Palæos: Paleozoic		Pennsylvanian Epoch
CARBONIFEROUS PERIOD		Pennsylvanian

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The Pennsylvanian

The Pennsylvanian Epoch of the Carboniferous Period: 318 to 299 Mya

Lasting some 33 million or so years, the Late Carboniferous or Pennsylvanian age was the high point of stem tetrapod evolution, especially during the Bashkirian and Moscovian epochs.  During this time the first reptiles and synapsids evolved and quickly diversified.   By the end of the period these new forms, especially the synapsids, had supplanted the stem tetrapods as the dominant life form on land.

Geography

During the late Carboniferous period Laurussia and Siberia collide to form Laurasia; meanwhile Gondwana comes up from the south. The resulting Appalachian, Ouachita, Marathon, Ural, Variscan, and Hercynian orogenies formed some of the largest mountains of all time.  As a result of the collision of Gondwana and Laurasia the supercontinent of Pangea comes into being.

Life - the Biosphere

Alethopteris from the Pennsylvanian of West Virginia, USA.  From Indiana9 Fossils (which has a whole page of Alethopteris images).

On land, great forest swamps covered extensive equatorial areas.  These forests consisted of diverse plants including tree ferns, which grew 15 meters in height, Calmites, a giant version of the modern "horsetail" plant, lycopods (e.g. Lepidodendron, which attained a height of 30 metres), the extinct group of plants called "seed ferns" (see illustration at left), and primitive Conifer-like plants (Cordaites) that reached 40 meters in height

In the moist oxygen rich atmosphere flying insects were abundant, and some attained huge size, such as Meganeura, with a wing span of 70 centimetres

Diplovertebron - a medium-sized semi-aquatic tetrapod
length 1 to 1.5 metres
Moscovian of Europe

Tetrapods were abundant, especially the "labyrinthodonts," so called because of the complex (labyrinthine) pattern of folded enamel in their teeth.  They filled every available ecological niche, from fully aquatic eel-like forms, to large semiaquatic crocodile like animals and small forms like modern day newts and salamanders, to terrestrial types similar to reptiles.  Some types (the Aïstopoda) lost their legs altogether, superficially resembling snakes.

The earliest Reptiles also evolved at this time, such as Hylonomus (left) but remained relatively insignificant until the end of the period.  Reptiles have a big advantage over stem tetrapods in that they do not have to return to water to breed; they can lay their eggs on dry land.  So it is likely that with the appearance of reptiles the tetrapods* (land animals) were able to colonize the uplands for the first time, where they fed on an abundance of insects.

Carbon Cycle

The name Carboniferous derives from the fact that most of the important coal producing strata are of this age.  however, it is specifically in the Late Carboniferous or Pennsylvanian sub-period that this is so.  During this time most of the world's coal deposits were laid down, the coal being formed from compressed layers of rotting vegetation.

Stratigraphic Divisions

Resources

Links

Pennsylvanian map page

PENNSYLVANIAN PERIOD

Browse the Fossil Gallery - Upper Carboniferous (Pennsylvanian) Period - a nice selection of fossils from Nova Scotia

Radiometric Dating Controversy

PENNSYLVANIAN TIME-SCALE PROBLEMS - the usual given for the Pennsylvanian is around 34 million years. A meticulous new study of central European stratigraphy now pegs the Pennsylvanian as spanning only 19 million years; a 44% change!  This figure, if it is genuine, casts doubt on the origin of the famous Pennsylvanian cyclothems (repetitive strata) in North America, previously correlated with sea level changes forced by variations in the earth's orbit (the Milankovitch periods). One wonders how reliable radiometric dating is?  Consider the discrepancy regarding dating for the base of Cambrian. I have therefore retained the old dating of the Pennsylvanian here, tending confirmation of these new findings.

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