Platyspondylia, Rage, 1974

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 : 575

Platyspondylia sp.

( Fig. 2 )

MATERIAL EXAMINED. — 11 trunk ( SPV 737) and four caudal ( SPV 738 to SPV 741) vertebrae.

DESCRIPTION

All vertebrae are small (length of centrum <3 mm). Trunk vertebrae are mainly characterized by their markedly depressed neural arch and by the presence of an obtuse posterior median notch.Ŋe neural spine is developed, but not high, and it does not reach the zygosphene anteriorly. Ŋe interzygapophyseal constriction is well expressed. Ŋe centrum does not markedly widen anteriorly.Ŋe most significant features occur on caudal vertebrae. Aside from ventral structures, the overall morphology, and more specifically the neural spine and neural arch of caudal vertebrae are similar to those of the trunk region. A vertebra (SPV738) from the anterior portion of the caudal region bears a hypapophysis; although damaged, it appears clearly that its extremity is hollowed by a shallow sagittal groove ( Fig. 2 A-C). Another caudal (SPV739) is provided with a haemal keel whose posterior part has a ventral groove ( Fig.2 D-F). It is regarded as a vertebra from the posterior part of the anterior portion of the caudal region. SPV740 possesses the bases of broken off haemapophyses ( Fig. 2 G-I); it comes from the mid-caudal region. Ŋe position within the caudal region of a vertebra (SPV741), the ventral structures of which are broken off, cannot be determined.

DISCUSSION

Trunk vertebrae do not clearly differ from those of Platyspondylia lepta Rage, 1974 (MP 28-MP 30). However,in the latter the anterior border of the neural spine is vertical whereas it is inclined posteriorly on the specimens from Saint-Privat-des-Vieux. Ŋis is apparently a minor morphological difference, but stratigraphically the inclined border appears to be permanent from MP 22 to MP 26 (it being understood that no fauna including Platyspondylia is known from MP 27) ( Szyndlar & Rage 2003), whereas the vertical border occurs from MP 28 to MP 30, which may be significant. Augé & Rage (1995) suggested that this form with an inclined anterior border may represent a species distinct from P. lepta .

At higher taxonomic level, the fossils from Saint- Privat-des-Vieux afford an important information. Ŋe sequence of ventral structures observed on caudal vertebrae characterizes the Tropidophiinae , or Tropidophiidae s.s. ( Szyndlar et al. 2008). Up to now, the only known caudals of Platyspondylia were provided with paired haemapophyses, i.e. the condition known in vertebrae from the mid-section of the caudal region of Tropidophiidae s.s. but also in the entire caudal region of most snakes. Ŋe fossils from Saint-Privatdes-Vieux show that haemapophyses are absent in the anterior portion of the caudal region of Platyspondylia . In this portion, the ventral structure is azygous; it is either a hypapophysis, anteriorly, or a haemal keel, posteriorly.Only the available vertebra from the midcaudal region bears haemapophyses.Ŋis sequence of ventral structures in the caudal region (hypapophysis, haemal keel, haemapophyses) is known only in the Tropidophiidae s.s. Unfortunately, no vertebra from Saint-Privat-des-Vieux represents the third portion of the caudal region. Nevertheless, the available caudal vertebrae from Saint-Privat-des-Vieux confirm the referral of Platyspondylia to the Tropidophiidae s.s., an assignment that was questioned by Holman & Harrison (1998).Today, tropidophiids are restricted to northern South America, Central America and Carribean islands. However, representatives of the family were recorded in Europe from the early Eocene to the early Miocene.

Figures

FIG. 2 — Serpentes from Saint-Privat-des-Vieux (Gard; Lower Chattian, MP 26), Platyspondylia sp.: A-C, anterior caudal vertebra (SPV738): A, anterior view; B, left lateral view; C, ventral view; D-F: caudal vertebra (SPV739) from the anterior caudal region, but posterior to SPV738:D, anterior view; E, left lateral view; F, ventral view; G-I: mid-caudal vertebra (SPV740); G, in anterior view; H, left lateral view; I, ventral view. Scale bars: 2 mm.