peirosaurid
Peirosauridae is a Gondwanan family of mesoeucrocodylians that lived during the Cretaceous period. It was a clade of terrestrial crocodyliforms that evolved a rather dog-like skull, and were terrestrial carnivores. It was phylogenetically defined ...
notosuchian
Notosuchia is a clade of primarily Gondwanan mesoeucrocodylian Crocodylomorpha, crocodylomorphs that lived during the Jurassic and Cretaceous. Some phylogeny, phylogenies recover Sebecosuchia as a clade within Notosuchia, others as a sister group ...
from the
Santonian
The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya ( million years ago) and 83.6 ± 0.7 m ...
of
Argentina
Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...
and part of the extensive peirosaurid record of Late Cretaceous Patagonia. It contains one species, ''Barrosasuchus neuquenianus''. ''B. neuquenianus'' is known from an almost complete skull and the majority of the articulated postcranial skeleton, making it the best preserved Patagonian peirosaurid.
Discovery and naming
In February 2001 the
Museo Carmen Funes
Museo Municipal Carmen Funes, or, the Carmen Funes Municipal Museum, is a museum of paleontology in Plaza Huincul, Neuquén Province, Argentina. It is best known for its collection of dinosaur fossils, including the only specimen of the largest r ...
conducted a joint expedition with the Royal Tyrell Museum at the Sierra Barrosa Locality, 30 km north-east of
Plaza Huincul
Plaza Huincul is a small city in Neuquen province, with a population of around 13,000 people, located in southwestern Argentina. It is approximately south-west from the capital, Buenos Aires. Plaza Huincul is located in the middle of the desert ...
,
Neuquén province
Neuquén () is a Provinces of Argentina, province of Argentina, located in the west of the country, at the northern end of Patagonia. It borders Mendoza Province to the north, Rio Negro Province to the southeast, and Chile to the west. It also me ...
. There the team uncovered the bones of dinosaurs and mammals, bird footprints and notably a nearly complete peirosaurid fossil from the
Bajo de la Carpa Formation
The Bajo de la Carpa Formation is a geologic formation of the Neuquén Basin that outcrop, crops out in northern Patagonia, in the provinces of Río Negro Province, Río Negro and Neuquén Province, Neuquén, Argentina. It is the oldest of two for ...
. The holotype, MCF-PV 413, was found lying on its ventral side, the skull articulated with the remaining skeleton which consisted of both forelimbs, most of the vertebral column up to the sacrals, one hindlimb and semi-articulate osteoderms that obscured parts of the fossil. The fossil was subsequently prepared in this state, keeping the elements in position.
The generic name derives from the Sierra Barrosa locality where the fossils have been found and the , () meaning crocodile. The species epithet refers to the Neuquén Province.
Description
The skull of ''Barrosasuchus'' is nearly complete, articulated with the lower jaw and the cervical vertebrae and measures a total of 315 mm, slightly smaller than the specimens known from '' Lomasuchus'' and ''
Gasparinisuchus
''Gasparinisuchus'' is an extinct genus of peirosaurid notosuchian known from the Late Cretaceous (Santonian to early Campanian stage) of Neuquén and Mendoza Provinces, western central Argentina. It contains a single species, ''Gasparinisuchus ...
''. Parts the dorsal surface of the skull has been subject to erosion, notably most of the skull table and the dorsal surface of the occipital area as well as patches of the skull anterior to the orbits. The entire skull is tubular in shape and moderately wide, heavily ornamented with pits and grooves of varying arrangement and density. The orbits are subcircular and face dorsolaterally, each orbit is topped by a heavily ornamented anterior palpebral bone. The
premaxilla
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...
is short and high with a prominent notch between it and the
maxilla
In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...
. It is unclear if a septum separating the anterior-facing external nares was present. As in other peirosaurs, a knob-like structure can be found on the anterior contour of the premaxillary symphysis. The maxilla is mediolaterally wide with a straight ventral age and laterally almost vertical. The maxilla's relationship to the lacrimal and
prefrontal Prefrontal may refer to:
*Prefrontal bone, a skull bone in some tetrapods
*Prefrontal cortex, a region of the brain of a mammal
*Prefrontal scales
The prefrontal scales on snakes and other reptiles are the scales adjacent and anterior to the fr ...
bones is uncertain due to the erosion that has affected this area of the skull. Due to damage the exact number of teeth is also unknown, however it is estimated that ''Barrosasuchus'' may have had up to 13 maxillary teeth (10 of which were preserved) on each side of the skull in addition to 4 teeth on each premaxilla. Both mandibular rami are preserved and more slender laterally than that of ''
autapomorphies
In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...
. The teeth of the dentary are closely spaced and sigmoidal is seen in dorsal view. Following the first 3 procumbent teeth comes the 4th tooth, which is the largest of the lower jaw. Following it the teeth decrease in size until the 8th, at which point dental size increases again up to the 13th dentary tooth. The dentaries preserve 16 and 17 teeth respectively, with a total number of 18 teeth per dentary being suggested by Coria ''et al.''
The last cervical vertebrae were found still in articulation with its corresponding cervical ribs, but the specimens preservation does not allow for a more detailed identification in the vertebral column. The vertebral centra are amphicoelous and shorter than they are wide. Each has a notch on the ventral border of the anterior articular surface and a distinct ventral keel. The shafts of the cervical ribs are short and overlap distally with the anterior projection of the following vertebra. Of the dorsal vertebrae only the anterior elements are unobscured and as the cervicals amphicoelous and short, however lack the ventral keel, at least 10 dorsal ribs are preserved on the left side. Of the pectoral girdle only the right
coracoid
A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is n ...
is preserved and elongated and plate-like in shape. Both forearms are preserved with the left of which being almost complete. Of the hindlimbs the
tibia
The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...
and
fibula
The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...
are preserved in articulation with the pes.
3 types of osteoderms are preserved, rectangular, square and round, most of which are no longer articulated and scattered over the ventral side of the holotype, obscuring other elements of the fossil, however a small section of the posterior still preserves articulate ventral armor. The rectangular osteoderms have been interpreted as being part of the dorsal armor, possibly having formed parasagittal rows while some of the narrower osteoderms are associated with the cervical region. There is no indication that these osteoderms would have overlapped. The square and rounded osteoderms contacted each other and would have formed the ventral shield. Occasionally appearing rounded osteoderms may be associated with the lateral armor of the limbs.
Phylogeny
The following phylogeny is a strict consensus tree under equal weighting of characters as published by Nicholl ''et al.'' in 2021. It is based on the character-taxon matrix of Pol ''et al.'' (2014), incorporating many of its daughter matrices that had been created parallel to one another into a single phylogenetic tree.