From Simple English Wikipedia, the free encyclopedia
The
Middle Jurassic
is the second
geological
epoch
in the
Jurassic
. It began 174.1
million
years ago, and ended at 163.5 million years ago.
In the Middle Jurassic,
Pangaea
began to split apart. It began to separate into
Laurasia
and
Gondwana
, and the
Atlantic Ocean
formed.
Tectonic
activities closed the
Paleo-Tethys Ocean
.
[1]
A subduction zone
[2]
on the coast of western
North America
continues to create the ancestral
Rocky Mountains
.
During this time, marine life (including
ammonites
and
bivalves
) flourished.
Ichthyosaurs
, although common, are reduced in diversity. A type of
crocodilians
first appeared.
Plesiosaurs
became common at this time. The top marine predators, the
pliosaurs
, grew to the size of
killer whales
and larger e.g.
Pliosaurus
,
Liopleurodon
.
New types of
dinosaurs
evolved on land.
Cetiosaurus
was an early sauropod found in England in the mid-19th century.
[3]
[4]
The environment in which
Cetiosaurus
lived was
floodplain
and open
woodland
.
Brachiosaurs
and
Megalosaurus
also lived in this
environment
.
The
cynodont
therapsids
flourished with the dinosaurs, but they were only
shrew
-sized. None grew larger than a
badger
. One group of cynodonts, the
Trithelodonts
were becoming rare and eventually became extinct at the end of this epoch. The
Tritylodonts
were still common, though. In this epoch "true"
mammals
evolved from a group of cynodonts.
Conifers
were dominant in the Middle Jurassic. Other plants, such as
ginkgoes
,
cycads
, and
ferns
were also common. These are the trees which the large herbivores ate.
- ↑
The Tethys Ocean: an ancient seaway approximately in the position of the
Mediterranean
.
- ↑
Formed by an oceanic plate sliding under a continental plate.
- ↑
"Cetiosaurus." In: Dodson, Peter et al.
The Age of Dinosaurs
. Publications International, p65.
ISBN
0-7853-0443-6
.
- ↑
Upchurch P & Martin J (2002). "The Rutland
Cetiosaurus
: the anatomy and relationships of a Middle Jurassic British sauropod dinosaur".
Palaeontology
.
45
(6): 1049?1074.
doi
:
10.1111/1475-4983.00275
.
S2CID
84628061
.