Marine Life in the
Mesozoic Era
No actual dinosaurs were aquatic but there were many sea-dwelling
animals living in the Mesozoic Era including a variety of toothed
giant reptiles ruling the sea while the dinosaurs ruled the land.
Plesiosaurs
Plesiosaurs were air breathing, longnecked, finned reptiles who first appeared
in the latest Triassic Period, and they
were particularly common in the Jurassic
Period, all over the world. They had a
broad, flat body with a short tail, with
four long flippers which appeared to ‘fly’
through the water.
They were among the first fossil reptiles
discovered, and since then more than
a hundred different species have been
described. There were two main types
– those with a ‘plesiosauromorph’ build,
Kronosaurus
Thalassomedon
Mosasaurs
with small heads and extremely long
necks who caught small sea animals and
were relatively slow, and then those who
had the ‘pliosauromorph’ build, with a
large head and smaller neck, who were
fast hunters of large prey.
Mosasaurs were a later arrival in the Mesozoic
Era, arriving in the Cretaceous Period. With the
extinction of the Ichthyosaurs and the decline of
the Plesiosaurs in the Late Cretaceous, Mosasaurs
became the dominant marine predators.
Perhaps the largest sea-based predator
of all time was the Liopleurodon, a short
necked Plesiosaur, with dagger-like teeth
twice as long as that of the T-Rex, and
possibly reaching lengths of up to twenty
five metres!
They could reach up to seventeen metres in length,
with double hinged jaws and flexible skulls (much
like snakes), meaning they could swallow their
prey almost whole! They had a body shape similar
to that of a monitor lizard, but more streamlined
and elongated for swimming. They had short
limbs, with their paddles formed by webbed digits
on these limbs and broad tails.
Plesiosaurs are believed to be the
inspiration for the Loch Ness Monster!
Platecarpus
Ichthyosaurs
Ichthyosaurs were also large air-breathing
marine reptiles who thrived in the
Mesozoic Era who first appeared in the
Triassic Period, with at least one species
surviving until the Late Cretaceous.
Although they were particularly successful
in the later Triassic and early Jurassic
Period, they were replaced as the top
aquatic predators in the late Jurassic by
the Plesiosaurs.
In the early nineteenth century, the very
first Ichthyosaur found was discovered in
England! They looked similar to a dolphin
or fish, as they varied from one metre,
to sixteen metres in length. They had
flippers, and at least some species had a
dorsal fin. They had pointed heads, with
some species equipped with conical teeth
to catch prey, others with large bladed
teeth to catch larger animals. They also
had very large eyes!
Ichthyosaur
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Other Life
As well as these large marine reptiles,
there would have been many
occupants in the Earth’s seas during
the Mesozoic Era that would have been
familiar to us. Snail fossils have been
found, corals managed to survive since
the time of the dinosaurs, jellyfish have
been around for about 400 million
years, Ichthyosaurs ate squid, shown
by fossil evidence and even the Great
White Shark’s ancestors date back to
the Cretaceous Period!
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