Media Releases

Canadian researcher helps put humans on the tree of life

February 7, 2013

International effort traces placental mammals back to a scampering common ancestor that appeared after extinction of dinosaurs.

TORONTO, ON — A Uni­ver­si­ty of Toron­to Scar­bor­ough researcher was part of a team that recon­struct­ed the fam­i­ly tree of pla­cen­tal mam­mals – a diverse group that includes cats, dogs, hors­es and humans. The research traces pla­cen­tal mam­mals back to a small, scam­per­ing, insect-eat­ing crea­ture that got its start 200,000 years or more after the extinc­tion of the dinosaurs.

The work is fea­tured in this week’s Sci­ence mag­a­zine.

Mary Sil­cox, assis­tant pro­fes­sor of anthro­pol­o­gy at UTSC, is a co-author on the paper and the only Cana­di­an mem­ber of the team. She was respon­si­ble for orga­niz­ing the den­tal traits used in the analy­sis and con­tributed to the col­lec­tion of the data that were used to clas­si­fy pri­mates, includ­ing humans.

“We were respon­si­ble for putting humans in the tree of life,” she says, refer­ring to her work with Drs. Jonathan Bloch of the Flori­da Muse­um of Nat­ur­al His­to­ry and Eric Sar­gis of Yale Uni­ver­si­ty.

The research team used the world’s largest dataset com­bin­ing genet­ic and phys­i­cal traits to recon­struct the pla­cen­tal mam­mal tree of life. A major find­ing is that pla­cen­tal mam­mals diver­si­fied much lat­er than pre­vi­ous the­o­ries had sug­gest­ed, with all of the major groups alive today orig­i­nat­ing after the extinc­tion of the dinosaurs. Genet­ic evi­dence alone had sug­gest­ed that pla­cen­tal mam­mals were already a diverse group in the Late Cre­ta­ceous peri­od, before the event that drove the dinosaurs and 70 per cent of oth­er then-exist­ing species extinct.

But by adding evi­dence from fos­sils, the team con­clud­ed that pla­cen­tal mam­mals arose a few hun­dred thou­sand years after the extinc­tion event.

To car­ry out the study, the researchers built a data­base that record­ed phys­i­cal – or phe­nom­ic – traits for 86 pla­cen­tal mam­mal species, includ­ing 40 species that are extinct and known only from fos­sils. More than 4,500 traits, includ­ing the pres­ence or absence of wings, teeth, and cer­tain bone types, were record­ed in the data­base and used to con­struct the tree of life, in com­bi­na­tion with genet­ic data.

The phe­nom­ic dataset is 10 times larg­er than those that had pre­vi­ous­ly been used to study mam­mal rela­tion­ships, is pub­licly avail­able online, and illus­trat­ed with over 12,000 images.

Sil­cox says that the work will serve as a mod­el for future projects that will give us a bet­ter idea of how species evolved and are relat­ed to one anoth­er.

The research was fund­ed by the Nation­al Sci­ence Foun­da­tion, and led by researchers at the Amer­i­can Muse­um of Nat­ur­al His­to­ry and oth­er insti­tu­tions from the U.S., Cana­da, and else­where.


For more infor­ma­tion, con­tact:

Mary Sil­cox
Assis­tant Pro­fes­sor, Depart­ment of Anthro­pol­o­gy
Uni­ver­si­ty of Toron­to Scar­bor­ough
Tel: 416–208-5132


Kurt Klein­er
Depart­ment of Com­mu­ni­ca­tions and Pub­lic Affairs
Uni­ver­si­ty of Toron­to Scar­bor­ough
Tel: 416–287-7008