Docodonta

Castorocauda, live reconstruction

• Eurasia, North America, South America

The Docodonta are a group of extinct mammal ancestors ( Mammaliaformes ) that lived in the Jurassic and the Cretaceous. Known representative of this group is probably the discovered 2004 and 2006, first described, adapted to life in water genus Castorocauda.

Description

An outstanding feature of Docodonta were widened molars ( back teeth ) with complex occlusal surfaces. These teeth allowed a more -grinding mastication than in other mammals. The teeth are usually only about 0.5 to 1.5 millimeters in size. For what food these teeth were optimized, is controversial, be discusses a plant or omnivorous diet. Castorocauda other hand, could have fed on fish.

Many genera except teeth or jaw parts unknown. From Haldanodon however, a nearly complete skeleton was discovered, the animal had very stocky and horizontally oriented limbs. This building has led to speculation about a subterranean grave -border or floating lifestyle, the second possibility since the discovery of Castorocauda with its unique adaptation to aquatic life has become more likely.

History of development

Almost all finds of Docodonta come from the period between the Middle and Upper Jurassic or earliest Cretaceous and are known almost exclusively from Europe, Asia and North America, suggesting that this group emerged about the former continent Laurasia, the northern, from Pangaea Great continent, was widespread. However, there are finds of teeth and jaw parts from the Upper Cretaceous of South America. The genus was named in question Reigitherium and could be an indication that the Docodonta could have survived in isolated regions longer. However, the findings are very poorly preserved, which makes a clear systematic assignment.

Outer systematics

Due to the primitive construction of the temporomandibular joint, the Docodonta be counted among a number of animals that have advanced mammal -like features, but still differ in details from today's mammals and therefore as Mammaliaformes ( mammal -like ) or as Mammalia sensu lato ( in the broad sense ) summarized be. Whether they are already referred to as mammal or even as a mammal ancestors, is a question of definition. Cladistic analyzes they arrange more advanced than Morganucodonta or Sinoconodon but primitive as Hadrocodium or the actual mammals one.

The findings of Castorocauda were surprising, as conspicuous specializations in mammals were much older than previously thought.

Known genera

• Haldanodon is a relatively original representatives of Docodonta. A nearly complete skeleton was discovered in the 1970s in the coal mine Guimarota in Portugal, next to numerous skull and dental finds. The genus is dated to an age of some 152 million years, and was the first known mammal from the Upper Jurassic, of which more than scant finds were present. As mentioned above, the stocky, horizontally mounted limbs could point to an aquatic lifestyle.
• Docodon also lived in the late Jurassic period, finds ( by Othniel Charles Marsh ) are known from North America and possibly England. The genus is particularly enlarged molars, but otherwise little is known about them.
• Castorocauda from the Upper Jurassic has been discovered in China in 2004 and is notable for its adaptations to aquatic life and by its size.
• Reigitherium is known by a jaw portion with three teeth, was found in Patagonia and from the Upper Cretaceous comes ( to around 70 million years ago ). Both the lower age and the locality are to the other representatives of this group in opposition. The excessive wear of the teeth and the poor condition of the finds do not allow an unambiguous assignment systematic. As already mentioned, it is conceivable that the Fund could be an indication that the group has survived in some regions longer.