In DepthPaleontology

Echidnas don't suck—but their ancestors did

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Science  20 Jul 2018:
Vol. 361, Issue 6399, pp. 213
DOI: 10.1126/science.361.6399.213

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Summary

Mammals suck. The ability to suckle milk is a defining characteristic of the group, and it is no small feat of evolution. Nursing—as well as drinking through a straw—requires complex anatomy to seal off the airway every time we suck and swallow. But one branch of mammals doesn't suckle: the egg-laying monotremes, which include today's platypus and echidna, or spiny anteater. These animals lack nipples. Instead, babies lap or slurp milk from patches on their mother's skin. Monotremes are thought to have diverged from other mammals roughly 190 million years ago, so most paleontologists figured that suckling evolved after that split. Now, a close look at modern animals and key fossils from before the split suggests monotreme ancestors could suckle after all, but the animals later lost the ability as their mouths evolved to eat hard-shelled prey. The finding gives researchers a new view of how and when suckling evolved.