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C O U R S E 
Paleontology: Early Vertebrate Evolution
Alison Murray, University of Alberta
C O U R S E   L E C T U R E 
Vertebrate Environments
Notes taken on February 24, 2017 by Edward Tanguay
what kinds of environments the earliest vertebrates inhabited
paleontology is blending of
to understand how and why certain features evolved, we need to interpret the rocks that fossils are found in
this tells us what kinds of environments the animals lived in
depositional environments on land are more common
depositional environments in the ocean are less common
since life began in the oceans, we need to understand this habitat and its depositional environments
most common place to find fossils of marine organisms like fish, corals, crustaceans, or clams
the continental shelf
in the shallow waters off the coasts of continents
beaches are high energy environments
delicate fossils can be broken and eroded
continental slopes and the deep ocean are hard for us to reach
how to tell what the environment was like when the fossil animals were alive
geologists interpret rocks in two ways
what the rock is made of
what kind of sedimentary structures were preserved when the rock was deposited
there are also fossils in carbonate rocks
made up of at least 50% calcium carbonate
mostly limestone
limestone is made up of the shells of marine animals such as mollusks
key fossil localities
most energetic near their sources in highlands
most rivers transport and deposit sand and mud
some with strong currents move gravel
lens shaped sand or gravel channel deposits are an indicator of a fluvial environment
as rivers travel over gradually flatter land, change to meandering rivers with shallower, wider channels
able to transport less material
rivers end up at an ocean, sea, or large lake
empties into sea at a delta or an estuary
here you find carbonate sediments
water here is brackish, i.e. not as salty as ocean water
some animals and plants are adapted to live in this type of water
heavily influenced by actions of the tidal current which produces sedimentary structures
herringbone cross-stratification
alternating parallel layers
this means the sediments were probably deposited in a tidal environment
horizontal beds are called cross beds
inclined layers are cross-strata
sediment was being deposited fast in order to preserve the cross-stratification
waves also affect cross-stratificaton
wave base
deeper during storms
shallower during fair weather
many fossil localities were deposited below storm wave base
usually have shales
rocks with the most ripples are from the shallowest environment
barrier islands
small point of land running into the sea, or a long, narrow shoal extending from the shore into the sea
areas of quiet, low-energy water
fine sediments can be deposited here
water evaporates and concentrates minerals
can become saltier than ocean water
forms evaporate
calcium carbonate
calcium sulfate
sodium chloride
usually what we mean when we say salt
interbedded with mud
if we find these minerals, there is a good chance we are looking at what used to be a shallow lagoon
good environments for preserving fossils
because the water is still
are still and salty
not a lot of things can live in them
becomes anoxic, i.e. little oxygen
this means if an animal falls into the lagoon and sinks to the bottom, there aren't many animals living their to scavenge the carcass
small grain size tells us that the waters were very still
good for preserving details
here we find some of the most exquisite fossils every found have come from lagoon or lagoon-like environments
deeper continental shelf environments
Man on the Hill
preserves 415 million year old vertebrate fossils
accumulated in deep water on the continental shelf
the environment was close enough to land for fine sediments to be deposited
but far enough offshore that most of the sedimentation was carbonate
ripples became less common
carbonate platforms
where you find marine fossils
the photic zone
where light penetrates
a few centimeters to 200 meters deep, depending on the clarity of the water
float and form the basis of the marine food chain
here we find reefs
corals thrive in nutrient-rich water
the steeper the slope, the less stable
plate corals
make the most use of the least light
in deeper waters, chances of finding vertebrate fossils becomes relatively small
deposits that can form in many environments
occur in deep water
Burgess Shale
most famous Cambrian fossil locality area in the world
famous for the exceptional preservation of the soft parts of its fossils
likely deposited by a turbidity current
ocean floor
here we don't find many vertebrates
find mostly skeletons of plankton
these animals are pelagic
spend their lives floating in the water column
fine-grained silica-rich microcrystalline or cryptocrystalline sedimentary rock that may contain small fossils
most of the sea floor in earth's history has been melted and recycled into new crust, taking its fossils with it
the old ocean crust still in today's ocean is about 150 million years old
not that old compared to the oldest continental rocks
over 4 billion years old
when an oceanic plate means a continental plate, the oceanic plate sinks
the oceanic crust is subducted beneath the continental crust
most marine fossils come from continental shelf deposits
when oceanic plates meat a continental plate, some contents get scraped off