Earlier (in seven prior blog posts) we looked at the new basalmost amniotes and how they evolved.
With the news
that the Amniota (and amniote eggs) extended back to the Viséan (326-345 mya) let’s take a look at those basalmost amniotes along with the genera that may have been more primitive, but survived more than 30 million years later, into the Westphalian (303-311 mya) and beyond to the Early and Late Permian. That’s a stretch of 80 million years for the most successful taxa. And what made them so successful? Or were they all just as successful, just not found yet in higher strata?
Figure 1. Click to enlarge. Basal amniotes to scale colorized according to the time strata in which their fossils were found. Visean, yellow; Namurian, pink; Westphalian, blue; Permian, tan.
It’s well worth remembering
at this point that in similar fashion, basal primates, like lemurs, also co-exist today with derived primates, like apes and humans. So that happens. At least some of these basalmost amniotes (the Permian forms, like Utegenia, Fig. 1) developed successful traits so well matched to their own niche they survived for tens of millions of years thereafter.
Also remember
that fossilization is a rare event. Even more rare is the discovery of rare fossils. So we’re very lucky to have even single examples of these taxa. They were probably more widespread both across the globe and through time.
Two important points
1) We don’t find amniotes prior to the Viséan. So these Viséan amniotes (Fig. 1) are likely the earliest representatives of their kind.
2) The Viséan is a short 15 to 35 million years after the very first tetrapods developed limbs from fins some 360 million years ago in the Late Devonian. So evolution was rapid during those first 15 million years. Not so rapid for the next 80 million years, at least for certain taxa.
That’s exciting to think about.
The Pterosaur Heresies 