Liaoconodon

• Liaoning (China)

Liaoconodon hui is an extinct mammal ( Mammalia) from the Cretaceous period. A well-preserved fossil was found in Jianchang in the Chinese province of Liaoning and described in 2011. It dates are dated from layered limestones belonging to Jiufotang lineup and on the Lower Cretaceous ( Aptian ). Liaoconodon is attributed to the Eutriconodonta, a group of Mesozoic mammals, which is mainly characterized by common features in the construction of the molars ( back teeth ).

Features

The fossil preserved example of Liaoconodon has a head -body length of 19.5 cm and 30.5 cm long including the tail. Since the cranial sutures are still visible and the molars of the permanent teeth are not fully erupted, it is believed that this is a young but full-grown animal.

From other Eutriconodonta to Liaoconodon differs mainly by the short incisors and proportionally enlarged canines and anterior premolars.

Importance

The description of Liaoconodon focuses mainly on the anatomy of the temporomandibular joint and ossicles. In reptiles and synapsids the TMJ is the articular by the combination of Os and Os quadratum formed (primary jaw joint ). However, these bones form during the recent mammals ossicles and to form with them the joint between the hammer and anvil. The jaw joint of mammals is therefore a secondary jaw joint and is the condyle of the lower jaw ( dentary ) and the shed portion of the temporal bone is formed.

Liaoconodon shows a transition stage between primary and secondary jaw joint. Os Os angular and articular have lost direct contact with the dentary and are only through the Meckel's cartilage is ossified to stabilize, connected to the dental. Hammer ( malleus ) and anvil ( incus ) have one main importance as ossicles, but not yet completely freed from its function as elements of the primary jaw joint.