Ornithoscelida
Ornithoscelidans | |
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A Triceratops horridus mounted skeleton (top) and a male house sparrow (Passer domesticus, bottom).
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Ornithoscelida Huxley, 1870 |
Subgroups | |
Ornithoscelida (
Huxley's concept
Thomas Henry Huxley originally defined the term in an 1869 lecture as a group comprising two subgroups: the large and heavy-set Dinosauria and the newly discovered Compsognathus, which he placed in a new grouping Compsognatha.[2] The former were defined by their shorter cervical vertebrae, and the femur length exceeding tibia length, and the latter with longer cervical vertebrae, and the femur length shorter than tibia length. He noted that the characteristics of their bones showed many features akin to birds. The dinosaurs Huxley had divided into three families:
- Megalosauridae: Teratosaurus, Palaeosaurus, Megalosaurus, Poekilopleuron, Laelaps, and Euskelosaurus (tentatively)
- Scelidosauridae: Thecodontosaurus, Scelidosaurus, Hylaeosaurus, Polacanthus (tentatively), and Acanthopholis
- Iguanodontidae: Cetiosaurus, Iguanodon, Hypsilophodon, Hadrosaurus, and Stenopelix (tentatively)
S. Williston (1878) included Compsognathus in Dinosauria and divided dinosaurs into Sauropoda and Ornithoscelida, the latter including taxa that would later be considered theropods and ornithischians.[3]
This classification quickly fell out of use, due to the dominant classification system by Harry Govier Seeley that grouped dinosaurs into two main branches: Saurischia and Ornithischia.[4]
Modern theory
In the beginning of the twenty-first century, improved descriptions of the early
Dinosauromorpha |
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A follow-up study, presented by Parry, Baron and Vinther (2017), demonstrated how, if using the same dataset, the Ornithoscelida hypothesis can also be recovered using a range of different phylogenetic analysis methods, including Bayesian maximum-likelihood. The same study, when analysing a modified version of the original Baron et al. (2017) dataset, also found some support for the Phytodinosauria hypothesis when using certain types of analysis.[6]
The Ornithoscelida hypothesis has been challenged by a team of international researchers in November 2017, following a reworking of the original anatomical dataset from Baron et al. (2017). This reworking produced the traditional model, with Ornithischia and Saurischia recovered as sister-taxa. However, this traditional tree was only weakly supported and not statistically significantly different from the alternative Ornithoscelida hypothesis. With only minor adjustments made by Baron and colleagues in response, Ornithoscelida was found to be preferred over the traditional model once more.[7][8]
See also
References
- ^ Whitney, William Dwight (1897), The Century Dictionary: An Encyclopedic Lexicon of the English Language, vol. V, New York: The Century Co., p. 4158
- doi:10.1144/gsl.jgs.1870.026.01-02.09 – via Wikisource.
- S2CID 85354215.
- PMID 28332523.
- S2CID 205254710.
- PMID 29134086.
- S2CID 205260354.
- S2CID 205260360.