The most catastrophic crisis on record—the Permo-Triassic mass extinction event (PTME), some 252 million years (Myr) ago—challenged the surviving organisms with extensive global warming, acid rain and forest loss. The response of terrestrial vertebrates to the PTME is the focus of novel enquiry. Some groups (temnospondyl amphibians; therocephalian synapsids; procolophonid parareptiles) passed through the PTME at low diversity and expanded in the Triassic. Others (anomodont therapsids) were diverse and abundant in the Late Permian, went through a bottleneck at the PTME and recovered in the Triassic.
Cynodont therapsids exemplify a group of land vertebrates that survived the PTME and diversified extensively in the Triassic. In addition, they offer an excellent model for studying clade diversification leading up to the origin of a successful and iconic vertebrate radiation—the mammals. Cynodonts gave rise to the mammals in the Jurassic. Their skeletal anatomy documents in exquisite detail major skeletal changes in the braincase, lower jaw, teeth and limbs that foreshadow the mammalian ground plan.
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