Embed Size (px)
Citation preview
2/7/2017
1
The Cambrian Explosion
635 million years ago.
Earliest animals may have been like today’s
sponges
attached to sea floor
filtered food particles from seawater.
The Cambrian Explosion
Over the next 100 million years or so, new
kinds of animals emerged.
Some were recognizable members of living
groups of animals,
Others were so bizarre that paleontologists
suspect they belonged to long-extinct
lineages.
2/7/2017
2
Cambrian
The Cambrian Explosion
Around 520 million years ago, the fossil record of
animals “explodes”.
Becomes very diverse – many kinds of animals
Many of the oldest known members of living animal
groups–including our own–appear during the
Cambrian Period.
All extant phyla are present in Cambrian fossil
record
Some animals have no modern-day
descendants
2/7/2017
3
Hallucigenia
A precursor to velvet worms --
a relationship first proposed
by Canadian paleontologist
Desmond Collins of the
University of Toronto in 2002 -
- which in turn are closely
related to arthoropods
(invertebrates with
exoskeletons, segmented
bodies and jointed limbs) and
tardigrades (aquatic
segmented micro-animals,
also known as waterbears).
These animals all belong to a
group called ecdysozoans,
animals that moult.
https://youtu.be/9-Z9Ssgb0Kg
The Cambrian Explosion
Many causes:
The Ecological Theater and the
Evolutionary Play
The Earth was undergoing drastic changes in
the millions of years leading up to this time
Increased oxygen in the oceans
Global ice ages
As the environment changed, new kinds of
animals evolved that could occupy new
niches.
The animal kingdom became both physically
and ecologically complex.
2/7/2017
4
The Cambrian Explosion
These changes in the environment set the
stage for big, active creatures to evolve.
As predators emerged, their prey became better
defended with spikes and shields;
The predators in turn became even deadlier.
Predator-Prey Coevolutionary Arms Race
Evolution of nervous systems, vision
Runaway evolution
The animals changed their environment
eg. Burrowing animals tunnelled through the
sediments on the sea floor
These changes opened up more new niches
The Cambrian Explosion
The diversity of the Cambrian had another
source: the DNA of the animals themselves.
Animals evolved genetic programs for turning
a single egg into a complex body.
With relatively minor mutations, they could
give rise to new forms.
(Niche: The sum of all the interactions an organism
has with its environment. For example, its food, its
predators, temperature, oxygen level etc.)
Maotianoascus and Ctenorhabdotus
were early relatives of today’s
jellyfish
2/7/2017
5
Wiwaxia corrugata
Wiwaxia may have been related
to today’s mollusks.
Orthozanclus, a relative of mollusks
2/7/2017
6
Jellyfish? Shrimp?
Sponge?
Parts of Anomalocaris were at first thought to be three separate animals.
Anomalocaris
2/7/2017
7
Anomalocaris
Anomalocaris
2/7/2017
8
Anomalocaris was a giant of the
Cambrian, reaching over a meter long
Diania had spiked, segmented legs that
show some similarities to those of insects
and other arthropods. Some scientists
see that as a sign of close kinship.
2/7/2017
9
Hurdia was a primitive cousin of insects
and other arthropods.
Fuxianhuia is a close relative of living
arthropods such as insects.
Opabinia had five eyes and a single
appendage extending from its head.
2/7/2017
10
Odontogriphus had a circular
mouth ringed with teeth.
Herpetogaster may be related to living
starfish and acorn worms
Pikaia was a relative of vertebrates
2/7/2017
11
Myllokunmingia may be the oldest known
vertebrate, with a skull made of cartilage and
other hallmarks of vertebrates (like us).
Banffia is baffling; it’s not clear yet what
its closest living relatives are.
Marrella splendens
