Aetosaurus is an extinct genus of archosaur 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 from South Africa, 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 the vertebrae) are considerably wider than they are long. The lateral scutes, which are beneath the paramedians and formed a row on either side of the animal, do not bear any spikes or other projections.

 Aetosaurus was first named with the description of the type species A. ferratus in 1877 by German paleontologist Oskar Fraas. At the time, Aetosaurus was known from 22 articulated skeletons that were 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 a maximum length of 150 centimetres (59 in) while A. ferratus reached a length of up to 90 centimetres (35 in).

 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 Fairfield, Connecticut. This cast consisted of the dorsal carapace. Several other casts are known that preserve the surface of the skull and tail, and have been found from the Passaic Formation in Hunterdon and Somerset counties, New Jersey and the Lower Sanford Formation within 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 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 the pelvis.

 Aetosaurs (aetosaur  /eɪˌɛtoʊˈsɔr/; order name Aetosauria /eɪˌɛtoʊˈsɔriə/; from Greek, ἀετός (aetos, "eagle") and σαυρος (sauros, "lizard")) are an extinct order of heavily armoured, medium- to large-sized Late Triassic herbivorous archosaurs. They have small heads, upturned snouts, erect limbs, and a body covered by plate-like scutes. All aetosaurs belong to the family Stagonolepididae. Two distinct subdivisions of aeotosaurs are currently recognized, Desmatosuchinae and Aetosaurinae, based primarily on differences in the morphology of the bony scutes of the two groups. Over 20 genera of aetosaurs have been described, and recently there has been controversy regarding the description of some of these genera.

 Aetosaur fossil remains are known from Europe, North and South America, parts of Africa and India. Since their armoured plates are often preserved and are abundant in certain localities, aetosaurs serve as important Late Triassic tetrapod index fossils. Many aetosaurs had wide geographic ranges, but their stratigraphic ranges were relatively short. Therefore, the presence of particular aetosaurs can accurately date a site that they are found in.

 Aetosaur remains have been found since the early 19th century, although the very first remains that were described were mistaken for fish scales. Aetosaurs were later recognized as crocodile relatives, with early paleontologists considering them to be semiaquatic scavengers. They are now considered to have been entirely terrestrial animals. Some forms have characteristics that may have been adaptations to digging for food. There is also evidence that some if not all aetosaurs made nests.

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 Neoaetosauroides is an extinct genus of primitive aetosaur. Its type and only species is N. engaeus. Fossils have been found from the Los Colorados Formation outcropping along the Sierra Morada River in La Rioja, Argentina, and date back to the Norian age of the Late Triassic. It was the first aetosaur known from the formation, with remains being discovered in the 1960s.

 The genus is one of the most well-represented aetosaurs from South America, with some specimens being fully articulated. Two rows of dorsal osteoderms run paramedially along either side of the spine. Ventral osteoderms were also present. Unlike most other aetosaurs, the fourth finger was longer than the second and third. Additionally, the number of phalanges in the fifth digit was lower than other aetosaurs. The upper tooth row of Neoaetosauroides runs anteriorly to the tip of the elongated snout, evidence that is incompatible with the theory of a keratinous beak proposed for other aetosaurs.

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 Stagonolepis is an extinct genus of stagonolepidid aetosaur known from the Late Triassic (Carnian stage) of Europe.

 Stagonolepis robertsoni was about 3 metres (10 ft) long. It was a quadrupedal animal covered in thick armoured scales that ran down the length of its body. A slow-moving browser, it would have used this heavy body armour to repel attacks from contemporary thecodont carnivores. Stagonolepis had a very small head for its size; it was only 25 centimetres (10 in), accounting for less than 10% of the total body length. It had no teeth in the front of its jaws, but instead had a beak-like tip that arched upwards. This would have allowed it to uproot plants in a similar manner to a modern pig. The peg-like teeth at the back of its mouth would have been suitable for chewing tough vegetation, including horsetails, ferns, and the newly evolved cycads.

 Fossil remains of S. robertsoni have been found in Lossiemouth Sandstone of Scotland, while S. olenkae is known from deposits near Krasiejów, Poland. S. olenkae is stratigraphically younger the type species of Stagonolepis, S. robertsoni. The genus Aetosauroides from South America has been considered a junior synonym of Stagonolepis by some paleontologists. Two species of Aetosauroides were named, A. scagliai and A. subsulcatus. In 2002, Andrew B. Heckert and Spencer G. Lucas proposed that smaller specimens of both species belong to Stagonolepis robertsoni, and larger specimens to S. wellesi. S. wellesi itself was originally named Calyptosuchus, a stagonolepidid from the Late Triassic Dockum Group of the United States, which was considered to be a species of Stagonolepis by Murray & Long in 1989. However, most of the sequential studies conclude that both Aetosauroides and Calyptosuchus are valid and monotypic genera, the former occures only in South America and the latter only in the United States. Stagonolepis is restricted to the Carnian stage of Scotland and Poland.

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 Typothorax is an extinct genus of aetosaur that lived in the Late Triassic. Its remains have been found in North America. Two species are known: T. coccinarum, the type species, and T. antiquum.

 Typothorax was a classic aetosaur, a crurotarsan related to modern crocodile. Unlike modern crocodiles, however, aetosaurs were herbivorous. They possessed small, leaf-shaped teeth which were unsuited for a diet consisting of meat. Unlike some aetosaurs like Desmatosuchus, Typothorax does not have large shoulder spikes. It does, however, have a pair of enlarged spikes on the neck projecting from the third row of scutes. It has lateral scutes that bear horns that are posteriorly hooked along its back, while its sides and underbelly are covered with ornamented scutes. Although fossils of aetosaurs are not as common as other Triassic archosaurs, with their armor plates being the most common, Typothorax has been represented by fewer skeletal elements than other aetosaurs. Typothorax was about 2.5 metres (8.2 ft) long and weighed 100 kilograms (220 lb).

 The vertebral column of Typothorax is shortened, with individual vertebrae being reduced in length. However, the osteoderms that overly the vertebrae are not shortened. Instead, they are reduced in number so that each dorsal paramedian osteoderm (osteoderm that covers the back) overlies several dorsal vertebrae. In nearly all other crurotarsans, there is one row of osteoderms per vertebra. T. coccinarum has around 20 rows of presacral osteoderms and about 26 presacral vertebrae. If the cervical spikes of Typothorax are homologous to those of Desmatosuchus, it is likely that rows of osteoderms were removed from the front. This is because in Desmatosuchus the spikes are present in the fifth row, while in Typothorax they are present in the third.

 In T. coccinarum, there are 10 thoracic columns and four caudal columns of ventral osteoderms on the underside. Unlike all other aetosaurs, Typothorax possesses spiked osteoderms on the underside of the tail, near the cloaca. This region is not covered by osteoderms to the extent that it is in other aetosaurs such as Aetosaurus and Coahomasuchus.

 Like all aetosaurs and many other early crurotarsans, Typothorax had erect hindlimbs held beneath the body. This is evident by a straight femur, an anteriorly directed pes (foot), and the projection of the lateral surface of the illium over the femur. Because the length of the femur is almost equal to that of the tibia and fibula (lower leg) and astragalus and calcaneum (ankle), Typothorax was probably slow-moving. The forelimbs are reduced in size and were directed outward in a sprawling position. This posture is also seen in ankylosaurs, ceratopsians, and the early cynodont Procynosuchus.

 Several aspects of the forelimbs have been interpreted as adaptations to digging. Like many digging tetrapods, the radius is significantly shorter than the humerus. Like other aetosaurs, there is a prominent deltopectoral crest on the humerus. The manus is short and wide, a characteristic of digging animals. There is also a entepicondyle on the humerus, which is the origin of forearm pronator and manual flexor muscles. Typothorax also possesses a relatively long olecranon process for the insertion of the M. triceps muscle, but not as long as those of digging animals. Heckert et al. (2010) concluded that Typothorax was not specifically adapted for a fossorial lifestyle but had an ability to dig that other aetosaurs didn't have. The upturned snout of Typothorax and other aetosaurs suggests that they may have searched for food by rooting around in soil.

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 Paratypothorax is an extinct genus of aetosaur. It was first named in 1985 from specimens collected from the Lower Stubensandstein in Germany and was also noted to be present in the Chinle Group of the southwestern United States in both the Dockum and Chinle Formations, which are latest Carnian and Rhaetian in age, respectively. The genus was described from osteoderms that were initially referred to the phytosaur Belodon kappfi. Material from Paratypothorax has also been reported from the Norian-age Fleming Fjord Formation in Greenland.

 Paratypothorax possesses paramedian scutes that are wide, strap-like, and have grooves and pits on them forming radial patterns. Like other typothoracisines such as Typothorax, the lateral scutes bear large horns that are posteriorly hooked. The rear of each scute is overlapped by a prominent knob.

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 Десматозух (Desmatosuchus — «имеющий связь с крокодилами») — род травоядных рептилий, живших в триасе в 230 млн. лет назад. Останки обнаружены в 1920 году в США. По неподтверждённым данным, являются предками анкилозавров (прим. - скорее всего, хуntа).

 Такие животные как десматозухи не могли ничего противопоставить хищникам, поэтому со временем они увеличились в размерах и приобрели надёжный костный панцирь, состоящий из скреплённых между собой пластин.

 Название рептилии можно перевести как «связанный с крокодилами». Эти животные были одними из первых четвероногих травоядных ископаемых триасового периода, предшественниками анкилозавров (прим. - персональное допущение автора данной статьи). В раннем триасе размеры травоядных животных были невелики: длина 1-2 метра, масса 100-120 кг. Но с появлением крупных хищных архозавроморф они стали увеличиваться. Совершенствовалось и оборонительное вооружение: к концу триасового периода рептилии оказались закованы в костяную броню, а от головы до хвоста они были покрыты шипами, защищавшими их от нападения.

 Функция челюстного аппрата и возможные диетические предпочтения текодонтового этозавра неоэтозавроида (Neoaetosauroides enqaeus) из триаса Южной Америки были проанализированы группой ученых и сравнены с этозаврами из Северного Полушария: десматозухом (Desmatosuchus haplocerus) и стагонолеписом (Stagonolepis robertsoni), а также с ныне живущим короткомордым миссисипским аллигатором (Alligator mississippiensis). Сжимающие и разжимающие мышцы и их функция были восстановлены на основе зубных и скелетных сравнений с видами, имеющими сходное строение челюстей, чтобы понять пищевые привычки ящера. Исследования и проектирования черепа этозавров показали, что строение мышц челюсти указывает скорее на сильный прикус, чем на быструю скорость укуса. Однако, именно среди этозавров Северного полушария чаще встречаются виды, имеющие более сильный укус, в то время как южноамериканский неоэтозавроид обладал более быстрым укусом. Эти различия указывают на более развитые приспособления для разрушения, раскалывания, и подрезания растений, особенно ярко выраженные на челюстях позади зубного ряда, для десматозуха и стагонолеписа.

 У этозавров имеются различия в строении зубов, в расположении верхнего височного отверстия, в положении соединения челюстей относительно зубного ряда, а также в форме нижней челюсти. У неоэтозавроида отсутствуют зубные зазубренности и следы износа на зубах, что, вероятно, связано с питанием мягкой пищей, например, мягкими листьями, насекомыми и их личинками, лишёнными твердых панцирей. Возможно, что неоэтозавроид был скорее насекомоядным, чем растительноядным животным, ориентируясь на пищевой ресурс, который был очень широко распространен и весьма разнообразен в рамках наземных экосистем триасового периода.

 Desmatosuchus (meaning "link crocodile") is an extinct genus of archosaur belonging to the Order Aetosauria. It was one of the largest aetosaurs, being 5 metres (16 ft) long and about 1.50 m (5 ft) high. It lived during the Late Triassic in Texas.

 Desmatosuchus looked like its relatives, possessing an armored body and pig-like head. It had a shovel-like snout and weak teeth that suggest it lived by uprooting soft plants. Like many of its relatives, it had heavy armoured plates along its back, tail, and parts of the underside. However, unlike most other aetosaurs, Desmatosuchus also had two rows of spikes along the sides of its back. The largest spikes, above the shoulders, were 45 centimetres (18 in) long. These probably gave it extra protection against predators.

 Two species are currently accepted: D. spurensis and D. smalli. Desmatosuchus chamaensis is recognized as a distinct genus, but there is some dispute about whether the name Heliocanthus or Rioarribasuchus applies.

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 Longosuchus (meaning "Long's crocodile") is an extinct genus of aetosaur from the Late Triassic of North America. It measured about 3 metre in length.

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