Evolution of Defensive and Weaponry
Bones
Josh Bailey and Justin Overstreet
Types of Defensive Bones
 Turtle Shell
 Bony Fish Scales
 Armadillo Plates
Question 1
 How did the turtle shell get to what it is
today?
Turtle Shell
• First shell type
structure found in
Odontochelys
• Odontochelys is at least
220 million years old.
• Shell only on bottom.
• Broadened ribs covered
by neural plates.
-The plastron evolved before the
carapace
-This ancestor shows that
broadening of ribs and
ossification of the neural plates
are the beginnings of the
carapace in the modern day
turtle
-this species was probably
marine and the shell on the
stomach was to protect it from
creatures coming up under it to
attack it.
Chinlechelys
-This turtle is
probably one of the
steps between the
Odontochelys and
Proganochelys
-Has both a carapace
and a plastron
-the carapace is very
thin compared to
more modern turtles
-the dorsal ribs are
not fully fused with
the bone overtop of
them
-Once turtles made
the move to land the
top shell was useful
to protect them from
predators
Proganochelys
-next step in
common day turtle
shell
-first arrived around
210 million years
ago
-has both the
plastron and the
carapace formed
-the ribs have fused
with the bone plates
to form the carapace
-cannot pull head
into shell to
completely protect
head
-the shell is much
thicker than
Chinlechelys
Modern day turtle
shell
-first seen in
Kayentachelys
around 190 million
years ago
-has a carapace and
plastron
-the ribs are
completely fused
with the bony layer
above it
-some modern day
turtles have the
ability to pull legs and
head into the shell
and close the shell for
complete protection
Question 2
 Where and why did bones evolve to be used
as weapons?
Bones Used as Weaponry
 Horns/Antlers
 Bones being used as
 Teeth
weapons by animals is a
very ancient tactic used for
hunting/feeding, fighting
for a mate, or just fighting
to survive
 Boney weapons such as
teeth, horns, and claws are
almost as ancient as animals
themselves
 Talons/Claws
Horns/Antlers
 Evolved many different times in




many different species
Different types have evolved even
in closely related species
Consist of a covering of keratin and
other proteins surrounding a core
of living bone
Only a male trait in many species
Evolved in species more for
intraspecific competition and
defense
Horns/Antlers (continued)
 The evolution of horns seems to
come about when the animals reach
a body size of around 15 to 18 kg,
eat a mostly folivorous diet, and
move from a closed thickly wooded
area to a more open grassland
habitat (ruminant artiodactyls)
 Antlers first showed up in a small
species of mammals about 40
million years ago when their tusks
began to disappear and were
replaced with antlers
 When horns/antlers start to show
up in a population there is strong
selection on the antlers to get
larger
Teeth
 Teeth are found in an extremely
high percentage of animals
however they evolved many
different times to take on
different forms and functions
 Tusks which are displayed by a
smaller number of species are
used for defense
 Predators have evolved large and
sharp teeth they use to hunt and
defend their territories
Teeth (continued)
 During the Jurassic period some
mammals started to evolve away
from rounded bug smashing teeth
to more sharp and pointed
carnivorous teeth
 However predatory mammals
during the Jurassic period were
forced to find their niches at night
where they could out compete
dinosaurs
 By the Tertiary period these sharper
toothed mammals were ready to
step into the place of the newly
extinct dinosaurs as daytime
predators
Talons/Claws
 Evolved many different
time in many different
species
 Used by predators for
hunting and defending
territory as well as other
animals for climbing and
simply picking things up
 Predatory birds, bears, and
big cats have some of the
most impressive
talons/claws in todays
animal kingdom
Talons/Claws (continued)
 Dinosaurs which we have fossils from
had claws which would explain why
their ancestors, birds, have the talons
they have used to perch and pick up
useful things for different aspects of
their lives
 Some dinosaurs such as velociraptor
had large and power claws which also
relate to the predatory birds of today
 Miacis was the first cat like animal
which evolved around 55 million
years ago and gave rise to the great
saber toothed cats which then evolved
into the big cats we see today with
their very impressive claws
Refrences
 http://www3.interscience.wiley.com/journal/120047176/abstract?CRETRY
=1&SRETRY=0
 The Differences Between the Sexes
Roger Valentine Short and Evan Balaban
1997
pg. 131
 Evolution of Carnivorous Mammals
R.J.G. Savage
Refrences
http://rspb.royalsocietypublishing.org/content/276/1656/507.full#sec-2
http://www.stlzoo.org/pictureview/2842.htm
Comprehensive survey of carapacial ridge-specific genes in turtle
implies co-option of some regulatory genes in carapace evolution
A geometric morphometric assessment of the effects of
environment and cladogenesis on the evolution of the
turtle shell
Development of the carapacial ridge: implications for the evolution of
genetic networks in turtle shell development
An ancestral turtle from the Late Triassic of southwestern China
http://www.amnh.org/science/papers/seaturtles.php