Limusaurus

The holotype skeleton of Limusaurus exhibited in Tokyo.

  • Xinjiang, China ( Shishugou Formation)
  • Limusaurus inextricabilis

Limusaurus is a genus of dinosaur from the group of Ceratosauria within the theropods. So far fragmentary to complete skeletons have been found of at least 15 specimens are from the Upper Jurassic of China's Xinjiang province. Limusaurus was about 1.7 meters long, bipedal running herbivores, which was characterized by toothless jaws, which resulted in a beak. It is so far the only known representative of the Cerato dinosaur that was not predominantly carnivorous. Limusaurus was first scientifically described by the single species, Limusaurus inextricabilis 2009.

For scientific dispute in particular caused the anatomy of the five-pointed hand of this animal, which shows a greatly reduced first finger. This could indicate that the typical three-rayed hand of the more advanced theropods was formed by reduction of the first and fifth ray, and not, as previously thought, by reduction of the fourth and fifth ray. If this hypothesis be true, there would be a three-rayed hand advanced theropods from the fingers 2, 3 and 4, corresponding to the constellation as they have today's birds.

Description

Limusaurus was a relatively small dinosaur Cerato. The holotype specimen is estimated to have a length of 1.7 meters; another specimen was larger by 15%. In both instances it was young adult animals, after the merger of Knochensuturen points. In contrast to all other known dinosaurs Cerato jaws were toothless and ended up in a fully developed beak ( rhamphotheca ) - This feature was previously only known from a few Coelurosauriern. The skull was shorter than that of other dinosaurs Cerato and only half as long as the thigh bone ( femur). The arms were short, as for Cerato dinosaur typical. The legs, however, were relatively long, with the lower legs and feet together account for about 120 to 130 % of the length of the femur. Such, designed for a fast running leg proportions are also present in some Coelurosauriern, and have the latter and Limusaurus probably developed independently ( convergent evolution ). Other unique features include the broad and short nose ( nasal ), which accounts for only one -third the length of the cranial vault, and the very short first toe with a. The latter has not touched the ground as in other theropods, and had at Limusaurus only 17 % of the length of the third metatarsal.

Paleobiology

Limusaurus is the only known herbivorous theropod outside the Coelurosauria. On a herbivorous diet suggest the small head, the long neck, the edentulous jaw and accumulations of small, rounded stones that have been discovered in the abdominal region of the skeletons and as Gastrolithe (stomach stones ) are interpreted. Gastrolithe serve in the stomach today herbivorous birds for crushing food. The Body of Limusaurus - especially the small head with toothless jaws and large eye sockets, the long neck and long hind legs - has distinct similarities with two distantly related groups, the Shuvosauridae and Ornithomimosauria. These parallels point to the occupation of similar ecological niches of these not more closely related animals and serve as an example of convergent evolution.

Controversy on the evolution of bird hand

Advanced theropods, as well as today's birds have three fingers, while original theropods still had five fingers. The three-engine theropod hand has formed, according to expert opinion from a lateral reduction of the fingers: The fifth and fourth fingers have receded, leaving only the first, second and third finger remained. This hypothesis is based on anatomical characteristics of the finger members can be observed both in the original five-pointed hand as well as in the more modern three-beam source. The hand of today's birds, however, from the second, third and fourth fingers, whereupon studies suggest to avian embryos: The primor modal finger approaches these embryos still show the original, five-pointed pattern, with the three fingers develop from the middle three of these approaches.

Limusaurus has a greatly reduced first finger, which indicates a bilateral ( two-sided ) reduction of the finger, wherein the first and the fifth finger regressed, with the fingers 2, 3 and 4 were the longest. This finding could indicate that the hand of the more modern theropods and birds arose through bilateral reduction, and that it was indeed the second, third and fourth fingers at the three fingers, and not the first, second and third fingers. This hypothesis of bilateral reduction was already established by Thulborn and Hamley (1982 ), found in the scientific community but little attention. According to this hypothesis, the apparent contradiction between the finger identity of theropods and birds would be resolved.

History of discovery and naming

Fossils of Limusaurus come from the Shishugou Formation ( Wucaiwan area) in the Junggar Basin of Xinjiang province of China. So far, the skeletons were discovered by at least 15 Limusaurus individuals who receive partial to complete and largely articulated were found ( in the original anatomical composite ). The skeletons were in a vertical position, nestled in several small, 1 to 2 meters deep pits, found that ( " mudstone " ) are filled with a deformed mudstone. Researchers suspect that it is at these mines is very large footprints of sauropods, such as Mamenchisaurus. The sauropods, wading through a water-saturated layer and partially sank in the ground would have liquefied the soil, so that small theropods stuck and sank.

Limusaurus was described in 2009 by Xu Xing and colleagues in the journal Nature for the first time scientifically. The first description was based on a nearly complete skeleton ( holotype, IVPP V 15923 copy number ) and another, skull -less skeleton ( specimen number IVPP V 15924 ). The name Limusaurus inextricabilis (Latin limus - " mud", saurus - " lizard", inextricabilis - " unable to free themselves ") means as much as "mud lizard that can not get free ." The name refers to the fact that the animals got stuck in the mud and died.

System

Limusaurus was a basal Cerato dinosaurs. Xu Xing (2009 ) summarizes Limusaurus and Elaphrosaurus, a Ceratosauria from the Tendaguru formation to a common clade together. Common with Elaphrosaurus are the long, rather atypical for Ceratosauria neck, the slim, graceful and long-legged body, but Limusaurus was significantly smaller than Elaphrosaurus.

Spinostropheus

Deltadromeus

Limusaurus

Elaphrosaurus

Ceratosaurus

Abelisauroidea

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