Asteroid that wiped out dinosaurs may have nearly knocked off mammals, too

December 17, 2014
This diagram is showing how severely metatherian mammals were affected when an asteroid hit Earth at the end of the Cretaceous, 66 million years ago. In North America, the number of metatherian species dropped from twenty species within the last million years of the Cretaceous Period, to just three species in the first million years of the Paleogene Period. Credit: Dr Thomas Williamson

The extinction of the dinosaurs 66 million years ago is thought to have paved the way for mammals to dominate, but a new study shows that many mammals died off alongside the dinosaurs.

Metatherian —the extinct relatives of living marsupials ("mammals with pouches", such as opossums) thrived in the shadow of the during the Cretaceous period. The new study, by an international team of experts on mammal evolution and mass extinctions, shows that these once-abundant mammals nearly followed the dinosaurs into oblivion.

When a 10-km-wide asteroid struck what is now Mexico at the end of the Cretaceous and unleashed a global cataclysm of , some two-thirds of all metatherians living in North America perished. This includes more than 90% of species living in the northern Great Plains of the USA, the best area in the world for preserving latest Cretaceous mammal fossils.

In the aftermath of the , metatherians would never recover their previous diversity, which is why marsupial mammals are rare today and largely restricted to unusual environments in Australia and South America.

Taking advantage of the metatherian demise were the placental mammals: species that give live birth to well-developed young. They are ubiquitous across the globe today and include everything from mice to men.

Dr. Thomas Williamson of the New Mexico Museum of Natural History and Science, lead author on the study, said: "This is a new twist on a classic story. It wasn't only that dinosaurs died out, providing an opportunity for mammals to reign, but that many types of mammals, such as most metatherians, died out too - this allowed advanced to rise to dominance."

A cast of the fossil remnants of Asiatherium reshetovi, one of the metatherian species that used to live on the planet millions of years ago. (scale bar: 1cm) Credit: Dr Thomas Williamson

Dr. Steve Brusatte of the University of Edinburgh's School of GeoSciences, an author on the report, said: "The classic tale is that dinosaurs died out and mammals, which had been waiting in the wings for over 100 million years, then finally had their chance. But our study shows that many mammals came perilously close to extinction. If a few lucky species didn't make it through, then mammals may have gone the way of the dinosaurs and we wouldn't be here."

The new study is published in the open access journal ZooKeys. It reviews the Cretaceous evolutionary history of metatherians and provides the most up-to-date family tree for these mammals based on the latest fossil records, which allowed researchers to study extinction patterns in unprecedented detail.

Explore further: New species of dinosaur discovered lying forgotten in a museum

More information: Williamson TE, Brusatte SL, Wilson GP (2014) The origin and early evolution of metatherian mammals: the Cretaceous record. ZooKeys 465: 1-76. DOI: 10.3897/zookeys.465.8178

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dgmb
2.8 / 5 (5) Dec 17, 2014
Asteroid that wiped out dinosaurs may have nearly knocked off "metatherian mammals"- not all mammals .
Only one word .and the meaning is so different.
JimF
5 / 5 (6) Dec 17, 2014
Note that the killing must have been more extensive than indicated by just how many mammal species went extinct. Conditions bad enough to wipe out 17 species would certainly affect populations of the 3 that survived. At a guess, maybe 90% mortality of the 3 remaining? Means an overall mortality of ca. 99% - maybe more!
jarfstrom
3 / 5 (2) Dec 17, 2014
I assume that North America got it especially bad being near the impact zone. So, this leaves me wondering what the worldwide distributions of the two classes of mammals were during that extinction period and how that ties into marsupial worldwide restriction and dominance in South America (before the more recent influx of modern mammals with the formation of the Central American land bridge) and Australia (until recently with the invasion associated with colonization). I mean, were marsupials somehow more vulnerable than placental mammals to the extinction event and why? Were marsupials mainly found in N. America? I need more resolution.
JVK
1.7 / 5 (6) Dec 18, 2014
The extinction of the dinosaurs 66 million years ago is thought to have paved the way for mammals to dominate, but a new study shows that many mammals died off alongside the dinosaurs.


What about birds?
The genomes of modern birds tell a story of how they emerged and evolved after the mass extinction that wiped out dinosaurs and almost everything else 66 million years ago.
http://www.scienc...2136.htm

What about coelacanths
this lineage of lobe-finned fish was thought to have become extinct 70 million years ago.
http://dx.doi.org...ure12027

What about the nutrient-dependent pheromone-controlled genomic stability of all vertebrates that was established via the substitution of the only achiral amino acid in the GnRH molecule?
Dynamic evolution of the GnRH receptor gene family in vertebrates http://www.ncbi.n...4232701/
Jonseer
4 / 5 (4) Dec 18, 2014
90% of 20 species isn't a huge # to go by.

I particularly have an issue with how the article depended on percentages, as in 90% of the species were wiped out in the Plains.

so do they mean 9 out of 10?
Torbjorn_Larsson_OM
3.7 / 5 (3) Dec 18, 2014
Seems that dinosaurs and mammal bottlenecked very similarly, with the dinosaur bottleneck possibly smaller and the following avian explosion larger. Dinosaurs still outdiversify mammals with a factor 2. (~ 10 000 bird vs ~ 6 000 mammal species.)

@Jonseer: Agreed on the general statistics.

But these lineages aren't independent, nor is the event that affected them, so the statistics can get by with surprisingly scant data. E.g. already 30 lineages means a lot of accuracy if not precision (inherently low resolution), and already 5-6 dice throws can tell us if the dice is loaded. (IIRC on the latter, at least it is surprisingly few for a binomial test of yes/no fair dice.)

I haven't read the paper, but I would assume the statistics is legit. (The journal is peer reviewed.)
Megapixel
1 / 5 (3) Dec 19, 2014
The fact that the marsupials were almost completely wiped out at the Cretaceous-Tertiary boundary is further proof that a rapid increase in surface gravity on Pangea (as it broke apart) occurred. The extinctions were more severe in N. America than S. America because it was further away from the equator. This is all explained in The Gravity Theory of Mass Extinction.

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