EPS SCI 17 Lecture Notes - Lecture 10: Coelophysis, Ornithischia, Dimetrodon
26 May 2018
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Lec 10: The Triassic - Convergence, Adaptation, and
Contingency
May 8
WHY DID WE LOSE THE INITIAL BATTLE?
●dinosaurs were not particularly dominant during the Triassic (though referred to as “the age
of dinosaurs”)
○not the only group in the Triassic
●mammals (synapsids) and crocodile = 2 other big groups of animals that competed with
dinosaurs to be the dominant animals on the planet
○dinosaurs only emerged as dominant group at end of Triassic → other groups
relegated to small ecological roles
CONVERGENT EVOLUTION
●convergent evolution
: the independent evolution of similar features in species of different
lineages
○creates analogous structures that have a similar form or function, but were not
present in the last common ancestor of those groups
○(Ex. bird wing vs. bat wing)
CHANGES IN DIVERSITY
●Permian
○many bizarre strange synapsids (one post-orbital fenestra) like Scutosaurus,
Inostrancevia, Dimetrodon
○share some traits with us, but not all traits
●Early Triassic
○much of this diversity disappears → only left with a couple types of animals left
■ex. Lystrosaurus
(a therapsid)
○for 35 million years, the familial diversification rate dips to only 1 additional family
every 25 million years
GEOGRAPHY IN THE TRIASSIC
●The Triassic was quite different as this time
○continents were all linked together → Pangea had started to break apart a little bit,
but still one major linked piece
●principle of lateral continuity
: most sedimentary rock units were originally deposited
over a large area, but later became isolated by erosion or faulting
○can look at different parts of the globe (regions of rock with same kinds of fossils in
them) → can piece together
○continental drift explained why similar rocks & species were found on (seemingly
random) portions of different continents → the continents were initially all
connected
CLIMATE
●weather
: short-term changes in wind, pressure, temperature, cloud cover, precipitation, etc.
●climate
: the long-term average of weather
○more stable
○ex. deserts are always deserts with a relatively low rainfall, but at specific times they
can get a lot of rain
●How do we find out climates in the past?
○historical records of climate data only go back about 400 years (longer in some
areas)
○we can use proxy data
: inference from indirect means → Examples:
■glacial deposits
■leaf shape
■tree rings
■oxygen isotopes
■etc.
●Cimate Variation Today:
○equator = hottest and wettest (ex. rainforest, tropics)
○at greater latitudes = still hot but drier (ex. deserts)
○at the poles = drier and colder
●Climate Variation in the Triassic
○most of the continents are covered in equatorial deserts
○large fluctuations in weather, due to large continents
■oceans cannot really cool down the land, to stabilize temperatures
○temperatures were 7-10 °C (13-18 °F) hotter than today
DIFFERENT ECOLOGICAL ROLES
●increased diversity
○Diictodon
= small burrowing herbivore
○Elephantosaurus
= very large herbivore
●cynognathus (“dog jaw”)
: close relative of mammals, but not actually a mammal
○does very well in the Triassic as a predator
○strong jaw
○akinetic skull (like mammals) → starting to evolve different types of teeth (starting to
differentiate between canine & molar teeth)
○small holes in top of jaw - look very similar to holes when mammals have sensory
whiskers
CRUROTARSI
●crocodiles & their relatives were part of a larger group Crurotarsi
○ankle joint that hinges in a different way → distinguishes crocodiles from relatives of
birds (synapomorphy
)
Document Summary
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