The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages, and a few new episodes were posted. Now, the blog/podcast is on an occasional schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Wednesday, September 3, 2014

September 3. Cynodonts



Triassic Dicynodont from Poland. Drawing by Dmitry Bogdanov.

A few days ago, talking about the end Permian extinction, I said something that’s wrong. I said the therapsids became extinct. That’s not true, since the therapsids include modern mammals. I should have made it clear that it was the early therapsids, dimetrodons and others, that did not survive into the Triassic. Other groups were decimated, but they did survive.

One surviving group was the cynodonts, whose name means “dog-teeth.” Cynodonts are generally seen as the early therapsids that ultimately gave rise to true mammals later in the Triassic, but as the Triassic began, only a few varieties existed. In addition to differentiated teeth, cynodonts had skull and jaw structures similar to modern mammals. It’s speculated that cynodonts were warm-blooded and laid eggs, like modern platypuses.

The recovery from the Permian extinction was slow, but cynodonts did diversify during the Triassic, increasingly through the period. The variety called dicynodonts, meaning “two dog teeth” for the pair of large tusks that they had, were perhaps the most diverse of the pre-mammalian therapsids. They started in late Permian time but were pretty common during the Triassic. Dicynodont species ranged from the size of a rat to the size of an ox, and despite the tusks they were herbivores. They probably used the tusks for digging, like modern boars. Dicynodonts were probably the most widespread large herbivores on land during the early Triassic, expanding from two families that survived the extinction to 14 or 15 families by mid-Triassic time.

The Triassic’s changing climates and arid conditions in many locations were probably both stimulating in terms of evolutionary pressure and challenging in terms of survival. The dicynodonts were essentially extinct by the late Triassic, but there is a possibility that some survived until the Cretaceous, based on fragmentary fossils from Queensland, Australia. But by the end of the Triassic, most of the terrestrial herbivores were dinosaurs, not pre-mammalian therapsids like the cynodonts and dicynodonts.
—Richard I. Gibson

Image by Dmitry Bogdanov under GFDL.

2 comments:

  1. 247 episodes so far.... non-stop, even during your busy summer! Thanks very much, it's a great podcast.

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  2. Thanks! It's been close (to missing a day) a couple times.... should be OK for the rest of the Mesozoic, barring asteroid impacts or other unforeseen events. :)

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