Monday, August 20, 2018

[Paleontology • 2018] Roxochampsa paulistanus • Reassessment of the Enigmatic Crocodyliform “Goniopholispaulistanus Roxo, 1936: Historical Approach, Systematic, and Description by New Materials

 Roxochampsa paulistanus (Roxo, 1936)

Piacentini Pinheiro, Pereira, de Souza, Brum, Lopes, et al., 2018.
exGoniopholis” paulistanus Roxo, 1936:  DOI: 10.1371/journal.pone.0199984 

The Crocodyliformes are the most represented vertebrate clade in the Upper Cretaceous sequences of the Bauru Group, Paraná Basin. However, some of the species described have an uncertain taxonomic status and phylogenetic position. For instance, “Goniopholispaulistanus has been assigned as a nomem dubium, due to its description being based on scarce material. The “G”. paulistanus specimens (i.e. teeth and a left tibia) were discovered in two different localities in São Paulo state: Mirandópolis and Valparaíso municipalities; where the upper interval of the Adamantina Formation (Early Maastrichtian of Bauru Group) crops out. Revisiting these specimens, we observed multicrenulated teeth in middle dentary toot- row, a remarkable feature only shared with teleosaurids Machimosaurus hugii (Upper Jurassic of Laurasia) and M. rex (Lower Cretaceous of Tunisia). This apomorphy was also recognized in new material from the Alfredo Marcondes municipality (Presidente Prudente Formation), which are here also referred to “G”. paulistanus. We recognized the teeth of “G.” paulistanus as the lectotype, however the tibia cannot be assigned to a species as it was not collected in association with the teeth. We performed a phylogenetic analysis with a data matrix composed of 388 characters and 86 taxa, analyzed in TNT. The strict consensus tree recovered Neosuchia and Ziphosuchia (Notosuchia + Sebecia) within Mesoeucrocodylia. The species “Gpaulistanus is valid, as a distinct and new genus within Sebecia, in a polytomy with Barreirosuchus, Pepesuchus, Itasuchus and Peirosaurus, forming the clade Itasuchidae. Stolokrosuchus is the sister taxon to Itasuchidae, the sister group of all other Sebecia (Peirosauridae (Mahajangasuchidae + Sebecidae and taxa affinis)). The clades Ziphosuchia, Sebecia and Itasuchidae are here redefined, and we find the last two clades to be more closely related to terrestrial notosuchids than to semiaquatic neosuchians.

Life reconstruction of Roxochampsa paulistanus.
(Illustration by Maurílio Oliveira)

Systematic paleontology

MESOEUCROCODYLIA Whetstone and Whybrow, 1983
ZIPHOSUCHIA modified from Ortega, Gasparini, Buscalioni and Calvo, 2000
SEBECIA modified from Larsson and Sues, 2007
ITASUCHIDAE modified from Carvalho, Ribeiro and Ávilla, 2004

Modified phylogenetic definition: all species closer to Itasuchus jesuinoi than to Barreirosuchus franciscoi, Montealtosuchus arrudacamposi, Mahajangasuchus insignis and Sebecus icaeorhinus (stem-based).

Roxochampsa gen. nov.

Genus etymology: Roxo in honor to an important vertebrate paleontologist from DGM, Mathias de Oliveria Roxo, and the Greek suffix Xαμψαι (Champsai Latinized as ‘‘champsa”) meaning crocodile.

Type species: Roxochampsa paulistanus Roxo, 1936.

Roxochampsa paulistanus (Roxo, 1936) comb. nov.

Basionym: Goniopholis paulistanus Roxo, 1936.

Lectotype: DGM 259-R, an isolated and acute tooth apex.

Paralectotype: DGM 258-R, an isolated and acute tooth apex (wider but lower than DGM 259-R).

Lectotype-paralectotype locality, lithology and horizon: Northwest of São Paulo state, between Três Lagoas (Jupiá old designation) and Araçatuba municipality, collected in a railway section of Noroeste do Brazil Railway. Top of the Adamantina Formation, Upper Cretaceous (Early Maastrichtian) of the Bauru Group, Paraná Basin.

Diagnosis: Roxochampsa paulistanus comb. nov. is a platyrostral notosuchian with an unique set of characters: at least nineteen teeth per hemimandible (eighteen teeth for Itasuchus and Pepesuchus, and at last twenty two for Caririsuchus); festooned dentary formed by two waves, being the first between d4-d5 and the second and more smoothy between d8-d14 (similar feature is shared with the others Itasuchidae species); presence of two alveoli couplets in mid-anterior portion of the mandible (d6/d7 and d8/d9) separated by a small diastema (shared with Itasuchus); splenial well participating in the mandibular symphysis, anteriorly reaching to d5-d6 (shared with Pepesuchus); mandibular symphysis is long, and is as broad as high (shared with Itasuchidae species); last two mandibular teeth sit in an alveolar groove (autapomorphy among Itasuchidae species); interlocking teeth arrangement known as "crocodyloid occlusion" (shared with Itasuchus and Pepesuchus); rostral and mid dentary teeth with apicobasal high relief ridges fully crenulated by pseudo-denticles (autapomorphy among Itasuchidae species).

Fig 2. Geological map of the Bauru Group, Paraná Basin (modified from Paula e Silva et al, 2009]). The outcrops that yielded Itasuchidae specimens is located with the crocodile outlines. A-B and C-D are regional geological sections.

Fig 6. Roxochampsa paulistanus comb. nov. (UFRJ-DG 501-R).
A- lateral view; B- medial view; C- detail, mesio-lingual surface view of tenth hemimandibular tooth; D- detail, lingual surface view of twelfth hemimandibular tooth; E- oclusal view; F- isolate tooth: a- lateral profile; b-lingual view; c- labial view.
Each scale bar = 10 mm. Legend in text.

Fig 7. Roxochampsa paulistanus comb. nov. (UFRJ-DG 451-R).
 A- lateral view; B- medial view; C- oclusal view; D- anterior view; E- posterior view. Each scale bar = 10 mm. Legend in text.

Fig 11. Calibrated strict consensus tree from 225 MLTs (1520 steps, CI = 0.304 and RI = 0.692). The phylogenetic relationships (thin lines) come from the strict consensus tree calibrated with the geological ages (chronostratigraphic chart). Thick lines represents the species temporal range based on specimens occurrence. Also, colors in thick lines represent the inferred habit for studied species.

Fig 12. Hemimandible comparisons between some mesoeucrocodylian taxa.
A- Roxochampsa paulistanus comb. nov. (UFRJ-DG 451-R), right hemimandible fragment; B- Roxochampsa paulistanus comb. nov. (UFRJ-DG 501-R), right hemimandible, lacking the anterior-most portion;
C- Itasuchus jesuinoi (DGM 434-R), left hemimandible fragment mirrored; D- Itasuchus sp. (MUGEO 218-V), right hemimandible fragment;
E- Pepesuchus deiseae (MCT 1788-R), left hemimandible fragment mirrored; F- Machimosaurus buffetauti (SMNS 91415) right hemimandible; G- Goniopholis simus (IPB R359), right hemimandible;
H- Crocodylus niloticus (PV. 6524-R), right hemimandible; I- Caiman latirostris (DGM 156-RR), left hemimandible mirrored, J- Gavialis gangeticus (DGM 289-RR) right hemimandible.
Each scale bar = 10 mm. Legend in text.

The enigmatic taxon “Goniopholispaulistanus was reanalyzed in the light of new material collected from the uppermost sequence of the Presidente Prudente Formation in Alfredo Marcondes municipality, Early Maastrichtian, correlated level in the Adamantina Formation first record of Valparaíso and Mirandópolis regions, allowing us to validate the species in a new taxonomic combination Roxochampsa paulistanus. Based on the dubious nature of Goniopholis occurrences in South America, and the disparity in mandibular morphology between Goniopholididae and this species, the new genus Roxochampsa is here proposed.

The new material reveals another tooth morphology present in the Bauru Group, just only verified for Roxochampsa paulistanus and the thalattosuchians teleosaurids: Machimosaurus hugii and M. rex, in which the tooth crown exhibits the main carinae and additionally secondary ones (high relief apicobasal ridges) crenulated by pseudo-denticles. However, the morphological tooth similarities among itasuchids with some neosuchians as goniopholids and some teleosaurids, it reveals a pattern of dental convergence within Mesoeucrocodylia, that lacks a phylogenetic signal.

In our cladistic analysis Roxochampsa paulistanus was recovered in the node Itasuchidae, being closed related to Caririsuchus, Itasuchus, and Pepesuchus. This clade is nested within Sebecia, which is here founded to be the major sister group to Notosuchia, both composing a more inclusive clade Ziphosuchia. Thus, the neocretacic mesoeucrocodylian fauna for South America was formed by terrestrialized and continental semi-aquatic forms from two distinct clades: notosuchians, well-adapted for terrestrial niches (e.g. Uruguaysuchidae, Sphagesauridae, Baurusuchidae), and sebecians as more generic forms that included numerous reversions to an semiaquatic lifestyle (e.g. itasuchids, Stolokrosuchus, Mahajangasuchus and Lorosuchus). In accordance with previous works, we found many homoplastic characters for Crocodyliformes, which could imply a mosaic evolutionary pattern, heavily influenced by the ancestral crocodyliform bauplan.

André E. Piacentini Pinheiro , Paulo Victor Luiz Gomes da Costa Pereira, Rafael G. de Souza, Arthur S. Brum, Ricardo T. Lopes, Alessandra S. Machado, Lílian P. Bergqvist and Felipe M. Simbras. 2018. Reassessment of the Enigmatic Crocodyliform "Goniopholis" paulistanus Roxo, 1936: Historical Approach, Systematic, and Description by New Materials.  PLoS ONE. 13(8): e0199984. DOI: 10.1371/journal.pone.0199984


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