Placerias
| Placerias | ||||||||||||
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Skeletal reconstruction of placerias in the Rainbow Forest Museum (Petrified Forest National Park) |
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| Temporal occurrence | ||||||||||||
| Upper Triassic ( Carnian ) | ||||||||||||
| 235 to 228 million years | ||||||||||||
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| Scientific name | ||||||||||||
| Placerias | ||||||||||||
| Lucas , 1904 | ||||||||||||
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Placerias was a herbivorous Therapside (a group that also includes the ancestors of mammals) belonging to the Dicynodontia . It was over three meters long and weighed around a ton. He lived in the late Triassic approximately 230 million years ago.
Find history
The first find, a single humerus, was made in 1899 in the Chinle Formation (Lower Petrified Forest Member, Upper Karn ) at "Tanners Crossing", a bridge over the Little Colorado River in Arizona . This humerus was described under the name Placerias hesternus in 1904 . The most important place where Placerias was found , however, is the "Placerias Quarry". Although it is located in the same layers of the Chinle Formation as the first site, it is located approximately 200 km further southeast near St. Johns , southeast of the Petrified Forest National Park in Arizona. There, the bones of at least 39 Placerias individuals were recovered. They were initially (1956) assigned to a new species, Placerias gigas , which was later synonymous with Placerias hesternus (1993) . These finds date back to 1930 when Charles Camp and Samuel Welles of the University of California, Berkeley first discovered fossils from Placerias there. Finds from outside the Chinle Formation come from the East of the USA from the Carnic strata (Pekin or Stockton Formation) of the Newark supergroup and from Morocco from the Carnic section (Timezgadiouine Formation) of the Argana Group . The species Eubrachiosaurus browni from the Popo-Agie formation of Wyoming , which was also synonymous with Placerias hesternus in 1993, has been revalidated as an independent taxon.
Appearance
Placerias was an extremely massive animal that had a very large and massive skull that reached two feet in length. The tusks were about four inches long. Otherwise he had no teeth. He had very heavy bones and was therefore not a fast runner. However, he had enormous strength. From a distance it would look very similar to today's hippopotamus . The similar physique and detailed investigations of the sites in the "Placerias Quarry" have led to the assumption that Placerias could have had a semi-aquatic way of life similar to that of the hippos. The site in the "Placerias Quarry" could have been a large pond, which could have had a strongly changing water level due to monsoon-like rainfall in the west of the supercontinent Pangea . Placerias' shovel-like legs may have been suitable for swimming.
Way of life
Placerias lived in herds and roamed the western coastal areas of what is now North America and what is now Morocco , which at that time also belonged to the western coast of Pangea, in search of plant food . The interior of Pangea consisted of deserts. The species had strong front legs that could be very useful when digging. The animals were able to do most of the work when digging for roots with the help of their two tusks. Dimorphism can be seen in both sexes . The tusks were more developed in the males than in the females. They were probably used to fight two rivals and could cause serious injuries. Life in the herd had the advantage that they could defend themselves against robbers together. The predators likely included Postosuchus , who belonged to the Archosauria and was not a dinosaur, and early dinosaurs like Coelophysis or perhaps Gojirasaurus . If the herds of Placerias lived partially in the water, as many researchers believe, the crocodile-like phytosauria may have been their main enemies.
Placerias and the closely related species Ischigualastia jenseni from the Ischigualasto Formation in Argentina are the only large herbivores from the Kannemeyeriidae family, which are common in the Triassic, that occur in the Carnian .
literature
- Charles L. Camp, Samuel P. Welles: Triassic dicynodont reptiles. part I: The North American genus Placerias. In: Memoirs of the University of California. 13, 1956, pp. 255-304.
- Fran Tannenbaum Kaye, Kevin Padian: Microvertebrates from the Placerias Quarry: a window on Late Triassic vertebrate diversity in the American Southwest. Pp. 171–196 in: Nicholas C. Fraser, Hans-Dieter Sues (Ed.): In the shadow of the dinosaurs: early Mesozoic tetrapods. Cambridge University Press, 1994, ISBN 0-521-45242-2
Individual evidence
- ^ Frederic A. Lucas: A new batrachian and a new reptile from the Trias of Arizona. In: Proceedings of the United States National Museum. 27, 1904, pp. 193-195, archive.org
- Jump up ↑ Anthony R. Fiorillo, Kevin Padian, Chayanin Musikasinthorn: Taphonomy and Depositional Setting of the Placerias Quarry (Chinle Formation: Late Triassic, Arizona). In: Palaios. 15, 5, 2000, pp. 373-386.
- ↑ a b Tannenbaum Kaye & Padian: Microvertebrates from the Placerias Quarry. 1994 (see literature ), pp. 171-172
- ↑ a b c Tannenbaum Kaye & Padian: Microvertebrates from the Placerias Quarry. 1994 (see literature ), pp. 191-193
- ^ Spencer G. Lucas, Adrian P. Hunt: A dicynodont from the Upper Triassic of New Mexico and its biochronologic significance. Pp. 321-325 in: Spencer G. Lucas, Michael Morales (Eds.): The Nonmarine Triassic. New Mexico Museum of Natural History and Science Bulletin, 3rd Albuquerque 1993 ( online ), pp. 323-324.
- ^ Spencer G. Lucas, Placerias (Reptilia, Dicynodontia) from the Upper Triassic of the Newark Supergroup, North Carolina, USA, and its biochronological significance. In: New yearbook for geology and palaeontology - monthly books. 1998, 7, 1998, pp. 432-448, doi: 10.1127 / njgpm / 1998/1998/432 .
- ^ Christian F. Kammerer, Jörg Fröbisch, Kenneth D. Angielczyk: On the validity and phylogenetic position of Eubrachiosaurus browni , a kannemeyeriiform dicynodont (Anomodontia) from Triassic North America. In: PLoS ONE. 8, 5, 2013, item no. e64203, doi: 10.1371 / journal.pone.0064203 .
- ↑ GM King, MA Cluver: The aquatic Lystrosaurus: An alternative lifestyle. In: Historical Biology. 4, 1991, pp. 232-341.
Web links
- Placerias Quarry - Photos of the excavations carried out by Charles Camp and Samuel Welles from the collection of the University of California Museum of Paleontology (UCMP), Berkeley, in the image database of the Berkeley Natural History Museums (calphotos.berkeley.edu)