Most Comprehensive Tree of Life Shows Placental Mammal Diversity Exploded After Age of Dinosaurs

Feb. 7, 2013 — An international team of scientists including University of Florida researchers has generated the most comprehensive tree of life to date on placental mammals, which are those bearing live young, including bats, rodents, whales and humans.


Appearing  February 7 in the journalScience, the study details how researchers used both genetic and physical traits to reconstruct the common ancestor of placental mammals, the creature that gave rise to many mammals alive today. The data show that contrary to a commonly held theory, the group diversified after the extinction of dinosaurs 65 million years ago. The research may help scientists better understand how mammals survived past climate change and how they may be impacted by future environmental conditions.

UF researchers led the team that analyzed the anatomy of living and fossil primates, including lemurs, monkeys and humans, as well as their closest living relatives, flying lemurs and tree shrews. The multi-year collaborative project was funded by the National Science Foundation Assembling the Tree of Life Program.

“With regards to evolution, it’s critical to understand the relationships of living and fossil mammals before asking questions about ‘how’ and ‘why,’ ” said co-author Jonathan Bloch, associate curator of vertebrate paleontology at the Florida Museum of Natural History on the UF campus. “This gives us a new perspective of how major change can influence the history of life, like the extinction of the dinosaurs — this was a major event in Earth’s history that potentially then results in setting the framework for the entire ordinal diversification of mammals, including our own very distant ancestors.”

Visual reconstruction of the placental ancestor — a small, insect-eating animal — was made possible with the help of a powerful cloud-based and publicly accessible database called MorphoBank. Unlike other reconstructions, the new study creates a clearer picture of the tree of life by combining two data types: Phenomic data includes observational traits such as anatomy and behavior, while genomic data is encoded by DNA.

“Discovering the tree of life is like piecing together a crime scene — it is a story that happened in the past that you can’t repeat,” said lead author Maureen O’Leary, an associate professor in the department of anatomical sciences in the School of Medicine at Stony Brook University and research associate at the American Museum of Natural History. “Just like with a crime scene, the new tools of DNA add important information, but so do other physical clues like a body or, in the scientific realm, fossils and anatomy. Combining all the evidence produces the most informed reconstruction of a past event.”

Researchers recorded observational traits for 86 placental mammal species, including 40 fossil species. The resulting database contains more than 12,000 images that correspond to more than 4,500 traits detailing characteristics like the presence or absence of wings, teeth and certain bones, type of hair cover and brain structures. The dataset is about 10 times larger than information used in previous studies of mammal relationships.

“It was a great way to learn anatomy, in a nutshell,” said co-author Zachary Randall, a UF biology graduate student and research associate at the Florida Museum. “While coding for humans, I could clearly see which anatomical features are unique, shared or not shared with other groups of mammals. This study is a great backbone for future work.”

Bloch and Randall collaborated with study co-authors Mary Silcox of the University of Toronto Scarborough and Eric Sargis of Yale University to characterize humans, plus seven other living and one fossil species from the clade Euarchonta, which includes primates, tree shrews and flying lemurs.

“I think this database is amazing because it’s being presented in such a way that it will be reproducible for the future generations,” Bloch said. “It illustrates exactly what we did and leaves nothing to the imagination — you can actually go to the pictures and see it.”

The evolutionary history of placental mammals has been interpreted in very different ways depending on the data analyzed. One leading analysis based on genomic data alone predicted that a number of placental mammal lineages existed in the Late Cretaceous and survived the Cretaceous-Paleogene extinction.

“It has been suggested that primates diverged from other mammals well before the extinction of the dinosaurs, but our work using direct evidence from the fossil record tells a different story,” Bloch said.

The team reconstructed the anatomy of the placental common ancestor by mapping traits most strongly supported by the data to determine it had a two-horned uterus, a brain with a convoluted cerebral cortex, and a placenta in which maternal blood came in close contact with membranes surrounding the fetus, as in humans.

Story Source:

The above story is reprinted from materials provided byUniversity of Florida.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

  1. M. A. O’Leary, J. I. Bloch, J. J. Flynn, T. J. Gaudin, A. Giallombardo, N. P. Giannini, S. L. Goldberg, B. P. Kraatz, Z.-X. Luo, J. Meng, X. Ni, M. J. Novacek, F. A. Perini, Z. S. Randall, G. W. Rougier, E. J. Sargis, M. T. Silcox, N. B. Simmons, M. Spaulding, P. M. Velazco, M. Weksler, J. R. Wible, A. L. Cirranello. The Placental Mammal Ancestor and the Post-K-Pg Radiation of PlacentalsScience, 2013; 339 (6120): 662 DOI: 10.1126/science.1229237
University of Florida (2013, February 7). Most comprehensive tree of life shows placental mammal diversity exploded after age of dinosaurs. ScienceDaily. Retrieved February 10, 2013, from

Division of Labor Offers Insight Into the Evolution of Multicellular Life

ScienceDaily (Aug. 7, 2012) — Dividing tasks among different individuals is a more efficient way to get things done, whether you are an ant, a honeybee or a human.

(Credit: Adele Conover)

A new study by researchers at Michigan State University’s BEACON Center for the Study of Evolution in Action suggests that this efficiency may also explain a key transition in evolutionary history, from single-celled to multi-celled organisms.

The results, which can be found in the current issue of the Proceedings of the National Academy of Sciences, demonstrate that the cost of switching between different tasks gives rise to the evolution of division of labor in digital organisms. In human economies, these costs could be the mental shift or the travel time required to change from activity to another.

Using the digital evolution platform Avida, self-replicating computer programs, a the team imposed a time cost on the organisms that had to perform different computational tasks to get rewards, said Heather Goldsby, who led the study and is now a postdoctoral researcher at the University of Washington.

“More complex tasks received more rewards,” she said. “They evolved to perform these more efficiently by using the results of simpler tasks solved by neighboring organisms and sent to them in messages.”

In this way, the organisms were breaking the tasks down into smaller computational problems and dividing them up among each other.

The division of labor did not come about by bringing together individuals with different abilities — each member of a community was genetically identical, in the same way that all of the cells in a human body contain the same genetic material. Instead, the organisms had to have flexible behavior and a communication system that allowed them to coordinate tasks.

The most surprising result was that the organisms evolved to become dependent on each other.

“The organisms started expecting each other to be there, and we tested them in isolation, they could no longer make copies of themselves,” said Charles Ofria, MSU associate professor of computer science and engineering.

Ben Kerr at the University of Washington and Ann Dornhaus with the University of Arizona contributed to this study. The research was funded by the National Science Foundation.



Journal Reference:

  1. Heather J. Goldsby, Anna Dornhaus, Benjamin Kerr, and Charles Ofria. Task-switching costs promote the evolution of division of labor and shifts in individuality. PNAS, August 7, 2012 DOI: 10.1073/pnas.1202233109


Michigan State University (2012, August 7). Division of labor offers insight into the evolution of multicellular life. ScienceDaily. Retrieved August 9, 2012, from­ /releases/2012/08/120807132211.htm

Superfast Evolution in Sea Stars

ScienceDaily (July 23, 2012) — How quickly can new species arise? In as little as 6,000 years, according to a study of Australian sea stars.

“That’s unbelievably fast compared to most organisms,” said Rick Grosberg, professor of evolution and ecology at UC Davis and coauthor on the paper published July 18 in the journal Proceedings of the Royal Society B.

Grosberg is interested in how new species arise in the ocean. On land, groups of plants and animals can be physically isolated by mountains or rivers and then diverge until they can no longer interbreed even if they meet again. But how does this isolation happen in the wide-open ocean?

Grosberg and colleagues studied two closely related “cushion stars,” Cryptasperina pentagona and C. hystera, living on the Australian coast. The animals are identical in appearance but live in different regions: Hystera occurs on a few beaches and islands at the far southern end of the range of pentagona.

And their sex lives are very, very different. Pentagona has male and female individuals that release sperm and eggs into the water where they fertilize, grow into larvae and float around in the plankton for a few months before settling down and developing into adult sea stars.

Hystera are hermaphrodites that brood their young internally and give birth to miniature sea stars ready to grow to adulthood.

“It’s as dramatic a difference in life history as in any group of organisms,” Grosberg said.

The researchers looked at the diversity in DNA sequences from sea stars of both species and estimated the length of time since the species diverged.

The results show that the species separated about 6,000 to 22,000 years ago. That rules out some ways new species could evolve. For example, they clearly did not diverge slowly with genetic changes over a long period of time, but were isolated quickly.

Over the last 11,000 years, the boundary between cold and warm water in the Coral Sea has fluctuated north and south. A small population of the ancestral sea stars, perhaps even one individual, might have colonized a remote area at the southern end of the range then been isolated by one of these changes in ocean currents.

Other authors on the paper are: Jonathan Puritz and Robert Toonen, University of Hawaii; at Simon Fraser University in British Columbia, Canada Michael Hart and Carson Keever, who earned his undergraduate degree from UC Davis; Jason Addison, University of New Brunswick, Canada (previously a postdoctoral researcher at UC Davis); and Maria Byrne, University of Sydney.

The work was supported by a grant from the National Science Foundation to Grosberg and Toonen, a former UC Davis graduate student.


Journal Reference:

  1. J. B. Puritz, C. C. Keever, J. A. Addison, M. Byrne, M. W. Hart, R. K. Grosberg, R. J. Toonen. Extraordinarily rapid life-history divergence between Cryptasterina sea star species. Proceedings of the Royal Society B: Biological Sciences, 2012; DOI: 10.1098/rspb.2012.1343


University of California – Davis (2012, July 23). Superfast evolution in sea stars. ScienceDaily. Retrieved July 26, 2012, from­ /releases/2012/07/120724104638.htm