Life in the Northern Hemisphere if Beringia Never Drowned

Question

When one hears the name "Beringia", we most often think the land bridge that formed as a result of a drop in sea levels during the Pleistocene, resulting in a connection between Alaska and Russia. But Beringia had been connecting East to West in a continuous cycle, the earliest so far being in the late Cretaceous, opening ceratopsians, troodontids and even tyrannosaurs from Asia to North America.

Nowadays, Beringia is submerged beneath sea level. As a result, North America has a different cast from Eurasia, the splits being listed as follows:

• Telemetacarpal deer (whitetails, caribou, moose, deer that are more common in North America than in Eurasia) and plesiometacarpal deer (chitals, fallows, wapitis, reds, deer that are more common in Eurasia than in North America)

• Peccaries and pigs

• Hyenas and dogs

• Old World porcupines (Hystricidae) and New World porcupines (Erethizontidae)

• Pronghorns and antelopes (No, this is not a typo, as pronghorn aren't true antelopes)

• Leopards and pumas/jaguars

• American sparrows (Passerellidae) and Old World sparrows (Passeridae)

• Condors and vultures

• Pandas and raccoons

Now, in this speculative scenario, Beringia has been open for permanent business for at least five million years. Beringia would obviously homogenize the animals of the northern hemisphere, but from the list above, which side of each split would be more successful at colonizing both North America AND Eurasia at once?

Answer 1

I pick the pig as being most successful European in North America, and the raccoon as most successful New Worlder in Eurasia.

There is data from historic times about how well introduced species do in their new homes, and one can use this to extrapolate back. Old World sparrows have been phenomenally successful in North America but I suspect this might be an artifact of human impacts on the environment and that old world sparrows might have done less well in the original North American ecosystem.

Pigs, though, are a safe bet. They are huge successes in their native lands and everywhere else. Pigs always do great. European explorers dropped off pigs wherever they went, so they would have something to eat when they went back. Everywhere they were placed, pigs (or wild boars) flourish. They are smart, opportunistic, adaptable, durable omnivores with a short generation time. Peccaries are really not competition for Eurasian pigs; peccaries are little, desert adapted animals and dry desert is the one ecosystem Eurasian pigs would struggle with.

Raccoons are my bet for the New World species that would best colonize Europe and for the same reasons: smart, opportunistic, adaptable omnivores, but small, arboreal and with hands. Monkeys occupy that niche in the tropics but with rare exceptions (e.g. snow monkeys, Barbary apes) the temperate Eurasian ecosystem did not and does not have any creatures like that. And also, current data shows that Europe is prime habitat for raccoons - although introduced in continental Europe only in the 1950s, they have hit the ground running.
https://www.businessinsider.com/germany-europe-raccoon-problem-2016-6

Answer 2

The best choice isn't on your list:

Mastodons vs Woolley Mammoths. Both, unlike their Elephant cousins, do well in the cold. They represent two distinct species of the Proboscidean family.

From your list though, I'm gonna say..

Dogs.

Wolves are already native to the American side of Beringia. And there are Asian wolves as well.

The closest living relative of the dog is the gray wolf and there is no evidence of any other canine contributing to its genetic lineage. The dog and the extant gray wolf form two sister clades, with modern wolves not closely related to the wolves that were first domesticated...the earliest dogs arose in the time of human hunter-gatherers and not at the dawn of agriculture.

Where the genetic divergence of dog and wolf took place remains controversial, with the most plausible proposals spanning Western Europe, Central Asia, and East Asia. This has been made more complicated by the most recent proposal that fits the available evidence, which is that an initial wolf population split into East and West Eurasian wolves, these were then domesticated independently before going extinct into two distinct dog populations between 14,000-6,400 years ago, and then the Western Eurasian dog population was partially and gradually replaced by East Asian dogs that were brought by humans at least 6,400 years ago. (ref)

If wolves, dogs, and people were able to go back and forth between Asia and the Americas continuously for the entirety of their existence, the domestic dog would be on both sides and there would be more standardization. We know these species (and humans at least back in the last 50-100k years) can handle the cold weather of Beringia, unlike most of the animals on your list.

I am not sure where hyenas come in to this.

Although phylogenetically they are closer to felines and viverrids, and belong to the feliform category, hyenas are behaviourally and morphologically similar to canines in several elements of convergent evolution; both hyenas and canines are non-arboreal, cursorial hunters that catch prey with their teeth rather than claws. Both eat food quickly and may store it, and their calloused feet with large, blunt, nonretractable claws are adapted for running and making sharp turns. However, the hyenas' grooming, scent marking, defecating habits, mating and parental behaviour are consistent with the behaviour of other feliforms. ...

Although the dog-like hyenas thrived 15 million years ago (with one taxon having colonised North America), they became extinct after a change in climate along with the arrival of canids into Eurasia.(ref)

With Beringia continuously open, it is likely that more than one member of the Hyaenidae family would have made it to the Americas. And more of the same kinds could come over and replenish the population.