Cuaca dingin : pendinginan iklim dan perubahan level laut yang menyebabkan penurunan pada buaya --T-REC-komunitas reptil-semarang--KSE-komunitas satwa eksotik--buaya-crocodile--berita tentang buaya

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Cuaca dingin : pendinginan iklim dan  perubahan level laut  yang menyebabkan penurunan  pada buaya 

Berfluktuasi permukaan laut dan pendinginan global menyebabkan penurunan yang signifikan dalam jumlah spesies buaya selama jutaan tahun

Date:

September 24, 2015

Source:

Imperial College London

Summary:

Berfluktuasinya  permukaan laut dan pendinginan global menyebabkan penurunan yang signifikan dalam jumlah spesies buaya selama jutaan tahun , menurut penelitian baru . Di masa depan , para peneliti menyarankan bahwa  pemanasan dunia  yang disebabkan oleh perubahan iklim global dapat mendukung diversifikasi crocodylian lagi .

......... Crocodylians termasuk spesies masa kini  dari buaya , alligator  , Caiman , gavials dan nenek moyang punah mereka . Crocodylians pertama kali muncul pada periode Kapur Akhir , sekitar 85 juta tahun yang lalu , dan 250 juta tahun catatan fosil kerabat punah mereka mengungkapkan sejarah evolusi beragam ....more

Cold snap: Climate cooling and sea-level changes caused crocodilian retreat

Fluctuating sea levels and global cooling caused a
significant decline in the number of crocodilian species over millions of years

Date:

September 24, 2015

Source:

Imperial College London

Summary:

Fluctuating sea levels and global cooling caused a significant decline in
the number of crocodilian species over millions of years, according to new
research. In the future, the researchers suggest that a warming world caused by
global climate change may favour crocodylian diversification again.

.........................

Fluctuating sea levels and global cooling caused a significant decline in
the number of crocodylian species over millions of years, according to new
research.

Crocodylians include present-day species of crocodiles, alligators, caimans
and gavials and their extinct ancestors. Crocodylians first appeared in the
Late Cretaceous period, approximately 85 million years ago, and the 250 million
year fossil record of their extinct relatives reveals a diverse evolutionary
history.

Extinct crocodylians and their relatives came in all shapes and sizes,
including giant land-based creatures such asSarcosuchus, which reached
around 12 metres in length and weighed up to eight metric tonnes. Crocodylians
also roamed the ocean -- for example, thalattosuchians were equipped with
flippers and shark-like tails to make them more agile in the sea.

Many crocodylians survived the mass extinction that wiped out almost all of
the dinosaurs 66 million years ago, but only 23 species survive today, six of
which are classified by the International Union for Conservation of Nature as
critically endangered and a further four classified as either endangered or
vulnerable.

In a new study published in Nature Communications, researchers
from Imperial College London, the University of Oxford, the Smithsonian
Institution and the University of Birmingham compiled a dataset of the entire
known fossil record of crocodylians and their extinct relatives and analysed
data about Earth's ancient climate. They wanted to explore how the group
responded to past shifts in climate, to better understand how the reptiles may
cope in the future.

Crocodylians are ectotherms, meaning they rely on external heat sources
from the environment such as the Sun. The researchers conclude that at higher
latitudes in areas we now know as Europe and America, declining temperatures
had a major impact on crocodylians and their relatives.

At lower latitudes the decline of crocodylians was caused by areas on many
continents becoming increasingly arid. For example, in Africa around ten
million years ago, the Sahara desert was forming, replacing the vast lush
wetlands in which crocodylians thrived. In South America, the rise of the Andes
Mountains led to the loss of a proto-Amazonian mega wetland habitat that
crocodylians lived in around five million years ago.

Marine species of crocodylians were once widespread across the oceans. The
team found that fluctuations in sea levels exerted the main control over the
diversity of these creatures. For example, at times when the sea level was
higher it created greater diversity because it increased the size of the
continental shelf, providing the right conditions near the coast for them and
their prey to thrive.

Interestingly, the Cretaceous-Paleogene mass extinction event, which wiped
out many other creatures on Earth nearly 66 million years ago including nearly
all of the dinosaurs, had positive outcomes for the crocodylians and their
extinct relatives. The team found that while several groups did go extinct, the
surviving groups rapidly radiated out of their usual habitats to take advantage
of territories that were now uninhabited.

In the future, the team suggest that a warming world caused by global climate
change may favour crocodylian diversification again, but human activity will
continue to have a major impact on their habitats.

Dr Philip Mannion, joint lead author from the Department of Earth Science
and Engineering at Imperial College London, said: "Crocodylians are known
by some as living fossils because they've been around since the time of the
dinosaurs. Millions of years ago these creatures and their now extinct
relatives thrived in a range of environments that ranged from the tropics, to northern
latitudes and even deep in the ocean. However, all this changed because of
changes in the climate, and crocodylians retreated to the warmer parts of the
world. While they have a fearsome reputation, these creatures are vulnerable
and looking back in time we've been able to determine what environmental
factors had the greatest impact on them. This may help us to determine how they
will cope with future changes."

The next step for the researchers will be for them to look at similar
patterns in other fossil groups with long histories, such as mammals and birds
to determine how past climate influenced them.







Story Source:

The above post is reprinted from materials provided byImperial
College London. Note: Materials may be edited for content and length.







Journal Reference:

1.   
Philip D. Mannion, Roger B. J. Benson, Matthew T. Carrano, Jonathan P. Tennant,
Jack Judd, Richard J. Butler. Climate constrains the evolutionary
history and biodiversity of crocodylians. Nature Communications,
2015; 6: 8438 DOI: 10.1038/ncomms9438

http://www.sciencedaily.com/releases/2015/09/150924082452.htm

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