Dinosauromorpha

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Dracohors
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Dinosauromorphs
Temporal range:
Ma
(possible Early Triassic record)
From top to bottom and left to right, different type of dinosauromorphs: Asilisaurus, Borealopelta, Triceratops and Giganotosaurus.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Ornithodira
Clade: Dinosauromorpha
Benton, 1985[1]
Subgroups

Dinosauromorpha is a

dinosauriforms and lagerpetids,[3] with later formulations specifically excluding pterosaurs from the group.[4] Birds
are the only dinosauromorphs which survive to the present day.

Classification

Pelvis of Marasuchus (=Lagosuchus?) specimen PVL 3870

The name "Dinosauromorpha" was briefly coined by

Michael J. Benton in 1985.[1] It was considered an alternative name for the group "Ornithosuchia", which was named by Jacques Gauthier to correspond to archosaurs closer to dinosaurs than to crocodilians.[5] Although "Ornithosuchia" was later recognized as a misnomer (since ornithosuchids are now considered closer to crocodilians than to dinosaurs), it was still a more popular term than Dinosauromorpha in the 1980s.[3] The group encompassed by Gauthier's "Ornithosuchia" and Benton's "Dinosauromorpha" is now given the name Avemetatarsalia.[4]

In 1991,

Pseudolagosuchus (now considered a synonym of the silesaurid Lewisuchus), Dinosauria (including Aves), and all its descendants. This definition was intended to correspond to a clade including lagerpetids and crownward bird-line archosaurs, but not pterosaurs or other archosaurs.[3][6]

In 2011, Dinosauromorpha was redefined by

Ornithodira, which encompasses almost all avemetatarsalians.[4]

Dinosauriformes was coined in 1992 by F.E. Novas, who used it to encompass dinosaurs, Lagosuchus, "Pseudolagosuchus" (=Lewisuchus), and the herrerasaurids, which he did not consider to be "eudinosaurs" (true dinosaurs like ornithischians and saurischians).[7] Contrary to Novas, most paleontologists since 1992 have considered herrerasaurids to be true dinosaurs, though many other dinosaur-like reptiles still fall within his definition of Dinosauriformes. Novas (1992) defined Dinosauriformes as a node-based clade containing the most recent common ancestor of Lagosuchus and Dinosauria, and all its descendants.[7] Nesbitt (2011) provided a roughly equivalent definition, using Marasuchus and Passer domesticus (the house sparrow, a representative of dinosaurs). In his analysis, Dinosauriformes included dinosaurs, silesaurids, and Marasuchus, but not lagerpetids, which were considered to be an earlier-branching family of dinosauromorphs.[4]

Phylogeny

A phylogenetic analysis by Andrea Cau in

Pan-Aves were synonyms, with Marasuchus in a clade with lagerpetids. Pisanosaurus was resolved within Silesauridae. Cau identified the synapomorphies of Dracohors as:[8]

The anterior tympanic recess, the axial epipophyses, the centrodiapophyseal laminae in the presacral vertebrae, the relative size enlargement of the postacetabular process of ilium, the elongation of the pubis, the proximal sulcus and the reduction of the ligament tuber in the femoral head, and the further reduction in length of the fourth metatarsal and toe compared to the third.

Skeletal diagram of Ixalerpeton

Following the discovery and description of more cranial and postcranial material of the genera

braincase and forelimb meant that the 2020 phylogenetic analysis of Ezcurra and colleagues placed Lagerpetidae next to pterosaurs within Pterosauromorpha, removing the family from Dinosauromorpha. The contents of Dinosauromorpha was thus restricted to only Silesauridae, Dinosauria, and individual genera like Lagosuchus.[9]

Simultaneously, Rodrigo Müller and Maurício Garcia published novel results that reduced the family Silesauridae to a grade of basal dinosaurs in Ornithischia. Pisanosaurus, considered by various authors to be either a silesaurid or basal ornithischian, was found to be intermediate between the grade of silesaurids and true ornithischians, explaining its peculiar combination of silesaurid and ornithischian features that has resulted in its phylogenetic inconsistency. Lewisuchus, a carnivorous form, was found to be the most primitive form of ornithischian, which was almost universally considered to be an only-herbivorous clade before. Dinosauromorpha was reduced to only including Lagerpetidae and Lagosuchus as a result of the reclassification of silesaurids.[10]

Below are the results of:

A variety of individual species and taxa have at times been found to place within Dinosauromorpha and its subgroups, but outside Dinosauria. The taxon Marasuchus has been consistently recovered as a dinosauromorph between lagerpetids and silesaurids, but may also be a junior synonym of the coexisting form Lagosuchus, another dinosauromorph.[11] Pisanosaurus, traditionally considered an ornithischian, was recovered in an unpublished analysis as a dinosauriform outside other clades,[12] but has since been recovered only as a member of Silesauridae or Ornithischia.[10][13][14][15] Saltopus, an enigmatic taxon from the Late Triassic of Scotland, has been placed closer to dinosaurs than Marasuchus, in a polytomy with Silesauridae and Dinosauria,[13] as a sister taxon to Marasuchus,[14][15] or within Dinosauria as a basal saurischian.[10] The British taxon Agnosphitys was originally described as a dinosauriform closer to Dinosauria than Herrerasaurus,[16] but has also been classified as a dinosauriform more derived than silesaurids but basal to Herrerasauridae and Dinosauria,[15] a silesaurid,[13] or a basal saurischian.[10][14] The genus Nyasasaurus from the early Late Triassic of Tanzania is known from multiple incomplete specimens, making it difficult to classify. It has been found as the direct sister taxon of Dinosauria, the basalmost ornithischian, a basal theropod,[17] or a deeply-nested sauropodomorph.[13][14][15]

Origins

Dinosauromorphs appeared putatively around 242 to 244 million years ago by the

Permian-Triassic extinction event. Their age suggests that the rise of dinosaurs was slow and drawn out across much of the Triassic.[18] The oldest known dinosauromorph is Asilisaurus, a silesaurid which may have lived as early as the Anisian age of the middle Triassic period, about 245 million years ago,[19] although it is possible that Nyasasaurus is a dinosaur of the same age, pushing the origins of the groups back further.[13]

Putative basal dinosauromorphs include

Diodorus from the Carnian(?) to Norian of Morocco.[29]

References

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  2. doi:10.4202/app.00372.2017
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  5. ^ Gauthier, J.A. (1986). "Saurischian monophyly and the origin of birds". In Padian, K. (ed.). The Origin of Birds and the Evolution of Flight. Memoirs of the California Academy of Sciences. Vol. 8. San Francisco: California Academy of Sciences. pp. 1–55.
  6. S2CID 84303547
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  7. ^ a b Novas, Fernando E. (January 1992). "Phylogenetic relationships of basal dinosaurs, the Herrerasauridae" (PDF). Palaeontology. 35 (1): 51–62.
  8. ^
    doi:10.4435/BSPI.2018.01. Archived from the original
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  10. ^
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  12. ^ Federico L. Agnolin (2015). "Nuevas observaciones sobre Pisanosaurus mertii Casamiquela, 1967 (Dinosauriformes) y sus implicancias taxonómicas" (PDF). XXIX Jornadas Argentinas de Paleontología de Vertebrados. 27–29 de Mayo de 2015. Diamante, Entre Ríos. Libro de Resúmenes: 13–14. Archived from the original (PDF) on 2016-01-27. Retrieved 2015-08-07.
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  16. ^ Nicholas C. Fraser, Kevin Padian, Gordon M. Walkden and A. L. M. Davis, 2002. Basal dinosauriform remains from Britain and the diagnosis of the Dinosauria. Palaeontology. 45(1), 79-95.
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  26. S2CID 85819339. Archived from the original
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  29. S2CID 55015883. Archived from the original
    (PDF) on 2012-03-14. Retrieved 2011-07-16.

External links

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