Lamarquesaurus cabazai, APESTEGUÍA & ROUGIER, 2007

APESTEGUÍA, SEBASTIÁN & ROUGIER, GUILLERMO W., 2007, A Late Campanian Sphenodontid Maxilla from Northern Patagonia, American Museum Novitates 3581 (1), pp. 1-12 : 3-4

Lamarquesaurus cabazai , n. gen et sp.

Lepidosauria Haeckel, 1866.

Sphenodontia Williston, 1925 .

HOLOTYPE: MML-PV-42. Right maxilla preserving 10 teeth with different degrees of completeness. The fossil material is threedimensional and tooth enamel and wear facets are well preserved.

ETYMOLOGY: Lamarque after the city of Lamarque in Rio Negro province and its inhabitants, who have strongly supported paleontological exploration of northern Patagonia for decades; saurus, Greek for ‘‘reptile’’; and Cabaza, after Tito Cabaza, amateur paleontologist who discovered the Cerro Tortuga locality and called the attention of professional paleontologists to the region.

LOCALITY AND HORIZON: Lower to middle part of Allen Formation, ca. 6 m from the base levels of exposures at the ‘‘Cerro Tortuga’’ locality (39 ° 26 9 50 0 S, 67 ° 19 9 20 0 W) and ca. 52 m below the K/T (Cretaceous- Tertiary) boundary, recognized in the overlying Jagüel Formation (Gasparini et al., 2003; Casadío, personal commun.) The fossiliferous layer is 60–65 cm thick and is composed of clean, yellowish to light brown, friable medium sandstone. The layer yields a rich collection of disarticulated fossils with a clear bias to small specimens; fish and snake remains are particularly abundant.

DIAGNOSIS: Sphenodontid with the following combination of features: additional teeth separated by wide spaces; strongly concave maxilla; anterolingual flanges and shallow lateral ridges in maxillary teeth; labial border splits in two portions ( fig. 2 , sdf); antorbital region of the labial border deeply furrowed ( fig. 2 , rar); and deep concavities in the maxillary dentina over the third and fifth tooth positions (the last three characters are possibly uniquely derived features).

DESCRIPTION: The preserved part of the maxilla of Lamarquesaurus is 36 mm long and about 15 mm tall. The complete length is estimated at 45 mm. The ascending and premaxillary processes are broken. It is evident, however, that the former was wide with respect to the total length of the maxilla ( fig. 2A ) and that the latter was short. The jugal process is tall and not forked. In medial view ( fig. 2B ), the maxilla is deeply concave, and part of the jugal facet is preserved.

The infraorbital region shows two conspicuous foramina. The first is located right under the end of the ascending process, and the second is under the mid-length of the orbit, probably reflecting the piercing of the cutaneous branches of the maxillary artery and the maxillary branch of the V (trigeminal) cranial nerve (Oelrich, 1956). Part of the maxillary foramen is present in the broken cranial border. The foramen is visible as a small notch, but the section also shows part of the canal. In lateral view, the ventral edge bears a strong, 5-mm-tall border ( fig. 2 , sd), dorsally limited by a ridge, whose profuse ornamentation suggest muscle attachments. The ridge splits at the level of the beginning of the orbit. One ridge follows the horizontal, slightly upwardly bent original orientation, while the other runs downward to reach the last pre- served tooth, as in the eilenodontine Priosphenodon ( Apesteguía and Novas, 2003) .

Toward the cranial region, on the dentine border and over the positions of the third and fifth additionals, there are deep cavities that resemble the common wear marks that sphenodontids with precision bite have in the lower jaw. However, as this is not possible in a maxilla, they are considered here as cavities with unknown function.

Additional teeth are conical in shape, with labial vertical ridges and posterolingual flanges, as in Tingitana annoulae ( Evans and Sigogneau-Russell, 1997) . The additional teeth bear strong medial wear facets that were produced by propalinal movements of the lower jaw. Additional teeth are separated by wide spaces; probably no more than one or two teeth are missing posteriorly. Although small teeth are present in the antorbital region, they are more probably abraded additionals than actual hatchling teeth. A slightly larger tooth is occupying the anteriormost preserved tooth position, so there is no clear evidence to consider it as a successional tooth.

Figures

Fig. 2. MML-PV-42. Drawings (left) and pictures (right) of the right maxilla in A, lateral view; B, medial view; C, oclusal view. Abbreviations: ap, ascendent process; fwm, false wear marks; jf, jugal facet; mf, maxillary foramen; pf, palatine facet; rar, rugose anterior region; sd, secondary dentine; sdf, secondary dentine fork point; ur, upper ridge; Scale bar: 10 mm.