A new study by researchers from the University of Illinois and University of Puerto Rico has compiled the mitochondrial genome of the venomous species Hispaniolan solenodon, completing the last major branch of placental mammals on the tree of life and suggesting that they might have lived with dinosaurs.

The study reveals that H. solenodon diverged from other living mammals approximately 78 million years ago, which is long before the dinosaurs met their demise from an asteroid collision.

"It's just impressive it's survived this long," said Adam Brandt, postdoctoral researcher at the University of Illinois and co-first author of the study. "It survived the asteroid; it survived human colonization and the rats and mice humans brought with them that wiped out the solenodon's closest relatives."

The results also suggest that the Dominican Republic contains northern and southern populations that are genetically distinct, with the southern population possessing little diversity and the northern population possessing a high level of diversity.

The team examined the mitochondrial DNA to trace the lineage of the solenodon, determining that it diverged from mammals during the Cretaceous period approximately 78 million years ago.

Not only is this number very close to the estimate of a previous study - 76 million years - it also supports the hypothesis regarding how the solenodon made its way to the island of Hispaniola using its connection with a volcanic arc connected to Mexico 75 million years ago.

"Whether they got on the island when the West Indies ran into Mexico 75 million years ago, or whether they floated over on driftwood or whatever else much later is not very clear," said Alfred Roca, professor of animal sciences, member of the Carl R. Woese Institute for Genomic Biology at University of Illinois and senior author of the study.

Today, all close ancestors of the solenodons are gone, making the modern species the last of an ancient group of mammals that might have lived alongside dinosaurs. Although the unique mammals are venomous and possess a somewhat scary appearance, they evolved in the absence of carnivores and are currently threatened by cats, dogs and habitat loss.

The findings were published in the April 20 issue of the journal Mitochondrial DNA.