Purussaurus sp.

Scheyer, TM & Delfino, M, 2016, The late Miocene caimanine fauna (Crocodylia: Alligatoroidea) of the Urumaco Formation, Venezuela, Palaeontologia Electronica 176 (4), pp. 1-57 : 37-43

Purussaurus sp. Barbosa-Rodrigues, 1892

Giant, massive, non-gavialoid cranial elements assignable to Purussaurus sp. are stored at UNEFM-CIAAP in Coro and the MCNC collections in Caracas ( Figure 30 ), which are fragmentarily preserved and largely unprepared, such as specimens UNEFM-CIAAP-1434, MCNC-URU-76-72 V, MCNC-URU-90-72 V, and MCNC-URU-111-72 V. The latter two specimens comprise also associated postcranial bones. Again, MCNC-URU-111-72 V might constitute a mixed assemblage of several individuals, because there are at least two different sized cranial tables presented. Because of the poor state of preservation and/or preparation only selected specimens are presented here .

In addition, new or yet undescribed material assignable to Purussaurus sp. (due to their giant size and morphological congruence with described Purussaurus material) includes: 1) a fragmentary left mandible with most of the dentary and eight teeth preserved as well as the angular-surangulararticular complex (AMU-CURS-384; Figure 31.1- 4 ); 2) a posterior skull portion and associated quadrate (AMU-CURS-606; Figure 31.5-6 ); 3) two associated anterior mandible fragments with a strongly deformed tooth row (AMU-CURS-394; Figure 31.7 ); 4) a large anterior portion of a left mandible with the anterior-most 17 alveoli (which shows two generations of replacement teeth at broken cross-sectional surface) and the symphyseal portion of the right mandible preserving the first three and a half alveoli (AMU-CURS-671; Figure 32 ).

Seven isolated large teeth (AMU-CURS-006, - 022, -033 [two specimens], -046, -101; UNEFM-CIAAP 1432 ) have been found in the Urumaco Formation. Although we acknowledge that isolated teeth are usually not diagnostic and thus cannot be referred to a species or genus, in these cases, given their sheer dimensions and their asymmetrical, non-recurved built, we tentatively identify them as belonging to a giant caimanine, mostly likely to Purussaurus ( Figure 33 ). The teeth range between 19 mm and 39 mm in diameter at their base, are slightly labiolingually compressed and carry mesiodistal carinae. In addition, AMU-CURS-006 appears to carry a wear facet on its medial side. Of the two teeth accessioned as AMU-CURS-033 only the smaller one has been figured previously in Aguilera et al. (2006) .

Specimens AMU-CURS-162 (skull and lower jaw fragments) and -442 (lower jaw fragments associated with few postcranial remains including two osteoderms) have not been sufficiently prepared and are not shown here.

Caimaninae indet.

Many of the specimens found in the Urumaco Formation are too weathered, encrusted (or even completely substituted) by gypsum crystals, or too fragmentary to allow generic and specific assignment, for which we tentatively assign those specimens to Caimaninae indet. herein. The following specimens (with the exception of AMU-CURS-090, -100, -110, and -601) are all identified as Caimaninae based on rather flat skull roofs, dermal bone rims overhanging the supratemporal fenestrae, and the presence of supraoccipitals (where identifiable) on the skull roofs.

AMU-CURS-090 ( Figure 34 ) is a fragmentary lower jaw of about 15 cm length, heavily weathered, with at least 12 alveoli, and a single preserved posterior tooth. The jaw fragment is massive and deep as in Caiman brevirostris and Globidentosuchus brachyrostris , with the tooth having the appearance of a crushing tooth with a swollen crown. The specimen was previously labelled as “ Caiman ”, but is here treated instead as Caimaninae indet. In agreement with caimanine morphology, this specimen shows a dorsal curvature posterior to the fourth dentary alveolus.

AMU-CURS-100 ( Figure 35 ) is a badly weathered, short and stout anterior skull, and lower jaw fragment. It is tentatively referred to Caimaninae because of its overall resemblance of the robustness and shape of snout to Globidentosuchus (note also the presence of few robust globular upper jaw teeth; there is indication that the nasals reach the external narial opening). The posterior part of the skull and lower jaw is missing from about the posterior rim of the orbits. The specimen lacks further features which would allow assignment to the generic or specific level.

The specimen AMU-CURS-105/106 consists of a cranium and associated lower jaw material of a clearly durophagous caimanine from Tío Gregorio locality, uppermost Urumaco Formation. The material was previously labelled as Caiman brevirostris , prior to the description of Globidentosuchus brachyrostris ( Scheyer et al., 2013) . However, due to weathering and encrusting, there are no diagnostic features visible that would allow a clear identification to either of the two species and therefore the specimen is treated as belonging to Caimaninae herein ( Figure 36 ).

AMU-CURS-110 ( Figure 37 ) is a strongly weathered and gypsum-encrusted anterior part of a left lower jaw ramus 9.7 cm in length. Posteriorly, the anterior border of a large external mandibular fenestra is visible. Anteriorly, two robust teeth are mostly preserved, and a total of 16 alveoli could be counted forming a lightly sigmoidal tooth row. Two further broken tooth stumps in the posterior part of the tooth row indicate the presence of enlarged, closely spaced teeth in that part of the jaw. Whether the latter were conical or globular cannot be reconstructed. As in Globidentosuchus , the largest alveoli posterior to the fourth alveolus in the dentary is the thirteenth or fourteenth.

AMU-CURS-113 is the posterior part of a skull of a short-snouted caimanine ( Figure 38 ). The specimen was referred to Caiman brevirostris and shown in left lateral view in Riff et al. (2010). The material, however, is heavily deformed and partially encrusted with gypsum, and the anterior part of the rostrum, the premaxillae, and the posterior part of the left quadrate and quadratojugal are missing. Furthermore, sutures between bones are not visible on the dorsal side of the skull. In the right maxilla, 12 alveoli are present, with the fourth being the largest. The alveoli posterior to the fourth form a

SCHEYER & DELFINO: CAIMANINES FROM URUMACO FORMATION rather straight line and are not enlarged towards the back of the jaw, which argues against assignment to either of the durophagous species, C. brevirostris or Globidentosuchus brachyrostris (but is somewhat similar to the condition of the holotype skull MCNC-234 [field no. MCNC-URU-1-72V] of Melanosuchus fisheri ; see Medina, 1976). The specimen also has only a small exposure of the supraoccipital on the skull table unlike in G. brachyrostris . Ventrally, the secondary palate and suborbital fenestrae are complete and, with the exception of the pterygoids, little deformed. Sutures between the premaxillae, maxillae, palatines, and pterygoids, however, are not traceable.

AMU-CURS-217, a skull and associated lower jaws from the Playa Larga locality (lower Middle Member of the Urumaco Formation) was listed by Scheyer et al. (2013) as belonging to Melanosuchus fisheri . Re-examination of the specimen revealed that osteological features are too far encrusted and substituted by gypsum minerals precluding assignment of the specimen to any genus or species.

The material AMU-CURS-429 from El Mamón locality, previously identified as Caiman brevirostris , is reconsidered herein as Caimaninae indet. ( Figure 39.1-4 ). The posterior skull part and braincase was associated with a fragmentary maxilla and few postcranial elements (including two vertebral centra and a well-preserved femur). The alveolar spaces of the maxillary fragment are large and the interalveolar spaces small, indicating the presence of robust teeth as found in the durophagous species C. brevirostris and Globidentosuchus brachyrostris . The proportions of the skull table with rather small supratemporal fenestrae with overhanging rims would be consistent with those seen in caimanines, but clear diagnostic features are otherwise missing.

AMU-CURS-451 ( Figure 39.5-7 ) is a weathered and partly encrusted, isolated skull table of a small caimanine from the Corralito locality, Urumaco Formation. The supraoccipital is small and has only a triangular to slightly trapezoidal exposure on the skull roof, unlike the large crescent-shaped exposure seen in Globidentosuchus brachyrostris . A similar trapezoidal exposure is,

PALAEO- ELECTRONICA.ORG however, present in MCNC-1829 ( Caiman brevirostris ). In addition, the specimen has only small supratemporal fenestrae with overhanging bone rims.

AMU-CURS-601 ( Figure 40 ) is a weathered part of a small caimanine skull from ‘North of El Picache’ locality, Upper Member of the Urumaco Formation, consisting of a left articulated jugal and left partial quadratojugal. Anterior to the postorbital bar there appears to be an oval-shaped, sediment-filled patch that could indicate the presence of a large jugal medial foramen as was described for Globidentosuchus brevirostris ( Scheyer et al., 2013) . There is not a deep longitudinal trough between the jugal horizontal bar and the inset postorbital pillar, a usual character encountered in many caimanines.

The specimens UNEFM-VF-06 (from Tío Gregorio locality, Urumaco Fm.; Figure 41 ), -019, and - 022 (both from El Hatillo locality, Urumaco Fm.), all represent isolated skull table and braincase remains in various stages of preservation and gypsum encrustation. UNEFM-VF-06 includes also two associated vertebral remains and UNEFM-VF-022 includes a single vertebra. UNEFM-VF-019 was previously identified as “ Melanosuchus ”; however, there are no diagnostic features visible that allow for such an assignment.

Figures

FIGURE 30. Photographs of cranial bones of several individuals of Purussaurus. 1, Strongly weathered lower jaw ramus (UNEFM-CIAAP-1434) in medial view. 2-7, associated lower jaw fragments (MCNC-76-72V). 2, 3, dentary symphyseal region showing the symphyseal region in ventral (2) and dorsal (3) view. 4-6, posterior portions of the left (4) and right dentary, the latter in medial (5) and lateral (6) view. Note that part of splenial is still attached to dentary in (5). 7, left articular, surangular and portion of angular in medial view. 8, right articular and surangular in medial view. 9-16, associated skull and lower jaw fragments (MCNC-URU-90-72V). 9, 10, left ramus in ventral and dorsal view. 11- 14, two premaxillary fragments in dorsal and ventral view each. 15, 16, two dentary fragments in dorsal view. 17-25, skull and lower jaw fragments (MCNC-URU-111-72V), which were found in an assemblage of at least two individuals of different size. 17, partial skull in dorsal view. 18, smaller partial skull in dorsal view. 19, strongly weathered maxillary fragment (?) in ventral view. 20, left dentary fragment in dorsal view. 21, 22, right articular and surangular in dorsolateral (21) and dorsal (22) view. 23, 24, left angular, surangular, and articular in medial (23) and lateral (24) view. 25, dentary symphyseal region and portion of right dentary in dorsal view.

FIGURE 31. Cranial and lower jaw specimens of Purussaurus sp. 1-4, lower jaw fragments (AMU-CURS-384). 1, 2, left dentary in dorsal and medial view. 3, 4, left articular and angular in dorsal and lateral view. 5, 6, quadrate and skull table (AMU-CURS-606) in dorsal view. 7, dentaries of lower jaw (AMU-CURS-394) in dorsal view. Note the evident deformation of the left dentary.

FIGURE 32. Photographs (1, 2) of the anterior portion of the lower jaw of Purussaurus sp. (AMU-CURS-671) and interpretative drawing of the natural cross-section (3) of the right dentary. Abbreviations: ab, alveolar bone; rf; functional tooth; rt1, first replacement tooth; rt2, second replacement tooth.

FIGURE 33. Photographs of isolated giant crocodylian teeth assignable to Purussaurus sp. All but the smallest specimen (19 mm) show maximal cross-sectional diameters between 27 and 39 mm, which lie in the alveolar diameters of the largest Purussaurus specimens from Urumaco. 1, 2, tooth AMU-CURS-006 in rostral (1) and medial (2) view, carrying a wear facet. 3, 4, strongly weathered tooth AMU-CURS-046 in rostral (3) and medial (4) view. 5, 6, two teeth labelled AMU-CURS-033. 7, tooth AMU-CURS-101. 8, small tooth AMU-CURS-022. 9, 10, tooth UNEFM-CIAAP- 1432 in medial view.

FIGURE 34. Photographs of caimanine lower jaw fragment (AMU-CURS-090) in lateral (1) and medial (2) view.

FIGURE 35. Photographs of heavily encrusted anterior portion of a partial caimanine skull and lower jaw (AMU- CURS-100) in dorsal (1) and ventral (2) view.

FIGURE 36. Photographs of skull (1-3, 5) and associated lower jaw fragment (4, 5) of small Caimaninae indet. (AMU- CURS105/106). 1, dorsal view. 2, ventral view. 3, occipital view. 4, left dentary in dorsal view. 5, Close-up of mounted specimen (not to scale) showing a preserved knob-like crushing tooth in the posterior part of the maxilla (marked by white arrow).

FIGURE 37. Photographs of heavily weathered and altered caimanine lower jaw fragment (AMU-CURS-110) in lat- eral (1), medial (2), and dorsal (3) view.

FIGURE 38. Photographs of strongly deformed partial caimanine skull (AMU-CURS-113) in dorsal (1) and ventral (2) view.

FIGURE 39. Photographs of remains including an associated posterior skull and maxilla fragments (AMU-CURS-429: 1-4) and a weathered and partly encrusted, isolated skull table of a small caimanine (AMU-CURS-451: 5-7). Posterior skull table and braincase in 1, dorsal, 2, ventral, and 3, occipital view. Maxillary fragment (4) in ventral view. Isolated skull table in dorsal (5), ventral (6), and occipital (7) view showing small exposure of supraoccipital on the skull roof.

FIGURE 40. Photographs of small caimanine skull part (AMU-CURS-601) consisting of an articulated left jugal and partial quadratojugal in lateral (1) and medial (2) view.

FIGURE 41. Photographs of small caimanine skull roofs. A-C, UNEFM-VF-06 in dorsal (1), ventral (2), and occipital (3) view. 4, 5, UNEFM-VF-019 in dorsal and occipital view. 6, 7, UNEFM-VF-022 in dorsal and occipital view.