Pezosiren
| Pezosiren | ||||||||||||
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Pezosiren |
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| Temporal occurrence | ||||||||||||
| early Eocene | ||||||||||||
| ~ 50 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Pezosiren | ||||||||||||
| Domning , 2001 | ||||||||||||
Pezosiren is an extinct species of manatee that lived about 50 million years ago, in the early Eocene . Two partial skeletons and numerous individual bones of the genus found in an anatomical association were found in the community of St. James 15 km south of Montego Bay in western Jamaica . The holotype is a partially preserved, 19 cm long lower jaw. The only described species of the genus is Pezosiren portelli . The generic name Pezosiren (composition from ancient Greek. Πεζός pezos 'walking, running' and Latin . Siren 'manatee') means “running manatee” and was given because of the fully developed quadruple of animals. The specific epithet portelli honors the discoverer of the fossil deposit Roger W. Portell.
features
Pezosiren had a barrel-shaped trunk, a relatively short neck, a manatee-like head, and four short legs. The animal grew slightly larger than a very large domestic pig and reached a body length of 2.1 meters. The skull is approximately 26.5 cm long and 14.5 cm wide. A low sagittal ridge distinguishes Pezosiren from Prorastomus , the second genus of manatees from the Prorastomidae family . In the case of Prorastomus , however, it could have been destroyed by erosion or during dissection. The lower jaw is long (19 cm) and narrow. Incisors and canines were parallel. The tooth formula is uncertain, but is probably 3 1 5 3 as with all Eocene manatees. The first upper incisor was enlarged and formed a small tusk.
The spine consists of 7 cervical vertebrae , 20 thoracic vertebrae , 4 lumbar vertebrae , 4 sacral vertebrae and probably about a dozen caudal vertebrae. Only the vertebrae near the trunk are preserved from the tail. Axis and other cervical vertebrae were not shortened as in later and today's manatees and are more reminiscent of the cervical vertebrae of Paleocene parent ungulates (condylarthra). The anterior thoracic vertebrae had high spinous processes to which a neck strap was likely attached that could carry the weight of the head and neck on land. The caudal vertebrae lacked the enlarged transverse processes of later manatees. The ribs were thick ( pachyostosis ), consisted of very dense bone tissue and served as ballast for the aquatic animals. The long, narrow pelvis and legs are reminiscent of the primitive ungulates. Only a few bones of the foot have survived; it is uncertain whether the forefoot or the hindfoot is the same. They are short and flat like those of land-based ungulates and show no signs of conversion of the feet into fins.
Way of life
The silt and sandstone deposits of the Chapelton Formation, from which the fossils of Pezosiren portelli were recovered, come from a lagoon , river delta or other river mouth shape. With its four well-developed legs, its sacrum (only one vertebra in recent manatees), and its powerful sacroiliac joint (sacrum-iliac joint), Pezosiren was well able to move around on land and spent most of the time but probably in the water. In this respect, the genus was similar to today's hippos or early amphibious whales such as Ambulocetus . The animal could not use a strong tail with a caudal fin to move in the water, as only today's manatees do, because the caudal vertebrae lacked the clearly developed transverse processes that are necessary for strong tail muscles. Pezosiren swam more like an otter with combined movements of body, tail and hind legs.
literature
- DP Domning: The earliest known fully quadrupedal sirenian. Nature 413, pp. 625-627, October 11, 2001, doi : 10.1038 / 35098072 , PDF .
