Uncovering the Osteodermic armor of Caririsuchus camposi (Sebecia, Crocodyliformes), Lower Cretaceous, Araripe Basin

Abstract

Caririsuchus camposi is a large and elusive mesoeucrocodylian that lived in the Araripe region during the Lower Cretaceous of Gondwana. The holotype consisting of a complete individual was illegally taken out of the country, but could be briefly described by Alexander Kellner in the 1980s, who also managed to secure a few fragments of the skeleton. The complete specimen was also briefly reanalyzed by Eric Buffetault when it arrived in Europe, before disappearing, perhaps ending up in a private collection. In the second study, Buffetaut highlighted C. camposi as “one of the most heavily armored of all known crocodilians”, noting the presence of potentially appendicular osteoderms and the tail entirely covered by them, but without further details. Two of the secured fragments of C. camposi were donated to the Museu Nacional (MN), in Rio de Janeiro, and so far were not recovered from the tragic fire that this institution suffered in 2018. However, a third specimen was donated to the Museu de Ciências da Terra (MCTer SGB) and is studied here. This specimen is preserved in a carbonate concretion typical from the Romualdo Formation (Late Aptian of Santana Group) which preserves part of the osteodermic dorsal shield. It consisting of six transverse rows of four osteoderms that comprise the biserial paravertebral scutum (dermostea paravertebralia - DP) with one accessory osteoderm on each side of the row. The osteoderms of DP are imbricated, rectangular in shape - wider than long, with presence of a wide and low central osteodermal keel, lacking an antero-lateral articular process, and fully ornamented by pits in an incipient radial pattern in the center towards the periphery of each element. The accessory elements are also rectangular in shape, but longer than wide, with similar keel morphology and ornamentation pattern. Comparing this specimen with the photographs and images of holotype, we consider this osteodermic set as part of the lumbar-sacral or anterior caudal armor. Parsimony cladistic analysis with new coding entries places C. camposi within Sebecia, as sister taxon of Mahajangasuchidae: (Caririsuchus (Mahajangasuchus + Kaprosuchus)), an interesting clade formed by Gondwanic taxa from Africa (Niger), Madagascar and Brazil, despite its limited content so far. This important specimen reinforces the homoplastic condition in the acquisition of accessory rows outside the eusuchian lineage, as seen in Mahajangasuchus and peirosaurids (i.e., Uberabasuchus and Montealtosuchus) for instance. [FAPERJ E-26/210.294/2021, CNPq 407158/2022-7; FAPERJ E-26/201.095/2022, CNPq 308707/2023-0, CNPq 406779/2021-0, CNPq 406902/2022-4]