Mastodon Ranges Fluctuated with Climate Changes

When I first began my blog I was unsure of my writing, so I submitted samples to an internet forum at absolutewrite.com.  One person criticized me for being redundant when I wrote about mammoths and mastodons because he wrongly assumed I was referring to the same animal.  I explained they were 2 completely different species: mastodons were a semi-aquatic animal that mostly ate leaves, twigs, and fruit; while mammoths were an upland species that mostly ate grass.  The lead author of a new study of mastodon genetics admitted he had the same misconception prior to studying the mastodon genome.  Emil Karpinski is a geneticist not a paleontologist, and his false assumption is understandable. Karpinski and his colleagues sequenced the complete genomes of 33 individual mastodon specimens and the partial genomes from an additional 12 individual specimens.  They found 5 major clades from different geographical locations including Alaska, Yukon, Alberta/Missouri, Mexico, and Virginia/Great Lakes.  A single specimen from Nova Scotia indicates the possible discovery of a 6th clade.  Genomes of mastodons from Alberta suggest a mixture of 3 different clades.  This region was a migratory corridor between the Cordilleran and Laurentide Glaciers during interglacial climate phases when Ice Sheets retreated.  Different populations came into contact here when mastodons expanded their range north during interglacials.

Image showing how mastodon ranges expanded during interglacials and contracted during Ice Ages.  Southern mastodons were more genetically diverse than northern mastodons because northern populations were extirpated during every Ice Age.  From the below reference.

Map showing location of mastodon specimens used in the genetic study.  Also from the below reference.

The genetic evidence clearly shows mastodons expanded their range into Canada and Alaska between Ice Ages, and the expansions occurred at least twice, probably more.  Spruce forests and wetlands in Alaska converted into dry grassland during Ice Ages–unsuitable habitat for a semi-aquatic species.  And of course Canada was covered with thick glacial ice–inhospitable to most life.

The authors of this paper express bafflement over why mastodons did not recolonize Alaska and Canada following the last Ice Age.  Wetlands and spruce forests expanded when glaciers retreated and left behind meltwater lakes and bogs.  The answer is obvious and no mystery at all.  Men disrupted mastodon migration routes and overhunted them to extinction.  Large areas of suitable mastodon habitat exist today all over North America, but they are devoid of these massive beasts because they could not co-exist with increasing human populations.

Reference:

Karpinski, E.; et. al.

“American Mastodon Mitochondrial Genomes Suggest Multiple Dispersal Events in Response to Pleistocene Climate Oscillations”

Nature Communications 11 Article 4048 (2020) 

https://www.nature.com/articles/s41467-020-17893-z

 

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