Official 30 - lecture 2
a lecture in paleontology class.
as we've discussed, birds are apparently descendants of dinosaurs, and share many commonalities with some dinosaurs species like feathers, even flight, and of course egg laying.
many paleontologist, myself included, have wondered about other similarities between dinosaurs and birds.
since adult dinosaur fossils has been sometime discovered near or on top of the nest. We have been looking into the dinosaurs parenting behavior.
parenting behavior, that sounds so gentle and caring.
but dinosaurs are ferocious reptiles, and reptiles don't take care of their young, do they?
some reptiles incubate their eggs, crocodiles do.
and as for popular attitude toward dinosaurs, take the Oviraptor for instance.
in the 1920s a paleontologist discovered fossil remains of small dinosaur near a nest containing eggs
he assumed the dinosaur was stealing the egg, so he named it Oviraptor.
that means egg thief in Latin which fueled the generally negative public image of such dinosaur.
but by the 1990 other experts have convincingly made the case that, instead of robbing the nest, the Ovirapter was probably taking care of these eggs
rob, robbery
dinosaur's closest living relatives bird and crocodile display nesting behavior.
dinosaur fossils have been found in the postures that we now believe to indicate brooding behavior that is sitting on the eggs until they hatch.
we've curious about types of care dinosaur given to their young, which dinosaur of parents, male or female gave to the kids.
shouldn't the behaviors of crocodiles and birds give us some clues, then
with crocodiles, it is the female who guards the nests, and with birds, it depends on species.
it can be the male or the female that takes care of the nest, or both.
over 90 percent of all birds, both parents take care of the eggs, and the young birds.
but sometimes it's just the male?
exclusive care by the male parent is much less common, but it does occur.
now for animal other than birds, the care of young by both parents is pretty unusual in the animal kingdom, male contributes to parental care in fewer than 5 percent of all mammalian species.
contribute to sth. in 5 percent
mammalian species
it is even less frequent among reptiles, and exclusive care by the male is very rare.
so researchers have wonder about the evolution of male parenting behavior on bird for quite some time.
and now there's research showing that, for some of birds' dinosaurs relatives, It's likely that the male parent was also in charge of taking care of the eggs
how did they figure that out?
first they looked at clutch volume, that is the number of eggs in the nest, of crocodiles, birds and 3 type dinosaurs including Oviraptor that are thought be closest relative to dinosaurs ancestors of birds.
dinosaurs ancestor of birds 古代鸟类
so when researchers examined fossilized remains in nests, they found that dinosaurs have larger clutch volume, more eggs in the nest that is.
then most of crocodiles and birds were studied, but it is import, their clutch volumes matched that those of birds that had only male parental care.
bird species in which only the male take care of the eggs tend to have the largest clutches of eggs.
what's the connection between bird and dinosaur behavior?
researchers now believe, because of the study, the male parenting behavior of birds might have the origins in the behavior of dinosaurs.
base only on evidence of clutch size, the number of eggs?
there is more, they also examined the fossilized bones of those 3 type dinosaurs that found on or near the nests to determine their sex
adult female birds during egg production produce a layer of spongy bone tissue inside certain long bones.
and so did female dinosaurs of the kinds that was investigated.
so did sb. 它也是
this spongy tissue serves as a source of calcium for eggshell formation.
but when the dinosaur fossils were examined there were no spongy tissue deposit.
meaning that those dinosaurs on nests were probably adult males, who wouldn't have needed calcium for making eggshells.
exactly, and then there is this.
birds, like kiki, the ostirch, and the emu, they share certain physical characteristics with these dinosaurs. And interestingly, they also show a consistent pattern of nest care by the male.