T05 Origin of Amniotes

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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?

(3) – _________

(4) – _________

� What is the sister group of Amniota?

� What taxa comprise the Amniota?

Pough et al 2004, Fig 2-1

Where are Amniotes on the

vertebrate phylogeny?

Benton 1997 Fig 4.21

What are some stem Amniotes?

� Palaeontological tree:

� Anthracinosauria, Seymouriamorpha, and Diadectomorpha as extinct outgroups to Amniotes

� Split between Amniota and Amphibia ~360 Mya


� “_________________”

� Anthracinosauria

� Seymouriamorpha

� Diadectomorpha

� Diverse and terrestrial

� Mainly predators

What are some stem Amniotes?


� Synapomorphies

� ______________ & associated membranes

� __________ fertilization

� ____________ maxillary teeth

� Various other skull and limb characters

What is an Amniote? The Amniotic Egg

� Contains extraembryonic membranes (4):

� Amnion

� Chorion

� Allantois

� Yolk sac

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The Amniotic Egg

� __________

� Surrounds embryo

� Forms space filled with amniotic fluid

� ______ exchange

� _________ embryo

� Dessication

� Concussion

� Chorion

� Allantois

� Yolk sac

The Amniotic Egg

� Amnion

� ___________

� Outer-most membrane

� Forms placenta in placental mammals

� Allantois

� Yolk sac

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

� Yolk sac

The Amniotic Egg

� Amnion

� Chorion

� Allantois

� _____________

� Filled with yolk, which is the nutrient source for the embryo

� Shrinks as yolk is used up

The Amniotic Egg

� What about the shell?

� The other membranes

� Form outside embryo

� Connected to embryo

� The shell is deposited by the _____________

� Can be calcified and hard or leathery and soft

� Involved in:

� _____________

� _____________ of the embryo

Photo © KP Bergmann

� Amphibians began moving away from the water

� Many are terrestrial

� However:

� Skin is still highly _______________ to gases and water

� Reproduction is mainly limited to __________

Photos © KP Bergmann, PJB

What changes were involved with the

transition to dry habitats?

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� Amniote lifecycle ______________ of water

� Many live in very dry habitats

� Facilitated mainly by adaptation of the:

� ________ (amniotic)

� ________

Photos © PJB



� Adaptations of the Egg

� Amnion, Chorion, Shell

� Protect embryo from _____________

� Forces are more jarring on land

� Protect embryo from _____________

� Less permeable to water

Photo © KP Bergmann



� Adaptations of the skin:

� ________________

� Deposition of __________ in epidermis

� Evolved independently in several groups

� ________, feathers, hair

� All act to limit water loss

Photo © PJB



� Three different amniote conditions

� 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

What are the three main groups of Amniotes?

� _____________� No temporal fenestrae

� _____________� One temporal fenestra

� Surrounded by postorbital, jugal and squamosal bones

� _____________� Two temporal fenestrae

� Lower one

� Homologous to synapsid

� Upper one

� Surrounded by postorbital, squamosal and parietal bones

What are the three main groups of Amniotes? 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


Synapsida

Anapsida

Diapsida

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Biodidac

What are the three main groups of Amniotes?

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?

Pough et al 2004, Fig 2-1Synapsida Anapsida Diapsida

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� Which condition is ancestral?� ___________

� ________________ ________________

� Derived?� A: ______________

� B: ______________



� What implications do the placements of Testudines (A or B) have on the evolution of the anapsid condition?

� A:

� B:



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� What kinds of data might be brought to bear on this problem?

� _________________

� _________________

� _________________

� Each has been used and says something slightly different…



� Traditional hypothesis: A

� Mainly based on extant taxa and ____________ data

� Includes only some fossil taxa

� Assumes that all ____________ are related



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� Traditional hypothesis: A

� Basal anapsids

� “Parareptiles”

� Pareisaurs

� Procolophids

Benton Fig 5.15


� Hypothesis B:

� Based on extensive fossil sampling and no a priori assumptions of relationship

� Testudines have a ___________________ anapsid condition

� ______________ with “Parareptiles”

� Sister to Sauropterygia

Pough et al. Fig 2-9


� Hypothesis B:

� Who are the sauropterygians?

� Plesiosaurs

� Ichthyosaurs

� Aquatic

� Only ___________ temporal fenestrae

Benton Fig. 6.7


� Hypothesis C?

� 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

Modified from Pough et al. Fig 2-9

A

Testudines

Testudines

B

C


� So, where do Testunides fit in?

� ________________

� Within the _______

� Molecular and morphological data suggest convergence with “Parareptiles”

Modified from Pough et al. Fig 2-9

A

Testudines

Testudines

B

C



� Who are the Amniota?

� _____________

� _____________

� _____________

� Crocodilians

� Birds

� _____________

� Rhynchocephalia

� Squamata

� Snakes

� Lizards

� Amphisbaenia


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� Mammalia synapomorphies:

� Synapsid

� Atlas vertebra

� 3+ sacral vertebrae

� ___ cervical vertebrae

� _________

� Mammary Glands

� Etc.


� Mammalia

� Not dealt with further in this course

Photos PJ Bergmann



� Reptilia (5)

� Includes the remaining

amniotes to be

monophyletic

� Without birds is ______________

� Many obscure

synapomorphies

� They have _________

(even birds – on feet)



� Archosauria synapomorphies:

� Muscular Diaphragm

� 2 ventricles in heart

� ______________

� No urinary bladder

� No vomeronasal organ


Nature 421, 335 - 340 (2003)

� Aves (Birds)

� Birds are dinosaurs, & dinosaurs are Archosaurs

• Aves have many synapomorphies:• No teeth• Wings• Feathers

(shared with some dinos)

• Not covered further in this

course


� Reptilia

� Lots of diversity

� ~8000 spp. without birds

� Online Reptile database: http://www.reptile-database.org/

Testudines 300

Rhynchocephalia 2

Squamata 7,750

Crocodylia 23

Aves 8,700

TOTAL ~ 17,000

Photos © PJB & KP Bergmann


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T05 Origin of Amniotes

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