Testudinidae

Luján, Àngel H., Čerňanský, Andrej, Bonilla-Salomón, Isaac, Březina, Jakub & Ivanov, Martin, 2021, Fossil turtles from the early Miocene localities of Mokrá-Quarry (Burdigalian, MN 4), South Moravian Region, Czech Republic, Geodiversitas 43 (20), pp. 691-707 : 698

Testudinidae indet. ( Fig. 4 )

LOCALITIES. — MWQ4/2018.

STUDIED MATERIAL. — Czech Republic. South Moravia Region, Mokrá-Quarry, shell and postcranial remains ( Fig. 4 A-M): Pal. 1363, shell fragment; Pal. 1364, scapula (i.e., anterodorsal process fragment); Pal. 1365, right fibula.

DESCRIPTION

Only a shell fragment formed by two portions of plates is known ( Fig.4 A-D).Pal.1363 corresponds most likely to a carapace portion, but it is poorly preserved and is not possible to assess this confidently. The length and maximum width of the preserved plate fragment is 6 cm. The external part is completely smooth and is not crossed by any sulcus ( Fig. 4C, D ). A suture is recognized on top of plate, which is concave and approximately 2 cm wide. A partial bone, belonging to the shoulder girdle, has been identified (Pal.1364: Fig.4 E-H). Only the anterodorsal process fragment is preserved.Pal.1364 is subcylindrical in cross-section and distally rounded.The distal surface ends in a rough rounded area to join with the visceral part of the carapace ( Fig. 4H ). The hind limb skeleton is restricted to one partial fibula ( Fig. 4 I-M) that is elliptical in cross-section. Its distal articular surface is slightly small, oval and convex ( Fig.4M ).Both postcranial bones are poorly preserved and no significant details can be discerned.

REMARKS

Fossil remains of giant tortoises are not very common in Miocene assemblages of Central Europe; their record being limited to few localities from Austria, Germany, Hungary and Switzerland (Alba et al. 2010, 2011; Carmona et al. 2011; Luján 2015). Loveridge & Williams (1957) proposed that all European giant tortoises should be transferred into the extant genus Geochelone . This proposal was adopted for some time, and consequently, large tortoise remains in Europe are still frequently referred to in the literature as Geochelone sp. (e.g., Auffenberg 1974; Młynarski 1976). However, current phylogenies do not support a close relationship between Mio- Pleistocene large tortoises and Geochelone . More recently, Bourgat & Bour (1983) referred all giant fossil tortoises to the genus Cheirogaster . Most subsequent works accepted this genus attribution (e.g., Luján et al. 2010, 2014), until recently when Pérez-García & Vlachos (2014) proposed that European Neogene giant tortoises constitute a clade that is more derived than the type species of Cheirogaster .To allocate these taxa, Pérez-García & Vlachos (2014) erected the genus Titanochelon , with Ti. bolivari (Hernández- Pacheco, 1917) as its type species. This genus is characterized by a shell reaching over 100 cm and the fusion of marginal scutes 12 (i.e., constituting a supracaudal scute). However, the evolution of gigantism amongst fossil tortoises is clearly a homoplastic phenomenon, mainly related to insular conditions, or adaptation to either global or local environmental changes ( Kear 2010; Luján et al. 2010, 2017b; Itescu et al. 2014). Similarly, the fusion of marginal scutes 12 occurs in many extant and extinct genera and cannot be considered autapomorphic for the genus Titanochelon . In summary, the taxonomy of the Miocene giant tortoises of Europe is still a subject of debate and will require improvement of existing data matrix (e.g., including more skull characters) in order to decipher the phylogenetic relationships of Titanochelon ( Luján et al. 2017b) .

Figures

FIG. 4. — Shell and postcranial remains of Testudinidae indet. from MWQ4/2018: A-D, Pal. 1363 (shell fragment); A, B, dorsal; C, D, visceral; E-H, Pal. 1364 (scapula); E, lateral; F, medial; G, anterior; H, dorsal; I-M, Pal. 1365 (fibula); I, dorsal; J, ventral; K, posterior; L, anterior; M, lateral views. Dotted lines indicate plate sutures and oblique lines denote missing plate portions. Abbreviations: fi, fibula; sc, scapula; sf, shell fragment. Scale bars: 1 cm.