Andrewsarchus
| Andrewsarchus | ||||||||||||
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Skull of Andrewsarchus ( holotype ) |
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| Temporal occurrence | ||||||||||||
| Middle Eocene | ||||||||||||
| 46.5 to 41.1 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Andrewsarchus | ||||||||||||
| Osborn , 1924 | ||||||||||||
Andrewsarchus is a genus of mammals that includes extinct, large, and possibly carnivorous representatives today, and lived in the Middle Eocene over 41 million years ago. It is onlyknownfrom a complete skull from Inner Mongolia , where it was discovered in 1923. Originally identified as the largest representative of the mesonychids , the systematic position of Andrewsarchus has not been clarified today, but it isassumedthat they are closely related to the artifacts .
features
Andrewsarchus was a large to very large representative of the higher mammals , but so far he is only known from a single skull. This is almost completely preserved and reached a total length of 83.4 cm, whereby the extremely strongly curved and widely spaced zygomatic arches stood up to 56 cm apart. The skull is about twice as large as that of a recent, full-grown grizzly bear . A striking feature was the long, drawn out rostrum , which measured a good 50 cm from the position of the first incisor to the rearmost molar , while the rear skull was correspondingly short and only 67% of the length of the snout. This long outstretched snout also exceeded that of the possibly closer relatives of Andrewsarchus , since the rostrum, for example in Harpalogestes, only barely reached the length of the rear skull. Assuming a body proportion comparable to that of the mesonychia , carnivorous representatives of the ungulates, the head-trunk length of Andrewsarchus - determined from the size of the skull - was probably around 3.82 m, while the shoulder height was around 1.89 m. That would make it one of the largest terrestrial carnivorous mammals that ever lived.
The dentition has not survived in full, but the existing alveoli can be used to determine the complete dentition of modern mammals, consisting of three incisors, one canine , four pre- and three molars per jaw arch. The second incisor in each case was conically shaped and greatly enlarged compared to the other incisors. the entire front row of teeth formed a clear arch, in contrast to Harpalogestes , in which the incisors were almost in a straight row. The canine teeth have not survived, but the enormous tooth sockets suggest extremely well-developed canines. The rear row of teeth began with a small, single-pointed front premolar, the second already had two points on the chewing surface and reached 4.6 cm in length, but was not even half as wide. All other molars had three enamel tips . The third premolar had the greatest length of all molars at 5.9 cm. The front molars were significantly shorter than the rearmost premolars, but the width increased towards the rear, so that the third molar was only 5 cm long, but 6.6 cm wide.
Fossil finds
So far, Andrewsarchus is only known from a single skull. This was discovered in 1923 during the Third Central Asiatic Expedition of the American Museum of Natural History under the direction of Roy Chapman Andrews (1884-1960) in the inner Mongolian part of the Gobi desert . This was found by expedition member George Olsen in the Erlian Basin . There it lay in the Irdin Manha Formation , a more than 5 m thick layer of rock made of grayish-white to grayish-yellow sandstones and sandy gravel, with numerous calcareous concretions of cylindrical shape. The formation dates to the Middle Eocene between 46 and 40 million years ago (locally stratigraphically called Irdinmanhan ).
Systematics
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Possible systematic position of Andrewsarchus within the ungulates according to Spaulding et al. 2009
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Possible systematic position of Andrewsarchus within the ungulates according to Geisler and Theodor 2009
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Andrewsarchus is a genus whose systematic allocation within mammals is unclear due to the fact that there has only been one find so far. In his first description from 1924, Henry Fairfield Osborn referred them to the order of Mesonychia , more precisely to the Mesonychidae family with close relations to Mesonyx and Harpalogestes . The mesonychia are found mainly in the Palaeogene in North America and Asia and represent an extinct group within the ungulates , which were mainly carnivorous, but partly also omnivorous. They were originally considered to be relatively closely related to the still terrestrial ancestors of modern whales , but due to the discovery of well-preserved hind legs of primeval whales at the beginning of the 21st century, a closer relationship between these and the hippos is more likely, which is also confirmed by molecular genetic studies . Today the mesonychia are mostly seen in a systematic vicinity of a clade consisting of the odd-toed ungulates and even-toed ungulates (including whales).
Initially, the Mesonychia were divided into three families: the Mesonychidae , the Hapalodectidae and the Triisodontidae . Andrewsarchus belonged to the Triisodontidae together with Eoconodon and Triisodon . However, recent studies show that this group is of paraphyletic origin and thus does not form a closed unit. In some phylogenetic analyzes, Andrewsarchus and Eoconodon form a rather closed unit, which has a systematic proximity to the Arctocyonidae , a carnivorous group of the common ungulates . In recent studies, Andrewsarchus is predominantly excluded from the mesonychia. One reason for this is, among other things, that the rearmost molar in the upper jaw in Andrewsarchus is largely unreduced, while the predominantly older representatives of the mesonychia often reduced it in size or not at all. Due to the small amount of fossil material, a clear position of Andrewsarchus within the ungulates is currently only inexactly possible.Depending on the investigation, a proximity to the extinct Entelodontidae and the common group of whales and hippos or a position as the sister taxon to all articulated ungulates and unpaired ungulates is possible favored, whereby a closer relationship with the odd-toed ungulates could exist.
Andrewsarchus is named after the paleontologist Roy Chapman Andrews , the director of the American Museum of Natural History's third expedition to Asia , during which the fossil skull was recovered. This also represents the holotype (copy number AMNH 20135) of the genus. Andrews first recognized that the skull belonged to a predatory animal. The generic name Andrewsarchus is made up of the surname of the expedition leader and the Greek word άpxός ( archos "guide", "leader"). The only recognized species is Andrewsarchus mongoliensis , whereby the species name refers to the region where it was found. A possible synonym is Paratriisodon , which was described in 1959 on the basis of an approximately 34 cm long lower jaw fragment and some upper jaw and tooth remnants from the Upper Ocene Lushih Formation in the Chinese province of Henan and whose reconstructed size is similar to that of Andrewsarchus , but the first processor saw this as Representatives of the Arctocyonidae.
literature
- Henry Fairfield Osborn: Andrewsarchus, giant mesonychid of Mongolia. American Museum Novitates; No. 146. The American Museum of Natural History, New York City 1924. PDF
- Haines, Chambers: The Complete Guide to Prehistoric Life . 2006.
Individual evidence
- ^ A b c d e Henry Fairfield Osborn: Andrewsarchus, giant mesonychid of Mongolia. In: American Museum Novitates. 146, 1924, pp. 1-6.
- ↑ a b Jin Meng, Yuanqing Wang, Xijun Ni, K. Christopher Beard, Chengkai Sun, Qian Li, Xun Jin, Bin Bai: New Stratigraphic Data from the Erlian Basin: Implications for the Division, Correlation, and Definition of Paleogene Lithological Units in Nei Mongol (Inner Mongolia). In: American Museum Novitates 3570, 2007, pp. 1–31.
- ↑ a b Michelle Spaulding, Maureen A. O'Leary, John Gatesy: Relationships of Cetacea (Artiodactyla) Among Mammals: Increased Taxon Sampling Alter Interpretations of Key Fossils and Character Evolution. In: PLOSone 4 (9), 2009, e7062 doi: 10.1371 / journal.pone.00070622009 .
- ↑ a b c Jonathan H. Geisler, Jessica M. Theodor: Hippopotamus and whale phylogeny. In: Nature 458, 2009, pp. E1-E4.
- ↑ Jin Xun: New Mesonychid (Mammalia) material from the Lower Paleogene of the Erelian basin, Nei Mongol, China. In: Vertebrata Palasiatica 50 (3), 2012, pp. 245-257.
- ^ A b Frederick S. Szalay: The Hapalodectinae and a Phylogeny of the Mesonychidae (Mammalia, Condylarthra). In: American Museum Novitates 2361, 1969, pp. 1-28.
- ^ A b Jonathan H. Geisler, New Morphological Evidence for the Phylogeny of Artiodactyla, Cetacea, and Mesonychidae. In: American Museum Novitates 3344, 2001, pp. 1-58.
- ↑ JGM Thewissen, Lisa Noelle Cooper, Mark T. Clementz, Sunil Bajpai, BN Tiwari: Whales originated from aquatic artiodactyls in the Eocene epoch of India. In: Nature 450, 2007, pp. 1190-1194.
- ↑ William A. Clemens: Eoconodon ( "Triisodontidae," Mammalia) from the Early Paleocene (Puercan) of northeastern Montana, USA. In: Palaeontologia Electronica 14 (3), 2011, 22A ( PDF ).
- ↑ Chow Minchen: A new arctocyonid from the Upper Eocene uf Lushih, Honan. In: Vertebrata Palasiatica 3 (3), 1959, pp. 133-138.
Web links
- Andrewsarchus, "Superb Skull of a Gigantic Beast," Now on View in Whales Exhibit American Museum of Natural History
- Andrewsarchus. Les Condylarthres Monde Animal Préhistorique (French)