Pelycosaur

Source: Wikipedia, the free encyclopedia.
Pelycosaurs
Temporal range:
Therapsida
survives to present.
Mounted skeleton of Dimetrodon mileri, Harvard Museum of Natural History
Mounted skeleton of Dimetrodon mileri, Harvard Museum of Natural History
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Synapsida
Informal group: †Pelycosauria
Cope, 1878
Groups included
Cladistically included but traditionally excluded taxa

Pelycosaur (

synapsids, excluding the therapsids and their descendants. Previously, the term mammal-like reptile had been used,[2] and pelycosaur was considered an order
, but this is now thought to be incorrect, and seen as outdated.

Because it excludes the advanced synapsid group

paraphyletic and contrary to modern formal naming practice.[3][4] Thus the name pelycosaurs, similar to the term mammal-like reptiles, had fallen out of favor among scientists by the 21st century, and is only used informally, if at all, in the modern scientific literature.[5][6]
The terms stem mammals, protomammals, and basal or primitive synapsids are instead used where needed.

Etymology

The modern word was created from Greek pélyx meaning 'basin' and saûros meaning 'lizard'.[7] The term pelycosaur has been fairly well abandoned by paleontologists because it no longer matches the features that distinguish a clade.[6]

Pelycosauria is a

monophyletic group. Caseasauria is a pelycosaur side-branch, or clade, that did not leave any descendants.[citation needed
]

Evolutionary history

See also: Evolution of mammals
Comparison of "pelycosaurian" skulls: 1 sphenacodont, 2 ophiacodont, 3 caseid. The quadratojugale is green, squamosale is red, jugale is blue.

The pelycosaurs appear to have been a group of synapsids that have direct ancestral links with the mammals, having differentiated teeth and a developing hard palate. The pelycosaurs appeared during the Late Carboniferous and reached their apex in the early part of the Permian, remaining the dominant land animals for some 40 million years. A few continued into the Capitanian, but they experienced a sharp decline in diversity in the late Kungurian.[8] They were succeeded by the therapsids.

Description

Cotylorhynchus (background), Ophiacodon and Varanops

Some species were quite large, growing to a length of 3 metres (10 ft) or more, although most species were much smaller. Well-known pelycosaurs include the genera Dimetrodon, Sphenacodon, Edaphosaurus, and Ophiacodon.[9]

Pelycosaur fossils have been found mainly in Europe and North America, although some small, late-surviving forms are known from Russia and South Africa.

Unlike

disputed – discuss] Fossil evidence from some varanopids shows that parts of the skin were covered in rows of osteoderms, presumably overlain by horny scutes.[5] The belly was covered in rectangular scutes, looking like those present in crocodiles.[10] Parts of the skin not covered in scutes might have had naked, glandular skin like that found in some mammals. Dermal scutes are also found in a diverse number of extant mammals with conservative body types, such as in the tails of some rodents, sengis, moonrats, the opossums and other marsupials, and as regular dermal armour with underlying bone in the armadillo
.

At least two pelycosaur

mating display
.

Taxonomy

Eothyris
Dimetrodon – a sphenacodontid

In phylogenetic nomenclature, "Pelycosauria" is not used formally, since it does not constitute a group of all organisms descended from some common ancestor (a clade), because the group specifically excludes the therapsids which are descended from pelycosaurs. Instead, it represents a paraphyletic "grade" of basal synapsids leading up to the clade Therapsida.[12]

In 1940, the group was reviewed in detail, and every species known at the time described, with many illustrated, in an important monograph by Alfred Sherwood Romer and Llewellyn Price.[13]

In traditional classification, the order Pelycosauria is paraphyletic in that the therapsids (the "higher" synapsids) have emerged from them. That means Pelycosauria is a grouping of animals that does not contain all descendants of its common ancestor, as is often required by phylogenetic nomenclature. In evolutionary taxonomy, Therapsida is a separated order from Pelycosauria, and mammals (having evolved from therapsids) are separated from both as their own class. This use has not been recommended by a majority of systematists since the 1990s,[6] but several paleontologists nevertheless continue using this word.[14][12]

The following classification was presented by Benton in 2004.[15]

See also

Notes

  1. JSTOR 982652
    .
  2. ^ Carroll, R.L. 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company, New York ISBN 0-7167-1822-7
  3. ISBN 0471278483
    .
  4. doi:10.1098/rspb.1996.0170
    .
  5. ^
    PMID 17848370
    .
  6. ^
    ISBN 978-0-520-26647-6
    .
  7. ^ Colbert, Edwin H. (Edwin Harris); Knight, Charles Robert (1951). The dinosaur book: the ruling reptiles and their relatives. New York: McGraw-Hill. p. 152.
  8. PMID 34966586
    .
  9. ISBN 978-1-11851-093-3
    .
  10. S2CID 84302993
    .
  11. ^ Tracy, C.R.; Turner, J.S.; Huey, R.B. (1986). "A biophysical analysis of possible thermoregulatoryadaptations in pelycosaurs". In MacLean, P.D.; Roth, J.J.; Roth, E.C.; Hotton, N. (eds.). Ecology and Biology of Mammal-Like Reptiles. Washington, DC: Smithsonian Press. pp. 195–205.
  12. ^
    S2CID 91487577
    .
  13. doi:10.1130/SPE28-p1
    .
  14. S2CID 56425905
    .
  15. ISBN 978-0-632-05637-8
    .

References

External links

Wikispecies has information related to Pelycosauria.
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