I do not think anyone really doubts that birds evolved directly from
dinosaur lineages. This work allows us to map the evolution of egg
brooding while this all took place. It certainly ensures parental
protection which may not have been an issue for crocs and turtles but
is certainly an issue for all others.
The modern world tells us as much when we observe the lengths that
birds must go to protect their young. In fact, the primary cause of
island extinctions and most of out biodiversity has been driven by
the advent of the rat eating eggs.
It is also pretty clear that upland dinosaurs who needed to function
in the heat of the day were largely feathered. The moa is a close
cousin.
Dinosaur egg study
supports evolutionary link between birds and dinosaurs
by Staff Writers
Calgary, Canada (SPX) Apr 22, 2013
Darla Zelenitsky from
the University of Calgary collaborated with David Varricchio at
Montana State University to closely examined the shells of fossil
eggs from a small meat-eating dinosaur called Troodon. Credit: Jay Im
(University of Calgary).
A small, bird-like
North American dinosaur incubated its eggs in a similar way to
brooding birds - bolstering the evolutionary link between birds and
dinosaurs, researchers at the University of Calgary and Montana
State University study have found.
Among the many
mysteries paleontologists have tried to uncover is how dinosaurs
hatched their young. Was it in eggs completely buried in nest
materials, like crocodiles? Or was it in eggs in open or non-covered
nests, like brooding birds?
Using egg clutches
found in Alberta and Montana, researchers Darla Zelenitsky at the
University of Calgary and David Varricchio at Montana State
University closely examined the shells of fossil eggs from a small
meat-eating dinosaur called Troodon.
In a finding published
in the spring issue of Paleobiology, they concluded that this
specific dinosaur species, which was known to lay its eggs almost
vertically, would have only buried the egg bottoms in mud.
"Based on our
calculations, the eggshells of Troodon were very similar to those of
brooding birds, which tells us that this dinosaur did not completely
bury its eggs in nesting materials like crocodiles do," says
study co-author Zelenitsky, assistant professor of geoscience.
"Both the eggs
and the surrounding sediments indicate only partial burial; thus an
adult would have directly contacted the exposed parts of the eggs
during incubation," says lead author Varricchio, associate
professor of paleontology.
Varricchio says while
the nesting style for Troodon is unusual, "there are
similarities with a peculiar nester among birds called the Egyptian
Plover that broods its eggs while they're partially buried in sandy
substrate of the nest."
Paleontologists have
always struggled to answer the question of how dinosaurs incubated
their eggs, because of the scarcity of evidence for incubation
behaviours.
As dinosaurs' closest
living relatives, crocodiles and birds offer some insights.
Scientists know that
crocodiles and birds that completely bury their eggs for hatching
have eggs with many pores or holes in the eggshell, to allow for
respiration.
This is unlike
brooding birds which don't bury their eggs; consequently, their eggs
have far fewer pores.
The researchers
counted and measured the pores in the shells of Troodon eggs to
assess how water vapour would have been conducted through the shell
compared with eggs from contemporary crocodiles, mound-nesting birds
and brooding birds.
They are optimistic
their methods can be applied to other dinosaur species' fossil eggs
to show how they may have been incubated.
"For now, this
particular study helps substantiate that some bird-like nesting
behaviors evolved in meat-eating dinosaurs prior to the origin of
birds. It also adds to the growing body of evidence that shows a
close evolutionary relationship between birds and dinosaurs,"
Zelenitsky says.
No comments:
Post a Comment