The
Triassic
is the first
geological period
in the
Mesozoic era
and the seventh period of the
Phanerozoic
eon
. It lasted 50.6
million
years. The period began 251.9 million years ago, and ended 201.3 million years ago.
[1]
[2]
Its start and finish were both notable extinction events.
[3]
The period before the Triassic was the
Permian
period, the last period in the
Palaeozoic
era. The
Jurassic
period came after the Triassic.
[1]
Many new groups arose during the Triassic period, including the first
dinosaurs
, the first
mammals
, the first
pterodactyls
, the first
ichthyosaurs
and the first
plesiosaurs
.
[4]
Great
extinction events
happened at the beginning and end of the Triassic period. The Triassic began after the great
extinction
at the end of the
Palaeozoic
era, the
Permian/Triassic extinction event
.
Nobody really knows the exact cause of the Permian/Triassic extinction, and experts have different
theories
.
[5]
[6]
The Triassic had several more extinction events, whose causes are also unknown. The most significant of these took place at the end of the Triassic, which was one of the 'big five'
Phanerozoic
marine
extinctions
.
[7]
[8]
The name 'Triassic' comes from the three
rock
strata
that formed during the Triassic period ("tri" means "three").
[4]
Three layers of rock strata formed during this period:
[4]
On average, the Triassic's
climate
was very different from today's:
[4]
- It had about 80% of today's
oxygen
levels
- There was about six times as much
carbon dioxide
in the air as there was before the
Industrial Revolution
- The Earth's average surface
temperature
was about 3
o
C
hotter than it is now
During the Triassic period, there were no separate
continents
as there are today. Almost all the Earth's land mass was together in a single
supercontinent
called
Pangaea
("all the land"). Pangaea was centred more or less on the
equator
.
[4]
and surrounded by the superocean
Panthalassa
. Later the
Tethys Ocean
developed.
The supercontinent Pangaea was
rifting
during the Triassic ? especially late in the period ? but had not yet separated again into different continents. In contrast to the present Earth with its distribution of continents, Pangaea was centred on the Equator. Probably, apart from some volcanic island chains, there was an unbroken sea stretching round the world: the
Panthalassa
.
Being a super-continental land mass, Pangaea had a limited
shoreline
. Because of this, Triassic marine deposits ?
fossils
from Triassic ocean life ? are rare in most of the world. In
North America
, for example, marine deposits are limited to a few exposures in the west. However, they are common in
Western Europe
, where the Triassic was first studied.
[4]
The first part of the Triassic had much less variety than the Permian, and showed signs of a deteriorated
environment
. This situation lasted for about five million years, then steadily improved. Into the vacant
ecological niches
, new forms
evolved
, replacing old with new. This rapid
adaptive radiation
happened to the
reptiles
on land, the
fish
in the
seas
, and a number of other groups, like the
insects
. Communities with complex
ecology
took 30 million years to re-establish.
[9]
New groups of
ferns
and
seed plants
were a feature of the Triassic.
The group of
bony fish
known as the
teleosts
first appeared during the Triassic period. The group now includes over 80% of all fish and 95% of all bony fish. The only other common group of fish are the
Chondrichthyes
(the
sharks
and
rays
). The rays also first appeared during the Triassic.
[4]
Many reptile groups first appeared during the Triassic period, possibly because so many niches were vacant at the time. Some of these new groups died out in the
End?Triassic extinction event
, but those that survived ruled the Earth for the rest of the Mesozoic.
[10]
Examples include:
This was a major change, because in the
middle Triassic
period, the
Synapsids
(
mammals
'
ancestors
) were still dominant.
Many reptile groups became
extinct
during the Triassic, including:
[10]
p. 41
Also, amongst the Synapsids (which used to be called
mammal-like reptiles
), the
Dicynodonts
died out during the end-Triassic extinction.
[10]
p. 41
The Triassic was a period of great change in
tetrapods
: many new and important groups appeared, but many others became extinct. Of all the periods in the Mesozoic era, there are the least number of
fossils
from the Triassic period. This makes it difficult for
scientists
to explain these events.
- ↑
1.0
1.1
Cohen, K.M.; Finney, S.; & Gibbard, P.L. (January 2013).
"International Chronostratigraphic Chart"
(PDF)
.
International Commission on Stratigraphy
. International Union of Geological Sciences
. Retrieved
June 12,
2016
.
{{
cite web
}}
: CS1 maint: multiple names: authors list (
link
)
- ↑
"ICS - Chart/Time Scale"
.
www.stratigraphy.org
.
- ↑
Sahney S. & Benton M.J. 2008. Recovery from the most profound mass extinction of all time.
Proceedings of the Royal Society B: Biological Sciences
275
(1636): 759?765. PMID
[1]
- ↑
4.0
4.1
4.2
4.3
4.4
4.5
4.6
Logan A. (2016).
"Triassic Period"
.
Encyclopædia Britannica
. Encyclopædia Britannica Inc
. Retrieved
June 12,
2016
.
- ↑
Erwin D.H. 1993.
The great Palaeozoic crisis: life & death in the Permian
. Columbia University Press,
New York
.
ISBN
978-0231074674
.
- ↑
Hallam A. and Wignall P.B. 1997.
Mass extinctions and their aftermath
. Oxford,
Cambridge
.
ISBN
978-0198549161
.
- ↑
Raup D.M. and Sepkoski J.J. 1982. Mass extinctions in the marine fossil record.
Science
215
, 1590.
- ↑
Raup D.M. and Gould S.J. 1992.
Extinction: bad luck or bad genes?
Norton, New York.
ISBN
978-0393309270
.
- ↑
Sahney S. and Benton M.J. (2008).
"Recovery from the most profound mass extinction of all time"
.
Proceedings of the Royal Society: Biological
.
275
(1636): 759?765.
doi
:
10.1098/rspb.2007.1370
.
PMC
2596898
.
PMID
18198148
.
- ↑
10.0
10.1
10.2
Benton M. 1990.
The reign of the reptiles
. Crescent, New York.
ISBN
978-0517025574
.