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Pre - reptil dapat dikenal lebih awal berjalan tegak merangkak

Date:

September 17, 2015

Source:

Brown University

Summary:

Berkeliaran wilayah yang gersang dari superbenua kuno Pangea sekitar 260 juta tahun yang lalu , pra - reptil Bunostegos akokanensis adalah yang tertua yang dikenal sebagai makhluk yang telah berjalan tegak merangkak , menurut sebuah studi baru yang diterbitkan 

........ Sampai saat semua pareiasaurs dikenal yang “roved” superbenua Pangea di era Permian seperempat miliar tahun yang lalu yang “sprawlers” dimana  anggota badan akan menganjur dari sisi tubuh dan kemudian lanjut keluar atau miring turun dari siku ( seperti beberapa kadal modern) . Morgan Turner , penulis utama dari studi dalam Journal of Vertebrate Paleontology , diharapkan Bunostegos akan “sprawler” , juga , tapi tulang lengan depan hewan menceritakan cerita yang berbeda .......more

Pre-reptile may
be earliest known to walk upright on all fours

Date:

September 17, 2015

Source:

Brown University

Summary:

Wandering an arid region of the ancient supercontinent of Pangea about
260-million years ago, the pre-reptile Bunostegos akokanensis is the oldest
known creature to have walked upright on all fours, according to a newly
published study.

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

A newly published analysis of the bones ofBunostegos akokanensis, a 260-million-year-old pre-reptile, finds that it
likely stood upright on all-fours, like a cow or a hippo, making it the
earliest known creature to do so.

To date all of the known pareiasaurs who roved the supercontinent of Pangea
in the Permian era a quarter of a billion years ago were sprawlers whose limbs
would jut out from the side of the body and then continue out or slant down
from the elbow (like some modern lizards). Morgan Turner, lead author of the
study in the Journal of Vertebrate Paleontology, expected Bunostegos would
be a sprawler, too, but the bones of the animal's forelimbs tell a different
story.

"A lot of the animals that lived around the time had a similar upright
or semi-upright hind limb posture, but what's interesting and special
about Bunostegos is the forelimb, in that it's anatomy is
sprawling-precluding and seemingly directed underneath its body--unlike
anything else at the time," said Turner who performed the analysis under
the supervision of Professor Christian Sidor while a student at the University
of Washington. Now Turner is a graduate student at Brown University. "The
elements and features within the forelimb bones won't allow a sprawling
posture. That is unique."

The findings allowed Turner, Sidor and her co-authors to characterize
how Bunostegos might have looked. Standing like a cow, and
about the same size.

"Imagine a cow-sized, plant-eating reptile with a knobby skull and
bony armor down its back," said co-author Linda Tsuji of the Royal Ontario
Museum, who discovered the fossils in Niger along with Sidor and a team of
paleontologists in 2003 and 2006.

Four forelimb findings

Turner examined much of the skeleton of several individuals. The findings
that matter most, however, are all in the forelimbs. In particular, four
observations make the case, she said, thatBunostegos stood differently
than all the rest, with the legs entirely beneath the body.

Starting at the shoulder joint, or the glenoid fossa, the orientation of it
is facing down such that the humerus (the bone running from shoulder to elbow)
would be vertically oriented underneath. It would restrict the humerus from
sticking out to the side, too.

Meanwhile Bunostegos's humerus is not twisted like those of
sprawlers. In a sprawler, the twist is what could allow the humerus to jut out
to the side at the shoulder but then orient the forearm downward from the
elbow. But the humerus ofBunostegos has no twist suggesting that
only if the elbow and shoulders were aligned under the body, could the foot
actually reach the ground, Turner said.

The elbow joint is also telling. Unlike in sprawling pareiasaurs, which had
considerable mobility at the elbow, the movement ofBunostegos's elbow is
more limited. The way the radius and ulna (forearm bones) join with the humerus
forms a hinge-like joint, and wouldn't allow for the forearm to swing out to
the sides. Instead, it would only swing in a back and forth direction, like a
human knee does.

Finally, the ulna is longer than the humerus in Bunostegos,
which is a common trait among non-sprawlers, Turner said.

"Many other sprawling 4-legged animals have the reverse ratio,"
she said.

Going back 260 million years

The idea that Bunostegos would be an outlier in terms of
its posture matches well with the idea that it was somewhat of an outlier in
its choice of habitat.

"Bunostegos was an isolated pareiasaur," Turner said.

Way back when, Niger was an arid place (like some of it is today) where
plants and water sources might well have been few and far between. Scientists
have associated walking upright on all fours with a more energy efficient posture
than sprawling. For the long journeys between meals, Turner said, the upright
posture might have been necessary for survival.

The significance of such an early example of the upright posture is
that Bunostegos dates very far back on the evolutionary tree,
pushing back the clock on when this posture shows up in evolution.

But Turner said she wouldn't be surprised if other animals of the time are
eventually also found to have similarities to this posture, which evolved
independently in reptiles and mammals several times over the eras.

"Posture, from sprawling to upright, is not black or white, but
instead is a gradient of forms," Turner said. "There are many
complexities about the evolution of posture and locomotion we are working to
better understand every day. The anatomy ofBunostegos is
unexpected, illuminating, and tells us we still have much to learn." At
Brown, Turner is working in the lab of Professor Stephen Gatesy, where she is
studying a continuum of postures and locomotion in ancient creatures. In
addition to Turner, Tsuji and Sidor, Oumarou Ide of the University of Niamey in
Niger is an author of the study.







Story Source:

The above post is reprinted from materials provided by Brown
University. Note: Materials may be edited for content and length.







Journal Reference:

1.   
Morgan L. Turner, Linda A. Tsuji, Oumarou Ide, Christian A. Sidor. The
vertebrate fauna of the upper Permian of Niger—IX. The appendicular skeleton
ofBunostegos akokanensis(Parareptilia: Pareiasauria). Journal of
Vertebrate Paleontology, 2015; e994746 DOI:10.1080/02724634.2014.994746

http://www.sciencedaily.com/releases/2015/09/150917110007.htm

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