Eunotosaurus
Name: Eunotosaurus
(original noded lizard).
Phonetic: Yew-no-to-sore-us.
Named By: Seeley - 1892.
Classification: Chordata, Reptilia, Sauropsida,
Parareptilia, Millerettidae.
Species: E. africanus (type).
Diet: Herbivore.
Size: 30 centimetres long.
Known locations: South Africa.
Time period: Wuchiapingian of the Permian.
Fossil representation: Several individual specimens.
Eunotosaurus
was long considered the ancestor to turtles. This theory came from
the specially enlarged and curved vertebrae and ribs that balloon
outwards that would have created the appearance of a skin covered
shell. It is now thought however that the vertebrae and rib
adaptation of Eunotosaurus and the evolution of
turtles are a case of
convergent evolution. This is where two animals form a similar
evolutionary adaption, even though they are not of the same animal
group, or direct descendent or ancestor to one another.
The
vertebrae of Eunotosaurus
are very similar to turtles in both structure and number. The ribs
are also broad to the point that they make contact with one another,
a feature also seen in turtles. The key difference is that the
pelvis of Eunotosaurus is placed behind the
specially adapted vertebrae
and ribs. In contrast, the pelvis of turtles is covered so that it
can be protected by the shell.
The
rib adaptations would
have given Eunotosaurus better protection from
predators, but exactly
how remains unclear. The enlarged cross section would have made it
difficult for some predators to swallow Eunotosaurus
whole. The ribs
would have also provided protection from the same predators that did
not have the strength to bite through them. However, these ribs
were not formed to provide protection for the head, limbs or tail.
At best this adaptation would only reduce the number of predators able
to eat Eunotosaurus, but that may have been
enough for the species to
survive for a time.
Further reading
- On a New Reptile from Welte Vreden (Beaufort West), Eunotosaurus
africanus (Seeley). - Quarterly Journal of the Geological
Society of
London 48:583-585. - H. G. Seeley - 1892.
- Eunotosaurus africanus Seeley and the ancestors
of the Chelonia. -
Proceedings of the Zoological Society of London 11: 1011–1020. - D. M.
S. Watson - 1914.
- The problematic Permian reptile Eunotosaurus. -
Bulletin of the
British Museum (Natural History), Geology Series 18 (5): 167–196. - C.
B. Cox - 1969.
- Eunotosaurus africanus from the Ecca–Beaufort
contact in Northern
Cape Province, South Africa — implications for Karoo Basin development.
- South African Journal of Science 95: 553–555. - B. S. Rubidge, S.
Modesto, C. Sidor & J. Welman - 1999.
- Eunotosaurus africanus and the Gondwanan ancestry
of anapsid
reptiles. - Palaeontologia Africana 36: 15–20. - S. P. Modesto - 2000.
- Biostratigraphic correlation in the Karoo: The case of the Middle
Permian parareptile Eunotosaurus. - South African Journal of Science.
109 (3/4): 1–4. - Mike Day, Bruce Rubidge, John Almond &
Sifelani Jirah - 2013.
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