Sauropodomorpha

Source: Wikipedia, the free encyclopedia.

Sauropodomorphs
Temporal range: 233.23–66 
Ma[1]
Montage of nine different representatives of sauropodomorph dinosaurs. Clockwise from upper left:
Brachiosaurus altithorax
.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade:
Eusaurischia
Clade: †Sauropodomorpha
Huene, 1932
Subgroups

Sauropodomorpha (

extinction at the end of the Cretaceous
.

Description

Nigersaurus taqueti
and head posture in sauropodomorphs

Sauropodomorphs were adapted to browsing higher than any other contemporary herbivore, giving them access to high

foliage. This feeding strategy is supported by many of their defining characteristics, such as: a light, tiny skull on the end of a long neck (with ten or more elongated cervical vertebrae) and a counterbalancing long tail
(with one to three extra sacral vertebrae).

Their

teeth were weak, and shaped like leaves or spoons (lanceolate or spatulate). Instead of grinding teeth, they had stomach stones (gastroliths), similar to the gizzard stones of montul birds and crocodiles, to help digest tough plant fibers. The front of the upper mouth bends down in what may be a beak
.

One of the earliest known sauropodomorphs,

kilograms (65–110 US short tons
) or more in mass.

Initially

theropods) was a carnivore
. Therefore, their evolution to herbivory went hand in hand with their increasing size and neck length.

They also had large nostrils (nares), and retained a thumb (pollex) with a big claw, which may have been used for defense — though their primary defensive adaptation was their extreme size.

Distinguishing anatomical features

Sauropodomorphs can be distinguished as a group on the basis of some of the following

synapomorphies:[3]

  • The presence of large nares.
  • The distal part of the tibia is covered by an ascending process of the astragalus.
  • Their hind limbs are short when compared to their torso length.
  • The presence of three or more sacral vertebrae.
  • The teeth are thin, flat and are spatula-like, with bladed and serrated crowns.
  • The presence of a minimum of 10 cervical vertebrae that are typically elongated
  • The presence of 25 presacral vertebrae
  • The manus had a large digit I.

Evolutionary history

Among the first dinosaurs to evolve in the

Period,[4] about 230 million years ago (Mya), they became the dominant herbivores by halfway through the late Triassic (during the Norian stage). Their perceived decline in the early Cretaceous is most likely a bias in fossil sampling, as most fossils are known from Europe and North America, but sauropods were still the dominant herbivores in the Gondwanan landmasses. The spread of flowering plants (angiosperms) and "advanced" ornithischians, another major group of herbivorous dinosaurs (noted for their highly developed chewing mechanisms), are most likely not a major factor in sauropod decline in the northern continents[citation needed]. Like all non-avian dinosaurs, the sauropodomorphs became extinct 66 Mya, during the Cretaceous–Paleogene extinction event
.

The earliest and most

theropod, to be an early member of the sauropodomorph lineage, which would make it the most basal sauropodomorph known.[7]

Classification

Restoration of Panphagia, one of the most basal sauropodomorphs known.
Plateosaurus is a well-known prosauropod.

Sauropodomorpha is one of the two major

Bakker
, have historically placed both sets of herbivores within a group called "Phytodinosauria" or "Ornithischiformes".

In

Prosauropoda, and their descendants, the giant Sauropoda
.

junior synonym of Plateosauridae as both contain the same taxa.[9][10]

Most modern classification schemes break the prosauropods into a half-dozen groups that evolved separately from one common lineage. While they have a number of shared characteristics, the evolutionary requirements for giraffe-like browsing high in the trees may have caused convergent evolution, where similar traits evolve separately because they faced the same evolutionary pressure, instead of (homologous) traits derived from a shared ancestor.[11]

Phylogeny

Skull comparison of several sauropodomorphs

Cladogram after

Novas et al., 2011:[10]

Sauropodomorpha

The phylogenetic analysis of Otero et al., 2015 found Sauropodomorpha to be in a polytomy with

Eusaurischia, with Herrerasauridae and Eoraptor external to it within Saurischia.[12] A large phylogenetic analysis of early dinosaurs published by Matthew Baron, David Norman and Paul Barrett (2017) in the journal Nature redefined Sauropodomorpha and Saurischia and recovered Herrerasauridae as the sister group to Sauropodomorpha within Saurischia. This resulted from the proposed removal of Theropoda from Saurischia and the formation of Ornithoscelida, a clade containing Theropoda and Ornithischia.[13]

Below is a cladogram of basal sauropodomorpha after Müller, 2019.[14]

Sauropodomorpha

Paleobiology

Comparisons between the

cathemeral, active throughout the day at short intervals.[15]

Sauropodomorphs reached the age of sexual maturity well before they were fully-grown adults.[16][17] A study by Griebeler et al. (2013) concluded that the maximum growth rates of sauropodomorphs were comparable to those of precocial birds and the black rhinoceros but lower than the growth rates of average mammals.[17]

A long-standing hypothesis has been that early sauropodomorphs were carnivorous, as expected for most early dinosaurs. This hypothesis is supported by the current basalmost sauropodomorph,

plesiomorphic, theropod-like teeth.[18] The teeth of more derived sauropodomorphs such as Eoraptor, Panphagia, and Pampadromaeus are better-suited for herbivorous (or possibly omnivorous) diets.[19] Regardless of the phylogenetic position of herrerasaurids or Eoraptor (which are in flux),[19][20][21] ancestral state reconstructions recover carnivory as being ancestral to sauropodomorphs.[18]

References

  1. doi:10.1016/j.gr.2018.01.005
    .
  2. OxfordDictionaries.com. Archived from the original
    on November 1, 2015. Retrieved 2016-01-20.
  3. ISBN 1-4051-3413-5
    .
  4. S2CID 92177386
    .
  5. PDF
    )
  6. PMID 19209223
    .
  7. S2CID 33506648
    .
  8. doi:10.1127/njgpa/210/1998/41
    .
  9. ^ Yates, Adam M. (2007). Barrett, Paul M.; Batten, David J. (eds.). "The first complete skull of the Triassic dinosaur Melanorosaurus Haughton (Sauropodomorpha: Anchisauria)". Evolution and Palaeobiology: 9–55.
  10. ^
    S2CID 128620874
    .
  11. PMID 21298087
    .
  12. hdl:11336/38019
    .
  13. S2CID 205254710
    .
  14. S2CID 209575985
    .
  15. S2CID 33253407
    .
  16. S2CID 86183725
    .
  17. ^
    PMID 23840575
    .
  18. ^
    PMID 27839975
    .
  19. ^
    S2CID 86006363
    .
  20. PMID 21490016
    .
  21. ^ Hendrickx, C.; Hartman, S.A.; Mateus, O. (2015). "An Overview of Non- Avian Theropod Discoveries and Classification". PalArch's Journal of Vertebrate Palaeontology. 12 (1): 1–73.

Sources

External links
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