Saurischia

Source: Wikipedia, the free encyclopedia.
Not to be confused with Sauropoda.

Saurischians
Temporal range:
Ma[1]
Possible Middle Triassic record[2]
Montage of six different representatives of saurischian dinosaurs.

1st row (early saurischians):

theropod
);
2nd row (
Tyrannosaurus rex
;
3rd row (
Plateosaurus engelhardti
.

Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Seeley
, 1888
Subgroups
Saurischians of
uncertain affinity

Saurischia (

dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithischia were originally called orders by Harry Seeley in 1888[4] though today most paleontologists classify Saurischia as an unranked clade rather than an order.[5]

Description

All

maniraptoran theropod dinosaurs, are a sub-clade of saurischian dinosaurs in phylogenetic classification.[6]

Saurischian dinosaurs are traditionally distinguished from

omnivorous diets.[7]

Classification

  • Saurischian pelvis structure (left side)
    Saurischian pelvis structure (left side)
  • Tyrannosaurus pelvis (showing saurischian structure – left side)
    Tyrannosaurus pelvis (showing saurischian structure – left side)

In his paper naming the two groups, Seeley reviewed previous classification schemes put forth by other paleontologists to divide up the traditional order Dinosauria. He preferred one that had been put forward by Othniel Charles Marsh in 1878, which divided dinosaurs into four orders: Sauropoda, Theropoda, Ornithopoda, and Stegosauria (these names are still used today in much the same way to refer to suborders or clades within Saurischia and Ornithischia).[4]

Seeley, however, wanted to formulate a classification that would take into account a single primary difference between major dinosaurian groups based on a characteristic that also differentiated them from other reptiles. He found this in the configuration of the hip bones, and found that all four of Marsh's orders could be divided neatly into two major groups based on this feature. He placed the Stegosauria and Ornithopoda in the Ornithischia, and the Theropoda and Sauropoda in the Saurischia. Furthermore, Seeley used this major difference in the hip bones, along with many other noted differences between the two groups, to argue that "dinosaurs" were not a natural grouping at all, but rather two distinct orders that had arisen independently from more primitive archosaurs.[4] This concept that "dinosaur" was an outdated term for two distinct orders lasted many decades in the scientific and popular literature, and it was not until the 1960s that scientists began to again consider the possibility that saurischians and ornithischians were more closely related to each other than they were to other archosaurs.

Although his concept of a

cladistic analysis of relationships among dinosaurs.[8] A node-base clade, Eusaurischia, was named for the least inclusive group containing sauropodomorphs (represented by Cetiosaurus) and theropods (represented by Neornithes). Any saurischian that diverged before the theropod-sauropodomorph split is therefore outside clade Eusaurischia.[9]

One alternative hypothesis challenging Seeley's classification was proposed by

segnosaurs were an unusual type of herbivorous theropod saurischian closely related to birds
, and the Phytodinosauria hypothesis fell out of favor.

A 2017 study by Matthew Grant Baron, David B. Norman and Paul M. Barrett did not find support for a monophyletic Saurischia, according to its traditional definition. Instead, the group was found to be

Pachypodosauria to include Sauropodomorpha and Herrerasauridae as subclades.[14] Cau (2018) also supported Ornithoscelida but placed herrerasaurids, Tawa and Daemonosaurus in a clade (Herrerasauria) outside Dinosauria.[15] Other recent studies support a view closer to the traditional Saurischia hypothesis, with theropods closer to sauropodomorphs than to ornithischians. Novas et al. (2021) support Cau's herrerasaur phylogeny but place this clade in Saurischia.[16]

Phylogenetic position of saurischians in different topologies
Müller & Garcia, 2020[17] Novas et al., 2021[16]
Dinosauria
Dracohors

†Silesauridae

Dinosauria

†Ornithischia

Saurischia
Ornithoscelida hypothesis. Taxa traditionally classified as saurischians are highlighted in green.
Baron et al., 2017[12] Cau, 2018[15]
Dracohors

†Silesauridae

Dinosauria
†Saurischia 
(=
Pachypodosauria[14]
)
Ornithoscelida
Dracohors

See also

References

  1. doi:10.1016/j.gr.2018.01.005
    .
  2. PMID 23221875
    .
  3. ^ Oxford English Dictionary
  4. ^
    S2CID 129792059
    .
  5. ^ Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.). (2004). The Dinosauria. 2nd edition. University of California Press, Berkeley. 833 pp.
  6. ISBN 978-0-520-24209-8
    .
  7. PMID 19605396
    .
  8. ^ Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.) (2004). The Dinosauria, Second Edition. University of California Press., 861 pp.
  9. ^ Weishampel, D. B., Dodson, P., & Osmólska, H. (Eds.). (2007). The dinosauria. Univ of California Press.
  10. ISBN 0-14-010055-5
    .
  11. ^ Paul, G.S. (1988). Predatory Dinosaurs of the World, a Complete Illustrated Guide. New York: Simon & Schuster. 464 p.
  12. ^
    S2CID 205254710
    .
  13. ^ "New study shakes the roots of the dinosaur family tree". 22 March 2017.
  14. ^
    S2CID 4395996
    .
  15. ^
    S2CID 44078918
    .
  16. ^
    doi:10.1016/j.jsames.2021.103341
    .
  17. S2CID 221298572
    .
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