First ‘reptiles’ were small and lizard-like; abundant in Permian

Characteristics of Cotylosauria (‘stem reptiles’):

(traits characteristic of amphibians / important as 1st reptiles)

1. Anapsid (A)

2. Pleurocentra formed vertebral column (R)

3. Skull high and narrow, not flat (R)

4. Skull bones similar to those of amphibians, with some loss of bones vs fishes (A)

5. Pineal opening on skull (A)

6. Lower jaw similar to amphibian (A), but with reduced number of elements (R)

6. Limbs short and stubby, with proximal elements projecting at right angles to body (A)

7. Pectoral girdle close to head; short neck (A)

8. Ilium of pelvic girdle elongated (R)

9. Reduced distal elements of limbs allows feet to point forward (R)

Amniotes began to radiate in the Carboniferous into many niches previously held by amphibians, plus new niches. The initial split was into synapsids (mammals and their relatives) and sauropsids (reptiles and birds).

Mammals branched off from other amniotes very early.

Several mammalian characteristics are ancestral.

Glandular skin (sweat, milk)

keratin in mammalian hair is similar to amphibian keratin, and is found

in association with sebaceous glands.

Urea, not uric acid

The first sauropsid diapsid reptile appeared in the fossil record in the Late Carboniferous: a small animal (60 - 70 cm long), agile, likely feeding on large insects and other arthropods

good color vision (diurnal)

ß keratin

The sauropsids split early into the parareptiles (leading to turtles) and the eureptiles (lizards, snakes, crocodilians, dinosaurs and birds).

Eureptiles split by mid-Permian into lepidosaurs (lizards, snakes) with hemipenes and archosaurs with muscular gizzard, upright stance

Continents moving closer together as amphibians arose in the Devonian.

By the late Devonian, the continents were joined into Pangea, and remained together for about 200 my.

Began to break up during the Jurassic, split into Laurasia and Gondwanaland.

Laurasia split into North America, Asia

Late Jurassic, Gondwanaland split up

By end of Mesozoic, modern continents were present.

Warm and moist during early Carboniferous

Drier and somewhat cooler into late Carboniferous, Permian

Mesozoic:

Triassic: warm and dry

Jurassic: warm and moist

Cretaceous: ditto, cooling into late Cretaceous

early to mid Mesozoic, gymnosperms were abundant: conifers, ginkgos, cycads

Cretaceous - appearance of angiosperms, establishment in mid-latitudes while Northern Laurasia and Southern Gondwana remained dominated by conifers and ferns

In the Triassic, ‘reptiles’ underwent a great adaptive radiation

* Turtles arose from the parareptile line.

* Within the synapsids, mammals arose from the mammal-like reptiles.

The main evolutionary trend during the Mesozoic was the huge radiation of diapsids.

The diapsids are a monophyletic group

- including the dinosaurs, pterosaurs and marine reptiles of the Mesozoic

- the living crocodilians, birds & squamates (lizards and snakes).

They are characterized by the two fenestrae or openings in the temporal region of the skull, although the fenestrae are modified in some groups (as seen in the lab).

Early Triassic diapsids:

* The early diapsids include Euparkeria, bipedal, 150 cm long

* Rhynchosaurs were the most abundant Triassic diapsids, making up >50% of all terrestrial vertebrates

2 meters long, powerful beaked jaws; chewed tough, seedless vascular plant flora

The diapsids split into two groups: the Archosauromorpha and the Lepidosauromorpha.

The Archosauromorpha include the crocodilians (Crurotarsi), pterosaurs, dinosaurs and birds.

The Lepidosauromorpha include the plesiosaurs and the ichthyosaurs and the living Lepidosauria ( the tuatara Splenodon and the squamates).

Phytosaurs were successful Triassic crocodile-like reptiles. They were outcompeted and eventually driven extinct by the crocodiles, who became very diverse by the Cretaceous.

The largest crocodiles were amazingly large: Deinosuchus (terrible crocodile) from the Cretaceous had a skull 2 m long, suggesting a total length of 12 - 15 m.

The crocodilians survived the Cretaceous extinctions: 21 living species, including alligators, caimans, crocodiles and the gharial.

Pterosaurs were very successful throughout the Jurassic and Cretaceous, ranging from sparrow size to the huge Quetzalcoatlus with a wingspan of 13 m.

** Pterodactylus slide and Pteranodon fossil

4th finger very elongated, with supportive membrane anchored to side of body and hind leg

Hollow long bones

Well developed sternum for pectoral muscle attachment

Long neck, teeth, other fingers

Large eyes, large cerebellum, poor olfaction

Most famous archosaurs were the dinosaurs: Saurischia and Ornithischia.

primarily bipedal, secondarily quadrupedal

Increased locomotor efficiency with bipedalism

Increased specialization and diversity in some dinosaurs with new roles for forelegs (e.g. seizing prey)

included Theropoda

carnivorous bipeds with mobile, S-shaped necks

bipedal

*T. rex was 15 m long, 6 m high

huge head with serrated 15 cm long teeth, with bacterial flora

large bony arches with huge elaborate fenestrae

and Sauropodomorpha

quadrupedal ‘long-necked’ herbivores

could stand vertically (e.g. Barosaurus in NY Natural History museum)

* Diplodocus

long necks allowed browsing on tall conifers

Jurassic and Cretaceous sauropods were the largest terrestrial vertebrates

25 m long

20,000 to 50,000 kg

1. Diplodocids

long necks with 15 cervical vertebrae

long, whiplash tails with 80 caudal vertebrae

short front legs, tails in air, elongate skulls with teeth at front of mouth

* gastroliths

* Mamenchisaurus

2. Camarasaurids

12 cervical vertebrae, 50 caudal vertebrae, no whiplash tails

* Brachiosaurus, with long forelimbs

Very heavy; large vertebrae with open structure

* Apatosaurus cervical vertebrae.

Great diversity of herbivores, with horny beaks (not teeth) at front of mouth

Three groups:

1. Armoured dinosaurs

stegosaurs and ankylosaurs: quadrupeds

* Ankylosaurs had osteoderms (bones embedded in skin) fused into shield-like pieces. Bony eyelids, bony club-like tails

2. Ornithopods (‘duck-billed dinosaurs")

* Corythosaurus

* Lambeosaurus

10 m long, 10,000 kg

resonating crests, specialized cheek teeth with serrated edges

4 tooth rows, each with 40 teeth combine to form a massive tooth plate

Several rows of replacement teeth

several hundred teeth in use, several thousand teeth in mouth

Increased diversity and abundance with rise of angiosperms, decline of sauropods

* Maiasaura

3. Pachycephaloaurs and ceratopsians

frill over neck, parrot like beak

battery of shearing, knife-like teeth vs crushing dentition of duckbills

* Psittacosaurus

include icthyosaurs and plesiosaurs

* Icthyosaurus fore and hindlimbs

vertebral column into lower lobe of tail

extinct during Cretaceous, before dinosaurs

Radiation of squamates during mid to late Cretaceous

Most modern lizard groups arose by late Jurassic

3000 species today, from 3 cm geckos to Komodo dragon

Snakes appeared by late Cretaceous

2500 species from 10 cm to 10 m long

lost pelvic girdle

Some snakes have hollow fangs with venom

e.g. rattlesnakes with tubular fangs that can be

* (69) erected for strike

* (70) folded away within mouth

forked tongues with widely spaced tips

‘bino-olfaction’

left lung reduced or lost

kidneys and gonads displaced

* python skull - very complex, with flexible joints

two halves of jaw joined by extensible tissues, can separate widely

upper and lower jaws can move backwards and forwards

left and right sides of jaw can move independently

reaches out alternately with right and left halves to draw prey into mouth; kill prey by constriction

recurved teeth

5.5 m python swallowed a leopard.