Podem chorar mais, criacionistas
Enviado: 23 Jan 2007, 19:56
Paleontologists discover most primitive primate skeleton
New Haven, Conn. -- The origins and earliest branches of primate evolution
are clearer and more ancient by 10 million years than previous studies
estimated, according to a study featured on the cover of the Jan. 23 print
edition of the Proceedings of the National Academy of Sciences.
The paper by researchers at Yale, the University of Winnipeg, Stony Brook
University, and led by University of Florida paleontologist Jonathan Bloch
reconstructs the base of the primate family tree by comparing skeletal and
fossil specimens representing more than 85 modern and extinct species. The
team also discovered two 56-million-year-old fossils, including the most
primitive primate skeleton ever described.
In the two-part study, an extensive evaluation of skeletal structures
provides evidence that plesiadapiforms, a group of archaic mammals once
thought to be more closely related to flying lemurs, are the most primitive
primates. The team analyzed 173 characteristics of modern primates, tree
shrews, flying lemurs with plesiadapiform skeletons to determine their
evolutionary relationships. High-resolution CT scanning made fine
resolution of inaccessible structures inside the skulls possible.
"This is the first study to bring it all together," said co-author Eric
Sargis, associate professor of anthropology at Yale University and
Assistant Curator of Vertebrate Zoology at Yale's Peabody Museum of Natural
History. "The extensive dataset, the number and type of characteristics we
were able to compare, and the availability of full skeletons, let us test
far more than any previous study."
At least five major features characterize modern primates: relatively large
brains, enhanced vision and eyes that face forward, a specialized ability
to leap, nails instead of claws on at least the first toes, and specialized
grasping hands and feet. Plesiadapiforms have some but not all of these
traits. The article argues that these early primates may have acquired the
traits over 10 million years in incremental changes to exploit their
environment.
While the study did not include a molecular evaluation of the samples,
according to Sargis, these results are consistent with molecular studies on
related living groups. Compatibility with the independent molecular data
increases the researchers' confidence in their own results.
Bloch discovered the new plesiadapiform species, Ignacius clarkforkensis
and Dryomomys szalayi, just outside Yellowstone National Park in the
Bighorn Basin with co-author Doug Boyer, a graduate student in anatomical
sciences at Stony Brook. Previously, based only on skulls and isolated
bones, scientists proposed that Ignacius was not an archaic primate, but
instead a gliding mammal related to flying lemurs. However, analysis of a
more complete and well-preserved skeleton by Bloch and his team altered
this idea.
"These fossil finds from Wyoming show that our earliest primate ancestors
were the size of a mouse, ate fruit and lived in the trees," said study
leader Jonathan Bloch, a vertebrate paleontology curator at the Florida
Museum of Natural History. "It is remarkable to think we are still
discovering new fossil species in an area studied by paleontologists for
over 100 years."
Researchers previously hypothesized plesiadapiforms as the ancestors of
modern primates, but the idea generated strong debate within the
primatology community. This study places the origins of Plesiadapiforms in
the Paleocene, about 65 (million) to 55 million years ago in the period
between the extinction of the dinosaurs and the first appearance of a
number of undisputed members of the modern orders of mammals.
"Plesiadapiforms have long been one of the most controversial groups in
mammalian phylogeny," said Michael J. Novacek, curator of paleontology at
the American Museum of Natural History. "First, they are somewhere near
primates and us. Second, historically they have offered tantalizing, but
very often incomplete, fossil evidence. But the specimens in their study
are beautifully and spectacularly preserved."
"The results of this study suggest that plesiadapiforms are the critical
taxa to study in understanding the earliest phases of human evolution. As
such, they should be of very broad interest to biologists, paleontologists,
and anthropologists," said co-author Mary Silcox, professor of anthropology
at the University of Winnipeg.
"This collaboration is the first to bring together evidence from all
regions of the skeleton, and offers a well-supported perspective on the
structure of the earliest part of the primate family tree," Bloch said.
http://www.eurekalert.org/pub_releases/ ... 012307.php
New Haven, Conn. -- The origins and earliest branches of primate evolution
are clearer and more ancient by 10 million years than previous studies
estimated, according to a study featured on the cover of the Jan. 23 print
edition of the Proceedings of the National Academy of Sciences.
The paper by researchers at Yale, the University of Winnipeg, Stony Brook
University, and led by University of Florida paleontologist Jonathan Bloch
reconstructs the base of the primate family tree by comparing skeletal and
fossil specimens representing more than 85 modern and extinct species. The
team also discovered two 56-million-year-old fossils, including the most
primitive primate skeleton ever described.
In the two-part study, an extensive evaluation of skeletal structures
provides evidence that plesiadapiforms, a group of archaic mammals once
thought to be more closely related to flying lemurs, are the most primitive
primates. The team analyzed 173 characteristics of modern primates, tree
shrews, flying lemurs with plesiadapiform skeletons to determine their
evolutionary relationships. High-resolution CT scanning made fine
resolution of inaccessible structures inside the skulls possible.
"This is the first study to bring it all together," said co-author Eric
Sargis, associate professor of anthropology at Yale University and
Assistant Curator of Vertebrate Zoology at Yale's Peabody Museum of Natural
History. "The extensive dataset, the number and type of characteristics we
were able to compare, and the availability of full skeletons, let us test
far more than any previous study."
At least five major features characterize modern primates: relatively large
brains, enhanced vision and eyes that face forward, a specialized ability
to leap, nails instead of claws on at least the first toes, and specialized
grasping hands and feet. Plesiadapiforms have some but not all of these
traits. The article argues that these early primates may have acquired the
traits over 10 million years in incremental changes to exploit their
environment.
While the study did not include a molecular evaluation of the samples,
according to Sargis, these results are consistent with molecular studies on
related living groups. Compatibility with the independent molecular data
increases the researchers' confidence in their own results.
Bloch discovered the new plesiadapiform species, Ignacius clarkforkensis
and Dryomomys szalayi, just outside Yellowstone National Park in the
Bighorn Basin with co-author Doug Boyer, a graduate student in anatomical
sciences at Stony Brook. Previously, based only on skulls and isolated
bones, scientists proposed that Ignacius was not an archaic primate, but
instead a gliding mammal related to flying lemurs. However, analysis of a
more complete and well-preserved skeleton by Bloch and his team altered
this idea.
"These fossil finds from Wyoming show that our earliest primate ancestors
were the size of a mouse, ate fruit and lived in the trees," said study
leader Jonathan Bloch, a vertebrate paleontology curator at the Florida
Museum of Natural History. "It is remarkable to think we are still
discovering new fossil species in an area studied by paleontologists for
over 100 years."
Researchers previously hypothesized plesiadapiforms as the ancestors of
modern primates, but the idea generated strong debate within the
primatology community. This study places the origins of Plesiadapiforms in
the Paleocene, about 65 (million) to 55 million years ago in the period
between the extinction of the dinosaurs and the first appearance of a
number of undisputed members of the modern orders of mammals.
"Plesiadapiforms have long been one of the most controversial groups in
mammalian phylogeny," said Michael J. Novacek, curator of paleontology at
the American Museum of Natural History. "First, they are somewhere near
primates and us. Second, historically they have offered tantalizing, but
very often incomplete, fossil evidence. But the specimens in their study
are beautifully and spectacularly preserved."
"The results of this study suggest that plesiadapiforms are the critical
taxa to study in understanding the earliest phases of human evolution. As
such, they should be of very broad interest to biologists, paleontologists,
and anthropologists," said co-author Mary Silcox, professor of anthropology
at the University of Winnipeg.
"This collaboration is the first to bring together evidence from all
regions of the skeleton, and offers a well-supported perspective on the
structure of the earliest part of the primate family tree," Bloch said.
http://www.eurekalert.org/pub_releases/ ... 012307.php
