Roxochampsa is an extinct genus of itasuchid notosuchian from the Late Cretaceous of Brazil. Fossil remains have been found in the sediments of the Adamantina and Presidente Prudente Formations and were originally described as a species of Goniopholis. Roxochampsa had narrow and elongated jaws that indicate a mesorostrine and flattened skull shape. The teeth were interlocking as in modern crocodiles and bear carinae with crenulations, making it pseudo-ziphodont. Among the most distinguishing features of Roxochampsa is the fact that the teeth furthermore bear prominent crenulated ridges that form secondary cutting edges in addition to the main carinae. It is interpreted as a semi-aquatic generalist predator, feeding both on small terrestrial vertebrates, fish, carrion and hard-shelled prey it was able to crack with its blunter posterior teeth. The genus is monotypic, the type species is R. paulistanus.
History and naming
Early discoveries Teeth similar to those of Roxochampsa have been recognized from Brazil's Bauru Group as early as 1911, when Hermann von Ihering analyzed two isolated teeth recovered a few years prior from a well in São José do Rio Preto municipality. Von Ihering compared the teeth to those of the thalattosuchian Machimosaurus and the neosuchian Goniopholis, but due to his own uncertainty simply assigned them to the family Goniopholididae rather than any particular genus. Concurrently with von Iherings description of the isolated teeth in 1911, a second collection of fossils from the region was assembled, including additional isolated teeth. These were described in 1913 by Joviano A. Pacheco, who like van Ihering recognized similarities to the European genus Goniopholis, but unlike the former actually assigned the material to it. Both von Iherings and Pacheco's fossils were then later studied by Friedrich von Huene in 1931. In the case of the van Ihering teeth, von Huene likewise drew comparison to Machimosaurus, specifically referring one of the teeth to the species Machimosaurus hugii. Von Huene was less certain on Pacheco's identification, instead simply regarding the teeth as having come from a long-snouted mesoeucrocodylian rather than Goniopholis specifically. In 1950 Llewellyn Ivor Price called the interpretation of the supposed Machimosaurus tooth into question, arguing that the morphological difference to the other tooth described by von Ihering could be due to tooth wear. Price also cast doubt over the "Goniopholis hypothesis", though the relevant fossil has now been lost.
Description of Goniopholis paulistanus Even more fragmentary remains were discovered through the early 1900s, including two teeth (DGM 259-R and DGM 258-R) recovered in 1935 near Amandaba city in Mirandópolis, which corresponds to the Cretaceous Adamantina Formation, a partial tibia (DGM 225-R) found in a well in Valparaíso and a now missing tail vertebra. This material was described under the name Goniopholis paulistanus in 1936 by Mathias Gonçalves de Oliveria Roxo, who regarded this new species as a close relative to "Goniopholis" affinis. While the two teeth found in 1935 served as the syntype material, Roxo also assigned the fragmentary postcrania as well as the teeth previously described by von Ihering and Pacheco to this new species. As a consequence, various teeth of similar morphology and even some other cranial remains from the Bauru Group came to be assigned to the family Goniopholididae in the subsequent years. However, even with a formal species of Goniopholis established from South America, some authors remained suspicious of the groups presence on the continent. After Eric Buffetaut established the family Trematochampsidae in 1974, several teeth of similar morphology to those of Goniopholis paulistanus were instead referred to this family and even several more complete longirostrine taxa such as Itasuchus and Pepesuchus. However, Trematochampsidae was eventually regarded as an unnatural grouping, being centered around a chimeric taxon and including multiple ultimately unrelated forms.
Revisions and reassessment 2011 saw a revision of the genus Goniopholis published by Andrade and colleagues. In this study, the team warned that though useful in recognizing broader morphotypes, tooth crowns alone are not sufficient in recognizing specific clades or even species and would require either the support of a phylogenetic framework of more substantial fossil remains. Accordingly Goniopholis paulistanus, which was named on the basis of isolated teeth, was regarded as a nomen dubium due to the absence of diagnostic features and overall scarcity of fossil material. Pinheiro et al. (2018) described new jaw material from the Presidente Prudente Formation of the Alfredo Marcondes municipality in São Paulo state, and noted that the tooth crowns in the jaw material morphologically matched the teeth in the syntype series of G. paulistanus. They coined the new genus name Roxochampsa for the species, designating DGM 259-R and DGM 258-R as the lectotype and paralectotype respectively, while regarding the tibia (collected at a different locality than the teeth) as having belonged to an indeterminate taxon. Five years after this redescription Pinheiro and colleagues published another study describing various additional itasuchid fossils, among them a mandibular symphysis from the same site as the 2018 material tentatively assigned to Roxochampsa paulistanus.
Etymology The name Roxochampsa combines the Greek suffix Xαμψαι (champsa), which translates to "crocodile" and the last name of Mathias Gonçalves de Oliveria Roxo, who originally described the species as Goniopholis paulistanus in 1936.
Description
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