Eodromaeus

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Eodromaeus
Temporal range: Late Triassic (Carnian)
~231.4–229  Ma
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Eodromaeus in Japan.jpg
Restored skeletal mount in Japan
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Genus:† Eodromaeus
Martinez et al., 2011
Species:
†E. murphi
Binomial name
†Eodromaeus murphi
Martinez et al., 2011

Eodromaeus (meaning "dawn runner") is an extinct genus of probable basal theropod dinosaurs from the Late Triassic of Argentina. Like many other of the earliest-known dinosaurs, it hails from the Carnian-age (~230 Ma) Ischigualasto Formation, within the Ischigualasto-Villa Unión Basin of northwestern Argentina. Upon its discovery, it was argued to be one of the oldest true theropods, supplanting its contemporary Eoraptor , which was reinterpreted as a basal sauropodomorph. [1]

Discovery

Skeletal diagram of Eodromaeus murphi, known remains depicted in white and light grey, unknown in dark grey. Eodromaeus skeletal.png
Skeletal diagram of Eodromaeus murphi, known remains depicted in white and light grey, unknown in dark grey.

Fossils from Eodromaeus were first discovered in 1996 by Argentinean paleontologist Ricardo N. Martinez and Earthwatch volunteer Jim Murphy, and it was first believed that the fossils were a new species of Eoraptor . However, as the researchers started to take a closer look at the fossils, they found that it had many skeletal features which were absent in Eoraptor, and they understood that it came from a new genus. [1] [2]

Eodromaeus is known from six specimens found at various levels of the Ischigualasto Formation of San Juan Province, Argentina. By far the most complete specimen is the holotype, PVSJ 560, a crushed but nearly complete articulated skeleton recovered from the base of the Valle de la Luna Member. The Valle de la Luna Member is the thick third-oldest member of the formation. It overlies the thinner Cancha de Bochas and La Peña Members, the second-oldest and oldest members of the formation, respectively. Other referred specimens include PVSJ 561, 562, and 563 from the Valle de la Luna Member, PVSJ 534 from the La Peña Member, and PVSJ 877 from the Cancha de Bochas Member. Every Eodromaeus specimen lived within the humid Scaphonyx - Exaeretodon - Herrerasaurus biozone, which occupies the first half of the Ischigualasto Formation. A bentonite deposit in the La Peña Member has been dated to 231 ± 0.4 Ma, indicating that the Ischigualasto Formation corresponds to the later part of the Carnian stage, the first stage in the Late Triassic. [1] [3]

Eodromaeus was named by Ricardo N. Martínez, Paul C. Sereno, Oscar A. Alcober, Carina E. Colombi, Paul R. Renne, Isabel P. Montañez and Brian S. Currie in 2011 and the type species is Eodromaeus murphi. The generic name is derived from the Greek words Eos ("Dawn", "Early") and Dromaeus ("Runner"). The specific name honors Jim Murphy, who used to work the area nearby where the fossils were found. [1]

Description

Size comparison between Eodromaeus and a human. Eodromaeus SIZE 01.png
Size comparison between Eodromaeus and a human.

Eodromaeus was a relatively small dinosaur, like most Carnian dinosaurs apart from herrerasaurids. [1] A press release estimated that its total length reach about 1.2 meters (3.9 feet) from nose to tail, with a weight of about 4.5 to 6.8 kg (9.9 to 15.0 lb). [2] Benson et al. (2018) estimated that Eodromaeus had a mass of 7.1 kg (16 lb). [4] The animal was lightly built and had long hindlimbs, suggesting that it was well-built for running even by the standards of most early dinosaurs. Kubo & Kubo (2012) found that, among 23 sampled Triassic archosaurs, only Marasuchus exceeded Eodromaeus in adaptations for cursoriality. [5] Paul Sereno has estimated that it could run about 32 km per hour (20 miles per hour). [2] Eodromaeus has been cited by Sereno as resembling a predicted common ancestor to all dinosaurs, the "Eve" of dinosaurs. [6]

Life restoration Eodromaeus murphi (2).jpg
Life restoration

The skull was low and rectangular, about 12 cm (4.7 in) in length. It had an expansive antorbital fenestra edged from below by a sharp ridge. The antorbital fenestra was preceded a promaxillary fenestra, an additional hole in the skull characteristic of theropods and Herrerasaurus . The braincase had deep depressions on its side like many theropods, and connected to the palate via thin and blade-like basipterygoid processes. The cranium had a relatively low number of knife-shaped teeth (fifteen in total) which were longest in the front half of the maxilla. There was also a row of tiny teeth on the pterygoid bone of the palate. Palatal teeth are very rare in dinosaurs (and true archosaurs in general), though they have also been found in Eoraptor . The lower jaw was slender, with widely spaced teeth extending to the tip of the snout as in early theropods. [1]

The cervicals (neck vertebrae) were significantly more elongated than those of Eoraptor, and those near the shoulders had large pits which would have housed air sacs. The shorter but more numerous dorsals (trunk vertebrae) were reinforced by hyposphene-hypantrum articulations, while the caudals (tail vertebrae) were connected by elongated prezygapophyses, as seen in other theropods. The shoulder girdle had a deep coracoid connecting to a long and rod-shaped scapula. The large forelimbs had closely-appressed forearm bones and strongly-developed wrist and elbow joints. The manus (hand) had five fingers, with the second and third elongating towards their tips. In contrast, the fourth and fifth fingers were very thin and short. The pelvis (hip) had a tall ilium which connected to three sacrals (hip vertebrae). It also included an elongated ischium and pubis, the latter of which tapers before expanding into a small pubic boot similar to that of other theropods. The hindlimb possessed several muscle scars characteristic of theropods, such as a depression on the femur for extensor muscles, and a flange for tibial ligaments on the fibula. [1]

Classification

Reconstructed skeletal mount Eodromaeus murphi.jpg
Reconstructed skeletal mount

When originally described in 2011, Eodromaeus was regarded as the earliest member of Theropoda. Theropods include the vast majority of carnivorous dinosaurs, such as Tyrannosaurus , Allosaurus , and Velociraptor , as well as the only living dinosaurs, birds. Eodromaeus was considered one of most basal theropod and placed outside of the group Neotheropoda, which contains coelophysoids and post-Triassic theropods. The only putative theropods found to be more basal were the herrerasaurids, a group of relatively large early carnivorous dinosaurs with an unstable relationship to other dinosaurs. [1] The discovery of Eodromaeus also lead to scrutiny regarding the contemporary early dinosaur Eoraptor. Eoraptor had previously been regarded as a theropod, but Martinez et al. (2011) instead concluded that it likely represented one of the most basal sauropodomorphs, the group that includes animals like Apatosaurus . [1] There is still a small amount of debate over the position of Eoraptor, with a few studies reclaiming it as a theropod alongside Eodromaeus. [7] [8] Most studies since 2011 have continued to place Eodromaeus as a basal theropod akin to the results of Martinez et al. There are some disagreements; many subsequent studies consider Eodromaeus to lie crownward (i.e. more 'advanced') relative to Tawa and/or Chindesaurus. [9] [10] [11] [12] A few also reject the notion of herrerasaurids being theropods. [8]

An alternative hypothesis, first presented by Cabreira et al. (2016), argues that Eodromaeus was not a theropod, but rather a more basal saurischian. [13] This means that its lineage would have evolved prior to the split between sauropodomorphs and true theropods. Other putative theropods such as Tawa, Chindesaurus, Daemonosaurus , and herrerasaurids fall even further stemwards than Eodromaeus according to this study and derived works. [14] [15] [16] A few other unusual placements have been found in studies relating to the controversial Ornithoscelida hypothesis of Baron et al. (2017). [8] Although Baron et al.'s original paper did place Eodromaeus as a theropod, a critique and recoding by Langer et al. (2017) recovered Saurischia and moved Eodromaeus out of Theropoda. [17] [18] A subsequent response to that critique, by Baron et al. (2017), placed Eodromaeus as a basal herrerasaurian and simultaneously shifted the entire family Herrerasauridae outside of Dinosauria. [19]

The following cladogram represents the original theropodan placement of Eodromaeus found by Martinez et al., 2011: [1]

Dinosauromorpha

The following cladogram represents the alternative hypothesis of Cabreira et al. (2016), placing Eodromaeus as a basal saurischian: [13]

Dinosauria

Related Research Articles

<i>Eoraptor</i> Extinct genus of dinosaurs

Eoraptor is a genus of small, lightly built, basal sauropodomorph dinosaur. One of the earliest-known dinosaurs and one of the earliest members of the sauropod family, it lived approximately 231 to 228 million years ago, during the Late Triassic in Western Gondwana, in the region that is now northwestern Argentina. The type and only species, Eoraptor lunensis, was first described in 1993, and is known from an almost complete and well-preserved skeleton and several fragmentary ones. Eoraptor had multiple tooth shapes, which suggests that it was omnivorous. Eoraptor was 1.5 feet (0.46 m) tall and 3 feet (0.91 m) long.

<span class="mw-page-title-main">Sauropodomorpha</span> Extinct clade of dinosaurs

Sauropodomorpha 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 long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The prosauropods, which preceded the sauropods, were smaller and were often able to walk on two legs. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the Late Triassic until their decline and extinction at the end of the Cretaceous.

<i>Staurikosaurus</i> Extinct genus of dinosaurs

Staurikosaurus is a genus of herrerasaurid dinosaur from the Late Triassic of Brazil, found in the Santa Maria Formation.

<span class="mw-page-title-main">Herrerasauridae</span> Extinct family of basal saurischian dinosaurs

Herrerasauridae is a family of carnivorous dinosaurs, possibly basal to either theropods or even all of saurischians, or even their own branching from Dracohors, separate from Dinosauria altogether. They are among the oldest known dinosaurs, first appearing in the fossil record around 233.23 million years ago, before becoming extinct by the end of the Carnian stage. Herrerasaurids were relatively small-sized dinosaurs, normally no more than 4 metres (13 ft) long, although the holotype specimen of "Frenguellisaurus ischigualastensis" is thought to have reached around 6 meters long. The best known representatives of this group are from South America, where they were first discovered in the 1930s in relation to Staurikosaurus and 1960s in relation to Herrerasaurus. A nearly complete skeleton of Herrerasaurus ischigualastensis was discovered in the Ischigualasto Formation in San Juan, Argentina, in 1988. Less complete possible herrerasaurids have been found in North America and Africa, and they may have inhabited other continents as well.

<i>Herrerasaurus</i> Extinct genus of dinosaurs

Herrerasaurus is likely a genus of saurischian dinosaur from the Late Triassic period. This genus was one of the earliest dinosaurs from the fossil record. Its name means "Herrera's lizard", after the rancher who discovered the first specimen in 1958 in South America. All known fossils of this carnivore have been discovered in the Ischigualasto Formation of Carnian age in northwestern Argentina. The type species, Herrerasaurus ischigualastensis, was described by Osvaldo Reig in 1963 and is the only species assigned to the genus. Ischisaurus and Frenguellisaurus are synonyms.

<i>Alwalkeria</i> Extinct genus of dinosaurs

Alwalkeria is a genus partly based on basal saurischian dinosaur remains from the Late Triassic, living in India.

<i>Chindesaurus</i> Extinct genus of dinosaurs

Chindesaurus is an extinct genus of basal saurischian dinosaur from the Late Triassic of the southwestern United States. It is known from a single species, C. bryansmalli, based on a partial skeleton recovered from Petrified Forest National Park in Arizona. The original specimen was nicknamed "Gertie", and generated much publicity for the park upon its discovery in 1984 and airlift out of the park in 1985. Other fragmentary referred specimens have been found in Late Triassic sediments throughout Arizona, New Mexico, and Texas, but these may not belong to the genus. Chindesaurus was a bipedal carnivore, approximately as large as a wolf.

<span class="mw-page-title-main">Dinosauromorpha</span> Clade of reptiles

Dinosauromorpha is a clade of avemetatarsalians that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lagerpetids, with later formulations specifically excluding pterosaurs from the group. Birds are the only dinosauromorphs which survive to the present day.

<span class="mw-page-title-main">Guaibasauridae</span> Extinct family of dinosaurs

Guaibasauridae is a family of basal sauropodomorph dinosaurs, known from fossil remains of late Triassic period formations in Brazil, Argentina and India.

<span class="mw-page-title-main">Santa Maria Formation</span> Geologic formation in Brazil

The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age, and is notable for its fossils of cynodonts, "rauisuchian" pseudosuchians, and early dinosaurs and other dinosauromorphs, including the herrerasaurid Staurikosaurus, the basal sauropodomorphs Buriolestes and Saturnalia, and the lagerpetid Ixalerpeton. The formation is named after the city of Santa Maria in the central region of Rio Grande do Sul, where outcrops were first studied.

<span class="mw-page-title-main">Ischigualasto Formation</span> Geological formation in Argentina

The Ischigualasto Formation is a Late Triassic geological formation in the Ischigualasto-Villa Unión Basin of southwestern La Rioja Province and northeastern San Juan Province in northwestern Argentina. The formation dates to the late Carnian and early Norian stages of the Late Triassic, according to radiometric dating of ash beds.

<i>Panphagia</i> Extinct genus of dinosaurs

Panphagia is a genus of sauropodomorph dinosaur described in 2009. It lived around 231 million years ago, during the Carnian age of the Late Triassic period in what is now northwestern Argentina. Fossils of the genus were found in the La Peña Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin. The name Panphagia comes from the Greek words pan, meaning "all", and phagein, meaning "to eat", in reference to its inferred omnivorous diet. Panphagia is one of the earliest known dinosaurs, and is an important find which may mark the transition of diet in early sauropodomorph dinosaurs.

<i>Tawa hallae</i> Extinct species of dinosaur

Tawa is a genus of possible basal theropod dinosaurs from the Late Triassic period. The fossil remains of Tawa hallae, the type and only species were found in the Hayden Quarry of Ghost Ranch, New Mexico, US. Its discovery alongside the relatives of Coelophysis and Herrerasaurus supports the hypothesis that the earliest dinosaurs arose in Gondwana during the early Late Triassic period in what is now South America, and radiated from there around the globe. The specific name honours Ruth Hall, founder of the Ghost Ranch Museum of Paleontology.

<span class="mw-page-title-main">Saturnaliidae</span> Late Triassic dinosaur clade

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<i>Sanjuansaurus</i> Extinct genus of dinosaurs

Sanjuansaurus is a genus of herrerasaurid dinosaur from the Late Triassic (Carnian) Ischigualasto Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina.

<i>Daemonosaurus</i> Genus of reptiles (fossil)

Daemonosaurus is an extinct genus of possible theropod dinosaur from the Late Triassic of New Mexico. The only known fossil is a skull and neck fragments from deposits of the latest Triassic Chinle Formation at Ghost Ranch. Daemonosaurus was an unusual dinosaur with a short skull and large, fang-like teeth. It lived alongside early neotheropods such as Coelophysis, which would have been among the most common dinosaurs by the end of the Triassic. However, Daemonosaurus retains several plesiomorphic ("primitive") traits of the snout, and it likely lies outside the clade Neotheropoda. It may be considered a late-surviving basal theropod or non-theropod basal saurischian, possibly allied to other early predatory dinosaurs such as herrerasaurids or Tawa.

Pampadromaeus is an extinct genus of basal sauropodomorph dinosaurs known from the Late Triassic (Carnian) Santa Maria Formation of the Paraná Basin in Rio Grande do Sul, southern Brazil.

<i>Buriolestes</i> Extinct genus of dinosaurs

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 alongside a specimen of the lagerpetid dinosauromorph Ixalerpeton.

<i>Nhandumirim</i> Genus of reptiles (fossil)

Nhandumirim is a genus of basal sauropodomorph dinosaur from the Carnian age of Late Triassic Brazil. It is currently considered a saturnaliid sauropodomorph. The type and only species, Nhandumirim waldsangae, is known from a single immature specimen including vertebrae, a chevron, pelvic material, and a hindlimb found in the Santa Maria Formation in Rio Grande do Sul.

<i>Incertovenator</i> Extinct genus of probable archosaur

Incertovenator is an extinct genus of archosauriform reptile, likely an archosaur, of uncertain affinities. Its unstable position is a result of possessing a number features found in both the bird-line avemetatarsalian archosaurs and the crocodylian-line pseudosuchians. The type and only known species is I. longicollum, which is known from single specimen discovered in the Late Triassic Ischigualasto Formation of Argentina. Incertovenator is known almost entirely by its vertebral column. This indicates that it had a relatively long neck, leading to its uncertain classification due to the convergent evolution of elongated neck vertebrae in both avemetatarsalian and pseudosuchian archosaurs.

References

  1. 1 2 3 4 5 6 7 8 9 10 Martínez et al., 2011
  2. 1 2 3 Weise E, "New dog-sized dinosaur discovered", www.usatoday.com, 2011-01-23.
  3. ↑ Martínez, R.N.; Apaldetti, C.; Alcober, O.A.; Colombi, C.E.; Sereno, P.C.; Fernandez, E.; Malnis, P.S.; Correa, G.A.; Abelin, D. (2013). "Vertebrate succession in the Ischigualasto Formation" (PDF). Journal of Vertebrate Paleontology. 32 (Supplement 1: Memoir 12: Basal sauropodomorphs and the vertebrate fossil record of the Ischigualasto Formation (Late Triassic: Carnian–Norian) of Argentina): 10–30. doi:10.1080/02724634.2013.818546. hdl:11336/7771. S2CID   37918101.
  4. ↑ Benson, Roger B. J.; Hunt, Gene; Carrano, Matthew T.; Campione, Nicolás (2018). "Cope's rule and the adaptive landscape of dinosaur body size evolution". Palaeontology. 61 (1): 13–48. Bibcode:2018Palgy..61...13B. doi: 10.1111/pala.12329 . ISSN   1475-4983.
  5. ↑ Kubo, Tai; Kubo, Mugino O. (2012-06-01). "Associated evolution of bipedality and cursoriality among Triassic archosaurs: a phylogenetically controlled evaluation". Paleobiology. 38 (3): 474–485. Bibcode:2012Pbio...38..474K. doi:10.1666/11015.1. ISSN   0094-8373. JSTOR   41684613. S2CID   85941954 – via jstor.
  6. ↑ Bowdler N, "'Dawn runner casts light on birth of the dinosaurs", www.bbc.co.uk, 2011-01-13.
  7. ↑ Bergman D.S., Sues H-D. (2011), "A late-surviving basal theropod dinosaur from the latest Triassic of North America", Proceedings of the Royal Society B , published online 2011-04-13.
  8. 1 2 3 Baron, Matthew G.; Norman, David B.; Barrett, Paul (2017). "A new hypothesis of dinosaur relationships and early dinosaur evolution" (PDF). Nature. 543 (7646): 501–506. Bibcode:2017Natur.543..501B. doi:10.1038/nature21700. PMID   28332513. S2CID   205254710.
  9. ↑ Bittencourt, Jonathas; Arcucci, Andrea; Marsicano, Claudia; Langer, Max (15 December 2014). "Osteology of the Middle Triassic archosaur Lewisuchus admixtus Romer (Chañares Formation, Argentina), its inclusivity, and relationships amongst early dinosauromorphs". Journal of Systematic Palaeontology. 13 (3): 189–219. doi:10.1080/14772019.2013.878758. hdl: 11336/18502 . S2CID   56155733.
  10. ↑ Nesbitt, Sterling J.; Ezcurra, Martin D. (13 July 2015). "The early fossil record of dinosaurs in North America: A new neotheropod from the base of the Upper Triassic Dockum Group of Texas" (PDF). Acta Palaeontologica Polonica . 60. doi: 10.4202/app.00143.2014 .
  11. ↑ Marsh, Adam D.; Parker, William G.; Langer, Max C.; Nesbitt, Sterling J. (2019-05-04). "Redescription of the holotype specimen of Chindesaurus bryansmalli Long and Murry, 1995 (Dinosauria, Theropoda), from Petrified Forest National Park, Arizona" (PDF). Journal of Vertebrate Paleontology. 39 (3): e1645682. Bibcode:2019JVPal..39E5682M. doi:10.1080/02724634.2019.1645682. ISSN   0272-4634. S2CID   202865005.
  12. ↑ Marsh, A.D.; Rowe, T.B. (2020). "A comprehensive anatomical and phylogenetic evaluation of Dilophosaurus wetherilli (Dinosauria, Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona". Journal of Paleontology. 94 (S78): 1–103. Bibcode:2020JPal...94S...1M. doi: 10.1017/jpa.2020.14 . S2CID   220601744.
  13. 1 2 Cabreira, S.F.; Kellner, A.W.A.; Dias-da-Silva, S.; da Silva, L.R.; Bronzati, M.; de Almeida Marsola, J.C.; Müller, R.T.; de Souza Bittencourt, J.; Batista, B.J.; Raugust, T.; Carrilho, R.; Brodt, A.; Langer, M.C. (2016). "A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet". Current Biology. 26 (22): 3090–3095. doi: 10.1016/j.cub.2016.09.040 . PMID   27839975.
  14. ↑ Pacheco, Cristian; Müller, Rodrigo; Langer, Max; Pretto, Flávio; Kerber, Leonardo; da Silva, Sérgio Dias (2019). "Gnathovorax cabreirai: a new early dinosaur and the origin and initial radiation of predatory dinosaurs". PeerJ. 7: e7963. doi: 10.7717/peerj.7963 . PMC   6844243 . PMID   31720108.
  15. ↑ Marsola, Júlio C. A.; Bittencourt, Jonathas S.; J. Butler, Richard; Da Rosa, Átila A. S.; Sayão, Juliana M.; Langer, Max C. (2019). "A new dinosaur with theropod affinities from the Late Triassic Santa Maria, South Brazil". Journal of Vertebrate Paleontology. 38 (5): e1531878. doi:10.1080/02724634.2018.1531878. S2CID   91999370.
  16. ↑ Müller, Rodrigo Temp; Garcia, Maurício Silva (2020-08-26). "A paraphyletic 'Silesauridae' as an alternative hypothesis for the initial radiation of ornithischian dinosaurs". Biology Letters. 16 (8): 20200417. doi: 10.1098/rsbl.2020.0417 . PMC   7480155 . PMID   32842895.
  17. ↑ Max C. Langer; Martín D. Ezcurra; Oliver W. M. Rauhut; Michael J. Benton; Fabien Knoll; Blair W. McPhee; Fernando E. Novas; Diego Pol; Stephen L. Brusatte (2017). "Untangling the dinosaur family tree" (PDF). Nature. 551 (7678): E1–E3. Bibcode:2017Natur.551E...1L. doi:10.1038/nature24011. hdl:1983/d088dae2-c7fa-4d41-9fa2-aeebbfcd2fa3. PMID   29094688. S2CID   205260354.
  18. ↑ Nesbitt, Sterling J.; Sues, Hans-Dieter (3 August 2020). "The osteology of the early-diverging dinosaur Daemonosaurus chauliodus (Archosauria: Dinosauria) from the Coelophysis Quarry (Triassic: Rhaetian) of New Mexico and its relationships to other early dinosaurs". Zoological Journal of the Linnean Society. 191: 150–179. doi: 10.1093/zoolinnean/zlaa080 .
  19. ↑ Matthew G. Baron; David B. Norman; Paul M. Barrett (2017). "Baron et al. reply". Nature. 551 (7678): E4–E5. Bibcode:2017Natur.551E...4B. doi:10.1038/nature24012. PMID   29094705. S2CID   205260360.

Bibliography

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