Late Paleozoic life

1
Paleogeography and life of the Late Paleozoic
World
EPSC 233 Earth Life History (Fall 2002)
2
Recommended reading STANLEY Earth System
History Chapter 15, pp. 414-431.
Keywords Carboniferous (Mississipian,
Pennsylvanian), Permian, Ancestral Rocky
Mountains, coal cyclothems, Mazon Creek
concretions., seasonal climates, cordaites
(primitive gymnosperm trees), winged insects,
amphibians, amniote egg, reptiles, pelycosaurs
(fin-backed reptiles), therapsids (mammal-like
reptiles). .
3
In Europe, the Carboniferous system is split in
Early, Middle and Late intervals. (The right hand
side names as stages defined on the basis of
biozones.
In North America, the Carboniferous system is
split in the Mississipian and Pennsylvanian
periods.
4
The Mississipian strata are separated from the
younger Pennsylvanian strata by a 4-million year
gap. This discomformity is an interval of
non-deposition. Bedding is parallel in strata
below and above it. Many genera of crinoids and
ammonoids disappear at that level.
5
Near the end of the Late Devonian ice age,
glaciers shrank. Sea level rose, warm seas
flooded continents, and crinoidal limestones
accumulated in shallow continental
seas. Throughout all (or nearly all) of
Carboniferous time, however, large areas of
Godnwanaland were blanketed by ice sheets.
6
When glaciers shrank, during the Upper
Carboniferous, lycopods and seed ferns were
replaced by spore ferns, which were better
adapted to moister conditions.
7
The reassembly of continents into the
supercontinent Pangea continued throughout the
late Paleozoic, giving rise to orogens (mountain
building events).
Most of these orogens are classic thrust-and-fold
belts but not the Ancestral Rockies.
8
Uplift and downfaulting in southwestern U.S. took
place along deep, nearly vertical faults. This
suggests that the crust was being stretched
rather than compressed. The exact cause is
unclear...
9
In Pennsylvanian (or Carboniferous) strata, coal
beds occur between other rock types. The
different rock types form remarkably repetitive
cycles at any one locality.
10
Throughout all (or nearly all) of Carboniferous
time, however, large areas of Gondwanaland were
blanketed by ice sheets.
(Gondwana seen from the south pole during the
late Paleozoic)
11
Ice caps grew and shrank repeatedly... Sea level
changes caused the cyclothems.
During the Carboniferous,Gondwanaland joins
Euramerica.
12
Coal forms from plant remains accumulating in
swamps found between channels of river deltas.
13
Sea level fluctuations caused these cycles
Predominantly marine section covers the coal.
Coal covers a predominantly non-marine section
14
Part of the non-marine sequence within cyclothems
is due to the movement of delta lobes, flooding
the swamps with coarser sediment (sands) carried
by the meandering river.
15
Climates became more seasonal at mid latitudes.
Yellow evaporites Green coal
16
Permian drier conditions became more widespread.
17
Gymnosperms, naked seed plants (think gymnasium
and athletees in Antique Greece), took over
terrestrial environments. Cordaites, tall trees
(up to 30 m high) formed large woodlands
resembling modern conifer forests (pines,
spruces, redwoods).
18
Joggins, Nova Scotia.
Cliffs are washed by the tides of the Bay of
Fundy. New material is constantly eroded and
exposed.
19
Lycopods (spore plants which today grow mostly to
sizes cm to lt 1 m) grew to tree-sized plants.
Sphenopsids, related to todays horsetails.
Glossopteris, a tree size seed fern widespread
throughout Gondwanaland.
20 m tall
20
A 2-meter long myriapod (as drawn by Dawson,
above), left trackways (right) at Joggins. The
same arthropod is known from other localities.
21
This tree trunk was buried in sediment on the
floodplain. Some tree trunks contain complete
skeletons of small animals, like this Hylonomous.
22
Insects (another member of the phylum Arthropoda)
started to assume a very important ecologic role
in terrestrial ecosystems. Fossils of
insect-like arthropods of late Devonian age were
wingless. However, by Late Carboniferous time,
many types of insects had wings. Some of the
earliest winged insects had wings that they could
not fold away.
23
Today, mayflies and dragonflies share that trait.
Their fossils are found in Upper Carboniferous
deposits. Most were normal size (a few cm) but
one species is known to have reached a wingspan
of nearly a half meter!.
Insects with foldable wings also appeared in some
Carboniferous beds.
24
Spectacular fossils of Carboniferous age are also
found south of Chicago, Illinois, in an area
named from a local river, Mazon Creek. By 1979,
320 species had been described from the deposit.
Most Mazon creek fossils can be assigned to
either a marine fauna or a freshwater-terrestrial
fauna.
25
myriapod
Tully monster
insect
The best fossils are found by cracking open
siderite (FeCO3) concretions that stick out from
the weathered siltstone.
26
The fossil-rich coal balls are rounded masses
of limestone or siderite. These concretions form
in coal beds during early burial. Carbonate
mineral (CaCO3) is dissolved and redistributed
within the sedimentary layers during
compaction. The carbonate mineral reprecipitates
as tiny crystals around an intact, dead animal.
This produces a hard envelope and preserves
delicate fossils from being crushed during deeper
burial.
27
The Carboniferous and Permian amphibians were
more diverse in size and shape than todays
relatively small frogs, toads and salamanders.
Eryops was a stubby alligator-like amphibian,
carnivorous, about 1.5 meter long.
Branchiosaurus is a smaller, salamander-like
amphibian.
28
There is a Carboniferous gap in our knowledge
of the origin of the earliest amphibians. This
corresponds to the drop in sea level that
separates the Mississipian and Pennsylvanian (the
disconformity). During periods of low sea level,
continents are more prone to erosion and our
knowledge of terrestrial life is fragmentary.
29
We know that a key evolutionary breakthough must
have occurred in some Carboniferous amphibians
the amniote egg. This innovation would
distinguish the earliest reptiles from their
amphibian ancestors if their remains were found.
30
The amniote egg provides the embryo with - food
(yolk) - 2 sacs - one containing the embryo
- the other one to collect waste products - an
outer shell to protect the embryo Just as seeds
allowed plants to reproduce in drier
environments, the amniote egg freed some
amphibian tetrapods from the need of having their
eggs and young develop fully in aquatic
environments.
31
Reptiles also evolved an advanced jaw structure
which could apply heavy pressure, and, when
combined with blade-like teeth, slice food.
32
During the Permian period, reptiles started
replacing amphibians in various ecologic roles
(carnivores, scavengers, specialized herbivores).
Ophiacodon, a 3.5 meter-long Permian pelycosaur
(extinct order of reptile) from Texas, shown here
eating an amphibian.
33
Dimetrodon, a carnivorous pelycosaur, was a
jaguar-size carnivore with serrated teeth.
Its fin (characteristic of pelycosaurs) may have
helped regulate its body temperature, by soaking
up the sun or helping to lose excessive heat.
34
Edaphosaurus, another pelycosaur, was
herbivorous. Carnivores and herbivores develop
different types of dentition (size and shape of
teeth can be used to tell them apart).
35
Some Permian therapsids, nearly mammal-like...
Lycaenops South Africa, 1-meter (wolf-sized)
predator.
Titanosuchus South Africa, a 2.5 meter long
carnivore.
Moschops South Africa, a 5 meter-long herbivore.
36
Among reptiles, the therapsids, also gained in
speed and agility by evolving legs positioned
more vertically beneath their bodies. Modern
reptiles are ectothermic, i.e. cold-blooded and
had to rest frequently in order to soak up heat
from their environment. Therapsids were clearly
built for action advanced jaws, complex set of
teeth, upright posture. They may have been among
the first tetrapods to become endothermic, i.e.
warm-blooded. By the Late Permian, they had
diversified into 20 or so families, while
carnivorous reptiles like the pelycosaurs were in
decline.