The Zoonomia Consortium developed an evolutionary timeline

The evolution of mammals through genomic comparisons.

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Environmental forces are essential for understanding placental mammals’ morphological and genomic diversity.

Mammals, which include the smallest pygmy shrew to the powerful blue whale and, of course, us, are an incredibly successful and diverse group of creatures.

The Zoonomia Consortium, led by MIT and Harvard University’s Broad Institute and affiliated with the Earth BioGenome Project, published a special issue of Science Today (April 27) that demonstrated how comparing the genomes of 240 modern mammals sheds light on mammalian evolution with implications for conservation and understanding human and animal health.

The study revealed sections of mammalian genomes, sometimes as few as a single base or letter of DNA, that had changed the least across millions of years and mammalian species. 

Harris Lewin, distinguished professor of evolution and ecology at UC Davis and collaborator in the consortium. Lewin, also chairs the executive working group of the Earth BioGenome Project, said, “The Zoonomia Consortium was formed around the idea that comparative genomics would reveal important details of mammalian evolution at the genomic level and provide a powerful new tool for understanding human diseases, With the incredible set of papers published this week, the consortium has fulfilled its promise and is poised to make more breakthrough discoveries as additional mammalian genomes are sequenced to a higher standard of quality.”

The group has fulfilled its promise and is poised to produce even more groundbreaking discoveries when more mammalian genomes are sequenced to a higher quality level.

One of the papers in the collection, co-authored by Lewin, used genomic data from modern mammals to reconstruct the evolution of the group since the first mammalian ancestor appeared around 180 million years ago. 

It has been unclear whether placental mammals evolved before the mass extinction or after it, once the dinosaurs had vanished.

Mammals coexisted with dinosaurs for 120 million years and, except for modern birds, survived the mass extinction that wiped off the dinosaurs. It has been unclear whether placental mammals evolved before the mass extinction or after it, once the dinosaurs had vanished.

Foley, Murphy, and UC Davis postdoctoral researcher Joan Murphy used data from the Zoonomia project on modern mammals to show that Even in the lack of a fossil record, the molecular clock affords us the ability to precisely determine when and where various mammalian lineages last shared ancestors. 

Murphy said, “The molecular clock gives us the power to precisely understand when and where different lineages of mammals last shared common ancestors, even in the absence of a fossil record.” 

They discovered that mammals began diversifying before the Cretaceous-Tertiary mass extinction as a result of continental drift, which caused the Earth’s land masses to move apart and then put together over millions of years.

Another wave of diversification happened immediately after the dinosaurs died out when mammals had greater space, resources, and stability.

This faster rate of diversification resulted in the vast array of mammal lineages that exist today, including carnivores, primates, and hoofed mammals. 

Lewin said, “This is the first time that the timing of chromosome rearrangements in mammalian evolution was able to help resolve important issues in mammalian phylogenetics, These data, provided as part of our collaboration with the Murphy group and the Zoonomia Consortium, have clarified the relationships of two mammalian orders to other groups. We think that this approach is going to be helpful to resolving disputed phylogenetic relationships in many other parts of the eukaryotic tree of life.”  

Other highlights from the special issue include the discovery that at least 10% of the human genome is highly conserved across other mammals, indicating regions critical to life and fundamental processes, identifying genomic regions associated with exceptional traits such as hibernation, brain size, or a superior sense of smell, and identifying mutations linked to both rare and common human diseases. 

The National Institutes of Health, Swedish Research Council, Knut, Alice Wallenberg Foundation, and National Science Foundation supported this research.

Journal Reference:

  1. Foley, N. M., Mason, et al. A genomic timescale for placental mammal evolution. Science. DOI: 10.1126/science.abl8189

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