LIFE AND DEATH AT THE PERMOTRIASSIC BOUNDARY

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LIFE AND DEATH AT THE PERMO-TRIASSIC BOUNDARY
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Pelycosaur and Therapsid Evolution
In their position on the family tree of life, the
Pelycosaurs are the earliest and most primitive
members of the synapsids, the group that (in the
old classification) leads to or (in the new
classification) includes mammals.  Thus the
mammal-line split off from the rest of the
reptile line (including turtles, lizards and
snakes, crocodiles, and dinosaurs and birds) very
early.
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• Pelycosaurs were abundant at low latitudes in
  early Permian, but disappeared by mid-Permian.
• At low latitudes, Diapsid Reptiles became
  important.
• At high latitudes, Therapsids (descendants of
  pelycosaurs) and Anapsid Reptiles became
  important.

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Pelycosaur vs. Therapsid Jaw
Although Therapsids resemble pelycosaurs in some
ways, they had a much larger hole in the outer
skull armor, flange on lower jaw for muscle
attachment, and shorter heads.  All these
differences from pelycosaurs are related to more
elaborate chewing.  In addition, some had a more
upright posture.
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Dinocephalians
Skeleton of the dinocephalian Moschops about 2,5
metres long, mounted in the American Museum, New
York. The skull bones of this herbivorous reptile
have undergone enormous thickening.
Ulemosaurus svijagensis -Rjabinin, 1938-
skull Therapsida Dinocephalia
Tapinocephalidae Locality Isheevo, Tatarstan,
eastern European Russia Age Late Permian, 255
million years ago

• Dinocephalians most were large, with massive
  bodies and thick skulls.  They had a
  differentiated tooth row (incisors, canines,
  flattened back teeth). Some had bizarre horns
  (head-butting?). Most were herbivores

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Dicynodonts
Dicynodonts wide range of sizes (from rat- to
cow-sized).  They reduced all their teeth except
the canines, and probably had a horny pad for
shearing food.  They were very diverse
herbivores, with many distinct modes of life,
including some burrowers.
Reconstruction of the Late Permian South African
dicynodont Diictodon
Dicynodon trautscholdi - skull, Age Late Permian
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Theriodonts
Thrinaxodon
Theriodonts Mostly active predators. They had
longer legs, saber teeth, and much more erect
posture. Some were large, but other were small
carnivores and insectivores.
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Summary

• The fact that these animals were able to invade
  high latitudes, as well as the fact that they are
  the group from which mammals arose, raises
  questions about how they regulated their body
  temperature. 
• Similarly, their upright posture raises
  questions about patterns of activity and
  exercise. 
• These issues will be discussed later in the
  context of dinosaur temperature regulation and
  activity patterns.

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• The Paleozoic Marine Fauna
• Dominant animals
• Articulate brachiopods, bryozoans, archaic
  corals, crinoids, cephalopods
• Dominant modes of life
• Sessile, filter feeders extremely common.
• Mobile detritus feeders (Cambrian-style
  organisms) are still around.
• Mobile carnivores and herbivores are more
  common.
• Free swimming and burrowing animals still
  somewhat rare.
• Range
• These organisms became important by end
  Ordovician, drop in importance after Permian.

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Some Example of Mid to Late Paleozoic Marine
Fauna
Articulate brachiopods
Crinoids
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• The Paleozoic Marine Fauna cont.
• Diversity
• Many more groups trying each mode of life.
• Local communities have more species 9 species
  in stressed zones, 18 in near shore zones, 30 in
  open marine regions
• Tiering
• One important ecological feature of Paleozoic
  marine communities.
• Non-mobile, filter-feeding organisms are
  intercepting particles from the water column at
  different heights above the sediment-water
  interface. 
• They are chopping up space vertically, kind of
  like land plants.
•  
•  

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• The End Permian Extinction
• The Paleozoic was marked by a series of major
  extinctions, including ones in the late
  Ordovician (takes out the Cambrian Fauna), the
  late Devonian (takes out armored fish) and the
  late Permian (takes out almost everything).
• In this end Permian extinction, 95 of marine
  species died.

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The End Permian Extinction cont.

• In the oceans
• Trilobites and Archaic corals gone for good.
• Brachiopods, bryozoans, crinoids, ammonoids
  (shelled cephalopods) hit very hard.
• Snails, clams, nautiloids (another type of
  shelled cephalopod) do ok.
• Absolutely no reefs known for the next 15
  million years
• Stromatolites spread into "normal" environments
  for the first time since the Ordovician.
• On land
•    
• J ust 2 groups of therapsids survive.
• 67 of the amphibians (including all
  reptile-like amphibians) go extinct.
• 30 extinction of the orders of insects go
  extinct.

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• What happened?
•    
• Asteroid or Comet Impact
• Volcanism
• Drop in sea Level
• Stagnant Ocean Hypotheses
• Drop in oxygen content of surface ocean water
• Belch of carbon dioxide from deep ocean
•             

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• After the fall the Triassic Recovery
• Recall that prior to the extinction, in the late
  Permian, land communities at high latitudes were
  dominated by a type of Synapsid Amniote, the
  Therapsids. 
• After the extinction, it is a different story. 
• Diapsid reptiles become increasingly important
  at all latitudes.

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There are two major groups of diapsids

• 1. Lepidosaurs
• Scaly Reptiles first appear in the late
  Permian.
• Their shared novelties include a forked tongue
  and a forked penis.
• Smallish lizard-like animals.
• Active insectivores and carnivores.
• Ancestors of modern snakes and lizards. 6000
  living lepidosaur species.

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Lepidosaurs - Scaly Reptiles
Tuatara from New Zealand
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• 2. Archosaurs
• Ruling Reptile also first appear in the
  Permian.

• Their shared novelties include one hole in the
  head armor in front of the eye, and teeth that
  are in separate sockets, rather than a long
  groove.
• When they first appear, they were also small
  lizard-like animals. 
• In the Triassic, they diversify in spectacular
  fashion, in a series of pulses or waves

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Archosaurs - Ruling Reptiles
Early Archosaur (?Dinosaur), Euparkeria
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The Three Waves of Triassic Archosaurs 1. Early
Triassic "Primitive" archosaurs 2. Middle
Triassic Crocodile-like archosaurs -
Phytosaurids - Crocodiles - Aetosaurs -
Rauisuchians 3. Late Triassic Dinosaurs and
Pterosaurs
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Rhynchosaurs Beaked lizard"
Cistecephalus - late Permian period
Abundant pig-sized herbivores. Triangular head,
large area for jaw muscles, beak, 2 tooth rows
above, 1 row below, jaws close like a pocket
knife, digging claws, sprawled gait. Primitive
carnivorous archosaurs medium-to-large (up to
2m), sprawling to semi-erect gait with limbs
swung out to side. Aquatic and terrestrial forms.
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Phytosauridae - "Plant lizard"
Rutiodon
The Phytosaurs (this unfortunate name means
"plant lizards", because it was originally
mistakenly believed that petrified.mud fillings
in the jaw of the first specimen found were
herbivore teeth) were crocodile-like semi-aquatic
thecodonts that suddenly appeared and became very
abundant during the latter part of the Triassic
period.
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Aetosaurs
Neoaetosauroides engaeus from the Upper Triassic
Aetosaurs were sizeable reptiles that grew to be
one to five meters long, the average being about
three meters (10 feet). Most aetosaurs possessed
possessed a rather narrow crocodile-like body,
although some had a broad turtle-like midsection,
probably expanded to contain a large fermenting
gut. The animal was protected throughout by an
armor covering over the neck and the upper and
under surfaces of the trunk and tail. Some
species, such as Desmatosuchus, also had heavy
spikes along the shoulders and flanks. Based on
their fossils and the fact that they were
herbivores, aetosaurs probably relied on their
armor and large size rather than speed to protect
them from predators.
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Rauisuchians
Saurosuchus is not a dinosaur, but it shares
Dinosaur World with other non-dinosaurs and
dinosaurs. With teeth like these, Saurosuchus is
a meat-eater with a lot to smile about.  Notice
that these teeth are in various sizes and degrees
of wear.  Throughout their lives meat-eaters
replaced old, worn teeth, probably broken from
biting into bone.  Old meat-eaters most likely
did not die of old age but of starvation, when
their last set of teeth wore out.
SAUROSUCHUS "Lizard crocodile"