An artist's rendering of the shrew-sized Cretaceous-age animal, Ukhaatherium nessovi.
Meet
your ancestor: This small and furry scampering insect-eater lies at the base of
the family tree for humans and most mammals, according to the largest-yet study
of mammalian evolution.
The
agile animal is the earliest among placental mammals -- the largest branch of
the mammal tree consisting of more than 5,100 living species. Only marsupials,
such as kangaroos, and monotremes (egg-laying mammals including the platypus
and echidna) fall outside of that huge group.
The
mammal "had a diet of insects, a fleshy nose, a light underbelly in its
fur, and a long tail," said Maureen O'Leary, an associate professor in the
Department of Anatomical Sciences in the School of Medicine at Stony Brook
University. O'Leary was lead author of a study about the mammal in the latest
issue of Science.
PHOTOS: Faces of
Our Ancestors
"It
was larger than a mouse, but smaller than a rat," added O'Leary, who is
also a research associate at the American Museum of Natural History
"As
for its bones, it lacked special bones that are found near the pelvis, and in
its ear had a small bone for hearing that was shaped like a stirrup."
Such
a detailed description was made possible due to an unprecedented combining of
both DNA and anatomical data for placental mammals. Humans again fall into that
mammal group, which is distinguished by certain reproductive features and
skeletal traits.
Recording
of the data employed a system called MorphoBank. Its data set, which includes
more than 4,500 traits detailing characteristics such as hair types and teeth
structure, is 10 times larger than what was previously used for studies of
mammal relationships.
In
addition to revealing what the "mother" of most mammals looked like,
the study shows that placental mammals arose 200,000 to 400,000 years after the
extinction of non-avian dinosaurs about 65 million years ago.
NEWS: Post-Dinos
Mammals Was Fat and Slow
"This
is about 36 million years later than the prediction based on purely genetic
data," said co-author Marcelo Weksler of the Museu National-UFRJ in Brazil.
Somehow
the distant relative of mammals that led to the "mother" of our
species and others survived the asteroid crash, dramatic climate change, and
other happenings that did in the dinos.
"Other
species that survived are some crocodiles, turtles and flowering plants,"
O'Leary said.
The
newly constructed mammal family tree indicates that the fragmentation of
Gondwana- one of two supercontinents formerly part of Pangaea- came well before
the origin of placental mammals, co-author John Wible of the Carnegie Museum of
Natural History shared.
This
negates an earlier theory, which held that mammal diversification was tied to
the breakup of the supercontinent. It previously was thought that this breakup
put the early mammals in different environments, leading to their different
evolutionary paths and the diversity that we see today among mammals.
It
now could be, however, that the earliest mammals traveled far distances of
their own accord and just evolved their broad diversity over long periods of
time.
Yet
another finding of the extensive study is that a branch of the placental mammal
tree called Afrotheria (a group ranging from elephants to aardvarks that today
lives in Africa) did not originate in Africa, but rather in the Americas.
"Determining
how these animals first made it to Africa is now an important research
question, along with many others, that can be addressed using MorphoBank and
the phylophenomic (physical traits) tree produced in this study," said
co-author Fernando Perini of Minas Gerais Federal University in Brazil.
Mary
Silcox, who years ago famously helped put humans on the tree of life, agreed
and said, "This project is not exhaustive, but exposes a way forward to
collect data on other phenomic systems and other species."
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