Voay robustus, Grandidier & Vaillant, 1872

Brochu, Christopher A., 2007, Morphology, relationships, and biogeographical significance of an extinct horned crocodile (Crocodylia, Crocodylidae) from the Quaternary of Madagascar, Zoological Journal of the Linnean Society 150 (4), pp. 835-863 : 840-841

VOAY ROBUSTUS ( GRANDIDIER & VAILLANT, 1872)

Neotype: MCZ 1006 , skull ( Fig. 1 ).

Referred material: AMNH FR 3100, partial skull; AMNH FR 3101, skull ( Figs 2 , 3); AMNH FR 3102, skull; AMNH FR 3103, mandible; AMNH FR 3104, right mandibular ramus (Fig. 4); AMNH FR 3105, mandible; AMNH FR 3106, vertebrae; AMNH FR 3107, osteoderms; AMNH FR 17008, ribs; AMNH FR 17709, right ilium; AMNH FR 17010, right ulna; AMNH FR 17011, metacarpal, phalanx; AMNH FR 17012, right astragalus; BMNH R 2001, osteoderms; BMNH R 2002, teeth; BMNH R 2026, skull and jaws; BMNH R 2027, osteoderms, including articulated nuchal elements; BMNH R 2081, squamosals and parietal; BMNH R 2083, partial right dentary and left articular, surangular, angular; BMNH R 2085, caudal and trunk vertebrae; BMNH R 2086, right ilium; BMNH R 2087, right femur; BMNH R 2088, two femora; BMNH R 2089, right ischium; BMNH R 2090, left humerus; BMNH R 2091, radius; BMNH R 2093, metatarsal; BMNH R 2097, left fibula; BMNH R 2102, partial skull table and braincase; BMNH R 2103, teeth; BMNH R 2192, braincase and skull table; BMNH R 2193, partial skull and jaws; BMNH R 2194, teeth; BMNH R 2195, vertebrae from at least two individuals; BMNH R 2196, two left humeri; BMNH R 2197, osteoderms; BMNH R 2198, three ulnae; BMNH R 2199, left fibula; BMNH R 2200, left coracoid; BMNH R 2201, calcaneum; BMNH R 2202, three femora; BMNH R 2203, two left ilia, one right ilium; BMNH R 2204, partial skulls; BMNH R 2205, partial right coracoid; BMNH R 2206, ribs and caudal vertebrae; BMNH R 2211, left fibula; BMNH R 2218, vertebrae (trunk, sacral, caudal) and cervical rib; BMNH R 2219, pathological dorsal vertebrae with fused centra; BMNH R 2220, partial left femur, complete left femur; BMNH R 2222, right radius; BMNH R 2223, ribs; BMNH R 2401, partial jaws; BMNH R 2402, two cervical vertebrae; BMNH R 3088, distal caudal vertebrae; MNHN 1906–16; MNHN 1932.80; MNHN 1908.5, postcranial material; MNHN 1932.80, partial skull.

Occurrence: Late Quaternary, Madagascar. The form is known from multiple sites across the island. The neotype was found near Antsirabe and described by Mook (1921: 26) as ‘probably late Pleistocene’. Although most Quaternary deposits in Madagascar are Holocene, some of the radiocarbon dates reported from Antsirabe by Burney et al. (2004) are slightly older than 20 Ka. It is thus possible that MCZ 1006 is from the uppermost part of the Pleistocene.

Etymology: Voay , Malagasy, ‘crocodile’. The name robustus refers to the robust construction of the skeleton.

Diagnosis: Osteolaemine crocodylid with a prominent triangular crest at the posterolateral corner of each squamosal and a pair of oval bosses on the frontal between the orbits. Supratemporal fenestrae constricted, with no dorsal fossae. Nasals form thin processes that penetrate the narial rim, but premaxillae approach each other closely behind external naris. Surangular–angular suture intersects external mandibular fenestra at the posteriormost end laterally and does not pass anteriorly along the ventral margin of the fenestra (reversal of derived feature in crocodylids). Circular boss on medial surface of splenial. Vaulted premaxillary and maxillary palate surfaces. Shares everted choanal margin (choanal ‘neck’) and lateral extension of squamosal on to quadrate ramus with other osteolaemines; shares broad supraacetabular buttress and altirostral skull with Osteolaemus .

Description

Primary cranial/mandibular openings: The circular external naris opens anterodorsally. The nasals enter the dorsal narial rim as a pair of thin processes. The narial chamber is comparatively deep, and the dorsal surface of the premaxillae is inflated around the narial rim.

The incisive foramen is subtriangular in shape, completely surrounded by the premaxillae, and nearly as large as the external naris.

The orbit is surrounded by the frontal, prefrontal, lacrimal, jugal, and postorbital. Because the skull is dorsoventrally deep, the orbits open laterally to a greater degree than in extant Crocodylus . Most of the orbital rim is upturned.

The infratemporal fenestra is triangular and anteroposteriorly short, resembling its counterpart in Osteolaemus . The jugal forms the anteroventral and posteroventral corners, and the quadratojugal intersects the fenestral margin above the posteroventral angle. The quadratojugal terminates shortly below the dorsal angle of the fenestra, which is formed by the postorbital.

The supratemporal fenestrae are very characteristic. They are relatively small and set forward on the skull table. The roofing bones (parietal, postorbital, squamosal) lap over the fenestral rim, obliterating the dorsal fossa. The frontoparietal suture does not intersect the fenestral margin. A small, circular opening for the temporal canal lies on the posterior wall of the supratemporal fenestra, surrounded dorsally by the squamosal and parietal and ventrally by the quadrate.

The external otic aperture is clover leaf-shaped in outline and surrounded dorsally by the squamosal and posteriorly, ventrally, and anteriorly by the quadrate. The quadrate–squamosal suture extends dorsally along the posterior margin of the aperture.

The suborbital fenestra is an anteroposteriorly elongate oval surrounded medially by the palatine,

Figures

Figure 1. MCZ 1006, neotype, Voay robustus, dorsal (A, C) and ventral (B, D) views. Scale = 5 cm.

Figure 2. AMNH 3101, Voay robustus, skull, right lateral view. Scale = 5 cm.