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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

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Evolution of defensive and weaponry bones l.jpg

Evolution of Defensive and Weaponry Bones

Josh Bailey and Justin Overstreet


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Types of Defensive Bones

  • Turtle Shell

  • Bony Fish Scales

  • Armadillo Plates


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Question 1

  • How did the turtle shell get to what it is today?


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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.


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-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.


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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


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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


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Modern day turtle shell

-first seen in Kayentachelysaround 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


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Question 2

  • Where and why did bones evolve to be used as weapons?


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Bones Used as Weaponry

  • Horns/Antlers

  • Teeth

  • Talons/Claws

  • Bones being used as 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


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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


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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


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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


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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


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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


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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


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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


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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


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