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''Lagerpeton'' is a genus of lagerpetid avemetatarsalian, comprising a single species, ''L. chanarensis''. First described from the
Chañares Formation The Chañares Formation is a Carnian-age geologic formation of the Ischigualasto-Villa Unión Basin, located in La Rioja Province, Argentina. It is characterized by drab-colored fine-grained volcaniclastic claystones, siltstones, and sandstones ...
of Argentina by A. S. Romer in 1971, ''Lagerpeton'' anatomy is somewhat incompletely known, with fossil specimens accounting for the
pelvic girdle The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...
, hindlimbs, posterior presacral, sacral and anterior caudal vertebrae. Skull and shoulder material has also been described. The name comes from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
(, "hare") plus (, "reptile").


Discovery

''Lagerpeton'' fossils have only been collected from the
Chañares Formation The Chañares Formation is a Carnian-age geologic formation of the Ischigualasto-Villa Unión Basin, located in La Rioja Province, Argentina. It is characterized by drab-colored fine-grained volcaniclastic claystones, siltstones, and sandstones ...
in
La Rioja Province, Argentina La Rioja () is a province of Argentina located in the west of the country. The landscape of the province consist of a series of arid to semi-arid mountain ranges and agricultural valleys in between. It is in one of these valleys that the capital ...
. The first of these fossils were discovered in a 1964-1965 expedition by the Museum of Comparative Zoology (MCZ) and Museo de la Plata (MLP), although some were also discovered in 1966 by paleontologists from the Miguel Lillo Institute (PVL) of the University of Tucuman.
Alfred Romer Alfred Sherwood Romer (December 28, 1894 – November 5, 1973) was an American paleontologist and biologist and a specialist in vertebrate evolution. Biography Alfred Romer was born in White Plains, New York, the son of Harry Houston Romer an ...
named ''Lagerpeton chanarensis'' in 1971, based on a complete right hindlimb discovered during the MCZ-MLP expedition. The specimen was initially stored at the Museo de la Plata with catalogue number MLP 64-XI-14-10, but by 1986 it had been transferred to the Paleontology Museum at the
National University of La Rioja The National University of La Rioja ( es, Universidad Nacional de La Rioja, UNLAR) is an Argentine national university A national university is mainly a university created or managed by a government, but which may also at the same time oper ...
(PULR) and given the designation PULR 06, though some studies alternatively call it UPLR 06 or UNLR 06. Some of the foot bones from this specimen have gone missing. Romer also mentioned PVL material collected by Jose Bonaparte. In 1972, Romer described MCZ 4121, which was a specimen smaller than the holotype. It was preserved in a nodule alongside the holotype of '' Lewisuchus admixtus'' and a few ''
Lagosuchus ''Lagosuchus'' is an extinct genus of avemetatarsalian archosaur from the Late Triassic of Argentina. The type species of ''Lagosuchus'', ''Lagosuchus talampayensis,'' is based on a small partial skeleton recovered from the early Carnian-age Cha ...
'' bones. MCZ 4121 represents a few vertebrae, a pair of
scapulocoracoid The scapulocoracoid is the unit of the pectoral girdle that contains the coracoid and scapula. The coracoid itself is a beak-shaped bone that is commonly found in most vertebrates with a few exceptions. The scapula is commonly known as the ''shoulde ...
s (mislabeled as belonging to ''Lagosuchus'') and portions of the hip and hindlimbs, including two complete
femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...
s. He also suggested that ''Lagerpeton'' was the probable identity of several incomplete
tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
e and
fibula The fibula 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. Its upper extremity ...
e preserved along with several gomphodont skeletons in slab MCZ 3691. However, later authors have doubted the referral of most MCZ material to ''Lagerpeton'', with only the MCZ 4121 femurs being confidently referred to the genus.
Andrea Arcucci Andrea is a given name which is common worldwide for both males and females, cognate to Andreas, Andrej and Andrew. Origin of the name The name derives from the Greek word ἀνήρ (''anēr''), genitive ἀνδρός (''andrós''), that re ...
described two PVL specimens, PVL 4619 and 4625, in 1986. PVL 4619, the PVL specimen mentioned by Romer, was a partial skeleton including a complete pelvis and left hindlimb, as well as a partial right hindlimb. PVL 4625 was another skeleton discovered later and originally described as including portions of the left hip, left hindlimb, and vertebral column.
Paul Sereno Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence" who has discovered several new dinosaur species on several continents, including at sites ...
and Arcucci redescribed the known material in 1994 and mentioned that an isolated partial femur of this species was also present at the PVL, although
Martin Ezcurra Martin may refer to: Places * Martin City (disambiguation) * Martin County (disambiguation) * Martin Township (disambiguation) Antarctica * Martin Peninsula, Marie Byrd Land * Port Martin, Adelie Land * Point Martin, South Orkney Islands Aus ...
(2016) noted that the provided catalogue number, PVL 5000, actually referred to a notoungulate
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...
. Further preparation of PVL 4625 has revealed the presence of a
scapula The scapula (plural 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 eithe ...
, dentary, and cranial fragments.


Description

''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 An ungual (from Latin ''unguis'', i.e. ''nail'') is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and ungulates have ungual phalanges, as did the sauropod Sauropoda (), whose members are known as sauropods (; ...
. Body mass has been estimated as no more than , based on the slender cross section of limb bones and estimates between more derived dinosauromorphs, such as '' Silesaurus'', and basal saurischians like ''
Eoraptor ''Eoraptor'' () is a genus of small, lightly built, basal sauropodomorph. One of the earliest-known dinosaurs, it lived approximately 231 to 228 million years ago, during the Late Triassic in Western Gondwana, in the region that is now northwes ...
''. 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 The femoral head (femur head or head of the femur) is the highest part of the thigh bone ( femur). It is supported by the femoral neck. Structure The head is globular and forms rather more than a hemisphere, is directed upward, medialward, and a ...
and the length of digit IV and
metatarsal The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the me ...
IV being greater than digit III and metatarsal III. ''L. chanarensis'' lacks many
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23  million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is ...
ian characters, such as the anterior trochanter, placing it basal within Dinosauromorpha or even outside the group altogether.


Classification

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 (anatomy) The pes ( Latin for ''foot'') is the zoological term for the distal portion of the hind limb of tetrapod animals. It is the part of the pentadactyl limb that includes the metatarsals and digits ( phalanges). During evolution, it has taken many ...
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. ''Lagerpeton'' is the namesake of the family Lagerpetidae, a group of small avemetatarsalians which coexisted alongside dinosaurs for much of the
Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...
. Lagerpetids are traditionally considered the most basal clade within Dinosauromorpha and the sister taxon to Dinosauriformes.Baron, M.G., Norman, D.B., and Barrett, P.M. (2017)
A new hypothesis of dinosaur relationships and early dinosaur evolution
''Nature'', 543: 501–506.
Cladogram simplified after Kammerer, Nesbitt & Shubin (2012): More recently described fossil material for the group instead suggests that lagerpetids are early pterosauromorphs, more closely related to pterosaurs than to dinosaurs.


Palaeogeography

The oldest fossils of ''L. chanarensis'' were found in the
Chañares Formation The Chañares Formation is a Carnian-age geologic formation of the Ischigualasto-Villa Unión Basin, located in La Rioja Province, Argentina. It is characterized by drab-colored fine-grained volcaniclastic claystones, siltstones, and sandstones ...
and originate from the Upper Middle Triassic (
Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between Ma and ~237 Ma (million years ago). The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic). ...
) of
Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period The Jurassic ( ) is a geologic period and st ...
, southern Pangaea. All ''Lagerpeton'' specimens share this geographic location, including other fossils from the Lower Late Triassic ( Carnian). Radiometric dating of volcanic material in the formation has narrowed the formation and entire fossil assemblage found there to between 236 and 234 million years old.


Locomotion

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.


Neural spines

The neural spines of the posterior dorsal vertebrae are inclined anteriorly, a character not observed in any other
archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian ...
, but common in saltatory mammals. This feature is suggested to allow for greater vertebral flexibility, correlated with leaping and bounding locomotor styles.


Pelvic girdle

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.


Didactyl foot

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.


References

{{Taxonbar, from=Q514042 Prehistoric avemetatarsalians Triassic archosaurs Middle Triassic reptiles of South America Triassic Argentina Fossils of Argentina Chañares Formation Fossil taxa described in 1971 Taxa named by Alfred Romer Lagerpetidae