Study Confirms Endangered Mammal Existence Before Dinosaurs' Extinction

A study confirmed that Hispaniolan solenodon, a venomous mammal has separated from all other living mammals 78 million years ago, long before an asteroid wiped all dinosaurs out.

Researchers from University of Illinois and University of Puerto Rico have finished sequencing the mitochondrial genome for the strange mammal that filled in the last major branch of placental mammals on the tree of life. Science Daily reported that researchers were able to catch the solenodon by allowing it to walk around at night in the forests of the Dominican Republic.

"It's just impressive it's survived this long," said co-first author Adam Brandt, a postdoctoral researcher at Illinois. "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."

Since a child's nuclear DNA is a mixture of genes from each parent, researchers used the mitochondrial DNA because it is directly passed from mother to offspring without any changes. This created a genetic record that researchers used to trace back the lineage of the mammal.

According to Carl R. Woese Institute for Genomic Biology, the study supports recent findings that the Dominican Republic contains genetically distinct northern and southern populations that should be conserved as separate sub-species. The study also found that the northern population is much more diverse than the southern population.

Because solenodons are endangered, it is difficult to collect DNAs from them. UPR Professor of Genetics, Tara Oleksyk and his team worked with colleagues from several universities in the Dominican Republic to collect samples from these mammals. They laid on the ground and waited for the solenodons to crawl across them.

Brandt and co-first author Kirill Grigorev, a bioinformatician at the Caribbean Genome Center then analyzed the samples using two different methods to verify the sequence of nucleotides, the building blocks that make up DNA, of the solenodon's mitochondrial genome. It later showed that the two methods showed the exact same results.

A past study used a different set of genes to estimate that the solenodons separated from other mammals during the Cretaceous Period some 76 million years ago. Basing from that study, this new study worked with an expert at Texas A&M and used a very different method but still came up with an estimate of 78 million years.

These estimates also aligned with a hypothesis that claims the solenodon inhabit the island of Hispaniola. Scientists believe that the island was part of a volcanic arc connected to Mexico 75 million years ago, and over time the arc has moved towards the east. "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 lead researcher Alfred Roca, a professor of animal sciences and member of the Carl R. Woese Institute for Genomic Biology.

What they do know is that any close ancestors are long gone, and today's solenodons are the only remnant of a very ancient group of mammals. While the solenodon is venomous and resembles a "giant rat with Freddy Krueger claws" (according to Roca), it evolved in the absence of carnivores. Today, it is threatened by cats and dogs introduced by humans as well as habitat loss.