Caiman, Daudin, 1802

Scheyer, TM & Delfino, M, 2016, The late Miocene caimanine fauna (Crocodylia: Alligatoroidea) of the Urumaco Formation, Venezuela, Palaeontologia Electronica 176 (4), pp. 1-57 : 44-50

Caiman latirostris and Caiman wannlangstoni

Based on MCNC-URU-145-72V and AMU- CURS-49, Aguilera (2004, p. 93) described the external naris in the extinct Caiman lutescens from Urumaco as being relatively small and heartshaped in comparison to that of the extant Caiman latirostris . Rovereto (1912), however, already mentioned that the length and shape of the nasals can be quite variable in the extant species (at least partly due to ontogenetic changes). This was corroborated by Bona and Desojo (2011), who pointed out that in some individuals of C. latirostris the nasals can be excluded from the external naris whereas, in other individuals, the nasals enter the external naris, creating a “heart-like outline” of the opening. Our re-analysis of AMU-CURS-049 and MCNC-URU-145-72V indicate that the specimens

PALAEO- ELECTRONICA.ORG do not belong to the same taxon. The snout shape in MCNC-URU-145-72V is more consistent with C. latirostris ( Bona and Desojo, 2011; personal obs. TMS on PIMUZ specimen) and corroborate the work of Riff et al. (2010) in substituting C. lutescens with C. latirostris in the crocodylian faunal list of Urumaco published previously ( Scheyer and Moreno-Bernal, 2010; Scheyer et al., 2013). On the other hand, we agree with the assignment of AMU-CURS-049 to Caiman wannlangstoni as proposed by Salas-Gismondi et al. (2015), based mainly on the strongly sinuous lateral margins of the rostrum in dorsal view and the presence of tightly packed, large and globular posterior teeth in the specimen.

Globidentosuchus brachyrostris and Globidentosuchus cf. G. brachyrostris

The new material referred to Globidentosuchus brachyrostris and Globidentosuchus cf. G. brachyrostris present a refined look at the lower jaw morphology of the taxon, extending previous descriptions of the species ( Scheyer et al., 2013). In particular, the more complete material of AMU- CURS-067 allows the elucidation of the bone configuration in the posterior part of the mandible, as well as the size and shape of the external mandibular fenestra and the foramen intermandibularis caudalis (which are overall similar to that of the extant broad-snouted Caiman latirostris ). Besides the crushing dentition, which consists of a unit of eight globular, tightly spaced teeth, and the participation of the splenial in the symphysis, the horizontal rather than an angled surangular-angular suture

SCHEYER & DELFINO: CAIMANINES FROM URUMACO FORMATION

(in lateral view) is another consistent feature separating G. brachyrostris from C. brevirostris .

The inclusion of the new material expands the occurrence of the taxon to the Lower Member of the Urumaco Formation at the Bejucal Creek locality (AMU-CURS-083, -084), the lower Middle Member, Urumaco Formation, at the Playa Larga locality (AMU-CURS-67), as well as to the El Hatillo locality (UNEFM-VF-017) in the Upper Member of the Urumaco Formation.

Caimaninae aff. Melanosuchus fisheri

AMU-CURS-234 lacks crushing dentition, which precludes assignment to either Globidentosuchus brachyrostris or Caiman brevirostris . Furthermore, the less laterally expanded skull shape, the proportions of the skull table, and the diameter of the upper temporal fenestra, as well as the arching of the interorbital ridge are similar to those of the holotype skull of Melanosuchus fisheri (MCNC-243) and MCZ 4336. Pending the revision of the holotype material of M. fisheri elsewhere, AMU- CURS-234 is treated as Caimaninae aff. Melanosuchus fisheri herein.

Mourasuchus

Re-analysis of the material of both species in the Caracas, Coro, and Urumaco collections and comparison with the detailed anatomical study of other pertinent Mourasuchus material from other regions in South America ( Bona et al., 2013a; Tineo et al., 2015) leads us to raise the question about the potential synonymy of the two species, M. arendsi and M. nativus . This is based on the fact that we found the posterior skull bone configuration and description of UNEFM-CIAAP-1297, the holotype skull of M. arendsi as reconstructed by Bocquentin Villanueva (1984), to be erroneous or ambiguous at best in several aspects. As such we interpret the dorsal skull bone configuration seen in M. arendsi ( Figures 13 , 14 , 15 , 16 ) to be much more similar to M. nativus than previously recognised. In the following, we list the most important anatomical aspects, on which we base the proposed synonymy of the two species: 1) Bocquentin Villanueva (1984) reconstructed the skull roof of the holotype of M. arendsi with a gentle concavity in occipital view, whereas a transverse

SCHEYER & DELFINO: CAIMANINES FROM URUMACO FORMATION robust ridge with prominent squamosal eminences was thought to be diagnostic for M. nativus ( Gasparini, 1985) . Variation in the height and development of these eminences among different specimens (of different ages) was interpreted as pertaining to sexual dimorphism ( Gasparini, 1985), ontogenetic growth variation linked to overall size ( Bona et al., 2013a), or thought to be connected to a “significant amount of superficial vasculature associated with the skull roof […] a concept forwarded by Gasparini (1985) for the genus “ Carandaisuchus .”” ( Bona et al., 2013a, p. 238). Reanalysis of UNEFM-CIAAP-1297 reveals that the specimen also had moderately developed squamosal eminences forming an incised V-shaped valley ( Figure 16 ). The skull of MCNC-URU-110-72V does not offer more information in this regard, because its skull table is completely reconstructed by plaster so that neither the posterior transverse ridge nor the squamosal eminences are original bone.

2) Four perforations of the premaxilla are present anteriorly and laterally to the external naris in the holotype skull UNEFM-CIAAP-1297 (also in AMU- CURS-395). Langston, (1965) showed interpretative drawings of the premaxilla of Mourasuchus atopus (type specimen UCMP 38012) from the Miocene of La Venta, Colombia, in which only the first and fourth tooth in each mandible pierced its respective occlusion pit; the second and third occlusion pits remained covered with bone. In contrast to M. atopus , the diameter of the perforations decreases slightly from the first to the fourth in the Urumaco specimens, which fits with a small but continuous decrease of the alveolar diameter of the four anterior-most teeth in the lower jaw (i.e., AMU-CURS-073). It cannot be stated with confidence whether the four pits in the specimens from Urumaco similarly resemble true perforations of the premaxilla that occurred during life, or if the bone covering the occlusion pits was fully or at least partly eroded in the heavily weathered fossils. It also remains unclear whether the number of teeth perforating the premaxilla in Mourasuchus from Urumaco increases during ontogeny, a notion also discussed in Langston (2008). Furthermore, there is no good description of the anterior rostral portion of the skulls of M. nativus from Argentina, which precludes comparison ( Bona et al., 2013a). Therefore, pending better preserved findings, taking the perforations as a diagnostic feature separating M. arendsi from other species of Mourasuchus should be treated with caution.

3) Similar to Mourasuchus nativus (Bocquentin and Souza Filho, 1990) there is a small but evident sagittal crest on the postero-dorsal surface of the parietal, which had not been noted before in the holotype (UNEFM-CIAAP-1297) of M. arendsi . A crest is also present in specimen AMU-CURS-218.

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4) The nerve openings of the braincase were regarded as diagnostic for Mourasuchus nativus ( Bona et al., 2013a). Unfortunately, the material of M. arendsi from Urumaco is insufficiently preserved to allow a detailed comparison of these features.

5) The presence of a notch at the lateral edge of the jugals separates Mourasuchus amazonensis and M. nativus from M. atopus , the latter lacking this anatomical feature (see Table 1). Our reanalysis shows that the holotype of M. arendsi also has a clear notch when the broken off jugals are rotated dorsally, back into their natural position. A clear notch is also present in another specimen (MCNC-URU-110- 72V), tentatively assignable to M. arendsi .

6) The absence of raised bony knobs at the rostral orbital margins has been stated before to separate Mourasuchus nativus from the three other species: M. amazonensis , M. atopus and M. arendsi ( Bona et al., 2013a). Salas-Gismondi (2015), however, showed a set of highly prominent eminences in specimen MUSM 2378 attributed to M. atopus from Peru, which indicates that the lack of eminences is restricted only to M. amazonensis . However, since this is isolated material its assignment to M. atopus remains questionable. In addition, AMU-CURS-218 from the Urumaco Formation has both raised orbital rims (the right is mostly broken off) and very prominent, raised bony knobs anteromedial to the orbits ( Figure 19 ), situated on the prefrontals. In UNEFM- CIAAP-1297, the orbital rim is extremely developed at the anteromedial sector, but the ridge continues along the orbit in the interorbital region. This ridge is much less developed in the lateral sector of the orbit, but it is clear that the orbital rim is also distinctly raised laterally. This is clearly visible on the right orbit, but the part which is preserved on the left orbit confirms what is visible on the right side. As the bony knobs at the orbital margins might not appear in all specimens (i.e., in the holotype of M. arendsi and referred specimen AMU-CURS-218 of M. nativus ), we would like to raise the possibility that these bony excrescences are a potential sexually dimorphic feature (compare to the soft-tissue narial excrescences, the ghara, of larger male Gavialis gangeticus ; Martin and Bellairs, 1977).

7) Bocquentin Villanueva (1984) noted that in Mourasuchus arendsi the palatine bones are expanded more transversely between the suborbital fenestrae than in M. atopus , although Langston (1966) pointed out the possibility that the holotype of M. atopus may represent a juvenile specimen. As such, this feature may vary throughout ontogeny and it might also vary intraspecifically with the species of Mourasuchus . Furthermore, this feature is not present in the holotype MLP 73-IV-15-8 (or in the referred specimen MLP 73-IV-15-9) of M. nativus ( Bona et al., 2013a, b). For now, the small sample size and poor preservation of many specimens hamper the usage of this character, and so it is treated as insufficient to separate species of Mourasuchus herein.

As outlined above, the presence/absence of:

1) squamosal eminences, 2) pronounced knobs at the orbits, 3) a prominent notch of the jugals, and

4) a median crest or ridge on the parietal are not sufficient to separate Mourasuchus arendsi ( Bocquentin Villanueva, 1984) from M. nativus ( Gasparini, 1985) ; and based on this synonymy M. arendsi would have priority. In summation, there could be only three separate species of Mourasuchus in South America: M. amazonensis from the late Miocene of Brazil, M. atopus from the middle Miocene of Colombia and likely Peru, and M. arendsi from the late Miocene of Argentina, Brazil and Venezuela. In addition, the genus Mourasuchus is also known from the late Miocene of Bolivia. As such, the dispersal of Mourasuchus over large areas of the South American continent could have started with the arrival of a Palaeogene ancestral form arriving from North/Central America (alternatively Mourasuchus could be an endemic taxon that evolved on the South American continent). During the mid-Miocene, Mourasuchus could then have spread from the proto-Amazonian areas of Colombia and Peru eastward, and inhabiting Venezuela and then Brazil and Argentina during the late Miocene.

Purussaurus mirandai

According to our revision and based on ongoing fieldwork, Purussaurus is considered to be a common element in the crocodylian community that is preserved in the Urumaco Formation. Many of the new, better preserved specimens can be assigned to Purussaurus mirandai or cf. P. mirandai , which so far appears to be the only species of Purussaurus present in Venezuela. We also tentatively refer AMU-CURS-541 from the ‘North of El Picache’ locality to Purussaurus cf. P. mirandai herein, because of the congruence with the holotype of P. mirandai . As in the holotype, the dentary is slightly wavy in lateral view and carries a tooth row with 21 alveoli, and the splenial reaches anteriorly to the eigth alveolus forming a medial border of the alveoli from the sixteenth to the twenty-first alveolus backwards. In addition, the position of Purussaurus within Caimaninae could be corroborated by identifying an ectopterygoid-pterygoid flexure in an adult specimen (AMU-CURS-528).

On the other hand, we noted several inconsistencies between the MCNC paratype material listed by Aguilera et al. (2006) and the original field notes by the ‘Harvard expedition’ ( Patterson et al., 1972). Accordingly, instead of the cranial material (a right premaxilla and maxilla in ventral view) shown in Aguilera et al. (2006, figure 3B), the field notes list only a single “part of symphysis” under MCNC-URU-115-72 V ( Figure 25.1 ) . Although still being assignable to Purussaurus , MCNC-URU-115-72V is not considered to be part of the paratype series of P. mirandai . We further hypothesise that the anterior skull fragments shown in Figure 25.2-4 belong to MCNC-URU-158-72 V instead of MCNC-URU-115-72V, because of the description in the ‘Harvard expedition’ field notes (“skull and jaw, disarticulated”; Patterson et al., 1972), the overall size of the bones, as well as the non-overlap with the remainder of the cranial bones labelled under that number (shown in Figure 25.5-21 ). Also, MCNC-URU-158-72V likely represents a mixed assemblage of several Purussaurus individuals. In addition, the ‘Harvard expedition’ field notes list a large number of postcranial remains of a “giant crocodile” under MCNC-URU-157-72V, and not a “dentary” as noted in Aguilera et al. (2006, p. 224; also erroneously figured under that number in Aguilera, 2004, page 91). We hypothesise that the two lower jaw fragments shown in Figure 25.23 complement MCNC-URU-158-72V, again based on the size of the specimen, non-overlap with other fragments, and lack of other data from the field notes that would indicate otherwise. In this case, the MCNC paratype material indicated in Aguilera et al. (2006) all would derive from MCNC-URU-158- 72 V .

Figures

FIGURE 13. Photographs (1, 3, 4-6) and interpretative drawing (2) of the holotype skull and associated lower jaw remains (UNEFM-CIAAP-1297) (3) of Mourasuchus arendsi. 1, 2, skull in dorsal view. 3, right mandibular ramus in dorsal view. 4-6, Fragment of left mandibular ramus in dorsal (4), medial (5) and lateral (6) view. Abbreviations: f, frontal; j, jugal; la, lacrimal; mx, maxilla; n, nasal; p, parietal; pmx, premaxilla; po, postorbital; prf, prefrontal; pt, pterygoid; q, quadrate; qj, quadratojugal; so, supraoccipital; sq, squamosal.

FIGURE 14. Photograph without (1) and with superimposed interpretative drawing (2) of the skull roof of holotype skull (UNEFM-CIAAP-1297) of Mourasuchus arendsi in left dorsolateral view. Abbreviations: f, frontal; mc, medial crest on parietal; p, parietal; po, postorbital; so, supraoccipital; sq, squamosal; stf, supratemporal fenestra.

FIGURE 15. Photograph without (1) and with superimposed interpretative drawing (2) of the right side of the posterior portion of holotype skull (UNEFM-CIAAP-1297) of Mourasuchus arendsi in angled lateral view. Note clear notch of jugal and system of cracks (indicated by dotted white lines and arrows) leading to displacement of right posterolateral portion of skull. Abbreviations: j, jugal; po, postorbital; q, quadrate; qj, quadratojugal; sq, squamosal.

FIGURE 16. Photograph (1) and interpretative drawing (2) of the holotype skull (UNEFM-CIAAP-1297) of Mourasuchus arendsi in occipital view. Note dorsoventral compaction of specimen. Abbreviations: bo, basioccipital; eo, exoccipital; oc, occipital condyle; pt, pterygoid; q, quadrate; so, supraoccipital; sq, squamosal.

FIGURE 19. Photographs and interpretative drawings of the posterior skull portion and orbitofrontal region as well as additional fragments (possibly jugal and lower jaw fragments) of Mourasuchus arendsi (AMU-CURS-218). 1, 2, skull fragment in dorsal view. Note squamosal eminences and orbital bony excrescences. 3, 4, skull fragment in occipital view. 5-9, skull fragments (partially from jugals?) found associated with the larger skull portions. Abbreviations: bo, basioccipital; eo, exoccipital; f, frontal; j, jugal; la, lacrimal; oc, occipital condyle; o, orbit, ok, orbital knob; p, parietal; po, postorbital; prf, prefrontal; pt, pterygoid; q, quadrate; qj, quadratojugal; so, supraoccipital; sq, squamosal; stf, supratemporal fenestra.

FIGURE 25. Photographs of skull and jaw material of Purussaurus. 1, right dentary fragment (MCNC-URU-115-72V) in dorsal view; 2-23, skull and lower jaw material belonging to several different individuals currently accessioned under a single collection number (MCNC-URU-158-72V). 2-3, anterior part of skull (electronically assembled to represent life position) in dorsal and ventral view. Only the right premaxilla and maxilla (2-4) were shown as part of the paratype series of P. mirandai by (Aguilera et al., 2006). 5, right part of skull table in dorsal view. 6, left part of skull table in lateral view. 7, isolated tooth. 8, 9, left quadrate in dorsal and ventral view. 10, right quadrate in dorsal view. 11, right ectopterygoid in posterolateral view. 12, lower jaw fragment in medial view with alveoli. 13, right jugal in lateral view. 14, 15, articulars with retroarticular processes in dorsal view. 16, 17, pterygoids? 18-21, lower jaw elements. 18, possible anterior fragment of left surangular in ventral view? 19, posterior fragment of surangular in lateral view? 20, fragment of right angular in medial view? 21, fragment of right surangular in medial view? 22, smaller skull table in the assemblage also assignable to Purussaurus in dorsal view. 23, anterior portion of lower jaw, initially referred to and figured as MCNC-URU-157-72V by (Aguilera, 2004).