Purussaurus, Barbosa-Rodrigues, 1892

Scheyer, TM & Delfino, M, 2016, The late Miocene caimanine fauna (Crocodylia: Alligatoroidea) of the Urumaco Formation, Venezuela, Palaeontologia Electronica 176 (4), pp. 1-57 : 31-36

Purussaurus cf. P. mirandai Aguilera, Riff, and Bocquentin Villanueva, 2006

AMU-CURS-057 was previously listed as a referred specimen of Purussaurus mirandai by Aguilera et al. (2006). These lower jaw remains of a smaller (likely juvenile) individual are here figured for the first time ( Figure 26.1 ). They resemble the lower jaw remains of the P. mirandai holotype in shape and proportions. In addition, the dentaries are less deep than those of P. amazonensis . In this specimen the anterior parts of the left and right dentaries are preserved, showing 13 alveoli and 14 alveoli, respectively. The presence and shape of splenials is not clear because of preservational reasons. Compared to the complete lower jaw of the holotype UNEFM-CIAAP-1369, both fragments represent about one third of the total lower jaw length. Given the fragmentary nature of the specimen, however, we refer to it as Purussaurus cf. P. mirandai herein.

Besides the holotype specimen (UNEFM-CIAAP 1369) of Purussaurus mirandai , the UNEFM collections house also two other specimens assignable to Purussaurus cf. P. mirandai . These include a smaller, badly weathered posterior skull fragment ( Figure 26.2 ; UNEFM-CIAAP 1368/ 1372, stored at the museum in Coro), as well as a specimen which consists of numerous associated cranial and postcranial bones (UNEFM-CIAAP 1367, stored at the collections at Taratara near Coro) of which we present here only the left and right premaxillae (which are low in height and frame a large external narial opening) and three isolated teeth of various height ( Figure 26.3-5 ). The dorsal, medial, and lateral borders of the left premaxilla are only partially preserved, with the bone showing only four and a half alveoli, and it misses the dorsal posterior process completely. Ventrally, a portion of the secondary palate of the maxilla appears to be still attached to the premaxilla. The right premaxilla appears more complete dorsally and laterally, but it also shows only four and a half alveoli ventrally, and it lacks the dorsal tip of the posterior process.

Although it lacks the anterior snout portion and thus the characteristic narial opening, UNEFM-CIAAP 1368/1372 has a rather low skull height as is typical for Purussaurus mirandai . The specimen further shows a triangular skull shape with a squared skull table and a posterior gently concave margin, as well as small supratemporal fenestrae. Due to poor preservation sutures are not well traceable (with the exception of the right quadratequadratojugal suture). The posterior skull fragment is accompanied by a smaller bone fragment of unclear position on the anterior part of the rostrum. There is also a collection of seven isolated teeth accessioned under UNEFM-CIAAP 1368 (stored at Taratara near Coro), which are recurved and much too large (up to 10 cm in length) to belong to the posterior skull fragment curated in the same institution. These teeth rather belong to a giant gavialid, such as Gryposuchus .

In addition, a new associated large specimen, AMU-CURS-541 ( Figure 26.6 ), was recovered from the ‘ North of El Picache’ locality in November 2013, which included most of the lower jaw and some skull fragments besides numerous postcranial elements. The lower jaw is rather low and virtually identical in shape and proportions to that of the Purussaurus mirandai holotype. As this specimen is currently under study together with the associated postcranium elsewhere, we refrain from adding to its morphological description here .

Two specimens ( Figure 27 ) are stored in the show rooms of the Museo Paleontológico Urumaco, namely a right mandibular ramus (AMU- CURS-685), and a well-preserved, articulated lower jaw, which lacks part of the left dentary tip, the left surangular and the retroarticular process (MCN-USB no number). AMU-CURS-685 measures 133 cm in length the maximum height is 24 cm. The retroarticular process has a length of 14 cm from the posterior tip to the articular facet. MCN-USB no number shows 21 alveoli in both rami, despite the bad preservation of the right ramus, whose length is 130 cm; the length of the symphysis measures 17 cm. The splenials reach anteriorly up to the eighth alveolus. Although both jaws are congruent with the morphology described for the lower jaw of the holotype of Purussaurus mirandai (Aguilera et al., 2006) , them being isolated findings, we refer them to Purussaurus cf. P. mirandai instead.

An isolated right premaxilla with most of its posterior process intact (AMU-CURS-602; Figure 28 ) and disarticulated skull remains found associated with some postcranial elements of a single specimen (AMU-CURS-528; Figure 29 ), all assignable to Purussaurus cf. P. mirandai , were recovered in November 2013 from the Upper Member of the Urumaco Formation, in the ‘North of El Picache’ and ‘Northeast San Rafael’ localities, respectively. The premaxilla AMU-CURS-602 has a maximum length of 35.5 cm and a maximum width of 19.5 cm. AMU-CURS-528 includes the right premaxilla ( Figure 29.1-2 ) with five alveoli, the right jugal ( Figure 29.3-4 ), the left and right ectopterygoids ( Figure 29.5-8 ), a dentary fragment ( Figure 29.9-10 ), and seven isolated teeth ( Figure 29.11 ). The cranial elements were associated with an ischium, possible ilium, rib, and metapodial fragments, currently under study elsewhere). The long posterior premaxillary processes framing a large external nasal aperture together with the restricted thickness (=height) of the premaxillae in AMU-CURS-528 and AMU-CURS-602 argue for an assignment of the material to P. mirandai . The premaxilla also preserves a large margin of the incisive foramen, which does not reach in between the first premaxillary alveoli. The dentary fragment preserves the anterior portion of the external mandibular fenestra. In medial view, the scar for the articulation with the splenial is visible ventrally, whereas the dorsal border of the dentary is broken off. The jugal has a deep anterior portion, a strong inset portion of the postorbital pillar, and a slender infratemporal bar.

The ectopterygoids have a triangular articulation with the jugal and maxilla with the anterior process pointing medially, indicating that the ectopterygoid does not extend parallel to the posterior maxillary tooth row. The left ectopterygoid preserves an ectopterygoid-pterygoid flexure, typical of the caimanine crown group ( Brochu, 1999). The teeth of AMU-CURS-528 ( Figure 29 ) are more strongly weathered so that their original shape is often obscured and details are no longer visible. The width of the teeth at the base ranges in diameter between 16 mm and 30 mm, falling well into the range of the teeth accessioned as AMU-CURS-033 (Aguilera et al., 2006).

Figures

FIGURE 26. Photographs of specimens referable to Purussaurus cf. P. mirandai. 1, referred specimen AMU-CURS- 057, right and left dentaries in dorsal view. 2, posterior skull fragment UNEFM-CIAAP-1368/1372 in dorsal view. 3, 4, premaxillae of UNEFM-CIAAP-1367 in dorsal and ventral view. 5, three isolated teeth of UNEFM-CIAAP-1367. 6, lower jaw of AMU-CURS-541 in dorsal view.

FIGURE 27. Photographs of lower jaw material of Purussaurus cf. P. mirandai in the show room of Museo Paleontológico Urumaco. 1, right mandibular ramus in lateral view (AMU-CURS-685). 2, lower jaw in dorsal view (MCN- USB no number).

FIGURE 28. Photographs of isolated right premaxilla of Purussaurus cf. P. mirandai (AMU-CURS-602). 1, specimen prior to collection in the field (dorsal view). 2-4, surface scan model of specimen (taken with an Artec Spider Surface Scanner) in (2) dorsal, (3) ventral, and (4) lateral view.

FIGURE 29. Photographs of associated cranial material (AMU-CURS-528) of Purussaurus cf. P. mirandai. 1-2, right premaxilla in dorsal (1) and ventral (2) view. 3-4, right jugal in lateral (3) and medial (4) view. 5-6, right ectopterygoid in ventral (5) and dorsal (6) view. 7-8, left ectopterygoid in ventral (7) and dorsal (8) view. 9-10, dentary fragment in external (9) and internal (10) view. 11, isolated teeth (note different scale bar).