Researchers Reconstruct the Common Ancestor of Placental Mammals


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.

local_offerevent_note February 28, 2020

account_box Gilbert Heid

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