It's a small, sort of brownish-grey species, bigger than a mouse, about
250 grams.
It was an insect-eating
mammal
and it lived in what's called the early Paleocene,
which is a time that just followed the extinction of the dinosaurs that people tend to be more familiar with.
Humans are definitely placental mammals and this ancestor that we've reconstructed is
part of our broad family tree.
Its official name is a hypothetical placental ancestor because
we don't actually have a fossil of this. We can take
information from fossil record, information from living species and then
look back at a time like the Paleocene and really say with some confidence
what we think
extinct animals looked like at that time.
What we do to reconstruct what any ancestor might have been like,
is in essence, mapping
the traits that we know about, and working our way back down the branches.
The only way that this was possible
was because we were working in MorphoBank. MorphoBank is a cloud based web
application
for scientists who are interested in
storing information about the phenome,
or the morphology anatomy of organisms and using it to build evolutionary trees
of those organisms. In a sense this is kind of like
our atom smasher project.
The next wave, the next possibility for work in what we call comparative and
evolutionary biology. DNA sequencing became
an enormous
transformation
in the way we look at organisms. At the same time, we can't forget all the
external features above the level of the genome, we call the phenome.
And what's great, is we now have some of the digital technologies that allow us
to study those things
in ways that are somewhat compatible with studying the genome.
So, that's what I think is the next part of the arc, and to me, the most
exciting one.
When we put all our observations together they sit in a thing called
a matrix. And that matrix can then be put through an algorithm
to produce a tree, and then that tree is what tells us
which species are related to each other. MorphoBank is one of many different
kinds of initiatives to bring anatomy
into the twenty-first century and to make it at a big science where teams of
collaborators can go and work in a shared context on a hypothesis that they're testing.
Over the course of this work, we had six different countries involved, so a team of 15 or 20 collaborators over the years.
We had a core team here at the American Museum of Natural History
another team based at the Carnegie Museum.
We had very important collaborators at several other institutions, SUNY Stony Brook,
University of Florida, University of Tennessee. This is probably
the biggest effort ever in this kind of way.
It shows some interesting things that aren't necessarily reproduced in the
genome trees. Indeed,
our results suggest that the timing of the evolution of this group was
a fairly late event.
Right after the
so-called dinosaur extinction event, the Cretaceous extension event.
And, you know, the inference there is that may have opened up a lot of
opportunities for this group of little meak mammals to
radiate all kinds of forms. Thinking about deep time is
hard to wrap your mind around. It's a very very long expanse, far
exceeds our own lifetimes,
and to be able to say something about that is, I think, a very exciting way to connect
our own evolution to the history of life
and the bigger picture of what's happened and how species have changed through time.