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Lagosuchus

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Lagosuchus
Temporal range: Middle—Late Triassic, 236–234 Ma
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Mounted skeleton
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Ornithodira
Clade: Dinosauromorpha
Order: †Lagosuchia
Paul, 1988
Family: †Lagosuchidae
Bonaparte, 1975
Genus: †Lagosuchus
Romer, 1971
Species:
†L. talampayensis
Binomial name
†Lagosuchus talampayensis
Romer, 1971

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 Chañares Formation. The holotype skeleton of L. talampayensis is fairly fragmentary, but it does possess some traits suggesting that Lagosuchus was a probable dinosauriform, closely related to dinosaurs.[1][2][3]

A second potential species of Lagosuchus, L. lilloensis, is based on an assortment of slightly larger and more well-preserved fossils.[4] These larger specimens have been considered much more diagnostic and informative than the small L. talampayensis skeleton. As a result, some paleontologists have placed the larger specimens into a new genus, Marasuchus. Marasuchus is generally considered one of the more complete early dinosauriforms, useful for estimating ancestral traits for the origin of dinosaurs. This would also render Lagosuchus a nomen dubium, simply a name referring to a fossil which is too fragmentary to have a formal genus.[2][5] However, other paleontologists support the argument that Lagosuchus is a valid genus, and that Marasuchus is a junior synonym of it.[6][3]

History

A diagram of PULR 09, the partial skeleton which serves as the holotype of Lagosuchus talampayensis.

The type species Lagosuchus talampayensis was first described by Alfred S. Romer in 1971, who considered it a "pseudosuchian" (then a collection of various non-dinosaurian "thecodonts").[1] In 1972 he named a second species, Lagosuchus lilloensis, known from larger and more well-preserved specimens.[4] A later review by Jose Bonaparte in 1975 synonymized the two species and considered Lagosuchus intermediate between "pseudosuchians" and saurischian dinosaurs.[6]

Modern authors now consider at least L. lilloensis to be firmly on the lineage of archosaurs leading to dinosaurs.[5] However, the genus Lagosuchus is regarded by some to be dubious. Paul Sereno and Andrea Arcucci considered L. talampayensis to be undiagnosable in a 1994 study, and reclassified L. lilloensis as a new genus, Marasuchus.[2] In 2019, PULR 09, the holotype skeleton of L. talampayensis, was redescribed by Federico Agnolin and Martin Ezcurra. They argued that the skeleton was not only diagnostic, but indistinguishable from specimens of Marasuchus lilloensis. As a result, they supported the synonymy proposed by Bonaparte, referring specimens of Marasuchus lilloensis back to Lagosuchus talampayensis.[3]

The Chañares Formation's age has been through much debate. It has traditionally been considered to belong to the Ladinian stage, the last stage of the Middle Triassic. Radiometric dating in 2016 has dated the main fossiliferous section of the formation to the early Carnian stage, near the start of the Late Triassic.[7]

Description

Artist's impressions and skeletal restoration

Lagosuchus is known from very incomplete remains (only a hind leg plus a shoulder blade and vertebrae can be definitely assigned to it). However, features of the leg show that it was a lightly built archosaur, and is notable for its long slender legs and well-developed feet - features it shares with certain dinosaurs. These features, as well as comparisons to close relatives, suggest that it could run on its hind legs for short periods, although it probably moved on all fours most of the time. Lagosuchus was likely an agile predator that could use speed to chase its prey and to escape larger predators.[8] Lagosuchus was about the size of a ferret.[9] Thomas Holtz gave a lenght of 1,7 ft (51 cm).[10]

Palaeobiology

Metabolism

It is believed that Lagosuchus and Marasuchus were transitional between cold blooded reptiles and warm blooded dinosaurs.[11]

References

  1. ^ a b Romer, Alfred Sherwood (15 June 1971). "The Chañares (Argentina) Triassic reptile fauna. X. Two new but incompletely known long-limbed pseudosuchians". Breviora. 378: 1–10.
  2. ^ a b c Sereno, Paul C.; Arcucci, Andrea B. (March 1994). "Dinosaurian precursors from the Middle Triassic of Argentina: Marasuchus lilloensis, gen. nov". Journal of Vertebrate Paleontology. 14 (1): 53–73. doi:10.1080/02724634.1994.10011538.
  3. ^ a b c Agnolin, Federico L.; Ezcurra, Martin D. (2019). "THE VALIDITY OF LAGOSUCHUS TALAMPAYENSIS ROMER, 1971 (ARCHOSAURIA, DINOSAURIFORMES), FROM THE LATE TRIASSIC OF ARGENTINA" (PDF). Breviora. 565 (1): 1–21. doi:10.3099/0006-9698-565.1.1. ISSN 0006-9698.
  4. ^ a b Romer, Alfred Sherwood (11 August 1972). "The Chañares (Argentina) Triassic reptile fauna. XV. Further remains of the thecodonts Lagerpeton and Lagosuchus". Breviora. 394: 1–7.
  5. ^ a b Nesbitt, S.J. (2011). "The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades" (PDF). Bulletin of the American Museum of Natural History. 352: 189. doi:10.1206/352.1. hdl:2246/6112. ISSN 0003-0090.
  6. ^ a b Jose, Bonaparte (1975). "Nuevos materiales de Lagosuchus talampayensis Romer (Thecodontia-Pseudosuchia) y su significado en el origen de los Saurischia: Chañarense inferior, Triásico medio de Argentina" (PDF). Acta Geológica Lilloana. 13 (1): 5–90.
  7. ^ Claudia A. Marsicano; Randall B. Irmis; Adriana C. Mancuso; Roland Mundil; Farid Chemale (2016). "The precise temporal calibration of dinosaur origins". Proceedings of the National Academy of Sciences of the United States of America. 113 (3): 509–513. Bibcode:2016PNAS..113..509M. doi:10.1073/pnas.1512541112. PMC 4725541. PMID 26644579.
  8. ^ Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 97. ISBN 978-1-84028-152-1.
  9. ^ Paul, Gregory (1988). Predatory dinosaurs of the world. Simon & Schuster.
  10. ^ https://www.geol.umd.edu/~tholtz/dinoappendix/HoltzappendixWinter2011.pdf
  11. ^ Pontzer, Herman; Allen, Vivian; Hutchinson, John R. (2009). "Biomechanics of Running Indicates Endothermy in Bipedal Dinosaurs". PLoS ONE. 4 (12): e7783. Bibcode:2009PLoSO...4.7783P. doi:10.1371/journal.pone.0007783. PMC 2772121. PMID 19911059.{{cite journal}}: CS1 maint: unflagged free DOI (link)


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