Paleothyris
| Paleothyris | ||||||||||||
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Reconstruction of the skull of Paleothyris |
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| Temporal occurrence | ||||||||||||
| Westfalium D ( Moskovium , Oberkarbon ) | ||||||||||||
| 308 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Paleothyris | ||||||||||||
| Carroll , 1969 | ||||||||||||
| Art | ||||||||||||
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Paleothyris is an extinct genus of early amniotes . Outwardly it resembled a lizard and lived in the late Carboniferous of Nova Scotia .
Etymology and history
The generic name is made up of the ancient Greek word παλαιός ( palaios , 'old') and the Latinized word thyris (from ancient Greek θυρίς, 'window'), part of the name of other "primitive" amniotes, such as Melanothyris or Protorothyris . Paleothyris and its only species P. acadiana (the species epithet is derived from Akadien , the old name for the maritime provinces of Canada) was named and described in 1969 by the important Canadian paleontologist Robert Lynn Carroll . The excavations, during which the material was collected, on which the first description of P. acadiana is based, were carried out in 1956 under the direction of the no less famous Alfred Romer .
features
Paleothyris was a rather small animal with a trunk length of about 10 cm and a skull length of 2 to 3 cm. The total length was probably 15-20 cm. The eye sockets are relatively large. The skull shows features that are generally considered "primitive" for amniotes, including the lack of a temple window in the posterior side wall of the skull (anapsid state) and an otic slit on the posterior edge of the skull side wall. The presence of bone elements on the posterior edge of the dorsal (upper) cranial roof (tabular, postparietal, supratemporal), an elongated lacrimal that extends from the front edge of the eye socket to the rear edge of the outer nostril, a " shagreen " of denticles are also considered to be original the bones of the roof of the mouth and on the parasphenoid (a base bone of the brain skull) and a transverse process of the pterygoid protruding horizontally into the subtemporal window. The stapes (Columella) was relatively massive and most likely did not serve to perceive high-frequency sounds. The jawbones each have over 20 small, pointed teeth. A pair of caniniform (fang-like enlarged) teeth in the anterior quarter of the maxillary are noticeable.
The total number of trunk and cervical vertebrae (presacral vertebrae) in paleothyris is estimated at 32 based on the material that has survived. Only a few caudal vertebrae are preserved. Their number was probably 50 to 70. The structure of the vertebrae corresponds to that of the earlier amniotes with a vertebral body mainly built up from the pleurocenter and a firmly attached neural arch with a low spinous process. In contrast to captorhinids , the neural arches are not thickened (swollen). The first two cervical vertebrae form an atlas-axis complex typical of amniotes. The pelvic girdle was suspended from the spine using two sacral vertebrae.
The tarsus (tarsus) in Paleothyris shows the more compact configuration with astragalus and calcaneus, which is typical for amniotes, which clearly speaks for an adaptation to a purely terrestrial life. The phalangeal formula of the forefoot (manus) is 2-3-4-5-3, that of the hind foot (pes) is 2-3-4-5-4. The toes are so long that the entire manus is more than twice as long as the lower leg of the front leg. The pes is even longer than the entire hind leg. The basin of Paleothyris shows the basal Amniota for typical triradiate (three-beam), of a relatively short forward facing pubis, a rear facing ilium and a rearwardly-upwardly facing ischium.
Way of life
Paleothyris lived in the tropical hard coal swamp forests of today's North America and moved there on dry terrain between the trees. His teeth with the many small, pointed teeth showed that he probably lived a predatory life. Given its rather small size, it presumably ate predominantly on insects or other small arthropods.
Reference
Paleothyris is so far only a single reference, an open pit in Florence in Sydney - coal revier on Cape Breton Iceland ( Nova Scotia , Canada known). The finds come from the layers in the area of the so-called Lloyd Cove coal seam of the Morien group. The Lloyd Cove seam is now completely placed in the lower Westfal D (Des Moines stage in North America, Moskov stage on the international time scale) and is therefore around 308 million years old. At that time the area was characterized by forests and swamps and the climate was warm and humid. The remains of Paleothyris are preserved in hollow fossilized trunks of club moss trees of the genus Sigillaria . The remains of Archaeothyris , the oldest known synapsid and possible predator of Paleothyris , were also found in the same site .
Systematics
After its discovery, paleothyris was long regarded as a prime example of a "stem amniote" and was assigned to the anapsida in the classical system and to the supposedly "primitive" group, the captorhinomorpha , within the anapsids . Within the Captorhinomorpha, Paleothyris was placed in the family Protorothyrididae (or Romeriidae) together with morphologically very similar representatives .
Since the mid-1990s, with the increasing importance of cladistics for paleobiological systematics, the view has been established that paleothyris is original, but less original than previously assumed. The cladistic analyzes showed that the genus already lived in different main lines after the amniotes were split up. According to this, Paleothyris is a basal representative of the so-called Eureptilia , a line to which the Diapsiden and thus all recent reptile groups as well as the birds belong. The captorhinids have an even more basal position within the eureptiles than paleothyris . The clade of Paleothyris and the Diapsids, which forms the sister group of the Captorhinids, is called Romeriida .
The fact that representatives of "higher" lines of the Sauropsids already lived in the Upper Carboniferous suggests that the separation of the Sauropsid and Synapsid lines could have occurred in the earliest Upper Carboniferous and that the origin of the amniotes thus possibly reaches back to the Lower Carboniferous.
literature
- Robert L. Carroll: Paleontology and Evolution of the Vertebrates. Thieme, Stuttgart et al. 1993, ISBN 3-13774-401-6 .
Individual evidence
- ^ A b c Robert L. Carroll: A Middle Pennsylvanian Captorhinomorph, and the Interrelationships of Primitive Reptiles. Journal of Paleontology, Vol. 43, No. 1, 1969, pp. 151-170 ( JSTOR 1302357 )
- ^ Robert L. Carroll, Pamela Gaskill: The Order Microsauria Memoirs of the American Philosophical Society. Vol. 126. The American Philosophical Society, Philadelphia PA 1978, ISBN 0-87169-126-4 .
- ^ A b Robert Reisz: Pelycosaurian Reptiles from the Middle Pennsylvanian of North America. Bulletin of the Museum of Comparative Zoology, Vol. 144, No. 2, 1972, pp. 27-60 ( full text on BHL ).
- ↑ a b Michel Laurin, Robert R. Reisz: A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society, Vol. 113, No. 2, 1995, pp. 165-223, doi : 10.1111 / j.1096-3642.1995.tb00932.x (alternative full-text access : ResearchGate ).
