Aphaurosuchus

Aphaurosuchus Temporal range: Late Cretaceous,
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauria
Clade:	Pseudosuchia
Clade:	Crocodylomorpha
Clade:	Crocodyliformes
Clade:	†Notosuchia
Clade:	†Sebecosuchia
Family:	†Baurusuchidae
Subfamily:	†Baurusuchinae
Genus:	†Aphaurosuchus Darlim, Montefeltro, and Langer, 2021
Type species
†Aphaurosuchus escharafacies Darlim, Montefeltro, and Langer, 2021

Aphaurosuchus is an extinct genus of baurusuchid mesoeucrocodylian known from the Late Cretaceous Bauru Basin of São Paulo, southern Brazil. It contains a single species, Aphaurosuchus escharafacies.

Discovery and naming

In 2012 the Laboratório de Paleontologia lead an expedition to the municipality of Jales, São Paulo State, excavating at the Fazenda Furnas site which had yielded baurusuchid remains during previous digs. This site, belonging to the Adamantina Formation/Vale do Rio do Peixe Formation, contained a nearly complete baurusuchid skeleton, specimen LPRP/USP 0697, broken into six main blocks. The first block contains the skull, all cervical vertebrae with associated osteoderms as well as the first four thoratic vertebrae, both scapulae and articulated coracoids. The second block is made up of most of the postcranial skeletal from the 8th thoratic to the 9th caudal vertebra with the associated double row of parasagittal osteoderms, the posterior thoratic ribs, gastralia, right forelimb, pelvic girdle and most of the hindlimbs. The humerus was originally preserved, however lost during the excavations. The left manus and left pes are preserved in individual blocks and two segments of caudal vertebrae have also been preserved as blocks. The placement in relation to one another is however unclear due to poor preservation of the anterior vertebrae of the more distally located caudal block. Two isolated caudals with osteoderms have also been discovered as well as rib fragments of uncertain placement.

The genus name is composed of the Greek words ἀφαυρός (aphauros), meaning "feeble" or "powerless in reference to the weak biteforce determined by Montefeltro et al. (2020), and σοῦχος (souchos) for crocodile. During excavation a rocksaw left a cut on the left jugal and dentary of the specimen, earning it the nickname "Scarface", which is the basis of the species epithet. Eschara (ἐσχάρα) meaning scar in Greek and the Latin facies meaning face.

Description

The skull of Aphaurosuchus is well preserved, showing the bones that make up its lateral, dorsal and ventral surface, there is however some damage in the area where the premaxillae connect to the paired nasal, making the exact anatomy of the nares hard to determine. The skull is deep and lateromedially compressed with a rostrum that makes up less than 55% of the basal skull length. The compression is the most extreme just behind the last maxillary teeth, before expanding laterally. The dorsal surface is highly ornamented, especially around the area where the maxillae contact the nasals. Like other baurusuchids Aphaurosuchus has a prominent, semi-circular notch between the maxillae and premaxillae that makes space for the lower caniniform teeth. Also like other baurusuchids, this taxa has a highly reduced number of teeth with 4 teeth in each half of the premaxillae followed by 5 maxillary teeth on each side. The largest maxillary tooth almost extends to the ventral margin of the dentary. The tooth count of the dentary is similarilly reduced, containing 10 teeth on each dentary, largest of which being the afforementioned caniniform that sits in the 4th dentary alveola. Notably, Aphaurosuchus preserves a notched border between of the quadrate-quadratojugal contact, previously believed to have been a synapomorphy of pissarrachampsine baurusuchids.

Phylogeny

Aphaurosuchus' placement within Baurusuchidae was determined using an expanded version of the matrix by Godoy et al., (2014). The single Most Parsimonious Tree (MPT) resulting from this can be seen below.

Notosuchia	Notosuchus Mariliasuchus Armadillosuchus Baurusuchidae Cynodontosuchus Gondwanasuchus Pissarrachampsinae Campinasuchus Pissarrachampsa Wargosuchus Baurusuchinae Aphaurosuchus Aplestosuchus Stratiotosuchus Baurusuchus B. albertoi B. salgadoensis B. pachecoi

Aphaurosuchus was recovered as the basal most member of Baurusuchinae, with Aplestosuchus and Stratiotosuchus being successive sister taxa to a monophyletic Baurusuchus. THe discovery of this taxon prompted some revisions to the definition of the two major baurusuchid clades, as Aphaurosuchus showcases features previously assumed to have been synapomorphies of Pissarrachampsinae. However new synapomorphies were identified for both baurusuchines and pissarrachampsines. Overall Aphaurosuchus showcases all but one of the baurusuchine synapomorphies and two of the three previously described pissarrachampsine synapomorphies (sensu Montefeltro et al., 2011). This is reflected by the phylogenetic tree recovering it as being nested closely to the dichotomy of the two clades. This unique combination of features may be read as a "zone of variability", wherein plesiomorphies persist across speciation and are to be read as homoplasies.