So how do dinosaurs become fossils, and what is a fossil anyway?
Hello and welcome to the Natural History of Dinosaurs. My name is Benjamin Burger,
and in this lecture at Utah State University we will explore “how to fossilize a dinosaur.”
Fossils are evidence of once living organisms (including plants and animals).
These organisms lived before the last glacial period (about 11,700 years before present).
Or prior to the modern Holocene Epoch.
Remains of life since the last glacial period (or within the Holocene) are sometimes called subfossils.
Bones of sub-fossils are often not lithofied, and appear to resemble modern bone,
whereas older true fossils have been lithofied into rock through chemical alteration
by a process called diagenesis, and this takes about 10,000 years or longer.
Many organisms can become fossils, including leaves,
bones, shells, and other hard parts of once living orgasms. Even traces left behind
such as tracks, impressions, trails, and borings can be fossilized.
Most fossils are found in sedimentary rock,
but some can be preserved in amber,
or sealed up in caves, or preserved in a volcanic ash.
There are two main types of fossils;
body and trace fossils.
Body fossils include the remains of organisms
that were once living and trace fossils
are the signs that organisms were present
(i.e. footprints, tracks, trails, and burrows,
and even dinosaur poop!).
Poop!
Most fossils are not dinosaurs
in fact dinosaurs are a very tiny number of fossils that have been found.
Most fossils are evidence of other life forms,
such as plants and other animals
such as sea creatures.
Dinosaurs are a small group of about 700 species of ancient creatures
that will explore in detail in this course.
So in a sense fossils are clues left behind that a particular organism once lived on Earth
in much the same way clues are left behind in a detective story
not all of the organism will be present
, but clues that can enable paleontologists to reconstruct the organism from fragmentary fossilized remains.
So how do you make a fossil dinosaur?
First you need a dinosaur, and then you need to kill that dinosaur.
Throughout the life span of the dinosaur
it will leave behind evidence that it lived.
Since dinosaurs were not building houses
or constructing monuments,
or even leaving behind trash
they left behind mostly foot prints, and well
poop
Once poop is fossilized it is called a coprolite
These remains can get buried and fossilized into rock
but dinosaur coprolites are a bit more rare than dinosaur foot prints,
and must be identified by key criteria.
Dr. Karen Chin at the University of Colorado is the leading expert
on coprolites, and she has developed 3 criteria for identification of coprolites:
1) Phosphate-rich
(poop has a lot of phosphate which is lost by the animal
, your poop has a lot of phosphate too.
This phosphate makes poop a great fertilizer
, in fact most commercial fertilizer is made of modern or fossilized poop.)
2) Shape,
does it have a shape that makes it look like poop, you know that
little swirly ontop.
3) Presence of bones within the poop
this is particularly good if the dinosaur was a meat eater,
but hard to explain if you are a plant eater.
This brings up and important question in dinosaur paleontology
Does dinosaur pee fossilize?
Several paleontologists have claimed that they have found fossil dinosaur pee.
These they call Urolites,
or liquid traces.
Now, these traces are a bit controversial
as to whether they really represent places that dinosaurs did a number 1,
but it does make you look more carefully at rocks that you find with strange indentations.
Fossilize footprints and trackways of much more common,
and tell you a great deal about how the dinosaurs moved around on the Earth.
In fact when scientists first found dinosaur footprints,
they thought they were ancient giant birds.
Today, there are a number of dinosaur specialists that only study dinosaur footprints,
paleontologists that study trace fossils are called Ichnologists,
and trace fossils are called Ichnofossils.
Ichno is Greek for trace or footprint.
Here is an example of my own fossilized Ichnofossil,
is a handprint I made when I was six years old in plaster,
and it shows how much I’ve grown since then.
Just got to 10, 000 years now, before it becomes a true fossil. Ummm…
But we want to fossilize a dinosaur,
Well the dinosaur then has to die.
Step 1: Death of Dinosaur.
The most destructive step toward fossilization happens in the few days after the dinosaur dies.
First the soft tissue, such as the intestine and organs rot.
During this process bones can become displacing.
Once exposed to the sunlight,
the bones began to splinter and desiccate,
and become very fragile.
Teeth will fall out of the skull and jaws.
And of course there are the scavengers who are going to carry off
the meaty portions, and break the bones to get at the marrow inside.
It is very common for a skeleton to become “disarticulated” or disassembled very quickly after death.
Step 2: Burial
One way to prevent the disarticulation of the skeleton is rapid burial.
This means that the dinosaur gets buried in sediment,
that is natural transported by either wind
(such as blowing sand in a desert),
or by water (such as in a river, or lake),
some dinosaurs have been found in marine sediments,
swept out to sea, and buried deep under water.
The process of burial will limit disarticulation of the skeleton,
although the dinosaur can continue to decompose,
even after burial,
the bones will likely stay in place.
One of the most remarkable discoveries is the articulated bones of a
Velociraptor and Protoceratops
preserved in the Gobi Desert of Mongolia.
Discovered by Polish paleontologists in 1971,
the two dinosaurs are locked together in the same pose as how they died.
The Velociraptor has its hand trapped in the tightly shut jaws of the Protoceratops,
while the sickle claw of the Velociraptor has eviscerated the belly of the Protoceratops.
Researchers discovered the top of the Protoceratops’s skull,
which eroded away,
but as they dug down into the rock,
they uncovered this deadly battle preserved over 80 million years ago.
One of the reasons that these dinosaurs were preserved
in such detail was that they were rapidly buried in wind blow sand,
or in the lee side of a sand dune.
Step 3: Diagenesis
Most of the body of the dinosaur is made up of organic compounds
composed of chains of Carbon and Hydrogen with other elements mix in,
as well as lots of water.
With heat and pressure,
, water is lost from the body, and the carbon and hydrogen start to break apart forming smaller chemical molecules,
such as methane, and other short chains of carbon-hydrogen molecules.
In the presence of oxygen,
these molecules will combust or oxidize and quickly be destroyed,
but at depth in the subsurface (lacking oxygen),
carbon molecules can migrate through the pore space of the rock,
but more rarely these organic molecules will remain behind.
Carbon films are often found in non-porous shales,
when animals die and buried in lakes or marine settings that have low oxygen values.
Bacteria are also needed for fossilization,
since they break down these carbon molecules for food,
and replace the tissue with inorganic minerals, such as hematite and calcite.
Bone and teeth are made of harder material.
Bone is calcium-sodium hydroxyl apatite mixed with organic collagen.
As groundwater moves through these harder remains of the buried dinosaur,
these harder tissues will slowly be dissolved away,
while the cavity that they occupy will be replaced with calcite (at lower temperatures)
or silica (at higher temperatures, often at deeper depths).
This process is called Permineralization,
the infilling of bone space with new minerals.
Bone can be completely replaced by new minerals, leaving only the form behind.
Molds are the impressions of these hard parts,
whereas Casts are the objects made by the infilling of the molds
of various minerals (often calcite or silica).
These objects resemble the original bone.
There is considerable debate among dinosaur paleontologists
on the preservation of soft tissue within some dinosaur remains.
Protein has been extracted from a preserved claw nail (keratin),
of a Cretaceous dinosaur from Madagascar.
But no DNA so far has been discovered from a Mesozoic dinosaur.
Many news stories of preserved soft tissue often are later disproved,
such as the supposed fossil heart announced a few years ago.
Mary Schweitzer and other researchers in Montana
have discovered flexible fibers or vessels in demineralized dinosaur bones
And a number of researchers have found proteins in bones,
in structures that resemble living osteocytes,
the cells that help grow bone,
so some of these complex protein molecules can stick around for millions of years.
Teeth are the hardest part of dinosaurs, and
often preserved without permineralization.
Enamel is a more pure crystalline lattice of calcium-sodium hydroxyl apatite
with less carbon molecules then in bone.
Hence, enamel found in dinosaur teeth is often the only original tissue preserved of a dinosaur.
Now you may have heard about dinosaur mummies,
like this amazingly well preserved fossil of Edmontosaurus discovered in Canada.
The fossils appear to have skin,
much like what you see in mummies from Egypt.
The biggest difference is that this skin,
is actually the cast of the original cavity that the dinosaur remains occupied.
The original material has been replaced by diagenesis,
with replacement minerals and other sediment.
Hence, the skin and other parts that make this dinosaur look like a preserved mummy is the cast, made from a mold.
A similar preservation of casts can be found of human remains in Pompeii,
when volcanic ash preserved a cast of the person killed 2,000 years ago.
It is important to remember that most fossils have been
significantly altered over the millions of years that they have been buried underground.
Step 4: Discovery
Most dinosaurs will remain underground to be buried so deep
were they eventual melt under the intense heat of the Earth’s interior
or they emerge on the surface through geologic uplift only to erode away forever,
never being seen by a human.
Both amateur and professional paleontologists search rocks of the right age for dinosaur bones,
and only a very few will be in the right place at the right time to be collected and studied.
There are two ways in which dinosaurs are collected in the field.
Either through a surface collection,
finding the bones eroded out on the surface,
or in a quarry,
where the bones are still within the rock and must be chiseled out.
The fossilization process is a risky game of chance,
and most dinosaur fossils are never discovered by science.
After watching this video you should be able to:
