| Peirosaurus | |
|---|---|
 | |
| Peirosaurus (top left) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Clade: | Crocodylomorpha |
| Clade: | Crocodyliformes |
| Clade: | †Notosuchia |
| Clade: | †Sebecosuchia |
| Clade: | †Sebecia |
| Family: | †Peirosauridae |
| Genus: | †Peirosaurus Price,1955 |
| Type species | |
| †Peirosaurus torminni Price, 1955 | |
Peirosaurus is anextinctgenus ofpeirosauridcrocodylomorph known from theLate Cretaceousperiod (lateMaastrichtian stage) ofMinas Gerais, southernBrazil. It contains a single species,Peirosaurus torminni. It is thetype genus of thefamilyPeirosauridae.
Peirosaurus is known from theholotype DGM 433-R, fragmentaryskull (leftpremaxilla bearing fiveteeth, isolated maxillary and dentary teeth and leftpalpebral bone) and partialpostcranialskeleton includingradius,ulna, leftpubis andischium, some presacral and a single caudal vertebrae, ribs, haemal arches and dermal plates. It was collected byLlewellyn Ivor Price in 1947-1949 at the Price Quarry 3,Peirópolis Site nearUberaba, in theSerra da Galga Formation (Bauru Group),[1][2] dating to the lateMaastrichtian stage of theLate Cretaceous, about 68-66 million years ago.[3]
A partial skull and several postcranial elements such asvertebrae anddermal plates from theBajo de la Carpa Formation[4] inArgentina and another partial skull and several unprepared postcranial elements from theAnacleto Formation, Argentina, were assigned toPeirosaurus by Gasparini, Chiappe and Fernandez (1991) and Praderio, Martinelli and Candeiro (2008), respectively. However, more recently Agustín G. Martinelli, Joseph J.W. Sertich, Alberto C. Garrido and Ángel M. Praderio concluded that the traits which used to unite the holotype (from Brazil) and the referred material from Argentina are shared with other peirosaurids and some othermesoeucrocodylians. They reassigned the Argentinian specimens to a new genus,Gasparinisuchus, and although overlapping materials between the genera are limited to the premaxilla and thedentition,Gasparinisuchus can be differentiated fromPeirosaurus on the basis of its broad, rounded rostrum, anteroposteriorly short premaxilla, reduced perinareal fossa, and short premaxillary interdental spaces. Hence,Peirosaurus is known only from its holotype.[5]
Peirosaurus has a ziphodont dentition that is somewhat heterodont, with conicalpremaxillary teeth and serratedmaxillary and posteriormandibular teeth. The rostrum is laterally compressed with a grove between the maxilla and premaxilla to accommodate for an enlarged mandibular tooth. A maxillary wedge-like anterior process is also present. The external nares face slightly forward and anteriorly protrude. The dorsal osteoderms are thin and sculptured with low longitudinal keels while the abdominal ones are smaller and lack keels.
Peirosaurus shares a number of features with the closely related genusUberabasuchus, found from a nearby locality in Uberaba. These include a similar tooth size pattern and the large maxillary anterior process. These genera were differentiated from each other as the rostrum ofUberabasuchus is more compressed than that ofPeirosaurus, which is relatively broad.[6] However, the rostrum wasn't preserved in the holotype ofPeirosaurus. The removal of MOZ 1750 PV (which preserved the rostrum) from the genusPeirosaurus suggests a possible synonymy betweenPeirosaurus andUberabasuchus.[5]
Though many of the features of the premaxilla and dentition of Peirosaurus are widespread among peirosaurids and many mesoeucrocodylians, several are shared exclusively withUberabasuchus. Among these features some are not observed in otherpeirosaurids. These include the relatively long anteroposterior facial length of thepremaxilla, the elongate and strongly anteromedially directed dorsomedial process of the premaxilla, and the sharply defined and elevated margin of the perinarial fossa. There are differences between the two taxa such as differences in the relative thickness of dorsal osteoderms and the absence of a denticulate mesial carina on the first premaxillary tooth inPeirosaurus, but not inUberabasuchus. However, these characters are considered to be minor and their taxonomic value may be individually variable. As postcranial materials of bothPeirosaurus andUberabasuchus are known but are not yet formally described, they are tentatively considered to be valid taxa.[5]
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