Liaoconodon
| Liaoconodon | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Aptium ( Lower Cretaceous ) | ||||||||||||
| 120 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Liaoconodon | ||||||||||||
| Meng , Wang & Li , 2011 | ||||||||||||
Liaoconodon hui is an extinct mammal (Mammalia) from the Cretaceous Period . A well-preserved fossil was found near Jianchang in the Chinese province of Liaoning and described in 2011. It comes from layered limestones belonging to the Jiufotang Formation and dated to the Lower Cretaceous ( Aptian ). Liaoconodon is assigned to the Eutriconodonta , a group of Mesozoic mammals, which are mainly characterized by common features in the structure of the molars (molars).
features
The fossil-preserved specimen of Liaoconodon has a head-trunk length of 19.5 cm and is 30.5 cm long including the tail. Since the cranial sutures are still clearly visible and the molars of the permanent set of teeth have not yet fully erupted, it is assumed that this is a young but fully grown animal.
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Liaoconodon differs from other eutriconodonts mainly in its short incisors and proportionally enlarged canines and anterior premolars .
meaning
The description of Liaoconodon focuses primarily on the anatomy of the temporomandibular joint and the ossicles . In reptiles and synapsids , the temporomandibular joint is formed by the connection of the articular and quadratic bones ( primary temporomandibular joint ). In recent mammals, however, these bones are transformed into auditory ossicles and form the joint between the hammer and anvil . The temporomandibular joint in mammals is therefore a secondary temporomandibular joint and is formed by the articular cartilage of the lower jaw ( dental ) and the scaly part of the temporal bone .
Liaoconodon shows a transition stage between the primary and secondary TMJ. The angular and articular bones have lost direct contact with the dental and are only connected to the dental by Meckel's cartilage , which is ossified for stabilization. The hammer ( malleus ) and anvil ( incus ) are primarily important as ossicles, but have not yet been completely freed from their function as elements of the primary temporomandibular joint.
literature
- Jin Meng, Yuanqing Wang & Chuankui Li: Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont. Nature 472, 181-185 doi : 10.1038 / nature09921