Yukon’s fos­sil mys­tery

Canadian Geographic - - CONTENTS - BY JOHN BEN­NETT

PALEONTOLOGISTS IN YUKON are work­ing to solve one of the North’s great mys­ter­ies — the rea­son for the ma­jor ex­tinc­tion of large mam­mals at the end of the last ice age — and gold min­ers and In­dige­nous hun­ters are help­ing gather the clues. Yukon lay be­yond the reach of the mas­sive glaciers that cov­ered most of Canada at var­i­ous times dur­ing the Pleistocene era, which lasted from 2.5 mil­lion to 12,000 years ago, and a rich di­ver­sity of large mam­mals (horses, woolly mam­moths, ground sloths, li­ons, camels and other ex­otic an­i­mals) thrived on its tun­dra land­scape. To­day their bones lie pre­served in the per­mafrost, but there’s no need for paleontologists to go dig­ging for them. Around Daw­son, min­ers who search for gold in stream beds are con­stantly un­earthing fos­sils, and Yukon pa­le­on­tol­o­gist Grant Zazula and his col­leagues have only to travel the back roads ev­ery sum­mer to visit the min­ers and col­lect what they’ve found — around 6,000 fos­sils each year. In Old Crow, the peo­ple of the Vun­tut Gwitchin First Na­tion are ex­perts at find­ing and iden­ti­fy­ing bones ex­posed by erod­ing river­banks, and play a prom­i­nent role in the re­search. Ge­netic anal­y­sis al­lows Zazula to dis­cover the re­la­tion­ships be­tween an­i­mals and how their pop­u­la­tions changed over time. Per­mafrost pre­serves DNA, and in­for­ma­tion can be coaxed from the tini­est of sam­ples — from where an an­i­mal uri­nated, for in­stance, or from mi­cro­scopic or­gan­isms. “With a chunk of frozen sed­i­ment,” says Zazula, “you can iden­tify the pres­ence of all kinds of dif­fer­ent species.” So what caused the ex­tinc­tions? A se­ries of cli­mate changes is part of the puz­zle. Dur­ing warm pe­ri­ods, camels, ground sloths, Amer­i­can mastodons and other warm-cli­mate an­i­mals mi­grated north, but died out when the cli­mate cooled again. The ar­rival of com­pe­ti­tion from Asia may be an­other fac­tor. Af­ter bi­son crossed the Ber­ing land bridge to North Amer­ica about 150,000 years ago, their pop­u­la­tion sky­rock­eted. “They ba­si­cally kicked ev­ery­one else out,” says Zazula. “Horses, mam­moths and other large her­bi­vores just couldn’t com­pete — and we know bi­son sur­vived the end of the ice age.” Cari­bou, which weren’t abun­dant dur­ing the Pleistocene, went on to be­come the North’s dom­i­nant large land mam­mal. Re­searchers are still search­ing for con­clu­sive an­swers about what caused all those an­i­mals to go ex­tinct, but it’s not just about ex­tinc­tion. “Some species were given new op­por­tu­ni­ties to thrive,” says Zazula. “And what we’re dis­cov­er­ing about how to­day’s north­ern mam­mals and en­vi­ron­ments came to be helps us un­der­stand changes we’re see­ing now, as cli­mate change brings warmer win­ters to the Yukon.”

An il­lus­tra­tion of Pleistocene-era mam­mals on Yukon’s tun­dra land­scape. Ter­ri­to­rial sci­en­tists are work­ing to de­ter­mine what caused many of these species to go ex­tinct.

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