Dyrosauridae, de Stefano, 1903

Jouve, Stéphane & Rodríguez-Jiménez, José Vicente, 2024, The youngest known South American dyrosaurid (Late Paleocene of Colombia), and evolution of Dyrosauridae (Crocodyliformes: Tethysuchia), Geodiversitas 46 (17), pp. 931-953 : 936

Dyrosauridae indet.

( Fig. 4 )

DESCRIPTION

The centrum is weakly amphicoelous with both facets concave ( Fig.4A, C, D ), and shield-shaped (larger dorsally and pointed ventrally) ( Table 1). The anterior facet is deeper (9.75 mm) than the posterior facet (2.82 mm). In lateral views ( Figs 4B, E, F ), the centrum has a sub-quadrangular outline, being slightly higher (facet heights 61.52 and 61.82 mm) than wide (facet greatest widths 56.31 and 56.47 mm). The ventral margin of the centrum is faintly concave and bears a short hypapophysis on its anterior half. The anterior margin of the hypapophysis is much more vertical than its gently convex posterior portion, so that its lowest part is in the anterior quarter of the hypapophysis. The neurocentral suture is visible and runs transversally along the lateral margin of the centrum and remains ventral to the parapophysis.In the right lateral view ( Figs 4B, E ), the centrum presents a rounded parapophysis, located dorsal to the level of the ventral margin of the neural canal, and just posterior to the midlength of the centrum. The basal part of the diapophysis is preserved, dorsal to the parapophysis, and its location suggests that both apophyses were grouped on the same lateral peduncle of the neural arch, and that the diapophysis projected more laterally than the parapophysis. The parapophysis seems to have been ventral or slightly anteroventral to the diapophysis in lateral view. A small part of the right prezygapophysis is preserved. In dorsal view, the apophyses of the neural arch are broken, which only preserved the basal parts of the neural spine and apophyses ( Fig. 4G ). In lateral view, its anterobasal margin is located at the level of the parapophysis, at the level of the centrum midlength. In ventral view ( Fig. 4H ), the centrum appears constricted, hourglass-shaped, and with the centrum narrowest (39.80 mm) at ~71% of the margins (facet greatest widths 56.31 and 56.47 mm).

TAXONOMICAL ATTRIBUTION

The known diversity of the late Paleocene - early Eocene crocodyliforms is restricted to three taxa:sebecosuchians, crocodylians and dyrosaurids.The amphicoelous articular surface of the centrum excludes that the specimen was a crocodylian. The shape of the articular surface of the centrum being dorsoventrally slightly ovoid and almost as high as wide, combined with the centrum being almost as long as high, plus the poorly concave ventral margin of the centrum in lateral view are characteristics observed in dyrosaurids ( Buffetaut 1982; Jouve et al. 2006). These differ from the centrum of sebecosuchians, which is wider than high and longer than high, and has a strongly dorsally concave ventral margin ( Pol et al. 2012).

So, the present vertebra can be considered to be from a dyrosaurid.

Figures

FIG. 4. — Actual (A, B) and 3D model (C-H) pictures of anterior dorsal (D4 or D5) vertebra UN-DG-Rp-1001 of the Piñalerita Section,Cuervos Formation (Thanetian- Ypresian).Views:A, anterior;B, right lateral;C, anterior;D, posterior;E, right lateral;F, left lateral;G, dorsal;H, ventral.Abbreviations:d, diapophysis;z, prezygapophysis;z’, postzygapophysis;ns, neural spine;p, parapophysis;h, hypapophysis;ncs, neurocentral suture.The 3D model of the vertebra is provided in Appendix 1.