Lagerpeton is a genus of basal dinosauromorph. First described by A. S. Romer in 1971, it includes only the species L. chanarensis. This species is incompletely known, with fossil specimens accounting for the pelvic girdle, hindlimbs and posterior presacral, sacral and anterior caudal vertebrae.
Lagerpeton is estimated to have been 70 cm (28 in) in length based on the length of the hindlimb; the most complete hindlimb specimen, from PVL 4619, measures 257.9mm from proximal femur to distal ungual. Body mass has been estimated as no more than 4 kilograms (8.8 lb), based on the slender cross section of limb bones and estimates between more derived dinosauromorphs, such as Silesaurus, and basal saurischians like Eoraptor. Twenty one autapomorphic characters have been identified in L. chanarensis, these include: the anterior inclination of the posterior dorsal neural spines, the hook-shaped femoral head and the length of digit IV and metatarsal IV being greater than digit III and metatarsal III. L. chanarensis lacks many dinosaurian characters, such as the anterior trochanter, placing it basal within Dinosauromorpha.
Early to late Olenekian trackways from Poland have yielded footprints of a Lagerpeton-like quadrupedal dinosauromorph. This ichnogenus, named Prorotodactylus shares multiple synapomorphic characters with Lagerpeton including approximately parallel digits II, III and IV, fused metatarsus, digitigrade posture and reduced digits I and V. Prorotodactylus also shares the, previously autapomorphic, pes morphology of Lagerpeton. If this ichnogenus represents a close relative of Lagerpeton, it would push back the origin of this taxon to the Early Triassic; as a quadrupedal basal dinosauromorph, it also raises questions debating the theory that bipedalism is ancestral to dinosaurs.
The genus Lagerpeton is currently accepted as the most basal clade within Dinosauromorpha and the sister taxon to Dinosauriformes. Presently, Lagerpeton sits within the family “Lagerpetidae”, also occupied by the more derived genus Dromomeron, known from Late Triassic rocks of the southwestern USA.
The oldest fossils of L. chanarensis were found in the Chañares Formation and originate from the Upper Middle Triassic (Ladinian) of Gondwana, southern Pangaea. All Lagerpeton specimens share this geographic location, including other fossils from the Lower Late Triassic (Carnian). Radiodating of volcanic material in the formation has narrowed the formation and entire fossil assemblage found there to between 236 and 234 million years old.
It has been suggested that the extant analogues most similar to L. chanarensis are small bipedal mammals, which are often saltators. Three morphological characteristics in L. chanarensis fossils have been putatively cited as evidence of saltation in this taxon.
The neural spines of the posterior dorsal vertebrae are inclined anteriorly, a character not observed in any other archosaur, but common in saltatory mammals. This feature is suggested to allow for greater vertebral flexibility, correlated with leaping and bounding locomotor styles.
Relative to the hindlimb length, the pelvic girdle is remarkably small. The distance from the pelvic girdle to the femur is therefore also small, more so than most other archosaurs apart from closely related taxa. This reduction in distance may increase the force production during hip extension in extant small mammals.
The narrow and functionally didactyl pes are a further similarity to modern saltators. By condensing into a single unit, the metatarsus gains strength without the drawback of increased weight. It also appears likely that, consequently to the reduction of digit II, digit IV may have elongated to balance the pes.
The hypothesis of saltatorial locomotion is debated, however. Vertebral adaptations of extant organisms exceed those seen in Lagerpeton; the sacral vertebrae of modern saltators are fused and the neural spines reduced. Furthermore, the size of the pelvic girdle and lateral digital reduction may be equally used as evidence for cursorial locomotion.
Avemetatarsalia (meaning "bird metatarsals") is a clade name established by British palaeontologist Michael Benton in 1999 for all crown group archosaurs that are closer to birds than to crocodilians. An alternate name is Pan-Aves, or "all birds", in reference to its definition containing all animals, living or extinct, which are more closely related to birds than to crocodilians. Almost all avemetatarsalians are members of a similarly defined subgroup, Ornithodira. Ornithodira is defined as the last common ancestor of dinosaurs and pterosaurs, and all of its descendants.Members of this group include the Dinosauromorpha, Pterosauromorpha, the genus Scleromochlus, and Aphanosauria. Dinosauromorpha contains more basal forms, including Lagerpeton and Marasuchus, as well as more derived forms, including dinosaurs. Birds belong to the dinosaurs as members of the theropods. Pterosauromorpha contains Pterosauria, which were the first vertebrates capable of true flight. Aphanosauria is a Triassic group of gracile carnivorous quadrupeds which was recognized in 2017.Averostra
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Chañares Formation
The Chañares Formation is a geologic formation of the Ischigualasto-Villa Unión Basin, located in La Rioja Provence, Argentina. The claystones and tuffs of the formation date to the Carnian stage of the Late Triassic and were deposited in a fluvial to lacustrine environment.
The formation represents the onset of the first syn-rift phase in the Triassic rift basin and is the lowermost stratigraphic unit of the Agua de la Peña Group, unconformably overlying the Tarjados Formation of the Paganzo Group. The Chañares Formation is overlain by the Ischichuca Formation and both formations have a combined maximum thickness of 750 metres (2,460 ft).
The Chañares Formation has provided a rich faunal assemblage, including many of the earliest crocodylomorph fossils, as Tropidosuchus, Chanaresuchus, and Gualosuchus, as well as other archosaurs; Lewisuchus admixtus, Lagerpeton, Marasuchus lilloensis, Gracilisuchus, Luperosuchus and Pseudolagosuchus major. Cynodonts are represented by Probainognathus and Massetognathus and other therapsids include Dinodontosaurus.Dinosauriformes
Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs and a partially to fully perforated acetabulum, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period.Dinosauromorpha
Dinosauromorpha is a clade of archosaurs that includes the clade Dinosauria (dinosaurs), and all animals more closely related to dinosaurs than to pterosaurs. Birds are the only surviving dinosauromorphs.Dromomeron
Dromomeron (meaning "running femur") is a genus of lagerpetonid dinosauromorph archosaur that lived around 220 to 211.9 ± 0.7 million years ago. The genus contains species known from Late Triassic-age rocks of the southwestern United States and northwestern Argentina. It is described as most closely related to the earlier Lagerpeton of Argentina, but was found among remains of true dinosaurs like Chindesaurus, indicating that the first dinosaurs did not immediately replace related groups.Based on the study of the overlapping material of Dromomeron and Tawa hallae, Christopher Bennett proposed that the two taxa were conspecific, forming a single growth series of Dromomeron. However, noting prominent differences between their femurs which cannot be attributed to variation with age, Rodrigo Muller rejected this proposal in 2017. He further noted that, while D. romeri is known from juveniles only, it shares many traits in common with D. gigas, which is known from mature specimens.Ixalerpeton
Ixalerpeton (meaning "leaping reptile") is a genus of small, bipedal dinosauromorphs in the lagerpetid family, containing one species, I. polesinensis. It lived in the Late Triassic of Brazil alongside the sauropodomorph dinosaur Buriolestes.Jeholosauridae
Jeholosaurids were herbivorous neornithischian dinosaurs from the Cretaceous Period (Aptian - Santonian, with a possible Campanian record) of Asia. The family was first proposed by Han et al. in 2012. The jeholosaurids were defined as those ornithischians more closely related to Jeholosaurus shangyuanensis than to Hypsilophodon foxii, Iguanodon bernissartensis, Protoceratops andrewsi, Pachycephalosaurus wyomingensis, or Thescelosaurus neglectus. The Jeholosauridae includes the type genus Jeholosaurus and Yueosaurus.Jingshanosaurus
Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.Lagerpetidae
The Lagerpetidae (; originally Lagerpetonidae) is a family of basal dinosauromorphs. Members of the family are known from Late Triassic of Argentina, Arizona, Brazil, New Mexico, and Texas. Lagerpetids were typically small, although some, like Dromomeron gigas, were fairly large. Lagerpetid fossils are very rare, the most common finds are of the hindlimbs, which possessed a number of unique features.Lagosuchus
Lagosuchus is a genus of small avemetatarsalian archosaurs from the middle Triassic period. It is generally thought to be closely related to dinosaurs, as a member of the Dinosauromorpha. Its fossils were found in the Chañares Formation of Argentina, the dating of which is uncertain; some sources date it to the Middle Triassic whilst others date it to the earliest Carnian.Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Prorotodactylus
Prorotodactylus is a dinosauromorph ichnogenus known from fossilized footprints found in Poland and France. The prints may have been made by a dinosauromorph that was a precursor to the dinosaurs, possibly closely related to Lagerpeton. Fossils of Prorotodactylus date back to the early Olenekian stage of the Early Triassic, making it the oldest known dinosauromorph. Its presence during this time extends the range of the dinosaur stem lineage to the start of the Early Triassic, soon after the Permian-Triassic extinction event. Prorotodactylus is the only ichnogenus within the ichnofamily Prorotodactylidae. Two ichnospecies are known, the type P. mirus and P. lutevensis.Pseudolagosuchus
Pseudolagosuchus (meaning "false Lagosuchus") is a genus of dinosauromorph from the Middle Triassic (Ladinian) Chañares Formation of Argentina. It may be a junior synonym of Lewisuchus, but there is very little overlapping material. It was a small reptile which was probably about 1 meter (3.3 ft) long, 30 centimeters (1 ft) tall, and weighed approximately 2 kilograms (4.4 lb). It is known only from a pubis, a femur, a tibia, and vertebrae. Both Sterling Nesbitt, Christian Sidor et al. (2010) and Matthew Baron, David Norman and Paul Barrett (2017) treated this taxon as being synonymous with Lewisuchus.Silesauridae
Silesauridae is an extinct clade of Triassic dinosauriformes consisting of the closest known relatives of dinosaurs. As indicated by coprolite contents, some silesaurids such as Silesaurus may have been insectivorous, feeding selectively on small beetles and other arthropods.Silesaurus
Silesaurus is a genus of silesaurid dinosauriform from the Late Triassic, approximately 230 million years ago in the Carnian faunal stage of what is now Poland.
Fossilized remains of Silesaurus have been found in the Keuper Claystone in Krasiejów near Opole, Silesia, Poland, which is also the origin of its name. The type species, Silesaurus opolensis, was described by Jerzy Dzik in 2003. It is known from some 20 skeletons, making it one of the best-represented of the early dinosauriformes.