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Tachyglossus in vivo
 
Tachyglossus

Tachyglossus aculeatus (Shaw 1792) is the echidna and the only other genus of egg-laying mammal. It protects itself with sharp spines and has a long, ant-catching tongue. The hands and feet are adapted to digging with short, almost immobile proximal elements and long claws. Prepubic bones precede the pubis. A proximal process sits atop the fibula. The leathery snout without whiskers is sensitive to vibrations.

Distinct for its sister, Ornithorhynchus, and many other mammals, the acetabulum is perforated. The lateral temporal fenestra is absent. So are the teeth. Like the hedgehog, the echidna can roll itself into a ball for protection.

 
Cifelliodon and Tachyglossus skulls

Cifelliodon wahkarmoosuch (Huttenlocker et al. 2018; Early Cretaceous, 126 mya) was originally considered a sister to Vintana nesting within the Multituberculata, but here nests with Tachyglossus as an ancestor echidna. It has fewer teeth that do not erupt above the alveoli, leading to toothlessness in echidnas. The pterygoid is deeper than the mandible in both.

 

Huttenlocker AD, Grossnickle DM, Kirkland JI, Schultz JA and Luo Z-X 2018. Late-surviving stem mammal links the lowermost Cretaceous of North America and Gondwana. Nature Letters  Link to Nature
Shaw G 1792. Musei Leveriani explicatio, anglica et latina.

wiki/Tachyglossus
wiki/Cifelliodon

 
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