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.
Ursus maritimus
Polar Bear
120 KYA
Svalbard
Ursus arctos
Brown Bear
500 KYA
Zhoukoudian
Ursus spelaeus
Cave Bear
1.2 MYA
France
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)
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
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.