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MESOZOIC ERA

TRIASSIC PERIOD

251-201 million years ago

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CYNODONT

skeleton

Advanced cynodonts evolved more mammalian modifications of their postcranial skeleton.

In advanced cynodonts, the ribs were reduced further and attached to the lumbar vertebrae. Because the transverse processes of cervical and lumbar ribs are actually composed of ancestral transverse processes plus vestiges of ribs, they are referred to as pleurapophyses.
In advanced cynodonts (such as Masetognathus), the glenoid cavity became more open, the coracoid bones were reduced, the clavicle attached to the acromion, and more movement was permitted at the shoulder. In the most advanced cynodonts, the humerus had become more slender and was held upright. In advanced cynodonts, the ilium extended forward and turned outward, the acetabulum became deeper and smaller, the anterior ilium was expanded, and the pubis further reduced.