Andrewsarchus
Skull of Andrewsarchus ( holotype )
- Mongolia, Asia
Andrewsarchus is a mammalian genus which today includes extinct, large and possibly carnivorous representatives and lived over 41 million years ago in the Middle Eocene. She is known only on the basis of a complete skull from Inner Mongolia, where he was discovered in 1923. Originally reported as the largest representative of the Mesonychiden, today the systematic position of Andrewsarchus is not clear, but it is assumed a close relationship with the even-toed ungulates.
Features
Andrewsarchus was a great to very great representative of the Higher mammals, but it is only known from a single skull. This is almost completely preserved and reached a total length of 83.4 cm, the extremely strong bent and wide apart, zygomatic arches apart were up to 56 cm. The skull is about twice as large as that of a recent, full-grown grizzly bear. A striking feature represented especially the long extended rostrum, the good 50 cm measured from the position of the first incisor to the posterior molars, while the rear skull was accordingly short and had only 67 % of the length of the snout. This long extended snout also excelled in the relationship of those possibly closer relative of Andrewsarchus because the rostrum for example Harpalogestes the length of the rear skull reached just barely. Assuming a similar body proportions as the Mesonychia, carnivorous representatives of ungulates, was the head -body length of Andrewsarchus - determined from the skull size - probably around 3.82 m, while the shoulder height was about 1.89 m. Thus, it would have been one of the largest terrestrial living, carnivorous mammals that ever lived.
The dentition is not fully narrated, on the basis of existing alveoli can be but the complete dentition of modern mammals determine, each consisting of three incisors, one canine, four pre- molars and three per arch. The respective second incisor was conically shaped and greatly enlarged compared to the other incisors. the entire front row of teeth forming a clear sheet, in contrast to Harpalogestes, in which the cutting teeth were nearly in a straight row. The canines are not recorded, but the enormous tooth compartments let on extremely strong trained canine close. The rear row of teeth began with a small, single-pointed anterior premolar, the second already had two peaks on the Kauoberfläche and reached 4.6 cm in length, however, was not even half as wide. All other molars had three enamel tips. The third premolar he pointed to the largest length of all molars with 5.9 cm. The front molars were significantly shorter than the posterior bicuspids, but increased the width rearwardly, so that the third molar, although a 5- cm length, but had 6.6 cm width.
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 led by Roy Chapman Andrews ( 1884-1960 ) in the Inner Mongolian part of the Gobi Desert. Found this was the expedition member George Olsen in the Erlian Basin. There he lay in the Irdin - Manha Formation, a more than 5 m thick rock layer of grayish white to grayish - yellow sandstones and sandy gravel, which are accompanied by numerous calcareous concretions of cylindrical shape. The formation dates to the Middle Eocene, 46-40 million years ago ( called lokalstratigraphisch Irdinmanhan ).
System
Mesonychia
Perissodactyla
Tylopoda
Suina
Entelodontidae
Andrewsarchus
Hippopotamidae
Mesonychia
Andrewsarchus
Perissodactyla
Tylopoda
Suidae
Entelodontidae
Ruminantia
Hippopotamidae
Cetacea
Andrewsarchus represents a genus whose systematic assignment within the mammals, due to the so far only a discovery unknown. In his first description of 1924 Henry Fairfield Osborn referred them to the order of Mesonychia, more specifically to the family of Mesonychidae with close relationship to Mesonyx and Harpalogestes. The Mesonychia are mainly found in the Paleogene in North America and Asia and are an extinct group is within the ungulates, the predominantly carnivorous, but also partly omnivorous feeding on. They were originally to be related relatively closely with the remaining terrestrial living ancestors of modern whales, but due to the discovery of well-preserved hind legs primitive whales start of the 21st century is now a closer relationship of these with the hippos more likely, which is also confirmed by molecular genetic studies. Today the Mesonychia be seen mostly in a system- matic close to a clade consisting of the odd-toed ungulates and even-toed ungulates (including the Whales ).
Initially, the Mesonychia were divided into three families: the Mesonychidae that Hapalodectidae and Triisodontidae. It was, together with Andrewsarchus Eoconodon and Triisodon to the Triisodontidae. Recent studies show, however, that this group is paraphyletic in origin, and does not form a closed unit. In some phylogenetic analyzes Andrewsarchus and Eoconodon form a more cohesive unit, which has a systematic proximity to Arctocyonidae, also a carnivorous group of Stammhuftiere. In the investigations of recent times Andrewsarchus is excluded mostly from the Mesonychia. One reason for this is, among other things, that the rearmost molar in the upper jaw at Andrewsarchus is largely unreduced, while the predominantly older representatives of Mesonychia often have reduced or no training this. Because of the little fossil material has a unique set of Andrewsarchus within the ungulates is currently only imprecisely So depending on the examination will, among other things close to the extinct Entelodontidae and the combined group of whales and hippos or a position as the sister taxon to all cloven-hoofed animals and odd-toed ungulates favored, in which case there could be a closer relationship to the odd-toed ungulates.
Andrewsarchus was named after the paleontologist Roy Chapman Andrews, the head of the third Asia Expedition of the American Museum of Natural History, during which the fossil skull was recovered. This also represents the holotype ( specimen number AMNH 20135 ) of the genus dar. Andrews had it first recognized the membership of the skull to a predatory animal. The genus name Andrewsarchus is composed of the surname of the expedition leader and the Greek word άpxός ( archos " leader ", " head "). The only recognized type represents Andrewsarchus mongoliensis, the species name refers to the reference region. As a possible synonym applies Paratriisodon, which was described in 1959 based on an approximately 34 cm long lower jaw fragment and some of the upper jaw and dental remains from the Upper Eocene Lushih formation in the Chinese province of Henan and its reconstructed size that resembles that of Andrewsarchus, the first processors saw this but as representatives at the Arctocyonidae.