''Ixalerpeton'' (meaning "leaping reptile") is a genus of

lagerpetid Lagerpetidae (; originally Lagerpetonidae) is a family of basal avemetatarsalians (early-diverging members of the reptile lineage leading to birds and other dinosaurs). Though traditionally considered the earliest-diverging dinosauromorphs (ar ...

avemetatarsalian Avemetatarsalia (meaning "bird metatarsals") is a clade of diapsid reptiles containing all archosaurs more closely related to birds than to crocodilians. The two most successful groups of avemetatarsalians were the dinosaurs and pterosaurs. Dinos ...

containing one

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

, ''I. polesinensis''. It lived in the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

alongside the

sauropodomorph Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lo ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

Buriolestes ''Buriolestes'' is a genus of early sauropodomorph dinosaurs from the Late Triassic Santa Maria Formation of the Paraná Basin in southern Brazil. It contains a single species, ''B. schultzi'', named in 2016. The type specimen was found alongsid ...

''.

Discovery and naming

The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen of ''Ixalerpeton'', numbered ULBRA-PVT059, consists of parts from the skull, vertebral column, and all four limbs. The specimen comes from the

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...

Santa Maria Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age (Late Triassic), and is notable for its fossils of cynodonts, " rauisuchian" pseudosuchians, and early dinosaurs and othe ...

, and it was found alongside two individuals of ''

'' as well as a set of femora belonging to second individual of ''Ixalerpeton''. The genus name of ''Ixalerpeton'' combines the Greek words ''ixalos'' ("leaping") and ''erpeton'' ("reptile"), and the species name ''polesinensis'' references the town of

São João do Polêsine São João do Polêsine is a municipality in the state of Rio Grande do Sul, Brazil. Paleontology In this city there are outcrops with fossils. Sauropodomorph dinosaur '' Buriolestes'' and dinosauromorph '' Ixalerpeton'' were found in the Car ...

, where the dig site is located.

Description

''Ixalerpeton'' was similar to other lagerpetids (namely ''

Dromomeron ''Dromomeron'' (meaning "running femur") is a genus of Lagerpetidae, lagerpetid Avemetatarsalia, avemetatarsalian which lived around 220 to 211.9 ± 0.7 million years ago. The genus contains species known from Late Triassic-age rocks of the South ...

'' and ''

Lagerpeton ''Lagerpeton'' is a genus of lagerpetid avemetatarsalian, comprising a single species, ''L. chanarensis''. First described from the Chañares Formation of Argentina by A. S. Romer in 1971, ''Lagerpeton'' anatomy is somewhat incompletely k ...

'') in having long hindlimbs with well-developed muscle attachments on the

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

; in particular, its

fourth trochanter The fourth trochanter is a shared characteristic common to archosaurs. It is a protrusion on the posterior-medial side of the middle of the femur shaft that serves as a muscle attachment, mainly for the '' musculus caudofemoralis longus'', the m ...

was quite large and formed a crest (which is unlike ''Dromomeron''). However, the last few

dorsal vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebra (anatomy), vertebrae of intermediate size between the ce ...

of ''Ixalerpeton'' do not have the forward-inclining

neural spines Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

of ''Lagerpeton'' (which were associated with the latter's hopping, or saltatory, lifestyle). In addition to the enlarged fourth trochanter, a suite of other traits differentiate ''Ixalerpeton'' from all previously-described lagerpetids; there is an antitrochanter on the ilium; the end of the shaft of the

ischium The ischium (; : is ...

is tall; there is no ambiens process on the pubis; the medial condyle on the femur is relatively flat at the front end but sharply angled at the back end; and the back face of the top end of the tibia has a deep groove. The head and forelimbs found with ''Ixalerpeton'' are the first of these elements that have been found among lagerpetids. Unlike dinosauriforms, the posttemporal fenestra at the back of the skull is large and unreduced; there is an extra bone, the postfrontal, bordering the eye socket; there is no supratemporal fossa, which is an indentation found on the

frontal bone In the human skull, the frontal bone or sincipital bone is an unpaired bone which consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bo ...

in dinosauriforms; and the

glenoid cavity The glenoid fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word ''glenoid'' is pronounced or (both are common) and is from , "socket", reflecting the shoulder joint's ball-and-socket form. It is a shallow, pyri ...

on the

scapula The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...

, where the scapula-

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

joint is located, faces slightly sideways instead of backwards. On the other hand, there is an anterior tympanic recess on the

braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...

, and the deltopectoral crest on the humerus is long, both of which are common among basal dinosauromorphs.

Classification

A 2016 phylogenetic analysis found that ''Ixalerpeton'' was the closest relative of ''

''. The phylogenetic tree recovered is partially reproduced below.

Paleoecology

Similar to the

Ischigualasto Ischigualasto Provincial Park (), also called ''Valle de la Luna'' ("Valley of the Moon" or "Moon Valley"), due to its moon-like appearance, is a provincial protected area in the north-east of San Juan Province, north-western Argentina, limiting ...

and Chinle Formations, the

preserves both ''Ixalerpeton'' (a non-dinosaur avemetatarsalian) and ''

'' (a dinosaur). This indicates that dinosaurs did not rapidly replace related groups once they had evolved.

References

{{Taxonbar, from=Q27844365 Lagerpetidae Late Triassic archosaurs Carnian genera Late Triassic reptiles of South America Triassic Brazil Fossils of Brazil Santa Maria Formation Fossil taxa described in 2016 Taxa named by Alexander Kellner Taxa named by Rodrigo T. Müller