Titanochelon cf. bolivari (Hernández-Pacheco, 1917)

Pérez-García, Adán, Suarez-Hernando, Oier, Hernández, Jose M., García, Salvador & Murelaga, Xabier, 2021, The freshwater and terrestrial turtles from Monte Pila and Fuenmayor (La Rioja, northern Spain): new data on the lower Miocene turtle diversity of the Ebro Basin, Geodiversitas 43 (3), pp. 75-94 : 88

Titanochelon cf. bolivari (Hernández-Pacheco, 1917) ( Fig. 12 )

MATERIAL EXAMIED. — Several generally disjointed and isolated remains, most of them corresponding to plates (e.g., MP 1b-418, MP 2-39, MP 2-79, MP 2-309, MP 2-313, MP 2-2018), but with some appendicular remains (e.g., MP 2-81-1, MP 2-81-5, MP 2-81- 3, MP 2-81-4) also being recognized ( Fig. 12 ).

LOCALITY AND HORIZON. — Monte Pila, municipality of Lardero, Autonomous Community of La Rioja, Spain. Levels MP 1 and MP 2. Western part of the Ebro Basin.Transitional facies between the Najera and Haro formations. Local zone Y, biozone MN 2, lower Miocene (see Figs 1 , 2 and the section Geographic and geological setting).

DESCRIPTION

A selection of the best preserved and most informative remains is presented in Fig. 12 . This taxon had a shell size of the adult individuals greater than one metre in length. The outer surface of the plates, both of the carapace elements and of those of the plastron, is granular. The carapace is interpreted as relatively low. Several costal plates are recognized. The medial margins of the costal plates indicates that this taxon showed an alternation of rectangular plates with non-rectangular ones, at least some of them probably being octagonal ( Fig. 12 A-C). At least some of the neurals are wider than long ( Fig. 12D ). The length of the first costal is interpreted as almost half of its width. Some costals were longer medially than laterally, but this condition was the reverse in others. The proximal region of the dorsal ribs was reduced. The vertebral scutes are interpreted as narrow, since they show a relatively short overlap on the costals. The sulci between the pleural and the marginal scutes were located on the contact area between the costal and the peripheral plates, which corresponded to well-developed sutures. This taxon lacked pointed tips in the region of contact of the sulci between two adjacent marginals with the lateral borders of the peripherals.

The entoplastron was noticeably wider than long ( Fig. 12E ). Due to its preservation, boundaries between scutes are not recognized on its ventral surface. The preserved postero-lateral area of a xiphiplastron, interpreted as belonging to a male considering the morphology of this plate in the genus Titanochelon , allows the identification of a well-developed ventral thickening posterior to the femoro-anal sulcus ( Fig. 12F ). That region shows a lateral protuberance. Ahead of this, the lateral margin of the xiphiplastron is almost straight. In fact, the posterior plastral lobe is trapezoidal, lacking a well-developed anal notch.

Several appendicular elements are recognized, including a fragment of the diaphysis of a robust femur, some elements of the carpal complex, and several phalanges. A medial fused with a lateral centrale is identified among the elements of the carpal complex ( Fig. 12 G-J). Among the preserved phalanges, several distal ones are recognized ( Fig. 12 K-S).

Figures

FIG. 12. — Several postcranial elements of the large tortoise Titanochelon cf. bolivari (Hernández-Pacheco, 1917) (Testudinidae), from the lower Miocene (MN2) of Monte Pila (Lardero, La Rioja, Spain): A, visceral view of a first right costal, MP2-313; B, dorsal view of the proximal region of a costal corresponding to an odd position in the costal series, MP2-309; C, dorsal view of the proximal region of a costal corresponding to an odd position, MP2-2018; D, lateral half of a third or fifth neural, MP2-39; E, visceral view of an entoplastron, MP2-79; F, ventral view of the latero-posterior region of a left xiphiplastron, MP1b-418; G-J, fused medial and lateral centrale, MP2-81-1, in proximal (G), anterior (H), posterior (I) and distal (J) views; K-M, distal phalanx, MP2-81-4, in proximal (K), lateral (L) and ventral (M) views; N-P, distal phalanx, MP2-81-5, in dorsal (N), lateral (O) and ventral (P) views; Q-S, distal phalanx, MP2-81-3, in dorsal (Q) and lateral (R, S) views. All of them come from the level MP2 except the partial xiphiplastron (F), from MP1. Scale bars: A-F, 5 cm; G-S, 1 cm.

FIG. 1. — Geographic and geological position of the fossil areas from which the remains of turtles studied in this paper come. 1, Fuenmayor (La Rioja); 2, Monte Pila (La Rioja); 3, the Bardenas Reales of Navarre (Navarre). All of them are located in the Spanish Ebro Basin.

FIG. 2. — Biostratigraphic diagram with the fossil areas studied in this paper situated in a stratigraphical table.The three outcrops indicated in the Bardenas Reales of Navarre correspond to Barranco de Tudela (BT), Nasa (N) and Rincón del Bu (RB). The chronological data are based on Larrasoaña et al. (2006) and Suarez-Hernando (2017).