A new study on the last common ancestor of today's penguins.
A cooling spell in
Antarctica may have helped penguins diversify into the numerous species
alive today, such as this Gentoo penguin. Photograph by Paul Souders, Corbis
for National Geographic
Published November 12, 2013
When did the earliest common ancestor of the penguins we know today first waddle the Earth, and why?
The question is surprisingly controversial, and may become more so with a new study suggesting a climate-change connection.
Possible
dates for the last common ancestor of living penguins have differed by
tens of millions of years. According to DNA evidence, the early ancestor
lived some 40 million years ago, while fossil evidence puts the date
closer to 10 million years ago.
Now a new genetic study, detailed in this week's issue of the journal Biology Letters,
suggests that today's major penguin lineages began diverging from one
another about 11 to 16 million years ago, and that their common ancestor
first appeared 20 million years ago.
The study also
suggests that a prolonged cooling spell in Antarctica may have helped
spur penguins to diversify into the 18 species living today.
Reconciling Evidence
The
new finding, based on more DNA points than past studies, helps
reconcile the genetic and fossil evidence, explained study leader Sankar Subramanian, a postdoctoral student at Griffith University in Australia.
"For
the first time we showed a more recent time of origin of penguins,
which was in agreement with that based on morphological data," he said.
Intriguingly,
the date that Subramanian's team estimates for the diversification of
modern penguins coincides with a time 10 to 15 million years ago when
scientists think Antarctica underwent a period of rapid cooling that
covered the continent in ice.
"So we connected these two
dots and speculated [about] a possible relationship," Subramanian said
in an email. He cautioned, however, that he and his colleagues "don't
have any proof for this connection, which is indeed hard to obtain."
A Mysterious Gap
Paleontologists
have found penguin-like fossils dating as far back as 62 million years,
tens of millions of years before the first ancestor of today's penguins
emerged on the scene.
"The big gap between these two
times raises questions like: What happened to the older lineages of
penguins? What caused the extinction of all other older lineages? Could
that be due to any change in Antarctic or global climate?" Subramanian
said.
Subramanian said his team is planning to look next
at the molecular signatures of penguins living in very different
environments, from the tropical Galápagos Islands to the frozen Antarctic.
"This might reveal valuable information, such as how they could adapt to live in these diverse climates," he said.
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