George R. McGhee

For me, the question with this type of book is whether it's going to be advanced enough that I feel as though I'm learning something but not so technical that it's simply impenetrable. On the whole McGhee maintains a nice balance in what feels a bit like a textbook for a junior grad student, meaning that this is not the first book one should read on the subject. What McGhee does really well is to make clear what the gaps are in our understanding when it comes to fitting existing hard data (in relation to fossils and geological structures) into plausible explanatory systems. The one bottom line is that it took the evolution of amniotic reproductive systems before terrestrial vertebrates really became viable.… (mehr)

The Late Palaeozoic (the Devonian, Carboniferous, and Permian periods, about 419-252 million years ago) is broadly characterized by "icehouse" conditions, that's to say low temperatures and permanent polar ice*, and high oxygen levels. Important evolutionary events include the invasion of land by tetrapods, the radiation of flying insects, and the formation of the first forests. The high oxygen enabled the evolution of giant arthropods, including flying insects the size of gulls and millipeds some three meters long. It ended with the end-Permian mass extinction, a near-apocalyptic event that reshaped the biosphere much more profoundly than the end-Cretaceous (dino-killer) one.

This book, then looks at various aspects of this era, especially the evolution of atmospheric oxygen, the advances and retreats of glaciation, and how this impacted the evolution of plants and animals. Much attention is also paid to the end-Permian extinction and the "minor" mass extinctions that preceded it - one of which, at the end of middle Permian, rivals the end-Cretaceous one for lethality. It's sort of sprawling, juggling a lot of balls, but I found it quite interesting.

* Yes, this means we're currently enjoying an icehouse climate, despite the end of "the" Ice Age about 10,000 years ago. Compared to the average for the last 600 million years or so, we're not living in a warm period, merely a less cold one.… (mehr)

The vertebrate invasion of land did not, of course, actually fail, but it was set back, and, in McGhee's estimation, redirected by the mass extinctions of the Late Devonian. One usually speaks of two, in the Frasnian and Famennian geological ages, but at least the first and probably both were actually series of closely (geologically speaking) spaced events. Collectively, the Frasnian ones in particular were very severe, comparable to the more famous one at the end of the Cretaceous (the dinosaur killer).

McGhee does a pretty good balancing act between readbility and scientific rigour, tho sometimes one wonders at what he thinks requires explanation and what not. A weakness is the phylogenetic classifications, where only differing levels of indentation allows you to see what's on a level with what - not easy to keep track of when there's a dozen entries in between. Cladograms showing the branching directly would've been more helpful. Another quibble is rather carefree way he speaks about "major clades" as if there were an objective cutoff from minor ones.

Such quibbles nonewithstanding, it's a good book. It's also an illustration of how fast things are moving in this field - a good deal has happened since Laurin's 2010 How Vertebrates Left the Water, say.… (mehr)