Plesiosaurus

Source: Wikipedia, the free encyclopedia.

Plesiosaurus
Temporal range:
Ma
Restored skeleton in Japan
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: †Sauropterygia
Order: †Plesiosauria
Superfamily: †Plesiosauroidea
Family: †Plesiosauridae
Genus: †Plesiosaurus
Conybeare
, 1821
Species:
†P. dolichodeirus
Binomial name
†Plesiosaurus dolichodeirus
Conybeare, 1824

Plesiosaurus (Greek: πλησίος (plesios), near to + σαῦρος (sauros), lizard) is a genus of extinct, large marine

Occitanosaurus
.

Discovery

Type specimen at Natural History Museum and letter concerning the discovery of same from Mary Anning

The first complete skeleton of Plesiosaurus was discovered by early paleontologist and fossil hunter Mary Anning in Sinemurian (Early Jurassic)-age rocks of the lower Lias Group in December 1823.[1][2] Additional fossils of Plesiosaurus were found in rocks of the Lias Group of Dorset for many years,[3][4][5] "until the cessation of quarrying activities in the Lias Group, early in this [20th] century."[2] although less complete remains were used by Henry De la Beche and William Conybeare to name the species two years earlier in 1821,[6] and despite being discovered first, Conybeare's remains were not the holotype; Anning's were.

Plesiosaurus was one of the first of the "

William Conybeare and Henry De la Beche, to indicate that it was more like a normal reptile than Ichthyosaurus, which had been found in the same rock strata just a few years earlier. Plesiosaurus is the archetypical genus of Plesiosauria and the first to be described, hence lending its name to the order. Conybeare and De la Beche coined the name for scattered finds from the Bristol region, Dorset, and Lyme Regis in 1821.[6] The type species
of Plesiosaurus, P. dolichodeirus, was named and described by Conybeare in 1824 on the basis of Anning's original finds.

Description

Skull and dentition

Plesiosaurus with a human to scale.

Compared to other plesiosaur genera, Plesiosaurus has a small head. The skull is much narrower than long,

braincase,[8] although the union is not as robust as in the pliosaurs Rhomaleosaurus and Pliosaurus.[8][11] "The palatal bones are thin, but there is no suborbital fenestra."[8]

The two

symphysis, is robust. The two rami are fused at the symphysis, making a pointed, shallow scoop-like shape.[12]

The teeth of Plesiosaurus are "simple, needle-like cones" that are "slightly curved and circular in transverse section". They are sharply pointed with fine striations running from tip to base, and point forward (procumbent). This procumbency becomes more pronounced near the leading end of the skull, where they may be only 10–15° above horizontal.[7] There are 20 to 25 teeth per upper jaw tooth row,[8] and 24 per low jaw tooth row.[7] Up to four teeth of a lower jaw's tooth row are found in the symphyseal region.[12]

Vertebral column

Illustration of the skeletal anatomy of a Plesiosaurus dolichodeirus from Conybeare's 1824 paper that described an almost complete plesiosaur skeleton found by Mary Anning in 1823

Plesiosaurus was a moderately sized plesiosaur that grew to 2.87–3.5 m (9.4–11.5 ft) in length.

centra of the cervical vertebrae are relatively elongated, being slightly longer than tall. The width, however, is usually greater than or equal to the length. The articular surfaces of the cervical centra are "slightly concave and kidney-shaped, with rounded, slightly rugose edges." Small holes called foramina subcentralia are found on the ventral surface of the centra. Some of the dorsals have rugose articular edges, like the cervicals; this feature is typically absent from the caudals.[15]

Ribs are found from the neck to the tail. Cervical ribs are hatchet-shaped and have two articular heads.

shoulder and pelvis. Each set is composed of seven elements: a bone on the midline flanked by three lateral elements.[16]

Limbs

Life restoration

The shoulder girdle is only partly known but appears to be typical for plesiosaurs. It includes fused

phalangeal formula is uncertain, but the count for one large individual, from "thumb" to fifth "finger", is 4-8-9-8-6.[18]

The pelvis includes equant pubic bones, ischia,[18] and blade-shaped ilia connecting the pelvis to the vertebral column.[19] The acetabulum is formed by surfaces on the pubic bones and ischia. Similar to the pectoral girdle, there is a pair of holes between the ischia and pubic bones.[18] The hindlimbs are long and narrow,[19] and in adults, they are much smaller than the forelimbs.[18] The thigh bones are straight. The lower hindlimb includes two roughly equal-sized bones, the robust tibia and the semilunate-shaped fibula. There are six bones in the ankle. The foot paddle includes five digits. Like the hand, the phalangeal formula is uncertain, but is at least 3-7-9-8-7 from innermost to outer "toe".[19]

Classifications

Referred specimen, the first Plesiosaurus skeleton found - used to name the species in 1821
Sculpture (left) in Crystal Palace Park
Modern restoration

Plesiosaurus has historically been a

Occitanosaurus
.

The following cladogram follows an analysis by Benson et al., 2012, and shows the placement of Plesiosaurus within Plesiosauria.[20]

 
Pistosauria
 

"Pistosaurus postcranium"

Pistosaurus

Yunguisaurus liae

Augustasaurus hagdorni

 
Plesiosauria
 

Bobosaurus forojuliensis

Anningasaura lymense

 Rhomaleosauridae 

Stratesaurus taylori

Macroplata tenuiceps

Avalonnectes arturi

Eurycleidus arcuatus

Meyerasaurus victor

Maresaurus coccai

Atychodracon megacephalus

Archaeonectrus rostratus

Rhomaleosaurus cramptoni

Rhomaleosaurus thorntoni

Rhomaleosaurus zetlandicus

Neoplesiosauria
 
 Pliosauridae 

Thalassiodracon hawkinsi

Hauffiosaurus spp.

Attenborosaurus conybeari

advanced pliosaurids (Peloneustes)

 Plesiosauroidea 

Eoplesiosaurus antiquior

Plesiosaurus dolichodeirus

Plesiopterys wildi

Cryptoclidus eurymerus

 Microcleididae 

Eretmosaurus rugosus

Westphaliasaurus simonsensii

Seeleyosaurus guilelmiimperatoris

Microcleidus tournemiensis

Microcleidus brachypterygius

Microcleidus homalospondylus

Palaeobiology

Restoration

Plesiosaurus fed mainly on clams and snails, and is thought to have eaten

belemnites, fish and other prey as well.[21] Its U-shaped jaw and sharp teeth would have been like a fish trap. It propelled itself by the paddles, the tail being too short to be of much use. Its neck could have been used as a rudder when navigating during a chase. Plesiosaurus gave live birth to live young in the water like sea snakes. The young might have lived in estuaries
before moving out into the open ocean. It has been postulated that the long neck of Plesiosaurus would have been a hindrance when trying to speed up, any bend in the neck creating turbulences.[22] If that is the case then Plesiosaurus would have had to keep its neck straight to achieve good acceleration, something that would make hunting difficult. For this reason it may be possible that these animals would actually lie in wait for prey to come close instead of trying to pursue them.

Palaeoenvironment

Tentatively referred specimen in Calgary

Unequivocal specimens of Plesiosaurus dolichodeirus are limited to the Lyme Regis area of Dorset.

ammonite fossil zones, these rocks date to the early Sinemurian stage. Some other Plesiosaurus fossils are from later Sinemurian rocks. The oldest specimen may be a skull thought to come from late Rhaetian or early Hettangian rocks.[25]

See also

References

Notes

  1. ^ Torrens 1995
  2. ^ a b c Storrs 1997 pp. 146
  3. ^ Andrew 1896
  4. ^ Lydekker 1889
  5. ^ Owen 1865
  6. ^ a b De la Beche, H. T. & W. D. Conybeare. (1821). Notice of the discovery of a new fossil animal, forming a link between the Ichthyosaurus and crocodile, together with general remarks on the osteology of the Ichthyosaurus. Transactions of the Geological Society of London 5: 559–594
  7. ^ a b c d e f Storrs 1997 pp. 166
  8. ^ a b c d e f g h i j k Storrs 1997 pp. 165
  9. ^ a b Storrs 1997 pp. 167
  10. ^ Cruickshank 1991
  11. ^ Taylor and Cruickshank 1993
  12. ^ a b Storrs 1997 pp. 169.
  13. S2CID 129977015
    .
  14. ^ Storrs 1997 pp. 149
  15. ^ a b c d e Storrs 1997 pp. 170
  16. ^ a b c Storrs 1997 pp. 171
  17. ^ Storrs 1997 pp. 173
  18. ^ a b c d Storrs 1997 pp. 176
  19. ^ a b c Storrs 1997 pp. 178
  20. PMID 22438869
    .
  21. ^ "Plesiosaur bottom-feeding shown". 17 October 2005.
  22. ^ "Sticking your neck out: How did plesiosaurs swim with such long necks?".
  23. ^ Storrs 1997 pp. 148
  24. ^ Storrs 1997 pp. 179
  25. ^ Storrs 1997 pp.180

Sources

  • Andrews, C. W. 1896. "On the structure of the plesiosaurian skull". Quarterly Journal of the Geological Society, London, 52, 246–253.
  • Brown, D. S. 1981. "The English Upper Jurassic Plesiosauroidea (Reptilia) and a review of the phylogeny and classification of the Plesiosauria". Bulletin of the British Museum (Natural History): Geology, 35, (4), 253–347.
  • Cruickshank, A. R. I.; Small, P. G.; and Taylor, M. A. 1991. "Dorsal nostrils and hydrodynamically driven underwater olfaction in plesiosaurs". Nature, 352, 62–64.
  • Lydekker, R. 1889. Catalogue of the fossil Reptilia and Amphibia in the British Museum (Natural History), Part II. Containing the Orders Ichthyopterygia and Sauropterygia. British Museum (Natural History)
  • Richard Owen, Fossil Reptili of the Liassic Formations, pt iii. (Monogr. Palaeont. Soc., 1865)
  • Persson, P. O. 1963. A revision of the classification of the Plesiosauria with a synopsis of the stratigraphical and geographical distribution of the group. Lunds Universitets Årsskrift, N. F. Avd. 2. 59, 1–59.
  • Storrs, G. W. 1991. "Anatomy and relationships of Corosaurus alcovensis (Diapsida: Sauropterygia) and the Triassic Alcova Limestone of Wyoming". Bulletin of the Peabody Museum of Natural History, 44, 1–151.
  • Storrs, G. W. and Taylor, M. A. 1996. "Cranial anatomy of a new plesiosaur genus from the lowermost Lias (Rhaetian/Hettangian) of Street, Somerset, England". Journal of Vertebrate Paleontology, 16, (3), 403–420.
  • Storrs, G. W. 1997. "Morphological and taxonomic clarification of the genus Plesiosaurus". 145–190. In Callaway, J. M and Nicholls, E. L. (eds.). Ancient Marine Reptiles. Academic press. London.
  • Taylor, M. A. and Cruickshank, A. R. I. 1993. Cranial anatomy and functional morphology of Pliosaurus brachyspondylus (Reptilia: Plesiosauria) from the Upper Jurassuc of Westbury, Wiltshire. Philosophical Transactions of the Royal Society of London, Series B, 341, 399–418.
  • Torrens, Hugh 1995. "Mary Anning (1799–1847) of Lyme; 'The Greatest Fossilist the World Ever Knew'". The British Journal for the History of Science, 25 (3): 257–284

External links

Wikibooks has a book on the topic of: Wikijunior:Dinosaurs/Plesiosaur
Wikimedia Commons has media related to Plesiosaurus.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Plesiosaurus&oldid=1196711213"