Chordates 3 – Lepidosaurs
Tetrapoda – key adaptations
of tetrapods are air breathing
and limbs with fingers –
evolve for life in water. As
tetrapods move onto land,
they move into new niches.
Tetrapod diversity – 30,000
species (amphibia = 7250,
mammalia = 5400 species,
reptilian = 10,272 species &
aves = 10,000 species)
Amniota
Amniotes (mammals, reptiles and birds) exhibit further specialisation for living
and reproducing on land.
Amniotic Egg = amniotes differ from amphibians and fish in having an amniotic
egg. Egg encased in membranes (amnion, chorion and allantois) that both
protect the egg from drying out, and provide gas exchange, allowing embryo to
extract oxygen from air.
Internal Fertilisation = reproductive shift associated with internal fertilisation
– eggs laid on land, can’t be fertilised by releasing sperm into water. Instead,
male and female genital openings contact to exchange sperm. Often associated
by an intromittent organ – penis of mammals, turtles, crocodilians and some
birds, hemipenes (double penis) of lizards and snakes.
Loss of the Larval Stage = juvenile amniotes have direct development – skip
the larval stage seen in lungfish and amphibians, hatch out as miniature adult
with limbs and lungs – and lacking gills or a tail fin.
Skin = tetrapods lack bony scales – instead they are covered by a skin that they
can shed. In amniotes, this skin is waterproof – not to keep water out, but to
keep it in.
First amniotes = a little over 300 mya in the Carboniferous, the first amniotes
appear. Small – a few inches to a foot long. Reproductive mode lets them exploit
habitats that amphibians (who must return to water to breed) can’t. Amniotes
stage adaptive radiations – the earliest amniotes have already differentiated into
the synapsid (mammal) and sauropsid (bird-reptile) lineages.
Synapsids (mammal lineage) take the lead = in the late Carboniferous and
Permian, mammal-like reptiles (forerunners of mammals) diversified and produce
large herbivores and carnivores.
Synapsids dominate terrestrial ecosystems from the late Carboniferous
to the Permian (299-252 mya) = mammal lineage produced specialised plant-
eaters and meat eaters, which were the dominant land animals for 50 million
years. 252 mya, a massive extinction devastates the environment – the Permo-
Triassic Extinction. Massive volcanic eruptions devastated the planet, wiping out
the mammal-like reptiles.
The Mesozoic (252-66 mya) = the Age of the Reptiles. Aftermath of the
extinction sees reptiles take over and diversify. Leads to the rise of the
dinosaurs, as well as reptiles still with us today (lizards, crocodilians and turtles).
, Mammals diversify as well, but are primarily small, insectivorous/omnivorous and
nocturnal forms.
Sauropsida and
Synapsida
Reptiles and Birds.
Sauropsid diversity =
Lepidosauria 9000
species, Chelonia 300
species, Crocodylia 23
species & Aves 10,000
species
Lepidosauria:
tuatara, lizards
and snakes
Tuatara = nocturnal and inhabit cool envirobments in New Zealand,
introduction of rats by Maori wiped them out on the mainland, so they exist only
on tiny offshore islands. They have specialised jaws with teeth that fuse to the
jawbone, and shear their prey apart. Superficially lizard-like, tuataras are distant
cousins of lizards.
Triassic Origin = tuataras branch off from lizards in the Early Triassic – more or
less modern looking forms appear 240 mya. Tuataras were diverse in the Triassic
before lizards appeared, and held their own for a while, producing marine and
plant-eating forms. They declined in the Cretaceous in the face of mass
extinctions and evolution of competing lizards.
Today there are just 2 species.
<=
Squamata = lizards and snakes. The most
Tetrapoda – key adaptations
of tetrapods are air breathing
and limbs with fingers –
evolve for life in water. As
tetrapods move onto land,
they move into new niches.
Tetrapod diversity – 30,000
species (amphibia = 7250,
mammalia = 5400 species,
reptilian = 10,272 species &
aves = 10,000 species)
Amniota
Amniotes (mammals, reptiles and birds) exhibit further specialisation for living
and reproducing on land.
Amniotic Egg = amniotes differ from amphibians and fish in having an amniotic
egg. Egg encased in membranes (amnion, chorion and allantois) that both
protect the egg from drying out, and provide gas exchange, allowing embryo to
extract oxygen from air.
Internal Fertilisation = reproductive shift associated with internal fertilisation
– eggs laid on land, can’t be fertilised by releasing sperm into water. Instead,
male and female genital openings contact to exchange sperm. Often associated
by an intromittent organ – penis of mammals, turtles, crocodilians and some
birds, hemipenes (double penis) of lizards and snakes.
Loss of the Larval Stage = juvenile amniotes have direct development – skip
the larval stage seen in lungfish and amphibians, hatch out as miniature adult
with limbs and lungs – and lacking gills or a tail fin.
Skin = tetrapods lack bony scales – instead they are covered by a skin that they
can shed. In amniotes, this skin is waterproof – not to keep water out, but to
keep it in.
First amniotes = a little over 300 mya in the Carboniferous, the first amniotes
appear. Small – a few inches to a foot long. Reproductive mode lets them exploit
habitats that amphibians (who must return to water to breed) can’t. Amniotes
stage adaptive radiations – the earliest amniotes have already differentiated into
the synapsid (mammal) and sauropsid (bird-reptile) lineages.
Synapsids (mammal lineage) take the lead = in the late Carboniferous and
Permian, mammal-like reptiles (forerunners of mammals) diversified and produce
large herbivores and carnivores.
Synapsids dominate terrestrial ecosystems from the late Carboniferous
to the Permian (299-252 mya) = mammal lineage produced specialised plant-
eaters and meat eaters, which were the dominant land animals for 50 million
years. 252 mya, a massive extinction devastates the environment – the Permo-
Triassic Extinction. Massive volcanic eruptions devastated the planet, wiping out
the mammal-like reptiles.
The Mesozoic (252-66 mya) = the Age of the Reptiles. Aftermath of the
extinction sees reptiles take over and diversify. Leads to the rise of the
dinosaurs, as well as reptiles still with us today (lizards, crocodilians and turtles).
, Mammals diversify as well, but are primarily small, insectivorous/omnivorous and
nocturnal forms.
Sauropsida and
Synapsida
Reptiles and Birds.
Sauropsid diversity =
Lepidosauria 9000
species, Chelonia 300
species, Crocodylia 23
species & Aves 10,000
species
Lepidosauria:
tuatara, lizards
and snakes
Tuatara = nocturnal and inhabit cool envirobments in New Zealand,
introduction of rats by Maori wiped them out on the mainland, so they exist only
on tiny offshore islands. They have specialised jaws with teeth that fuse to the
jawbone, and shear their prey apart. Superficially lizard-like, tuataras are distant
cousins of lizards.
Triassic Origin = tuataras branch off from lizards in the Early Triassic – more or
less modern looking forms appear 240 mya. Tuataras were diverse in the Triassic
before lizards appeared, and held their own for a while, producing marine and
plant-eating forms. They declined in the Cretaceous in the face of mass
extinctions and evolution of competing lizards.
Today there are just 2 species.
<=
Squamata = lizards and snakes. The most
