Castorocauda

Castorocauda, Life Picture

• China (Inner Mongolia, Jiulongshan Formation)

• Castorocauda lutrasimilis

Castorocauda ( " beaver tail" ) is an extinct genus mammal- like animals ( Mammaliaformes ) from the group of Docodonta. It lived in the Middle Jurassic period about 164 million years ago and showed in his physique significant adaptations to a semiaquatic (partly taking place in water) of life. The hitherto only known species is Castorocauda lutrasimilis.

Description

Castorocauda reached a length of about 42 centimeters ( the skull was about 6 inches long ), its weight is estimated at 500 to 800 grams. Thus, it was bigger than all other mammals and mammal-like animals of the Jura.

The animal had a broad, largely hairless and scaly tail, which probably resembled that of the beaver ( Castoridae ). The toes of the hind legs were webbed, the front legs were short and strong. Presumably, leaves his life compare with that of the platypus, the floating searches for food in the water. The front legs could have served for paddling or for digging burrows.

Clearly the remains of a fur can be seen on the fossil, which was made up of guard hairs and undercoat and already similar to that of present-day mammals. This makes it the oldest known mammal -like animal in which a coat is clearly demonstrated and an indication that the body hair - perhaps associated with thermoregulatory abilities - evolved before the evolution of true mammals.

The lower jaw has well-preserved half to four per jaw incisors, one canine, five premolars and six molars. The construction of the molars is true in the broad crowns with that of the other Docodonta largely the same. However, an unusual feature are the two front molars, which had five successively arranged cusps. From the construction of the teeth, it is concluded that Castorocauda has fed on fish and invertebrates wasserbewohnenden.

Discovery and designation

Castorocauda is known by an almost completely preserved skeleton, the interior in the Jiulongshan Formation in the Chinese province of Mongolia and found in 2006 by Qiang Ji, Zhe - Xi Luo, Chong- Xi Yuan, and Alan R. Tabrum was first described. The genus name comes from the Latin Castorocauda "castor " for beaver and " cauda " tail for which lutrasimilis epithet is derived from the words " lutra " ( Otter ) and " similis " (similar ) from.

System

Castorocauda shows in his physique similarities with today's wasserbewohnenden mammals such as beavers, otters or platypus. However, these similarities are not based on kinship but on convergent evolution, as the lineages of modern mammals have developed only at a much later date. Castorocauda is classified in the group of Docodonta, a widespread mainly in the Jurassic and Early Cretaceous in Eurasia and North America taxon. They belong to a group of animals, although largely similar to the present-day mammals, but differ in details such as the construction of the ossicles and the temporomandibular joint, and therefore not in the mammals in the strictest sense (sensu stricto ), but as " mammal -like" animals ( Mammaliaformes ) or mammals in the broader sense are called (sensu lato ). Even with a previously discovered representatives of Docodonta, Haldanodon, the stocky limbs had been interpreted as a possible adaptation to a grave end or aquatic life.

Significance of the find

Castorocauda was the largest known mammal ( or mammal- like animal ) of the Jura and adopted by its adaptations to aquatic life, a development anticipated, was known hitherto only from mammals of the Cenozoic era ( 100 million years later). Until recently, it held all the mammals of the Mesozoic for small, relatively unspecialized animals that were mostly nocturnal insectivores. Castorocauda but adds in a number of discovered recently Mesozoic mammals, demonstrating that it was already in that epoch was significant specializations, such as the predatory genus Repenomamus that ameisenbärähnliche genus Fruitafossor or provided with Gleitmembranen Volaticotherium.