Archosauromorphs and birds
1. Chelonia – Turtles & Tortoises
o Chelonia: freshwater, marine and terrestrial. Plant-eaters,
carnivores, omnivores. Modest diversity – 300 species. 14 different
families, most originate in the age of the dinosaurs.
o Trionychidae – softshells, emydidae – pond turtles, chelonoidea –
sea turtles, testudinidae – tortoises, chelydridae – snapping turtles,
pleurodira – sideneck turtles.
o Armour: turtles are heavily armoured. The top of the shell
(caracpace) is composed primarily of the rib cage, with additional
bones added around the edge. Large, tough scales cover the hard
bone. The bottom of the shell is composed of belly ribs (gastralia).
Arms, legs, tail and head can be retracted inside the shell.
o Evololution: successful, ancient design. Turtles go back over 200
million years – early turtles were terrestrial. Emerge after Permian-
Triassic extinction.
2. Crocodilia – Crocodiles, Alligators, Caimans & Gharials
o 23 living species: crocodiles – 13 species, alligators – 2 species,
caimans – 6 species, gharial – 2 species.
o Large bodied: living crocodilians are all relatively large bodied.
Small species like the Chinese Alligator or Dwarf Crocodile are 5 feet
and 50 lbs, the Saltwater Crocodile is up to 22 feet and 4000
pounds.
o Semiaquatic: highly specialised for an aquatic lifestyle. Flattened,
oarlike tail for sculling. Webbed feet for swimming. Massive bones
help them sink to the bottom. Eyes and nostrils sit atop the head,
letting crocodiles breathe and look for food while the body remains
submerged. Crocodiles (but not alligators) have salt glands – they
can excrete excess salt, which gives them the ability to drink
seawater.
, o Predators: apex predators, tend to feed on a wide range of food
items – insects, fish, crustaceans, molluscs, turtles and other
vertebrates – taking larger prey as they grow larger. Being large,
heavily armed and heavily armoured, they have few predators of
their own. As a result, crocodilians have long lifespans. They do
have one very dangerous predator, however…
o Cannibalism: the biggest threat to a crocodilian is another
crocodilian. Cannibalism probably serves multiple purposes: a)
source of protein, b) eliminates competitors for food, c) eliminates
the offspring of others from the gene pool. Yet crocodilians are not
entirely heartless…
o Parental Care: females build nests of mud and vegetation – rots
and produces heat to incubate the eggs. Females guard the nest
and, when the eggs hatch, dig up the hatchlings and carry them to
water. Female then guards her offspring. Similar, although more
elaborate parental care is seen in the closest living relatives of the
crocodiles – the birds. The implication is that this habit is inherited
from a common ancestor living in the early Triassic, 250 mya.
o Once much more diverse: crocodilians grew much larger in the
past (40-foot long crocodilians appeared several times). Climate was
much warmer at this time, which may have allowed them to grow
rapidly and achieve giant size.
o Marine crocodilians: in Jurassic and early Cretaceous, marine
Geosauridae (crocodilians with flippers and a shark-like tail) were
major marine predators. Another group (Dyrosauridae) were
moderately successful in the Late Cretaceous, and then exploded in
the early Cenozoic to exploit niches left vacant by the extinction of
the mososaurs. Marine crocodiles declined as the planet entered the
ice age.
o Terrestrial crocs: the aquatic crocs are just one branch of a
formerly diverse tree, however. In the Late Cretaceous, small cat-
sized crocs prowled the sands of Mongolia. And as recently as the
Eocene, 35 mya, terrestrial, predatory crocs hunted in the Pampas
of South America (again, they disappear when the climate cools).
Although many were carnivores, others were omnivores, or even
herbivores. The pug0snouted Simosuchus, from the Late Cretaceous
had leaf-shaped teeth like an iguana – and adaptation for chewing
leaves. The modern crocs are a specialised offshoot of this diverse
radiation.
o Triassic Crocodilians: crocodilians hit their peak in the Triassic,
252-201 mya, when they radiated to take the place of mammal-like
reptiles. They produced armoured herbivores, bipedal, ostrich-like
plant eaters, tyrannosaur-like meat eaters and agile, greyhound-like
pursuit predators. They actually rivalled Triassic dinosaurs in
diversity. Massive eruptions at 200 mya – the break-up of Gondwana
1. Chelonia – Turtles & Tortoises
o Chelonia: freshwater, marine and terrestrial. Plant-eaters,
carnivores, omnivores. Modest diversity – 300 species. 14 different
families, most originate in the age of the dinosaurs.
o Trionychidae – softshells, emydidae – pond turtles, chelonoidea –
sea turtles, testudinidae – tortoises, chelydridae – snapping turtles,
pleurodira – sideneck turtles.
o Armour: turtles are heavily armoured. The top of the shell
(caracpace) is composed primarily of the rib cage, with additional
bones added around the edge. Large, tough scales cover the hard
bone. The bottom of the shell is composed of belly ribs (gastralia).
Arms, legs, tail and head can be retracted inside the shell.
o Evololution: successful, ancient design. Turtles go back over 200
million years – early turtles were terrestrial. Emerge after Permian-
Triassic extinction.
2. Crocodilia – Crocodiles, Alligators, Caimans & Gharials
o 23 living species: crocodiles – 13 species, alligators – 2 species,
caimans – 6 species, gharial – 2 species.
o Large bodied: living crocodilians are all relatively large bodied.
Small species like the Chinese Alligator or Dwarf Crocodile are 5 feet
and 50 lbs, the Saltwater Crocodile is up to 22 feet and 4000
pounds.
o Semiaquatic: highly specialised for an aquatic lifestyle. Flattened,
oarlike tail for sculling. Webbed feet for swimming. Massive bones
help them sink to the bottom. Eyes and nostrils sit atop the head,
letting crocodiles breathe and look for food while the body remains
submerged. Crocodiles (but not alligators) have salt glands – they
can excrete excess salt, which gives them the ability to drink
seawater.
, o Predators: apex predators, tend to feed on a wide range of food
items – insects, fish, crustaceans, molluscs, turtles and other
vertebrates – taking larger prey as they grow larger. Being large,
heavily armed and heavily armoured, they have few predators of
their own. As a result, crocodilians have long lifespans. They do
have one very dangerous predator, however…
o Cannibalism: the biggest threat to a crocodilian is another
crocodilian. Cannibalism probably serves multiple purposes: a)
source of protein, b) eliminates competitors for food, c) eliminates
the offspring of others from the gene pool. Yet crocodilians are not
entirely heartless…
o Parental Care: females build nests of mud and vegetation – rots
and produces heat to incubate the eggs. Females guard the nest
and, when the eggs hatch, dig up the hatchlings and carry them to
water. Female then guards her offspring. Similar, although more
elaborate parental care is seen in the closest living relatives of the
crocodiles – the birds. The implication is that this habit is inherited
from a common ancestor living in the early Triassic, 250 mya.
o Once much more diverse: crocodilians grew much larger in the
past (40-foot long crocodilians appeared several times). Climate was
much warmer at this time, which may have allowed them to grow
rapidly and achieve giant size.
o Marine crocodilians: in Jurassic and early Cretaceous, marine
Geosauridae (crocodilians with flippers and a shark-like tail) were
major marine predators. Another group (Dyrosauridae) were
moderately successful in the Late Cretaceous, and then exploded in
the early Cenozoic to exploit niches left vacant by the extinction of
the mososaurs. Marine crocodiles declined as the planet entered the
ice age.
o Terrestrial crocs: the aquatic crocs are just one branch of a
formerly diverse tree, however. In the Late Cretaceous, small cat-
sized crocs prowled the sands of Mongolia. And as recently as the
Eocene, 35 mya, terrestrial, predatory crocs hunted in the Pampas
of South America (again, they disappear when the climate cools).
Although many were carnivores, others were omnivores, or even
herbivores. The pug0snouted Simosuchus, from the Late Cretaceous
had leaf-shaped teeth like an iguana – and adaptation for chewing
leaves. The modern crocs are a specialised offshoot of this diverse
radiation.
o Triassic Crocodilians: crocodilians hit their peak in the Triassic,
252-201 mya, when they radiated to take the place of mammal-like
reptiles. They produced armoured herbivores, bipedal, ostrich-like
plant eaters, tyrannosaur-like meat eaters and agile, greyhound-like
pursuit predators. They actually rivalled Triassic dinosaurs in
diversity. Massive eruptions at 200 mya – the break-up of Gondwana
