Shastasaurus

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Shastasaurus
Temporal range:
Ma[1]
Partial skull of Shastasaurus pacificus (UCMP 9017)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: †Ichthyosauria
Suborder: †
Longipinnati
Node: †Merriamosauria
Family: †Shastasauridae
Merriam, 1895
Genus: †Shastasaurus
Merriam, 1895
Type species
†Shastasaurus pacificus
Merriam, 1895
Species

†S. pacificus
Merriam, 1895
†S.? liangae
(Yin et al., 2000 [originally Guanlingsaurus])
†S.? sikanniensis
(Nicholls & Manabe, 2004 [originally Shonisaurus])

Synonyms
  • ?Guanlingsaurus Yin et al., 2000

Shastasaurus ("

ichthyosaur from the Late Triassic.[2] Specimens have been found in the United States, Canada, and China.[3]

Description

Size of Shonisaurus popularis (green) and S. sikanniensis (red), a possible species of Shastasaurus, compared with a human

Shastasaurus lived during the late

Pardonet Formation British Columbia, dating to the middle Norian age (about 210 million years ago).[5] By comparison, S. sikanniensis was one of the largest known ichthyosaurs, similar in size to modern-day cetaceans, measuring up to 21 metres (69 ft) in length and weighing 81.5 metric tons (89.8 short tons).[6]

Shastasaurus was highly specialized, and differed considerably from other ichthyosaurs. It was very slender in profile. S. sikanniensis had a ribcage slightly less than 2 metres (6.6 ft) deep despite a distance of over 7 metres (23 ft) between its flippers.

cephalopods.[7] However, current research indicates that the jaws of shastasaurid ichthyosaurs do not fit the suction-feeding profile, since their short and narrow hyoid bones are unsuitable to withstand impact forces for such kind of feeding,[8] and since some species like Shonisaurus had robust sectorial teeth with gut contents of mollusk shells and vertebrates.[9][10]

It is unknown whether Shastasaurus had a dorsal fin; however, the smaller, more basal ichthyosaur Mixosaurus had one.[11] The upper fluke of the tail was probably much less-developed than the shark-like tails found in later species.[12]

Species and synonyms

Restoration of S. pacificus

The type species of Shastasaurus is S. pacificus, from the late Carnian of northern California. It is known only from fragmentary remains, which have led to the assumption that it was a 'normal' ichthyosaur in terms of proportions, especially skull proportions. Several species of long-snouted ichthyosaur were referred to Shastasaurus based on this misinterpretation, but are now placed in other genera (including Callawayia and Guizhouichthyosaurus).[7]

Royal Tyrrell Museum

Shastasaurus may include a second species, Shastasaurus liangae. It is known from several good specimens, and was originally placed in the separate genus Guanlingsaurus. Complete skulls show that it had an unusual short and toothless snout. S. pacificus probably also had a short snout, although its skull is incompletely known.[7] However, a new juvenile specimen discovered in 2013 shows that the hyoid bone of Guanlingsaurus is much shorter, and considered it as a distinct genus based on phylogenetic analysis.[13]

S. sikanniensis was originally described in 2004 as a large species of

Pardonet Formation British Columbia, dating to the middle Norian age (about 210 million years ago).[5]

In 2009, Shang & Li reclassified the species Guizhouichthyosaurus tangae as Shastasaurus tangae. However, later analysis showed that Guizhouichthyosaurus was in fact closer to more advanced ichthyosaurs, and so cannot be considered a species of Shastasaurus.[7]

Austrian Alps and S. neubigi (Sander, 1997) from the German Muschelkalk.[3] S. neubigi, however, was re-described and reassigned to its own genus, Phantomosaurus.[16]

Synonyms of S. / G. liangae:
Guanlingichthyosaurus

lapsus calami
)

Synonyms of S. pacificus:
Shastasaurus alexandrae Merriam, 1902
Shastasaurus osmonti Merriam, 1902

See also

References

  1. ^ "†Shastasaurus Merriam 1895 (ichthyosaur)". Paleobiology Database. Fossilworks. Retrieved 17 December 2021.
  2. ISBN 0-520-23315-8
    , at pages 90-91.
  3. ^ a b Shang Qing-Hua, Li Chun (2009). "On the occurrence of the ichthyosaur Shastasaurus in the Guanling Biota (Late Triassic), Guizhou, China" (PDF). Vertebrata PalAsiatica. 47 (3): 178–193.
  4. ^ Michael W. Maisch and Andreas T. Matzke (2000). "The Ichthyosauria" (PDF). Stuttgarter Beiträge zur Naturkunde: Serie B. 298: 1–159. Archived from the original (PDF) on 2011-07-18.
  5. ^
    doi:10.1671/0272-4634(2004)024[0838:GIOTTN]2.0.CO;2
    .
  6. S2CID 245444783
    .
  7. ^
    PMID 21625429
    .
  8. PMID 24348983
    .
  9. S2CID 254874088
    .
  10. S2CID 129908740
    .
  11. ISSN 0567-7920
    .
  12. ^ Wallace, D.R. (2008). Neptune's Ark: From Ichthyosaurs to Orcas. University of California Press, 282pp.
  13. ^
    S2CID 83784699
    .
  14. ^ Moon, B. (2019). "A new phylogeny of ichthyosaurs (Reptilia: Diapsida)". Journal of Systematic Palaeontology. 17: 1–27.
  15. hdl:11573/1682932
    .
  16. doi:10.1671/0272-4634(2006)26[598:TBOPNS]2.0.CO;2
    .
  17. doi:10.1111/j.1475-4983.2007.00735.x
    .
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