Globidentosuchus, Scheyer, Aguilera, Delfino, Fortier, Carlini, Sanchez, Carrillo-Briceno, Quiroz and Sanchez-Villagra, 2013

Scheyer, TM & Delfino, M, 2016, The late Miocene caimanine fauna (Crocodylia: Alligatoroidea) of the Urumaco Formation, Venezuela, Palaeontologia Electronica 176 (4), pp. 1-57 : 11-16

Globidentosuchus cf. G. brachyrostris Scheyer, Aguilera, Delfino, Fortier, Carlini, Sánchez, Carrillo-Briceño, Quiroz and Sánchez-Villagra, 2013

AMU-CURS-083, -084 and UNEFM- VF-017 represent remains of small, broad-snouted caimanines with deep jaws and robust dentition. Based on comparison with the type material of Globidentosuchus brachyrostris and the newly referred specimen AMU-CURS-067 described above, specimens AMU-CURS-083, -084 and UNEFM- VF-017 likely belong to the same taxon. However, we use “confer” in classifying these latter specimens because, although the splenial participates in the symphysis, the material is otherwise fragmentary. The material differs from the Peruvian material of Gnatusuchus pebasensis , the other Miocene taxon in which the splenial participates in the symphysis, in the shape of the mandibles, the size and shape of the dentary alveoli, and in having less procumbent teeth.

The so far best-preserved material thus assigned herein to Globidentosuchus cf. G. brachirostris derives from a locally restricted coquina layer at the Bejucal Creek locality, ca. 500 m south of Urumaco town, in which the usually disarticulated bones and teeth are black to dark brown in colour. It also lacks any gypsum crystal crusts or infillings, which cause the most severe preservational biases of vertebrate fossils in the Urumaco Formation. The material assigned to G. cf. G. brachyrostris thus includes ( Figure 10 ): AMU- CURS-083, an associated left and right dentary and one isolated right dentary ( Figure 10.1-6 ); and AMU-CURS-084, one right maxilla (in two fragments with a neat contact fracture and therefore belonging to the same element), one right angular fragment, one left articular sutured to the surangular, one right surangular sutured to a posterior portion of a dentary, an isolated right surangular, as well as two isolated teeth ( Figure 10.7-18 ).

One right and one of the left dentaries were not only found in close proximity to each other but they belong to the same specimen because their symphyseal suture is clearly complementary ( Figure 10.1 ). The right one ( Figure 10.4-6 ) preserves the first 12 alveoli and half of the thirteenth; the left preserves the first nine and a half alveoli. The alveolus length – width (and interalveolar length) are reported in millimetres for these two dentaries (note that * indicates approximation): right dentary:?-10.6 (4.4); 6.6-5.4 (4.5); 7.4-6.1 (3.1*); 11.6*-12.0 (1.9); 7.3-6.0 (2.0); 5.5*-5.0 (?); 6.4*-4.7(?); 4.5-4.0 (2.1*); 4.0-4.0 (?); 4.5*-4.1* (?);?-? (?);?-7.9. Left dentary: 11.0*-10.9* (5.9); 8.9-6.1 (6.0); 7.0-5.5 (2.0*); 11.1-? (2.2); 7.4-7.1 (5.0); 6.3-4.9 (2.0); 5.2- 4.3 (1.6); 5.0*-4.4 (2.3). In lateral view, the dorsal edge of the dentary is undulated, with convexities corresponding to the first and fourth alveolus and the deepest point of the concavities corresponding to the second interalveolar space and the seventh alveolus. The splenial scar clearly indicates that this element was involved in the symphysis. In all the three specimens the dentary symphysis reaches the anterior edge of the seventh tooth (the splenial was probably rather thin and therefore it did not considerably increase the anteroposterior thickness of the symphysis). The Meckelian canal of the right and left dentaries belonging to the same specimen ( Figure 10.1 ) is equally narrow in the anterior portion of the dentary, and placed closer to the ventral than to the dorsal edge of the dentary. The other right dentary ( Figure 10.2-3 ) apparently has a much broader Meckelian canal, although this specimen experienced some crushing that could have widened the canal. The symphysis is broad (up to about 46 mm in the left dentary), long (about 55 mm), and relatively thin (22 mm). Several small (much smaller than the alveoli), deep foramina are aligned medially to the tooth row.

The poorly preserved maxilla corresponds to the first 11 alveoli ( Figure 10.7-8 ). In lateral view, it is rather flat and the ventral edge is undulated, with a ventral convexity corresponding to approximately the middle of the preserved portion of the maxilla. The fourth alveolus is the largest of the preserved series, but precise sizes of the alveoli cannot be measured because of preservational reasons. Tooth fragments are present in the alveoli 2, 8-10 and even if not complete, they seem to be quite slender and labiolingually compressed. Welldefined occlusal pits are present medially to the fifth alveolus (and the fifth interalveolar space), the sixth interalveolar space (and the seventh alveolus), and the tenth interalveolar space (and eleventh alveolus).

The right angular fragment ( Figure 10.9-10 ) preserves the anterior portion of the bone, so the articulation with the surangular and articular are not preserved. Anteriorly on the medial side, part of the ventral and posterior border of the foramen intermandibularis caudalis is preserved, whereas dorsally the scar for the articulation with the dentary is visible. Furthermore, two foramina are visible dorsally within the Meckelian groove.

In the fragment preserving the left articular and surangular ( Figure 10.11-12 ), the articular surangular suture is nearly rectilinear in the glenoid fossa when seen in dorsal view (it is only slightly bowed) and is rather simple ventrally to the fossa. The largest foramen in the area of the angular/ articular suture opens on the surangular only (very close to the glenoid fossa) and could represent the lingual foramen for the articular artery. There is no marked sulcus on the anterior face of the articular. The posterior tip of the retroarticular process has broken off.

The posterior portion of a right dentary (sutured to surangular; the contact surfaces with the anterior portion of the available dentaries are not preserved; Figure 10.13-14 ) hosts the lateral wall of the last six alveoli, which are clearly very large (probably up to at least 10 mm long) if compared to most of the anterior alveoli preserved in the other remains. The size of the alveoli slightly decreases towards the back of the row, but the last alveolus is nevertheless rather large. It seems that the medial wall of the alveoli was formed by the missing splenial. Also the other posterior portion of a right dentary shows the presence of enlarged alveoli. This dentary fragment is associated to a part of the corresponding surangular showing the smooth and widened dorsal edge. The isolated right surangular fragment ( Figure 10.15-16 ) preserves only the portion roofing the external mandibular fenestra. Anteriorly the contact to the dentary is not visible. The dorsal surface and the anterior portion of the lateral surface is smooth, whereas the posterior portion of the lateral surface shows pitting and foramina. Medially the scar for the articulation with the dentary is observable.

The best preserved right dentary ( Figure 10.4- 6 ) still hosts teeth in the fifth to seventh, tenth and eleventh alveoli. All these teeth are slender and pointed; labiolingually compressed, with an evident mesiodistal carina; the crown is slightly constricted at the base. The base of the eleventh tooth is 6.6 mm long and 5.2 mm broad, the crown 10.6 mm tall. Two isolated teeth ( Figure 10.17-18 ) associated with this material are bigger in size but not blunt, with the larger of the two having a wrinkled surface and the smaller also showing a constriction of the crown at the base. It remains unclear whether these teeth belonged to the skull or the mandibles.

Finally, the material of UNEFM-VF-017 (El Hatillo locality, lower Upper Member, Urumaco Fm.) includes ( Figure 11 ): three right dentaries ( Figure 11.1-4 ; one associated with its splenial) and one left dentary ( Figure 11.5-6 ), as well as one left angular ( Figure 11.7-8 ). Compared to the Bejucal Creek specimens, those from El Hatillo are mostly whitish or cream-coloured and one is light brownish in colour. The morphology of the incomplete dentaries from El Hatillo is fully congruent with that of the dentaries described from Bejucal Creek above. The best preserved element is the right dentary associated with the splenial ( Figure 11.4 ; both light brownish in colour). The alveoli from 2 to 11 are present, but a section of the first alveolus is visible along the anterior fracture. The fourth alveolus (the third preserved) is by far the largest. The splenial is relatively massive, being up to 4.2 mm thick. Its anterior tip clearly reaches the symphyseal area (at the level of the seventh alveolus) where it splits into two branches. Even considering that they could be only partially preserved, the lower branch seems to be the smallest and the shortest. It does not develop any sutural surface for the left splenial. Conversely the dorsal branch has an irregular surface that indicates at least a modest involvement in the jaw symphysis. The possible left angular ( Figure 11.7-8 ) does not provide additional information because of preservational reasons.

Figures

FIGURE 10. Photographs of Globidentosuchus cf. G. brachyrostris. 1-6, AMU-CURS-083. 7-18, AMU-CURS-084. 1, articulated left and right associated dentary in dorsal view. 2, 3, isolated right dentary in dorsal and angled medial view. 4-6, right dentary of (1) in lateral (4), dorsolateral (5) and angled medial view (6). 7, 8, right maxilla in angled lateral and angled medial view. 9, 10, right angular in medial and dorsal view. 11, 12, left articular and portion of surangular in angled medial and lateral view. 13, 14, right surangular sutured to part of dentary in angled medial and lateral view. 15, 16, left surangular in medial and lateral view. 17, 18, teeth. Abbreviations: d, dentary; ds, scar for dentary articulation; fic; foramen intermandibularis caudalis; fo, foramen; sa, surangular.

FIGURE 11. Images of Globidentosuchus cf. G. brachyrostris (UNEFM-VF-017) including three right dentaries (1-4), one left dentary (5, 6), and one left angular in angled dorsal (7) and medial (8) view. Images of dentaries in 3, 4, and 5 in dorsal view, 2 and 6 in ventral view. Note splenial associated with dentary and reaching the symphysis in (4).