Tetrapods Characterized by - PowerPoint Presentation

Slide1

Tetrapods

Characterized by

chiridium

= muscular limb with digits

Derived

from Crossopterygian ancestors;

Tetrapods

first appear in the fossil record toward the end of the Devonian (

~

360 mya

).

First

Tetrapods

were the

Labryinthodonts

.

Terrestrial

transition may have occurred in response to:

migration to new ponds during drought periods in late Devonian

escape from aquatic predators

dispersal to new breeding ponds

or any combination of the above selective factors

Slide2

Class Labyrinthodontia

Class

Labyrinthodontia

– diagnostic vertebrae and teeth, retained bony scales

Paraphyletic stem Tetrapod group

Some attained size of crocodiles

Largely aquatic, but capable of short travels on land

Relationships uncertain, but customarily divided into 3 Orders:

Ichthyostegalia

= earliest forms in Devonian very similar to Crossopterygian ancestors, but had limbs with digits and weight-bearing limb girdles

Temnospondyli

= diagnostic vertebrae, flat skulls, many aquatic as adults, often quite large

Anthracosauria

= deep, rather than flattened skull; mostly terrestrial as adults; perhaps ancestral to Amniotes (= reptiles, birds and mammals)

Slide3

Acanthostega

Order

Ichthyostegalia

Slide4

Order

Temnospondyli

Order

Anthracosauria

Slide5

Class Amphibia

Divided into 2 Subclasses:

Class

Lepospondyli

– diagnostic vertebrae; some forms lost limbs; early Carboniferous into

Permian (350-250 mya). Generally smaller body size than in

Labyrinthodonts

Some terrestrial as adults

Class

Lissamphibia

= modern amphibians; probably not a natural (monophyletic) group – but gaps in fossil record obscure ancestry.

3

Orders:

Anura

= frogs and toads,

Urodela

= salamanders,

Gymnophiona

= caecilians – small, limbless tropical burrowers that resemble worms

Modern

amphibians are highly specialized and occur as far back as the Triassic and Jurassic Periods (

~

180 mya), so ancestry somewhat difficult to establish.

Unknown

Labyrinthodont

or

Lepospondyl

ancestors

.

Slide6

Diplocaulus

– a

Nectridian

Lepospondyl

Pantylus

,

a

Microsaur

Lepospondyl

Slide7

Caecilian

Blanchard’s Cricket Frog

N. Leopard Frog

Tiger Salamander

Lissamphibia

Slide8

Fig 3.21

– Amphibian Phylogeny

Slide9

Amniotes

First vertebrates to completely break ties to water (amphibians lay eggs in water, or at least a very moist nest

)

The

adaptation permitting complete freedom from water is the

amniotic egg

= egg in which embryo develops surrounded by a fluid-filled sac (allows direct development from embryo to adult, bypassing the larval stage) All

animals with this type of egg or this type of development are

Amniotes

(= reptiles, birds and mammals)

First amniotes included in the

Cotylosaurs

(“stem-reptiles”).

Early forms were structurally

intermediate between amphibians and later

reptiles

Probably not a monophyletic group; became

extinct in

Triassic, but

perhaps gave rise to all other reptile groups.

Initially

they were rather small animals, but later forms were as long as 2

meters

Reptiles (Class Reptilia) first appear in the fossil record in the Carboniferous (~

320 mya).

Slide10

Classification of Amniotes

Amniotes composed of two major lineages (diverged by Carboniferous):

Sauropsida

(

Reptilia

) = includes modern reptiles, dinosaurs and birds. Two reptilian Subclasses +

MesosaursSubclass

Mesosauria

Subclass

Parareptilia

Subclass

Eureptilia

Synapsida

= Lineage consisting of mammals and their ancestors,

pelycosaurs

and therapsids (mammal-like reptiles).

Slide11

Mesosaurs

Secondarily aquatic lifestyle, with paddle-like feet and long, laterally compressed tail for swimming

Primitive skull condition separates them from reptiles (in the narrow sense)

Elongate snout with long, sharp teeth that have been hypothesized to function in filter feeding or fish capture

From late Permian (

~

260 mya) of South America and Africa

Slide12

Mesosaurs

Slide13

Traditional Classification of Reptiles

Traditional classification system of reptiles based

on the number and position of temporal openings in the skull.

Formerly divided

into 4

Subclasses (based on skull type):

Anapsid = no temporal openings.

This

skull type present in

early Amniotes,

as in

Labyrinthodont

ancestors, so it is the primitive condition

.

Also present in

Cotylosaurs

and Turtles.

Synapsid

= single temporal opening in skull, situated relatively low in the skull.

Found in mammalian ancestors.

Now considered a separate Class from Reptiles.

Slide14

Traditional Classification of Reptiles

Diapsid

= 2 temporal openings in skull

Includes basal

Order

Eosuchia

(appeared in early Permian, extinct by late Triassic) and the majority of living

reptiles

Euryapsid

= one

opening high in skull (modified

from

diapsid

condition)

Includes aquatic Ichthyosaurs, Plesiosaurs and

Nothosaurs

Slide15

Fig 3.28

–

Amniote

skull types

Cotylosaurs

and Turtles

Mammal ancestors

Extinct aquatic reptiles

Living

reptiles,

Dinos

, etc.

Slide16

Current Classification of Reptiles

Two Subclasses:

Parareptilia

and

Eureptilia

Parareptilia

members allied by distinctive ear region and unique ankle-digit joint in feet

Parareptilia

includes 2 Orders:

Order

Pareiasauria

= Permian fossils only

Order

Testudinata

= Turtles

Turtles first

appear in the fossil record in the late Triassic.

Possess unique body plan with limb skeletons housed inside bony shell

Slide17

Pareiasaurus

was a large

quadruped, about

8

ft

long, with

elephant-like legs

, walking in a typically

sprawling reptilian

posture.

Its

skull had several spine- and wart-like protrusions.

Possessed

leaf-shaped teeth, ideal

for

biting through tough plant fibers, indicating

it was

an

herbivore.

Slide18

Subclass Eureptilia

Includes 3 major lineages (Infraclasses), all allied by a

diapsid

skull condition

Infraclass

IcthyopterygiaInfraclass

Lepidosauromorpha

Infraclass

Archosauromorpha

Infraclass

Ichthyopterygia

=

Ichthyosaurs

Porpoise-like

reptiles adapted for aquatic

lifestyle

Triassic

to Cretaceous

Slide19

Ichthyosaurs

Slide20

Infraclass Lepidosauromorpha

Consists of 2

Superorders

:

Lepidosauria

and

Sauropterygia Superorder

Lepidosauria

=

terrestrial

lepidosaurs

Order

Eosuchia

= late Permian/early Triassic fossil group, likely ancestral to all modern groups

Order

Sphenodonta

: Only a single living member, the Tuatara=

lizard-like from New

Zealand

Represents the last

remnant of this

Order

which first appeared in early Mesozoic (

~

200 mya

)Retains primitive Eosuchian skullOrder Squamata

= lizards, snakes, and amphisbaenians (= limbless, tropical burrowers with scales arranged in rings). Lizards = late Permian, Snakes = Cretaceous, Amphisbaenians

= Tertiary (?).

Slide21

Eosuchia

–

from

Triassic period

Eudibamus

–

from

late Permian period

Eosuchians

Slide22

Tuatara – from

New Zealand

Slide23

Komodo Dragon

Virgin Islands' amphisbaenas

Living

Squamates

Slide24

Infraclass Lepidosauromorpha

Superorder

Sauropterygia

= includes

marine

plesiosaurs and

nothosaurs – aquatic fish-eaters with flippers

Nothosaurs

= Triassic period

Long necks with flattened head

Limbs modified to form flippers

May have lived like seals

Plesiosaurs = Jurassic and Cretaceous periods

Heavy body, usually with long neck

Limbs modified to form flippers

Slide25

Nothosaur

Plesiosaur

Slide26

Infraclass Archosauromorpha

The “ruling

reptiles,” includes dinosaurs.

Basal stock was

Order

Thecodontia

– not a monophyletic groupAppear

in early

Triassic

Some

were

quadrupedal

, but some became

bipedal

Gave

rise to 4 other Orders that became dominant for the remainder of Mesozoic Era.

Order

Crocodylia = alligators and crocodiles

F

irst

appear in

mid-Triassic

Some

Cretaceous forms reached 17 meters (over 50

ft

) longOrder Pterosauria = flying reptilesFirst

appear in mid-Triassic, extinct at end of CretaceousWing

formed from skin stretched between body and extremely elongated

4

th

f

inger

. Probably capable of some flapping flight, but principally gliders.

Some

forms with a wingspan of 16 meters (50

ft

)

Slide27

Longisquama

–

a

Thecodont

Thecodont

Pterodactyl

American

Crocodile

Non-Dinosaur

Archosaurs

Slide28

Order

Ornithischia

= bird-hipped dinosaurs, pelvis superficially similar to bird pelvis.

Most

were

quadrupedal, although some became bipedalAll

were herbivores Includes

Stegosaurus, Triceratops,

Ankylosaurus

,

Duckbills

Order

Saurischia

= reptile-hipped

dinosaurs.

Includes

Apatosaurus (Brontosaurus)

– 23 meters (75 ft)

long and 30 tons,

Brachiosaurus

– 77 tons, and

Tyrannosaurus

rex

(50

ft

long, 7 tons)Early split into carnivorous (Theropods) and herbivorous (Sauropods

) groupsTheropods further split into large (

Carnosaurs

) and small-medium (Coelurosaurs).

Coelurosaurs

are most likely ancestors of birds, although some have suggested

Thecodont

ancestor

Both groups of dinosaurs appeared in Triassic and thrived during Jurassic and Cretaceous, but all extinct at end of Cretaceous

.

Infraclass

Archosauromorpha

-

Dinosaurs

Slide29

Ornithischian

Dinosaurs

Stegosaurus

Duckbill Dinosaur

Triceratops

Slide30

Tyrannosaurus

rex

Coelurosaur

Saurischian

Dinosaurs

Slide31

Classification of Class

Synapsida

Formerly considered a Subclass of Reptiles

Pelycosaurs

= appeared in late Carboniferous (

~300 mya)

Includes

“fin-backs” like

Dimetrodon

(often included in plastic dinosaur sets

)

Probably not monophyletic

Radiated

in

Permian, ancestral to Therapsids

Therapsids

= mammal-like reptiles

Appeared

in late Permian (

~

250 mya) and radiated during

Triassic

Both

carnivore and herbivore types were

presentOutcompeted by dinosaurs, so extinct by end of Triassic. But before extinction, gave rise to mammals.

Slide32

Dimetrodon

–

a

Pelycosaur

Lycaenops

– a

Therapsid

Synapsids

– note

heterodontous

teeth

in

Therapsid

Slide33

Fig 3.27

–

Phylogenetic

relationships

among the

Amniotes

Slide34

Fig 3.42

–

Phylogenetic

relationships

among the

Synapsids