GEOL 102 Historical Geology

Spring Semester 2011
The Late Paleozoic Era IV: Permian Life and the Permo-Triassic Extinction

Arthropods on Land During the Carboniferous:
Arthropod diversity increases during Mississippian, but especially during Pennsylvanian (in concert with spread of forests). Some new aspects of Carboniferous arthropods:

Pennsylvanian arthropods include many gigantic forms:

Why so giant?

Permian terrestrial arthropods:
Few new groups, although the giant forms disappear.

The Permo-Triassic extinction is the ONLY mass extinction to effect insect diversity: sail through K-T extinction, etc., with no discernible effect, yet many clades killed off by Permo-Triassic event.

Other Terrestrial Invertebrates:
During later Paleozoic, freshwater snails and clams appear.

Late Paleozoic terrestrial vertebrates:
"Romer's Gap": few terrestrial stegocephalians between Late Devonian and Late Mississippian, as well as little diversity increase in arthropods at this time. Why the delay? Possibly a sampling issue, but it has been suggested that lower oxygen level may have held back terrestrial radiations.

High diversity of Late Carboniferous stegocephalians (many are true tetrapods):

Ecological breakthrough during Middle Pennsylvanian:

Amniotes divided into two main branches:

The synapsids were the first group to radiate (during the Early Permian), including such forms as:

These early synapsids would have had the sprawling stance found in primitive tetrapods in general. They almost certainly would have been "cold-blooded" (the ancestral state for vertebrates). So traditionally these animals have been considered "reptiles". However, they lack the shared derived features of reptiles (see below), and are instead simply primitive synapsids. (In traditional taxonomy, these were put in the group "Pelycosauria", but this is a paraphyletic group: all synapsids except for therapsids). New discoveries show that even early synapsids had some parental care.

The early synapsids evolved themselves into extinction: that is, they were replaced in the Middle and Late Permian Epoch by the Therapsida: the advanced synapsids. Once called the "mammal-like reptiles", they are not true reptiles. Instead, they are the advanced branch of the synapsid phylogeny. They differed from earlier synapsids by:

The Middle and Late Permian therapsids included:

Ancestrally, all vertebrates are cold-blooded (warm their bodies primarily using sunlight). However, some evidence suggests that the advanced therapsids of the Late Permian may have had elevated metabolisms (that is, were at least partially warm-blooded):

What is "warm-bloodedness"? Ectotherms ("cold-blooded" animals) get most of their heat from outside the body (mostly the sun). This is much less expensive in terms of metabolism, but it means that they are less active overall, grow slower, have slower recovery times after period of activity, and are limited to environments or times of day and year when they can get sufficient warmth from the sun. Endotherms ("warm-blooded" animals) generate most of their heat internally (from extra, leakier mitochondria) and have greater activity levels, grow faster, have quicker recovery times after periods of activity, and can live in colder environments. This comes at a cost, however: to fuel their bodies, they need as much as ten times the amount of food of an ectotherm of the same body size.

Additionally, some therapsids seem to have had parental care of the young, keeping them in burrows.

True reptiles tended to be relatively rare in the Carboniferous and Permian Periods. Reptilia is characterized by a number of particular skeletal features (which we aren't going to deal with here, as they are fairly technical). Modern reptiles (and by inference, their concestor and all of its descendants) share a number of soft-tissue features:

In general, compared to typical Mesozoic and Cenozoic ecosystems, the late Paleozoic land vertebrates were smaller (few ox- or hippo-sized, none larger), slower (no real speed specialists), and close to the ground (only a few gliders and no powered fliers; few tree-climbing specialists).

The Permo-Triassic Extinction:
Largest mass extinction of Phanerozoic. Total of all Permo-Triassic events may be 80-96% of species (or, in the flip side, only 4-20% of species survived)

Victims include:

Was once thought to be gradual (extended over 9 Myr), but now seems be in two main pulses (or maybe just even one!). Some evidence suggests that there is a first pulse, between the Capitanian Age of the Middle Permian (or Guadalupian) Epoch and the Wuchiapingian Age of the Late Permian (or Lopingian) Epoch. It was smaller, but still powerful: 34% genus level extinction in the seas (comparable to the Cretaceous-Paleogene extinction!) and fairly powerful on land, too. The event showed a marked reduction of members of the Paleozoic fauna, but not the loss of entire major clades. (However, some statistical evidence suggests that this may not be a real event, and that all extinction is concentrated at the end of the Changhsingian.)

The BIG ONE is at the end of the Changhsingian Age of the Lopingian Epoch, was the worst mass extinction in the history of multicellular life:

Regardless of precise scenario, extinction reorganizes the world. After the event, the Paleozoic marine evolutionary fauna becomes subordinate to the Modern marine evolutionary fauna. Also, the size and diversity of the animals present is greatly reduced.

Some basic patterns of extinction vs. survivorship:

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Last modified: 14 January 2011