8/19/2013
Topic 5: The Origin of Amniotes
Where do amniotes fall out on the
vertebrate phylogeny?
What are some stem Amniotes?
What is an Amniote?
What changes were involved with
the transition to dry habitats?
What are the three main groups of
Amniotes?
How are Amniote taxa related?
Where are Amniotes on the
vertebrate phylogeny?
(3) – _________
(4) – _________
What is the sister
group of Amniota?
What taxa comprise
the Amniota?
Pough et al 2004, Fig 2-1
What are some stem Amniotes?
Palaeontological tree:
Anthracinosauria, Seymouriamorpha, and
Diadectomorpha as extinct outgroups to Amniotes
Split between Amniota and Amphibia ~360 Mya
What are some stem Amniotes?
“_________________”
Anthracinosauria
Seymouriamorpha
Diadectomorpha
Diverse and terrestrial
Mainly predators
Benton 1997 Fig 4.18
Benton 1997 Fig 4.21
The Amniotic Egg
What is an Amniote?
Synapomorphies
______________ &
associated membranes
__________ fertilization
____________ maxillary
teeth
Various other skull and
limb characters
Contains
extraembryonic
membranes (4):
Amnion
Chorion
Allantois
Yolk sac
Pough et al 2004, Fig 2-1
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The Amniotic Egg
__________
Surrounds embryo
Forms space filled
with amniotic fluid
______ exchange
_________ embryo
The Amniotic Egg
Amnion
___________
Dessication
Concussion
Chorion
Allantois
Yolk sac
Allantois
Yolk sac
The Amniotic Egg
The Amniotic Egg
Amnion
Chorion
____________
Sac formed from
posterior part of GI tract
Collects ___________
during development,
growing as it fills
Involved in formation of
_______________ in
placental mammals
Amnion
Chorion
Allantois
_____________
Filled with yolk, which
is the nutrient source
for the embryo
Shrinks as yolk is used
up
Yolk sac
What changes were involved with the
transition to dry habitats?
The Amniotic Egg
Outer-most membrane
Forms placenta in
placental mammals
What about the shell?
The other membranes
The shell is deposited by
the _____________
Can be calcified and hard
or leathery and soft
Involved in:
Form outside embryo
Connected to embryo
Amphibians began
moving away from the
water
Many are terrestrial
However:
_____________
_____________ of the
embryo
Photo © KP Bergmann
Skin is still highly
_______________ to
gases and water
Reproduction is mainly
limited to __________
Photos © KP Bergmann, PJB
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What changes were involved with the
transition to dry habitats?
Amniote lifecycle
______________ of
water
Many live in very dry
habitats
Facilitated mainly by
adaptation of the:
What changes were involved with the
transition to dry habitats?
Adaptations of the Egg
Amnion, Chorion, Shell
Protect embryo from
_____________
Forces are more
jarring on land
Protect embryo from
_____________
Less permeable to
water
________ (amniotic)
________
Photo © KP Bergmann
Photos © PJB
What changes were involved with the
transition to dry habitats?
Adaptations of the skin:
________________
Three different amniote conditions
Deposition of
__________ in
epidermis
What are the three main groups of Amniotes?
Evolved independently
in several groups
________, feathers, hair
All act to limit water loss
Different patterns of temporal fenestration
Temporal region of the skull is posterior to the orbit
A fenestra is an opening without a structure
running through it (L. – “window”)
An~ none
Syn~ one
Di~ two
Photo © PJB
What are the three main groups of Amniotes?
_____________
_____________
No temporal fenestrae
What are the three main groups of Amniotes?
Synapsida – _____________ and stem mammals
Anapsida – ______________ and stem turtles
Diapsida – Archosauria (birds & crocodilians), Lepidosauria
(squamates and rhynchocephalians) and various stem
groups
One temporal fenestra
Surrounded by postorbital,
jugal and squamosal bones
_____________
Two temporal fenestrae
Lower one
Upper one
Homologous to synapsid
Synapsida
Anapsida
Diapsida
Surrounded by postorbital,
squamosal and parietal
bones
Benton 1997 Fig 5.18
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What are the three main groups of Amniotes?
Biodidac
How are Amniote taxa related?
Which condition is
ancestral?
Derived?
What implications do the
alternative placements of
Testudines (A or B) have
on the evolution of the
anapsid condition?
What kinds of data might
be brought to bear on this
problem?
Synapsida
Anapsida
Diapsida
Pough et al 2004, Fig 2-1
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How are Amniote taxa related?
Which condition is
ancestral?
___________
________________
________________
Derived?
A: ______________
B: ______________
Synapsida
Anapsida
Diapsida
Pough et al 2004, Fig 2-1
How are Amniote taxa related?
What implications do the
placements of Testudines
(A or B) have on the
evolution of the anapsid
condition?
A:
B:
Synapsida
Anapsida
Diapsida
Pough et al 2004, Fig 2-1
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How are Amniote taxa related?
What kinds of data
might be brought to
bear on this problem?
_________________
_________________
_________________
Each has been used
and says something
slightly different…
Synapsida
Anapsida
Diapsida
Pough et al 2004, Fig 2-1
How are Amniote taxa related?
Traditional
hypothesis: A
Mainly based on
extant taxa and
____________ data
Includes only some
fossil taxa
Assumes that all
____________ are
related
Synapsida
Anapsida
Diapsida
Pough et al 2004, Fig 2-1
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How are Amniote taxa related?
Traditional
hypothesis: A
How are Amniote taxa related?
Hypothesis B:
Based on extensive
fossil sampling and no
a priori assumptions of
relationship
Testudines have a
___________________
anapsid condition
______________ with
“Parareptiles”
Sister to Sauropterygia
Basal anapsids
“Parareptiles”
Pareisaurs
Procolophids
Pough et al. Fig 2-9
Benton Fig 5.15
How are Amniote taxa related?
Hypothesis B:
How are Amniote taxa related?
What do __________
data have to say?
Limitation: no ______
_____ can be included
Testudines are placed
within ____________
(support for B)
BUT: Testudines
cluster with the
___________, not the
Lepidosauria
Who are the
sauropterygians?
Plesiosaurs
Ichthyosaurs
Aquatic
Only ___________
temporal fenestrae
B
Hypothesis C?
C
Testudines
A
Testudines
Modified from Pough et al. Fig 2-9
Benton Fig. 6.7
How are Amniote taxa related?
How are Amniote taxa related?
B
So, where do
Testunides fit in?
________________
Within the _______
Molecular and
morphological data
suggest
convergence with
“Parareptiles”
C
Testudines
Who are the Amniota?
_____________
_____________
_____________
Crocodilians
Birds
_____________
Rhynchocephalia
Squamata
A
Snakes
Lizards
Amphisbaenia
Testudines
Modified from Pough et al. Fig 2-9
Pough et al 2004, Fig 2-1
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How are Amniote taxa related?
Mammalia
synapomorphies:
Synapsid
Atlas vertebra
3+ sacral vertebrae
___ cervical vertebrae
_________
Mammary Glands
Etc.
How are Amniote taxa related?
Mammalia
Not dealt with further
in this course
Photos PJ Bergmann
Pough et al 2004, Fig 2-1
How are Amniote taxa related?
Reptilia (5)
Includes the remaining
amniotes to be
monophyletic
Without birds is
______________
Many obscure
synapomorphies
How are Amniote taxa related?
Archosauria
synapomorphies:
They have _________
(even birds – on feet)
Muscular Diaphragm
2 ventricles in heart
______________
No urinary bladder
No vomeronasal organ
Pough et al 2004, Fig 2-1
Pough et al 2004, Fig 2-1
How are Amniote taxa related?
Aves (Birds)
Birds are dinosaurs, & dinosaurs are Archosaurs
How are Amniote taxa related?
Reptilia
• Aves have many
synapomorphies:
• No teeth
• Wings
• Feathers
(shared with
some dinos)
Lots of diversity
~8000 spp. without
birds
Online Reptile
database:
http://www.reptiledatabase.org/
Testudines
300
Rhynchocephalia
2
Squamata
7,750
Crocodylia
23
Aves
8,700
TOTAL
~ 17,000
• Not covered
further in this
course
Photos © PJB &
KP Bergmann
Nature 421, 335 - 340 (2003)
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