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:

• Insects (winged hexapods) show up in Early Pennsylvanian
• Most early winged insects have fixed wings (stick out to side, as in dragonflies)
• By Late Pennsylvanian: foldable wings, allows insects to move into cracks and in between plants more easily
• Also in Late Pennsylvanian, advanced metamorphosis (with maggots/caterpillars/ etc. instead of nymphs)
• Diverse types of insects: plant eaters, carnivores, etc.

Pennsylvanian arthropods include many gigantic forms:

• Giant dragonfly relatives ("griffinflies") with 72 cm+ wingspan (largest known insects)
• Giant terrestrial eurypterids (once thought to be giant spiders!), with 34 cm long body and possibly 70 cm or wider leg spread!
• Scorpions (NOT eurypterids, but true scorpions) over 60 cm long!
• Arthropleurids ("godzillapedes", giant relatives of millipedes) over 2 m long and 15 cm wide!!

Why so giant?

• No effective predators on land to prevent giant size
• Also, new data suggests that oxygen represented up to 35% (rather than 18%) of the atmosphere during Pennsylvanian: could more easily oxygenate the tissues of giant forms than today

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):

• Most fish eaters, or ate other stegocephalians
• Some very small (few centimeters), others a couple of meters long
• Many stayed in water all their lives; others lived mostly on land
• Almost all had to return to water to lay eggs
• Some were earliest true Amphibia (fresh-water limited, reduced bones in body)
• Tetrapods (four-footed ones):
  • Name restricted to Amphibia + Amniota and all descendants of their most recent common ancestor

Ecological breakthrough during Middle Pennsylvanian:

• Amniotic egg:
  • Self-contained egg with leathery shell, and tissues to keep embryo moist, oxygenated, fed, etc.
  • Allowed possessors (amniotes) to live entire life cycle without going into the water to breed
• Led to a series of adaptive radiations
• Amniotes become the dominant group of large bodied terrestrial animals

Amniotes divided into two main branches:

• Synapsids: Enlarged jaw muscle opening for increased chewing power
• Reptiles: better color vision, better water retention

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

• Small-headed, heavily-built herbivores
• Semi-aquatic fish-eaters
• Sail-backed plant and/or mollusk-eaters
• Sail-backed carnivores with different-sized teeth in different parts of the jaw
  • The sails of these latter two may have been used to catch sunlight allowing them to warm up faster than other animals and/or as display structures
  • The different-sized teeth of the latter allowed more specialization of food processing: a trait passed onto later synapsids

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:

• Greatly expanded infratemporal fenestra
• Teeth divided into nipping incisors, biting canines, and grinding cheek teeth
• Forelimbs more powefully developed than hindlimbs

The Middle and Late Permian therapsids included:

• Various types of predators
• Large slow-moving herbivores
• Beaked, two-tusked burrowing omnivores
• and some smaller but specialized carnivores and omnivores

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):

• Some had a more upright stance than typically sprawling tetrapods
• Some may have had a diaphragm, allowing more effective breathing (more in the third part of the course)
• Similarly, some had a secondary palate, allowing them to breath while biting/feeding
• Additionally, the complex cheek teeth of most therapsids allowed them to grind food up more effectively
• In the more advanced therapsids, fossils show pits in the front of the snout that in mammals are associated with the nerves and blood vessels of whiskers. As whiskers are modified hair, this suggests that at least some of the Late Permian therapsids had fur

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:

• Aglandular skin: skin of fish, lissamphibians, and mammals have numerous glands (mucous, sweat, etc.). Reptile skin has few glands.
• "Waterproof" skin: reptile skin has a special form of keratin that makes it relatively stronger and less likely to lose moisture than in other reptiles.
• Water conserving kidneys: waste released as uric acid instead of urea (although turtles still primarily use urea)
• Excellent color vision: four-to-five type of color receptors, as opposed to the three of humans and many other primates and two in most placental mammals. (Once thought to be a shared derived feature of Reptilia, but may simply be retained from the ancestral amniote: we'll see more when we look at the origin of mammals)

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:

• Trilobites
• Rugose and tabulate corals
• Graptolites
• Fusulinids
• Eurypterids
• Many brachiopod clades
• Many lacy and stony bryozoans
• Blastoids, all but one crinoid clades
• All but a few species of ammonoids
• Many primitive therapsids

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:

• Huge
• Fast (less than 1 Myr, probably much less than 300 kyr!!)
• Tropics hit worse than poles: reef communities destroyed
• Continental and marine communities affected around the same time
• Occur during a major regression
• Coincides with the largest flood basalt of Phanerozic (Siberian Traps)
  • Event itself would have been relatively non-gaseous, but did erupt through a HUGE Siberian coal deposit, so would dump a large amount of carbon dioxide into atmosphere, leading to extreme global warming
• Associated with a major anoxic pulse on both land and sea
  • Extreme global warming may have led to shallow water anoxia
    • Due in part to the lower solubility of carbon dioxide in warm water (think warm soda vs. cold soda!)
    • Also, if poles and equator have similar temperature, there is reduced wind, and thus reduced oceanic current, and thus little mixing of shallow water and deep water, and thus little reoxygenation of shallow water from the depths (think what happens if an aerator fails in an aquarium.)
  • Some evidence suggests a "burp" of hydrogen sulfide, perhaps due to blooms of hydrogen sulfide-producing purple sulfur bacteria in anoxic shallow water
    • If so, would have the additional effect of destroying ozone layer, adding UV radiation damage to the mix!
• Possibly associated with major pulse of hypercapnia (high carbon dioxide levels) in sea
• Also associated with major carbon isotope fluctuations
  • Carbon isotope flucation too extreme to be explained by biomass
  • However, these would be consistent with melting of oceanic methane hydrates
    • Higher deep sea water, due to Siberian Traps related global warming, would melt the clathrates (deep sea ices) rich in methane
    • As the latter rose to the atmosphere, they would greatly increase greenhouse effect (methane a stronger greenhouse gas than carbon dioxide)
    • Via a positive feedback loop, clathrate-driven global warming would melt more clathrates, and so on...
• In Feb. 2001, first reports of possible extraterrestrial residue suggesting an asteroid impact at P-Tr boundary: however, these are contraversial and still have not been successfully replicated at present (January 2011)

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:

• Marine Realm:
  • Light calcifiers or non-calcifiers survived better than heavy calcifiers
  • Motile survive better than sessile
  • Forms with sophisticated respiration buffering their internal organs from the outside (e.g., complex gills, closed circulatory systems, etc.) survive much better than those whose internal organs in greater contact with outside world
  • As a side effect of all these, the extinction shifts a world to one dominated more by swimming and predation than one dominated by sessile calcified suspension feeders
• Continental Realm:
  • Survivors are typically those adapted to low oxygen and/or temporarily high carbon dioxide levels: burrowers, mountain dwellers, semi-aquatic forms
  • Victims include many with only moderately sophisticated respiration: those with sophisticated respiration or with low metabolic rates survived better
  • Smaller body size generally favored

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Last modified: 14 January 2011