''Lagerpeton'' is a genus of
lagerpetid avemetatarsalia
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. ...
n, 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 sandstone ...
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 p ...
,
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 sandstone ...
in
La Rioja Province, Argentina. The first of these fossils were discovered in a 1964-1965 expedition by the
Museum of Comparative Zoology
A museum ( ; plural museums or, rarely, musea) is a building or institution that cares for and displays a collection of artifacts and other objects of artistic, cultural, historical, or scientific importance. Many public museums make thes ...
(MCZ) and
Museo de la Plata
The La Plata Museum ( es, Museo de la Plata) is a natural history museum in La Plata, Argentina. It is part of the (Natural Sciences School) of the UNLP (National University of La Plata).
The building, long, today houses 3 million fossils an ...
(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 Argentina, Argentine national university, situated in the city of La Rioja, Argentina, La Rioja, capital of La Rioja Province (Argentina), La Rioja Provinc ...
(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
Jose is the English transliteration of the Hebrew and Aramaic name ''Yose'', which is etymologically linked to ''Yosef'' or Joseph. The name was popular during the Mishnaic and Talmudic periods.
* Jose ben Abin
* Jose ben Akabya
*Jose the Galile ...
.
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 i ...
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
Austra ...
(2016) noted that the provided catalogue number, PVL 5000, actually referred to a
notoungulate
Notoungulata is an extinct order of mammalian ungulates that inhabited South America from the early Paleocene to the Holocene, living from approximately 61 million to 11,000 years ago. Notoungulates were morphologically diverse, with forms resemb ...
mammal.
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 eith ...
,
dentary
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
, 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 ]saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
ns 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 spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
, 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 l ...
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 t ...
ian characters, such as the anterior trochanter, placing it basal within Dinosauromorpha[ or even outside the group altogether.]
Classification
Early to late Olenekian
In the geologic timescale, the Olenekian is an age in the Early Triassic epoch; in chronostratigraphy, it is a stage in the Lower Triassic series. It spans the time between Ma and Ma (million years ago). The Olenekian is sometimes divided i ...
trackways from Poland have yielded footprints of a ''Lagerpeton''-like quadrupedal dinosauromorph. This ichnogenus
An ichnotaxon (plural ichnotaxa) is "a taxon based on the fossilized work of an organism", i.e. the non-human equivalent of an artifact. ''Ichnotaxa'' comes from the Greek ίχνος, ''ichnos'' meaning ''track'' and ταξις, ''taxis'' meaning ...
, named ''Prorotodactylus
''Prorotodactylus'' is a dinosauromorph or pterosauromorph 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 ...
'' 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 forms ...
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
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
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 sandstone ...
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, southern Pangaea
Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...
. All ''Lagerpeton'' specimens share this geographic location, including other fossils from the Lower Late Triassic (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 m ...
). Radiometric dating
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares ...
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, 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