|We have been discussing reptiles. Looking
forward, one of my students inquired about the
first mammal. Has the fossil record been able to
pinpoint one mammal in particular as the ancestor
for all mammals?
|Question Date: 1999-05-10|
I am waiting for a reply to this question from
people in the geology department who are experts
in vertabrate fossils. My guess is that there was
not a single species ancestor. About the only
other thing I know is that the early mammals were
small and shrew-like. Also, I think they were
nocturnal, able to fill a niche the cold-blooded
reptiles could not because of low night-time
temperatures. But, let's see what the experts
say...I hope to get back to you again soon.
I don't have a solid answer to this question, but
I think I can clarify some points.For starters,
many people have been using differences in the
genetic sequence to determine how related
different animals are. If the animals are closely
related (e.g. us and monkeys), there sequences of
DNA are very similar. If they are distant
relatives (e.g. monkeys and slime molds) the
sequences are very dissimilar. Anyway, if you map
this all out using a computer program, you get
these lines called "branches" (just like branches
of a tree). Thats where they get the "tree of
life" which shows how related animals and plants
and bacteria are. Anyway, these branchews have to
meet somewhere, and the computer programs
extrapolate out the lineages to form branch
points. People often ask "what creature is at
that branchpoint, that is the ancestor of all the
mammals?" Well, that's an artificial construct.
There is in theory an animal or animals that is
the ancestor of all mammals, but I don't know what
it is, and that branch point on a tree is an
artificial construct. There are some very good
paleontology sites (The american museum of natural
history website is fantastic), and I would
recommend going to those sites and contacting on
of the curators of the fossil exhibits. They'll
have the best idea of which animals are the likely
ancestors to the mammals.
I hope this
helps! By the way, the people at the National
museum (div of paleontology) are very friendly and
will answer your question quickly.
This is a great time to ask such a question
because in the last couple of months papers came
out describing a new, fully articulated mammal
skeleton that is the best, earliest one found yet.
Nature v. 398, 25 March, 1999 shows a proposed
mammalian 'family tree' on page 283 and skeletal
drawings on page 327. Science v 283, 26 March
1999 p. 1990 shows an artist's conception of it.
It is a very cool specimen with reptile-like
hindlimbs and mammalian type forelimbs. It was
found abut 400km northeast of Beijing. They think
it's 120 million yers old.
Have fun with
the mammals, I'd be happy to answer any mammal
questions you have.
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