Amniote Origins

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Natural Sciences 360 Legacy of Life Lecture
13 Dr. Stuart S. Sumida
Living Amphibians the Environmental
Monitors REPTILES AND THEIR RELATIVES
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Living Frogs and Salamanders (Batrachia) the
environmental monitors.
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• Possible causes of amphibian declines include
• Changes in climate - acid rain, ultraviolet
  radiation, drought, ozone layer depletion, etc.
• Loss of wetlands
• Invasive predators (such as trout and bullfrogs)
• Disease (bacteria, viruses, fungus) or parasites
• Pollution - pesticides, fertilizers, heavy
  metals, etc.

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New Discovery! A LUNGLESS FROG!
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What we used to think...
Mammals
Birds
Mammal-like Reptiles
PRIMITIVE REPTILES
Amphibians
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Um.........NO.
Mammals
Birds
Mammal-like Reptiles
PRIMITIVE REPTILES
Amphibians
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Panderichthyid Most

Reptilia Sarcoptrygians Amphibians
Diadectomorpha Synapsida (including Aves)
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Panderichthyid Most
Synapsida
Reptilia Sarcoptrygians Amphibians
Diadectomorpha (Mammals) (including Aves)
AMNIOTA (FOR SURE)
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Panderichthyid Most
Synapsida
Reptilia Sarcoptrygians Amphibians
Diadectomorpha (Mammals) (including Aves)
AMNIOTA (FOR SURE)
Amniota?
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Panderichthyid Most
Synapsida
Reptilia Sarcoptrygians Amphibians
Diadectomorpha (Mammals) (including Aves)
AMNIOTA (FOR SURE)
Amniota?
TETRAPODA
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Panderichthyid Most
Synapsida
Reptilia Sarcoptrygians Amphibians
Diadectomorpha (Mammals) (including Aves)
AMNIOTA (FOR SURE)
Amniota?
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• Amniotes have four embryonic structures that
  reside outside the embryo to help it survive
• Amnion
• Yolk sac
• Chorion
• Allantois

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Other Sarcopterygians Panderichthyids Ichthyoste
galia Dissorophoids Lissamphibia Anthracosauria
Seymouriamorpha Diadectomorpha Amniota
Sarcopterygii
Tetrapoda
The road to reptiles
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• Diadectomorpha
• No intertemporal bone like other amniotes
• Very terrestrially adapted

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Amphibia Amniota
Seymouriamorpha Diadectomorpha Synapsida
Parareptilia Captorhinidae Diapsida
Archosauromorpha
Reptilia
Amniota
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• Amniotes have four embryonic structures that
  reside outside the embryo to help it survive
• Amnion
• Yolk sac
• Chorion
• Allantois

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Amphibia Amniota
Seymouriamorpha Diadectomorpha Synapsida
Parareptilia Captorhinidae Diapsida
Archosauromorpha
Reptilia
Amniota
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Basal Synapsida (Pelycosauria) A single
opening on side of skull
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Amphibia Amniota
Seymouriamorpha Diadectomorpha Synapsida
Parareptilia Captorhinidae Diapsida
Archosauromorpha
Reptilia
Amniota
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• PARAREPTILIA Includes
• Mesosauria
• Bolosauridae
• Procolophonia
• Paraiesauria

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Mesosaurus A member of Mesosauria
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Eudibamis a member of Bolosauridae
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Eudibamus cursoris The earliest known bipedal
vertebrate From the Early Permian (280 million
years old) of central Germany.
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Bradysaurus A member of the Parieasauria
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Parieasaurs have lumpy, bumpy skulls Scutosaurus
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Common North American painted turtle
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Amphibia Amniota
Seymouriamorpha Diadectomorpha Synapsida
Parareptilia Captorhinidae Diapsida
Archosauromorpha
Reptilia
Amniota
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Basal Captorhinid Eocaptorhinus
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Amphibia Amniota
Seymouriamorpha Diadectomorpha Synapsida
Parareptilia Captorhinidae Diapsida
Archosauromorpha
Reptilia
Amniota
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Basal Diapsid Petrolacosaurus Note TWO holes
(fenestrae) on side of skull Known back to Late
Pennsylvanian
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• Diapsida includes
• Many extinct forms
• Squamata
• Archosauromorpha
• Squamata includes living lizards and snakes.

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• Squamata
• Lizards (including limbless lizards)
• Snakes

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Crotaphytus (local, collared lizard)
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Horny-toads are not toads.
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Komodo dragon largest living lizard
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Meditteranean chaemelon
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Monitor lizard
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Amphisbaenia limbless lizards
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Amphisbaenia limbless lizards
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Cobra
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Hog-nosed pit viper
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Long-nosed vine snake
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Amphibia Amniota
Seymouriamorpha Diadectomorpha Synapsida
Parareptilia Captorhinidae Diapsida
Archosauromorpha
Reptilia
Amniota
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• Archosauromorpha Includes
• Crocodilians
• Numerous other extinct groups
• Pterosauria
• Dinosaurs
• Birds

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Archosauria includes Crocodilians, Pterosaurs,
Dinosaurs (including Birds), and a variety of
other extinct groups.
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• Crocodylomorpha Still extant - known from the
  Middle Triassic to present day.
• In brief
• Low, flat skull.
• All but a few marine forms have 24 vertebrae
  cranial to the hip and 2 sacral vertebrae for
  attaching to the hip.

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Alligator mississippiensis
Note presence of bony scutes or osteoderms in
skin.
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Crocodilians are capable of a variety of types of
locomotion swimming slow-sprawling walk a
moderate speed high walk and even galloping in
some young or smaller ones.
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Nile crocodile
Some crocodilians have extremely complex social
behavior and communication.
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Reconstruction of Sarcosuchus imperator
(Supercroc) Over 40 feet long.
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The Diversity of Extinct Marine Reptiles Examples
of Convergent Evolution
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Duria antiquior
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• Mesozoic marine reptiles are not dinosaurs.
• All are a variety of diapsid reptilies.
• We will survey them from approximately more
  primitive diapsid derivatives to somewhat more
  derived diapsid derivatives.

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Amphibia Amniota
Seymouriamorpha Diadectomorpha Synapsida
Parareptilia Captorhinidae Diapsida
Archosauromorpha
Reptilia
Amniota
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Reall the Basal Diapsid Petrolacosaurus Note
TWO holes (fenestrae) on side of skull
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Petrolacosaurus A primitive diapsid
reptile Fenestrae color-coded green here
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Mesozoic Marine Reptiles Diapsida
Sauropterygia Placodontia
Nothosauria Pleisosauria
Ichthyosauria Squamata Mosasauria
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Diapsida Sauropterygia
Placodontia Nothosauria
Pleisosauria Ichthyosauria Squamata
Mosasauria
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Diapsida Sauropterygia
Placodontia Nothosauria
Pleisosauria Ichthyosauria Squamata
Mosasauria
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Placodonts were fusiform but large animals that
lived in the Middle to Upper Triassic. Similar
to manatees in the niche they filled.
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Placodus gigas (type) Large teeth and palatal
teeth indicate that it probably ate molluscs.
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Placodus gigas
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Paraplacodus
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Diapsida Sauropterygia
Placodontia Nothosauria
Pleisosauria Ichthyosauria Squamata
Mosasauria
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• Nothosauria
• Middle to Upper Triassic
• Very short snout end of skull, relatively longer
  caudal (postorbital) region of skull.
• Large, procumbent rostral (frontmost) teeth,
  often developed as fangs.

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Often have elongate necks. Humerus and femur
longer than more distal elements.
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Nothosaurus mirabilus Reconstruction of skull and
jaw musculature
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Nothosaurus reconstruction
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Diapsida Sauropterygia
Placodontia Nothosauria
Pleisosauria Ichthyosauria Squamata
Mosasauria
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• Plesiosauria
• Much larger than nothosaurs.
• Forelimbs and hindlimbs look much more similar.
• EXTREMELY elongate necks, even more so than
  nothosaurs.
• Note that despite paddle-like nature of hand
  (manus) and foot (pes), each still retains only
  five digits.

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Plesiosaurs have HYPERPHALANGY additional
segments to the digits of the fingers and toes.
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Cryptoclidus (plesiosaurid)
Plesiosaurs have HYPERPHALANGY additional
segments to the digits of the fingers and toes.
Hydrothecrosaurus (elasmosaurid)
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Cryptoclidus (plesiosaurid)
Hydrothecrosaurus (elasmosaurid)
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Cryptocleidus (about 30 meters long)
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Liopleurodon (about 80 feet long)
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Diapsida Sauropterygia
Placodontia Nothosauria
Pleisosauria Ichthyosauria Squamata
Mosasauria
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• Ichthyosauria
• Triassic to Cretaceous However, more extreme
  members of group lived in Jurassic and
  Cretaceous.
• Most highly specialized of marine reptiles. They
  converged on fish and cetacean forms.
• Highly modified skull large orbit, reduced
  cheek region, elongate snout.
• Limbs modified into flippers hyperdactyly.
• Viviperous gave birth to live young.

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Mixosaurus reconstruction

• Most highly specialized of marine reptiles. They
  converged on fish and cetacean forms.

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Highly modified skull large orbit, reduced
cheek region, elongate snout. Most highly
specialized of marine reptiles. They converged
on fish and cetacean forms.
Ichthyosaurus
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Limbs modified into flippers hyperdactyly and
hyperphalyngy.
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Juvenile at moment of birth.
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Juvenile Ophthalmosaurus
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Diapsida Sauropterygia
Placodontia Nothosauria
Pleisosauria Ichthyosauria Squamata
Mosasauria
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• Mosasaurs
• Not closely related to Sauropterygians or
  Ichthyosaurs.
• Actually highly derived members of the lizard
  family Varanidae.
• Late Cretaceous ecological replacements for
  Ichthyosauria.

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• Mosasaur Anatomy
• Extremely elongate tail, body narrower and
  slimmer than other groups surveyed. (Probably
  swam in a more eel-like fashion.)
• However, neck, remains relatively short.
• Limbs modified for steering as opposed to
  propulsion.
• Have HYPER PHALANGY, but not hyerdactyly.

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Plotosaurus, a mosasaur over 10 meters in length.