| Pennsylvanian | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 323.2 ± 0.4 – 298.9 ± 0.15Ma | |||||||||||||||
.png) A map of Earth as it appeared 310 million years ago during the Pennsylvanian Subperiod, Moscovian Age | |||||||||||||||
| Chronology | |||||||||||||||
| |||||||||||||||
| Etymology | |||||||||||||||
| Name formality | Formal | ||||||||||||||
| Usage information | |||||||||||||||
| Celestial body | Earth | ||||||||||||||
| Regional usage | Global (ICS) | ||||||||||||||
| Time scale(s) used | ICS Time Scale | ||||||||||||||
| Definition | |||||||||||||||
| Chronological unit | Subperiod | ||||||||||||||
| Time span formality | Formal | ||||||||||||||
| Lower boundary definition | First appearance of theConodontDeclinognathodus nodiliferus. | ||||||||||||||
| Lower boundary GSSP | Arrow Canyon, Nevada, United States 36°44′00″N114°46′40″W / 36.7333°N 114.7778°W /36.7333; -114.7778 | ||||||||||||||
| Lower GSSP ratified | 1996[2] | ||||||||||||||
| Upper boundary definition | First appearance of theConodontStreptognathodus isolatus within themorphotypeStreptognathodus wabaunsensis chronocline. | ||||||||||||||
| Upper boundary GSSP | Aidaralash,Ural Mountains,Kazakhstan 50°14′45″N57°53′29″E / 50.2458°N 57.8914°E /50.2458; 57.8914 | ||||||||||||||
| Upper GSSP ratified | 1996[3] | ||||||||||||||
ThePennsylvanian (/ˌpɛnsəlˈveɪni.ən/pen-səl-VAYN-i-ən,[4] also known asUpper Carboniferous orLate Carboniferous) is, on theICSgeologic timescale, the younger of twosubperiods of theCarboniferous Period (or the upper of twosubsystems of the Carboniferous System). It lasted from roughly323.4 million years ago to298.9 million years ago. As with most othergeochronologic units, therock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain by a few hundred thousand years. The Pennsylvanian is named after the U.S. state ofPennsylvania, where the coalbeds of this age are widespread.[5]
The division between Pennsylvanian andMississippian comes from North American stratigraphy. In North America, where the earlyCarboniferous beds are primarily marinelimestones, the Pennsylvanian was in the past treated as a full-fledged geologic period between the Mississippian and thePermian. In parts of Europe, the Mississippian and Pennsylvanian are one more-or-less continuous sequence of lowland continental deposits and are grouped together as the Carboniferous Period. The current internationally used geologic timescale of theICS gives the Mississippian and Pennsylvanian the rank of subperiods, subdivisions of the Carboniferous Period.
All modernclasses offungi have been found in rocks of Pennsylvanian age.[6]
The major forms of life at this time were the arthropods. Arthropods were far larger than modern ones.Arthropleura, a giantmillipede, was a common sight and the giantgriffinflyMeganeura "flew the skies".[7] It is commonly considered that is because of high oxygen level, however some of those large arthropod records are also known from period with relatively low oxygen, which suggest high oxygen pressure may not have been a primary reason for their gigantism.[8][9]
Amphibians were diverse and common; some were several meters long as adults. Thecollapse of the rainforest ecology in the mid-Pennsylvanian (between the Moscovian and the Kasimovian) removed many amphibian species that did not survive as well in the cooler, drier conditions. Amniotes, however, prospered due to specific key adaptations.[10] One of the greatest evolutionary innovations of the Carboniferous was theamniote egg, which allowed for the further exploitation of the land by certaintetrapods. These included the earliestsauropsid reptiles (Hylonomus), and the earliest known "pelycosaur"synapsids (Archaeothyris). Small lizard-like animals quickly gave rise to many descendants. Amniotes underwent a major evolutionary radiation, in response to the drier climate that followed the rainforestcollapse.
For some reason, pelycosaurs were able to reach larger sizes before reptiles could, and this trend continued until theend of the Permian, during which theircynodont descendants became smaller andnocturnal, as the reptilianarchosaurs took over, althoughdicynodonts would remain megafaunal until their extinction at theend of the Triassic.[10][11] Most pre-rainforest collapse tetrapods remained smaller, probably due to the land being primarily occupied by the gigantic millipedes, scorpions, and flying insects. After the rainforest collapse, the giant arthropods disappeared, allowing amniote tetrapods to achieve larger sizes.
The Pennsylvanian has been variously subdivided. The international timescale of theICS follows the Russian subdivision into four stages:[12]
North American subdivision is into five stages, but not precisely the same, with additional (older) Appalachian series names following:[13][14]
The Virgilian or Conemaugh corresponds to the Gzhelian plus the uppermost Kasimovian.The Missourian or Monongahela corresponds to the rest of the Kasimovian.The Desmoinesian or Allegheny corresponds to the upper half of the Moscovian.The Atokan or upper Pottsville corresponds to the lower half of the Moscovian.The Morrowan corresponds to the Bashkirian.
In the European subdivision, the Carboniferous is divided into two epochs:Dinantian (early) andSilesian (late). The Silesian starts earlier than the Pennsylvanian and is divided in three ages:[15]
