdongemys pingi and Banhxeochelys train.
Major extant clades of Geoemydidae retrieved as monophyletic are marked in colors. Banhxeochelys trani is retrieved at the base of ingroup, Pan-Testuguria.
Figure 15
Figure 15. Summary of the individual position of each fossil species in the strict consensus of 133,736 MPTs, keeping only one fossil species at a time.
This figure is based on the consensi from Appendix S5. Clades were reduced to genus name to minimize differences between consensi. Sharemys hemisphaerica and the species of Sinohadrianus are omitted here, as their consensus was not in agreement with that from other species.
Figure 16
Figure 16. Strict consensus of eight most parsimonious trees resulting from analysis that includes Banhxeochelys trani as the only active fossil species.
This phylogenetic analysis followed the same parameters as the one for Fig. 13. Banhxeochelys trani is retrieved as sister to all extant geoemydid species. Major extant clades of Geoemydidae retrieved as monophyletic are marked in colors.
See this image and copyright information in PMC

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