Thaumastosaurus, DE STEFANO, 1903

Rage, Jean-Claude, 2016, Frogs (Amphibia, Anura) From The Eocene And Oligocene Of The Phosphorites Du Quercy (France). An Overview, Fossil Imprint 72 (1 - 2), pp. 53-66 : 59-60

Thaumastosaurus sp.

( Text-fig. 4 : 3, 4)

Among specimens referable to Thaumastosaurus sp. are a humerus, a 8 th presacral and a sacral vertebrae that were all regarded as belonging to a large Ranidae RAFINESQUE, 1814 by Rage (1984b: fig. 2A, C, D). During the recent excavations, specimens referable to Thaumastosaurus sp. were recovered in localities ranging from MP 16 (localities of Le Bretou and Lavergne; late middle Eocene) to MP 19, perhaps MP 20 (latest Eocene); the youngest specimen is a fragment of maxilla from Tabarly (MP 20) that is tentatively assigned to the genus.

Indeterminate ranoids

( Text-fig. 4 : 5–9)

Indeterminate ranoids from the Phosphorites include part of the ‘Ranidae’ reported by Rage (1984b). These ‘Ranidae’ are all represented by isolated bones. At that time, the concept of Ranidae was broader than it is today. The available bones closely resemble those of Recent European ranids and, therefore, they were assigned to the Ranidae ( Rage 1984b) . Sanchiz (1998) even suggested they probably represent the genus Rana LINNAEUS, 1758 ( Pelophylax FITZINGER, 1843 included in Sanchiz’s concept of a broader Rana ). However, it does not seem possible to demonstrate that these remains all belong to the Ranidae sensu stricto, as that family is now defined by Frost et al. (2006). In addition, as stated above, some bones (but not all) allocated to the ‘large form’ by Rage (1984b) actually belong to Thaumastosaurus sp.

In addition to Thaumastosaurus , at least three taxa of ranoids are present in the Phosphorites. This number of taxa is based on humeri. Indeed, three clearly distinct sizes are recognized. These specimens may be regarded as humeri of adult individuals ( Text-fig. 4 : 5–7), on the basis that for each morph the articular ball is entirely preserved and well shaped.

The small-sized ranoid ( Text-fig. 4 : 5) apparently occurs only in Eocene localities, from MP 16 (Lavergne) to MP 18 (Sainte-Néboule). In addition to humeri, at least one ilium, one scapula and some vertebrae may be referred to this small ranoid ( Rage 1984b). The size and the morphology of the bones are homogenous, which suggests that this small form likely represents a single taxon.

The mid-sized ranoid is present in the Eocene (Textfig. 4: 6) and Oligocene. Bones are rare and scattered in various localities. It is not possible to determine whether only one taxon is represented.

The size of the large form is similar to that of Thaumastosaurus . Humeri are distinguished from those of Thaumastosaurus by their more projecting articular ball, more developed lateral epicondyle and less slender diaphysis ( Text-fig. 4 : 7). A coracoid ( Text-fig. 4 : 9) from Escamps (MP 19) may be referred to this large taxon. It differs from that of Thaumastosaurus ( Text-fig. 4 : 2) in having a neck (corpus coracoidis, Špinar 1972) with more parallel borders and a more flaring pars epicoracoidalis. This large ranoid is reliably known from MP 16 to MP 19. It should be noted that Rage (1984b: fig. 2) reported a large ranoid from Lavergne (MP 16). However, as stated above, it is now possible to refer the humerus and vertebrae of this ranoid to Thaumastosaurus . The ilium of Thaumastosaurus being unknown, the ilium illustrated by Rage (1984b: fig. 2B) cannot be assigned within ranoids. Among ranoid bones from the Phosphorites figured by Rage (1984b), only the coracoid appears to belong to the large, indetermined ranoid.

As far as ranoids from the Eocene of the Phosphorites are concerned, the case of Rhacophoridae must be briefly addressed. This family was reported by Sanchiz (1998) from the Eocene of Escamps (MP 19). However, Sanchiz did not provide descriptions and he did not indicate on what bone(s) he based this identification. In view of the difficulty of identifying taxa within ranoids on the basis of isolated bones, neither the presence nor absence of rhacophorids may be confirmed. Today, the family occurs in sub-Saharan Africa and in southern and southeastern Asia. Fossils are known only from the Quaternary of Japan and perhaps from the Pliocene of eastern Europe ( Sanchiz 1998).

Ranoids from the Oligocene of the Phosphorites are less frequent than in the Eocene. The few available bones do not permit reliable comparisons with specimens from the Eocene. Ranoid bones are unknown at Phosphorites from the basal Oligocene (MP 21) and apparently from MP 24 to MP 27. A report from the late Oligocene of Pech-du-Fraysse (MP 28; Crochet 1972) is not confirmed. This scarcity of material likely reflects increasing aridity during the Oligocene.

Problematic taxa

Figures

Text-fig. 4. Ranoids from the Phosphorites du Quercy. 1: Thaumastosaurus gezei, urostyle in left lateral (a), dorsal (b), and anterior (c) views. 2: T. gezei, left coracoid in medial view (the urostyle and coracoid are parts of the ‘mummy’ MNHN.F.QU17279). 3: Thaumastosaurus sp., left scapula UM-ECA 2537, from the late Eocene of Escamps (MP 19), in lateral (a) and medial (b) views. 4: Thaumastosaurus sp., left humerus UM-MAL 619, from the late Eocene of Malpérié (MP 17), in ventral (a) and medial (b) views. 5: Ranoid indeterminate, small-sized form, right humerus UM-LAV 1280, from the late Eocene of Lavergne (MP 16), in ventral view. 6: Ranoid indeterminate, mid-sized form, left humerus UM-ECA 2558, from the late Eocene of Escamps (MP 19), in ventral view. 7: Ranoid indeterminate, large sized form, left humerus UM-ECA 2557, from the late Eocene of Escamps (MP 19), in ventral (a) and medial (b) views. 8: Ranoid indeterminate, mid-sized form, left scapula UM-ECA 2560, from the late Eocene of Escamps (MP 19), in lateral (a) and medial (b) views. 9: Ranoid indeterminate, large-sized form, left coracoid UM-ECA 2559, from the late Eocene of Escamps (MP 19), in medial view. (1 and 2, redrawn from images segmented by F. Laloy in 2012). Each scale bar = 3 mm.