Cranial shape variation in jacarean caimanines (Crocodylia, Alligatoroidea) and its implications in the taxonomic status of extinct species: The case of Melanosuchus fisheri

FOTH, CHRISTIAN; FERNÁNDEZ BLANCO, MARÍA; BONA, PAULA; SCHEYER, TORSTEN

JOURNAL OF MORPHOLOGY

WILEY-LISS, DIV JOHN WILEY & SONS INC

Lugar: New York; Año: 2017

0362-2525

Melanosuchus niger (Crocodylia, Alligatoroidea) is one of the six living caimanine species widely distributedthroughout the Amazon River basin today. Although there is only one extant species ofMelanosuchus, fossil material assigned to this genus, represented by M. fisheri, has been reportedfrom the late Miocene in South America. However, the validity of this taxon has been questionedand a recent investigation indicates that the referred specimen of M. fisheri (MCZ 4336) actuallybelongs to Globidentosuchus brachyrostris, while those diagnostic characters present in the holotype(MCNC 243) fall into the spectrum of intraspecific variation of M. niger. Here, we compare the skullshape of the holotype of M. fisheri with the ontogenetic series of the four jacarean species (M.niger, Caiman yacare, Caiman crocodilus, and Caiman latirostris) using 2D-geometric morphometricanalyses in two different views. The analyses indicate that MCNC 243 falls into the morphospaceof M. niger and C. latirostris. Despite strong shape similarities between juveniles of C. latirostris andMCNC 243, further anatomical comparisons reveal notable differences between them. In contrast,no concrete anatomical differences can be found between MCNC 243 and M. niger, althoughshape analyses indicate that MCNC 243 is relatively robust for its size. Thus, this study is able toconfirm that the genus Melanosuchus was present in the late Miocene, but it still remains unclear ifMCNC 243 should be treated as a junior synonym or probably a sister species of M. niger. ItsMiocene age favors the second option, but as the shape analyses were also not able to extract anydiagnostic characters, it should be retained as Melanosuchus cf. niger.