Striatochelys baba, Massonne & Augustin & Matzke & Bohme, 2023

Massonne, Tobias, Augustin, Felix J., Matzke, Andreas T. & Bohme, Madelaine, 2023, A new cryptodire from the Eocene of the Na Duong Basin (northern Vietnam) sheds new light on Pan-Trionychidae from Southeast Asia, Journal of Systematic Palaeontology (2217505) 21 (1), pp. 1-25 : 4-6

Striatochelys baba sp. nov.

( Figs 2–7 )

Diagnosis. Striatochelys baba can be differentiated from Striatochelys impressa comb. nov. by the combination of the following characters: (1) a larger costal VIII, forming the posterolateral margin of the carapace; (2) presence of ridges on the neurals, which are straight anteriorly and sinusoidal posteriorly; and (3) entoplastron callosity in the shape of a bulge (unknown for S. impressa and possibly a synapomorphy for S. baba + S. impressa ).

Etymology. The species name is derived from the Vietnamese word ‘Ba ba’, meaning softshell turtle, declared as substantive.

Holotype. GPIT-PV-112860, carapace, xiphiplastron, thoracic vertebrae (GPIT-PV-112860-1) and partial plastron (entoplastron, GPIT-PV-112860-2; hyoplastron right, GPIT-PV-112860-3; hyoplastron left, GPIT-PV-112860-4; hypoplastron right, GPIT-PV-112860-5) and further postcranial material (cervical vertebra, GPIT-PV-112860-6; left pectoral girdle, GPIT-PV-112860-7; left humerus, GPIT-PV-112860-8; right radius, GPIT-PV-112860-9; right ulna, GPIT-PV-112860-10; phalanx, GPIT-PV-112860-11).

Referred material. Additional material consists of: a nearly complete carapace missing only the nuchal with a right hyo- and hypoplastron (GPIT-PV-122867); a fragmentary carapace with a complete row of neurals and a nuchal (GPIT-PV-122879); the anterior part of a carapace associated with an entoplastron (GPIT-PV-122872); fragmented costals belonging to a larger individual (GPIT-PV-122875); fragmented costals and a right hypoplastron (GPIT-PV-122871); a costal fragment (GPIT-PV-122874); a medial part of a hypoplastron (GPIT-PV-122873); an anterior part of the carapace and right hyo- and hypoplastron (GPIT-PV-112861); a part of the carapace and plastron and a first thoracic vertebra (GPIT-PV-112862 and GPIT-PV-112863); multiple isolated costal fragments belonging to a single individual (GPIT-PV-112864); multiple carapace fragments belonging to a single individual (GPIT-PV-112865); left xiphiplastron and a right costal VIII (GPIT-PV-112866); and a single costal fragment (GPIT-PV-112867).

Additionally, an isolated pectoral girdle (GPIT-PV-122869) and skull (GPIT-PV-122870) putatively belonging to a single individual of a pan-trionychid turtle, as well as additional postcranial material consisting of an isolated costal fragment (GPIT-PV-122877), a phalanx (GPT-PV-122878) and a plastron fragment (GPIT-PV-112868) are tentatively referred to S. baba .

Type locality and horizon. The fossils were recovered from the base of layer 80 of the Na Duong coal mine (Bohme et al., 2013) in northern Vietnam (21 Ǫ 42.2 ĮN, 106 Ǫ 58.6 ĮE); Na Duong Formation, Eocene, late Bartonian–Priabonian age (39–35 Ma) .

Remarks. The holotype carapace of S. baba was embedded with its ventral part facing upwards. This allowed for a negative relief of the dorsal carapace, especially the ridges, in the sediment below. Based on those ridges, a cast was modelled for the missing posterior most part, but does not cover the correct outline, as seen in the posteriorly complete specimen GPIT-PV-122867.

Figures

Figure 2. Striatochelys baba, holotype, GPIT-PV-112860-1, Na Duong Formation, middle–upper Eocene, Vietnam. Carapace in A, B, dorsal and C, D, ventral views. Abbreviations: co, costal; cp, costiform process; dr, dorsal rib; ne, neural; nu, nuchal; tv, thoracic vertebra; xi, xiphiplastron. Scale bar equals 5 cm.

Figure 3. Striatochelys baba, GPIT-PV-122867, Na Duong Formation, middle–upper Eocene, Vietnam. Carapace in A, B, dorsal and C, D, ventral views. Abbreviations: alp, anterolateral process; co, costal; dr, dorsal rib; hyo, hyoplastron; hyp, hypoplastron; ne, neural; plp, posterolateral process; tv, thoracic vertebra. Scale bar equals 5 cm.

Figure 4. Striatochelys baba, Na Duong Formation, middle–upper Eocene, Vietnam. Carapace of GPIT-PV-122872 in A, dorsal and B, ventral views. Carapace of GPIT-PV-112862 in C, dorsal and D, ventral views. Carapace of GPIT-PV-112861 in E, dorsal and F, ventral views. Carapace of GPIT-PV-122879 in G, dorsal and H, ventral views. Abbreviations: co, costal; dr, dorsal rib; ent, entoplastron; epi, epiplastron; hyo, hyoplastron; hyp, hypoplastron; ne, neural; nu, nuchal; tv, thoracic vertebra. Scale bar equals 1 cm.

Figure 5. Striatochelys baba, Na Duong Formation, middle–upper Eocene, Vietnam. Plastron of holotype (GPIT-PV-112860-2, GPIT-PV-112860-3, GPIT-PV-112860-4, GPIT-PV-112860-5, GPIT-PV-112860-1) in A, B, dorsal and C, D, ventral views. Missing bones are mirrored and faded. Right medial hypoplastron fragment (GPIT-PV-122873) in E, dorsal and F, ventral views. Left xiphiplastron (GPIT-PV-122866) in G, dorsal and H, ventral views. Abbreviations: alp, anterolateral process; amp, anteromedial process; ent, entoplastron; hyo, hyoplastron; hyp, hypoplastron; plp, posterolateral process; xi, xiphiplastron. Scale bars equal A–D, 5 cm; E–H, 1cm.

Figure 6. Striatochelys baba, holotype, Na Duong Formation, middle–upper Eocene, Vietnam. Left pectoral girdle (GPIT-PV- 112860-7) in A, dorsal and B, ventral views. Cervical vertebra (GPIT-PV-112860-6) in C, dorsal and D, ventral views. Left humerus (GPIT-PV-112860-8) in E, dorsal, F, ventral, G, anterior and H, posterior views. Right radius (GPIT-PV-112960-9) in I, dorsal and J, ventral views. Left ulna (GPIT-PV-112860-10) in K, dorsal and L, ventral views. Phalanx (GPIT-PV-112860-11) in M, dorsal and N, ventral views. Abbreviations: acd, anterior condylus; ap, acromion process; ca, capitellum; cor, coracoid; dp, dorsal process; gf, glenoid fossa; hh, humerus head; if, intertubercular fossa; lp, lateral process; mp, medial process; ph, phalanx; prz, prezygapophysis; pz, postzygapophysis; sc, scapula. Scale bar equals 1 cm.

Figure 7. Skull of a Pan-Trionychidae referred to Striatochelys baba, Na Duong Formation, middle to upper Eocene, Vietnam. Skull of GPIT-PV-122870 in A, dorsal and B, ventral views. Scale bar equals 1cm.