The Timeline of Bears

Amniotes
320 MYA

Mammals
180 MYA

Caniformia
43 MYA

Common Ancestor
Raccoons, Bears, and Seals
40 MYA

Ursavus
17.5 MYA

Ursinae
Bears
1.25 MYA

Ailuropodinae
Giant Panda
3 MYA

Sauropsids
300 MYA

Seals
27 MYA

Ursus Arctos
Brown Bear
500 KYA

Ursus Maritimus
Polar Bear
150 KYA

Present

Extensive debate exists on the speciation of polar bears. With estimates ranging from 5 MYA to 150 KYA.

ancient-polar-bear-jawbone1
Ursus maritimus
Polar Bear
120 KYA
Svalbard

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Ursus arctos
Brown Bear
500 KYA
Zhoukoudian

Cave_Bear_(Ursus_Spelaeus)1
Ursus spelaeus
Cave Bear
1.2 MYA
France

1598px-Ursavus_tedforti1
Ursavus tedforti
8 MA
China

The genus that beget modern bears but itself went extinct.

Tremarctinae
Short Faced Bears
12 MA

The common ancestor for Mammals, Reptiles, and Birds

Dogs
35 MYA

Bears that crossed the Panamanian isthmus into North America

Largely extinct bar the spectacled bear of South America

McLellan, B., Reiner D. (1994)

Between a cat and wolf in size

Bears got big

McLellan, B., Reiner D. (1994)

Basically unseen in regions without caves

McLellan, B., Reiner D. (1994)

Expanded into Europe and Africa 250 KYA

McLellan, B., Reiner D. (1994)

Liu et al. (2014)

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GettyImages-8838299421

Spectacled+Bear51

768324-panda-bear-background-3840x2160-computer1

Ailuropoda melanoleuca
Giant Panda

Poor fossil record and disputed lineage, particularly as related to raccoons.

Genetic analysis pegs pandas firmly as a subspecies of bear, their closeness to raccoons is remarkable however.

O'Brien et al. (1985)

Ailuropoda_microta-removebg-preview1

Ailuropoda microta
2 MYA
Guangxi

Much smaller than great pandas

Distant Cousins
Though the giant panda is from 3 MYA, their ancestors' divergence from mainline bears began nearly 15 MYA. Thus pandas are the most estranged living members of the bear family.

Nine species of ursavus have been identified

Ursavus elmensis, the dawn bear, is the oldest of the genus and what we would consider to be the first bear.

What we see as bears develop is that they are increasing in size and their dentition is changing. Wolves have the teeth of a carnivore, whereas at this point bears begin moving towards an omnivoric existence.

As a result of their environment, polar bears are the most carnivorous of the living bears.

Due to the fact that polar bears are descended from brown bears, hybridization can occur. This results in the pizzly or grolar bear. This has been observed both in the wild and in captivity.