Thereutherium thylacodes Filhol, 1876

Vianey-Liaud, Monique, Comte, Bernard, Marandat, Bernard, Peigné, Stéphane, Rage, Jean-Claude & Sudre, Jean, 2014, A new early Late Oligocene (MP 26) continental vertebrate fauna from Saint-Privat-des-Vieux (Alès Basin, Gard, Southern France), Geodiversitas 36 (4), pp. 565-622 : 608-610

Thereutherium thylacodes Filhol, 1876

HOLOTYPE. — MNHN.F.QU8588, anterior part of skull with left and right C-M2 ( Filhol 1877: figs 194-196).

DISTRIBUTION AND AGE. — France only: Quercy (“old collections” and, for the recent, well-dated localities Itardies and Le Garouillas), Saint-Privat-des-Vieux; Oligocene, from MP 23 to MP 26 for the material from the well-dated localities.

MATERIAL AND MEASUREMENTS. — Distal fragment of right M1 ( SPV 621). Length of the metastyle (from the carnassial notch to the distal rim) = 1.85 mm; height of the paracone (greatest distance between the cusp tip to the dentine/enamel junction) = 2.95 mm; angle between the metastyle and a line connecting the tip of the paracone to that of the metacone = 123°.

COMMENTS

Filhol (1876) created the species based on a single specimen. Ŋe brief description of this specimen (“[…] face avec le maxillaire inférieur en place et toutes les dents”; Filhol 1876: 289) does not make easy its precise identification in the collections. According to Lange-Badré (1979: 171), “Il est probable que la pièce Qu 8588 du M.N.H.N., portant la mention “type”, est effectivement celui de Filhol, bien que la mandibule n’y soit plus associée. C’est en tout cas le spécimen qu’a choisi cet auteur pour le figurer (1877, fig. 189-196)”. Ŋis definition of the name-bearing type needs some revisions, however. Indeed, in Filhol (1877), the figures 189 to 196 refer to three different specimens: two fragments of hemimandibles, MNHN.F.QU8592 ( Filhol 1877: fig. 190, 191, 193) and MNHN.F.QU8583 ( Filhol 1877: fig.189, 192), and the anterior part of skull with the upper dentition, MNHN.F.QU8588 (figs 194-196, where the incisors row, said to be unpreserved by Filhol, is shown reconstructed). Ŋe two fragments of hemimandibles (MNHN.F.QU8592, MNHN.F.QU8583) are from two distinct individuals and there is no evidence (size, wearing pattern, or preservation state) that one of them belongs to the same individual as MNHN.F.QU8588. In his contribution, Filhol (1877: 222) states that he possesses three specimens documenting the lower dentition, while he provides illustrations of only two of them. In 1877, he, then, had only in hands three more or less completely preserved hemimandibles and a single upper dentition. If the latter (MNHN.F.QU8588) certainly belongs to the individual on which Filhol based the species in 1876, none of the three fragmentary hemimandibles studied by Filhol in 1877 can be confidently identified as “le maxillaire inférieur en place et toutes les dents” that he mentioned earlier ( Filhol 1876) when he created the species. MNHN.F.QU8593 is the only of the two figured fragmentary hemimandibles to preserve a complete cheektooth row, but we know nothing about the third lower dentition mentioned by Filhol (1877). Ŋe lower dentition of the holotype individual cannot be identified.

DESCRIPTION

Ŋe specimen ( Fig. 17B ) preserves the metastyle, the metacone and a part of the paracone that includes the cusp tip. Ŋe metastyle is much lower than the metacone-paracone. Ŋe crowns of the two latter cusps are fused along most of their height; their tips remain well separated and a labial groove is still visible on the labial face. Ŋe paracone, the mesial part of which is not preserved, is taller than the metacone. A shallow notch is present between the metastyle and the metacrista.

COMPARISON AND DISCUSSION

Ŋe size and morphology of this fragmentary tooth support its assignment to T. thylacodes , one of the smallest known hyaenodontids (same size as the extant carnivoran Mustela putorius ). Ŋe specimen of Saint-Privat-des-Vieux is fragmentary, allowing only the length of the metastyle and the height of the paracone to be measured and compared to those of M1 from Quercy stored in the MNHN (material from the old collections and a few specimens from Itardies, MP 23). Ŋe length of the metastyle is lesser than in the material from the old collections of Quercy (2.17-2.35; n = 3), but it is similar to that of the metastyle of the only available M1 from Itardies (ITD 573 = 1.87). Ŋe height of the paracone is also lesser than in the material from the old collections (3.17 and 3.28 mm for the two specimens on which this cusp is preserved and not heavily worn), but it is greater than in ITD 573 (2.69; paracone slightly worn, however). Overall the individuals from Itardies are smaller-sized than those from the old collections. Morphologically, the specimen of Saint-Privat-des-Vieux cannot be dis- tinguished from the material from the Quercy. Ŋe paracone and the metacone are slightly less fused in Saint-Privat-des-Vieux M1 than in the holotype MNHN.F.QU8588, but this is also observed in other specimens from Quercy (e.g., MNHN.F.QU8590, MNHN.F.QU.ITD573). hvereutherium was assigned to the Limnocyonidae Wortman, 1902 (Lange-Badré 1979, 1995) before Morlo & Gunnell (2003) excluded it from this family. According to these authors, the presence, in T. thylacodes , of strong cingulids on premolars, the reduction of the metaconid on the lower molars and of the metacone on the upper molars may indicate a closer relationships to the Apterodontinae Szalay, 1967 (especially the genera Apterodon Fischer, 1880 and Quasiapterodon Lavrov, 1999 ) than to any other hyaenodontid subfamily. Such a close relationship must be strengthened, however, because T. thylacodes possesses more derived characters such as the loss of M3/m3 and a nearly complete fusion of the metacone and paracone on M1. Ŋe phylogenetic position of T. thylacodes remains uncertain and shall be addressed by including this genus in a wider phylogenetic framework. So far, the species was known only from Quercy. It is scarce in collections compare to other creodonts. Ŋe known material is essentially from old, imprecisely-dated collections from Quercy (a relatively abundant material is known, for example, in the collections of the MNHN and of the Naturhistoriches Museum, Basel). A few specimens (stored in the MNHN) were recently discovered from Itardies (MP 23; Lange-Badré 1979) and Le Garouillas (MP 25; Lange-Badré 1995). Ŋe specimen from Saint-Privat-des-Vieux is significant by extending both the stratigraphic (now, until MP 26) and geographic distributions of T. thylacodes .

Figures

FIG. 17. — Carnivors from Saint-Privat-des-Vieux (Gard; Lower Chattian, MP 26). A: Carnivora Gen. and sp. indet. cf. Palaeogale sp., fragmentary left p3, SPV680: A1, occlusal view, A2, labial view, A3, mesial view, A4, distal view; B, Thereutherium thylacodes Filhol 1876, distal fragment of right M2, SPV681: B1, labial view, B2, occlusal view, B3, lingual view, B4, mesial view. Scale bar: 1 mm.