Study of Fossils : Cynodont Fossil
Origin:
Late Permian.
This mammal-like reptiles were one of the most diverse groups of therapsids.
They are named after their dog-like teeth.
Extensively diversified after the Permian–Triassic extinction event.
Characters:
Their braincase bulged at the back of the head.
Their teeth were fully differentiated.
Many of them walked in an upright manner unlike reptiles.
They also have the secondary palate that other primitive therapsids lacked, except the therocephalians, the closest relatives of cynodonts.
Their temporal fenestrae was much larger than its ancestors, and the widening of the zygomatic arch allowed for more robust jaw musculature supporting the evidence of a more mammal-like skull.
Dentary was the largest bone in their lower jaw, as other smaller bones moved into the ears.
They were probably warm-blooded, and covered in hair.
Cynodonts still laid eggs, as all Mesozoic proto-mammals probably did.
Evolutionary Significance:
Together with the extinct Gorgonopsians and the Therocephalians, the cynodonts themselves are part of a group of therapsids called Theriodonts.
The oldest and the most basal cynodont is Charassognathus (Late Permian). Other basal cynodonts were the Procynosuchids,[ a family that includes Procynosuchus and Dvinia].
Cynodonts were among the few groups of synapsids that survived the Permian–Triassic extinction event and had a slow recovery after the extinction.
The most derived cynodonts are found within the clade Eucynodontia, which also contains the members of Mammalia. Representative genera of non mammalian cynodonts include the large carnivorous Cynognathids, the equally large herbivorous Traversodonts, and the small mammal-like Tritylodontids and Ictidosaurs.
The presence of respiratory turbinates, suggests a rapid metabolism and possibly endothermy.
During their evolution, the number of cynodont jaw bones reduced. This move towards a single bone for the mandible paved the way for other bones in the jaw, the articular and angular, to migrate to the cranium, where they function as parts of the mammalian hearing system.
Cynodonts also developed a secondary palate in the roof of the mouth. This caused air flow from the nostrils to travel to a position in the back of the mouth instead of directly through it, allowing cynodonts to chew and breathe at the same time. This characteristic is present in all mammals.
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