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23-456: Aetosauroides (meaning " Aetosaurus -like") is an extinct genus of aetosaur from the Late Triassic of South America . It is one of four aetosaurs known from South America, the others being Neoaetosauroides , Chilenosuchus and Aetobarbakinoides . Three species have been named: the type species A. scagliai , A. subsulcatus and A. inhamandensis . Fossils have been found in

46-435: A juvenile specimen in 2014, Polesinesuchus aurelioi , was found to be similar in its vertebrae and the basioccipital of its braincase to juvenile specimens of Aetosauroides in two 2021 studies, and it was proposed as a junior synonym of the latter. A phylogenetic analysis presented by Julia B. Desojo, Martin D. Ezcurra and Edio E. Kischlat in 2012 found that Aetosauroides lies outside Stagonolepididae. If this phylogeny

69-728: A maximum length of 150 centimetres (59 in) while A. ferratus reached a length of up to 90 centimetres (35 in). In addition to the Stubensandtein in Germany, A. ferratus is also known from the Calcare di Zorzino Formation in Cene , Italy. Specimens of Aetosaurus that have been recovered from the Fleming Fjord Formation in Greenland likely represent A. ferratus . Some material from

92-451: A row of scutes following the lateral line on either side. Sturgeon have five rows of scutes instead of scales. The tarsometatarsus and toes of most birds are covered in two types of scales. Large scutes run along the dorsal side of the tarsometatarsus and toes, whereas smaller scutellae run along the sides. Both structures share histochemical homology with reptilian scales; however, work on their evolutionary development has revealed that

115-479: Is also used in insect anatomy, as an alternative name for the anterior portion of the mesonotum (and, technically, the metanotum , though rarely applied in that context). In the hard ticks , the Ixodidae , the scutum is a rigid, sclerotised plate on the anterior dorsal surface, just posterior to the head. In species with eyes, the eyes are on the surface of the scutum. The flexible exoskeleton posterior to

138-590: Is correct, Stagonolepididae and Aetosauria would not be equivalent groupings, and Aetosauroides would be the first non-stagonolepidid aetosaur. Aetosaurus Aetosaurus is an extinct genus of pseudosuchian reptile belonging to the order Aetosauria . It is generally considered to be the most primitive aetosaur. Three species are currently recognized: A. ferratus , the type species from Germany and Italy ; A. crassicauda from Germany; and A. arcuatus from eastern North America . Additional specimens referred to Aetosaurus have been found in

161-427: Is not accepted, with several studies identifying unique features that distinguish Aetosauroides from Stagonolepis . Among these are maxillae that do not touch the nostrils, oval-shaped holes on the centra of the vertebrae , and a convex margin of the lower jaw. In a 2011 study, A. subsulcatus and A. inhamandensis were proposed to be synonymous with A. scagliai . Additionally, a contemporary aetosaur named from

184-401: Is shed piecemeal, and not in one continuous layer of skin as seen in snakes or lizards. The dermal base may contain bone and produce dermal armour . Scutes with a bony base are properly called osteoderms . Dermal scutes are also found in the feet of birds and tails of some mammals , and are believed to be the primitive form of dermal armour in reptiles. The term is also used to describe

207-436: Is used to describe the heavy armour of the armadillo . The turtle's shell is covered by scutes formed mostly of keratin . They are built similarly to horn, beak, or nail in other species. Some fish, such as pineconefish , are completely or partially covered in scutes. River herrings and threadfins have an abdominal row of scutes, which are scales with raised, sharp points that are used for protection. Some jacks have

230-586: The Chinle Group of the southwestern United States , and the Fleming Fjord Formation of Greenland . Specimens of Aetosaurus occur in Norian -age strata. Aetosaurus was a small, primitive aetosaur. Unlike more derived aetosaurs such as Desmatosuchus or Typothorax , the carapace was long and narrow and lacked spikes. The paramedian scutes that covered the back (with one row on each side of

253-721: The pelvis . The following cladogram is simplified after an analysis presented by Julia B. Desojo, Martin D. Ezcurra and Edio E. Kischlat (2012). Aetosauroides scagliai Aetosaurus ferratus Coahomasuchus kahleorum Neoaetosauroides engaeus Calyptosuchus wellesi Stagonolepis robertsoni Aetobarbakinoides brasiliensis Typothorax Redondasuchus Tecovasuchus chatterjeei Rioarribasuchus chamaensis Paratypothorax andressorum Sierritasuchus macalpini Longosuchus meadei Lucasuchus hunti Acaenasuchus geoffreyi Desmatosuchus haplocerus Desmatosuchus smalli Scute Scutes are similar to scales and serve

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276-860: The Cancha de Bochas Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin in northwestern Argentina and the Santa Maria Formation in the Paraná Basin in southeastern Brazil. The strata date to the late Carnian and early Norian stages, making Aetosauroides one of the oldest aetosaurs. Most individuals of Aetosauroides measured around 1.3 metres (4 ft 3 in) in length, with one large individual reaching 2.4 metres (7 ft 10 in) (with histology suggesting an age of 23 years). Sexual maturity

299-624: The Chinle Group in the southwestern United States probably represent A. ferratus , as well. In 1998, the genus Stegomus was synonymized with Aetosaurus . In 1896, paleontologist Othniel Charles Marsh named Stegomus arcuatus from a cast of an aetosaur known as YPM 1647 from the New Haven Formation in the Fair Haven Heights neighborhood of New Haven. This cast consisted of the dorsal carapace. Several other casts preserving

322-413: The caudal scutes. A. arcuatus has paramedian scutes that are much wider than they are long, even in comparison to other species of Aetosaurus . There is very little pitting on the surface of the scutes, although the porosity of the sandstone that makes up the casts has been mistaken for pitting. The tail narrows significantly past the base. The carapace is "waisted", meaning that it narrows in front of

345-535: The heavy armour of the armadillo and the extinct Glyptodon , and is occasionally used as an alternative to scales in describing snakes or certain fishes, such as sturgeons , shad, herring, and menhaden. Prehistoric ancestors of mammals, the synapsids , are thought to have scutes which were later reduced and replaced by hair. Excluding the attachment surface of fingernails , armoured scutes or scales are almost never seen in modern mammals . The horny scales of pangolins are only rarely called scutes, but "scute"

368-399: The rigid scutum of the female tick, is called the alloscutum , the region that stretches to accommodate the blood with which the mature female tick becomes engorged . Males do not engorge nearly as drastically as females, so they do not need a flexible alloscutum; instead the rigid scutum covers practically the entire dorsal surface posterior to the head, and may be referred to specifically as

391-433: The same function. Unlike the scales of lizards and snakes, which are formed from the epidermis , scutes are formed in the lower vascular layer of the skin and the epidermal element is only the top surface . Forming in the living dermis , the scutes produce a horny outer layer that is superficially similar to that of scales. Scutes will usually not overlap as snake scales (but see the pangolin ). The outer keratin layer

414-429: The scales in bird feet have secondarily evolved via suppression of the feather-building genetic program. Unblocking the feather suppression program results in feathers growing in place of scales along the tarsometatarsus and toes. Dinosaur species very close to the origin of birds have been shown to have had "hind wings" made of feathers growing from these areas, suggesting that the acquisition of feathers in dinosaurs

437-676: The surface of the skull and tail have been found in the Passaic Formation of Hunterdon and Somerset counties , New Jersey and an outcrop of the Lower Sanford Formation at the Triangle Brick Co. Quarry in Durham County, North Carolina . Stegomus arcuatus was found to be synonymous with Aetosaurus on the basis of several similarities, including a lack of spikes and a distinctive radial pattern of grooves on some of

460-479: The vertebrae) are considerably wider than they are long. The lateral scutes, which are beneath the paramedian and formed a row on either side of the animal, do not bear any spikes or other projections. A 2023 study based on a fossil assemblage found in Kaltental , suggested that juvenile A. ferratus were likely gregarious animals, possibly to increase their chances of survival and to deter predators. Aetosaurus

483-447: Was a whole-body event. The bottoms of bird feet are covered in small, keeled scale-like structures known as reticulae. Evolutionary developmental studies on these scale-like structures have revealed that they are composed entirely of alpha keratin (true epidermal scales are composed of a mix of alpha and beta keratin). These data have led some researchers to suggest that reticulae are in fact highly truncated feathers. The term "scutum"

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506-523: Was first named, with the description of the type species A. ferratus , in 1877 by German paleontologist Oscar Fraas . At the time, Aetosaurus was known from 22 articulated skeletons that had been found in the Lower Stubensandtein of Germany. Thirty years later, Fraas' son Eberhard described a second species, A. crassicauda , also from Germany. A. crassicauda can be distinguished from A. ferratus by its larger size; A. crassicauda reached

529-490: Was probably reached at 1 metre (3 ft 3 in) in length, although these individuals were not yet fully grown. Sexual dimorphism has been suggested for Aetosauroides , with males reaching the 2-metre (6 ft 7 in) size range. Aetosauroides was proposed to be synonymous with the genus Stagonolepis in 1996 and 2002. Smaller specimens of both species were placed with Stagonolepis robertsoni , and larger specimens were considered to be S. wellesi . This synonymy

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