Plionarctos

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search

Template:Short description Template:Automatic taxobox

Plionarctos is an extinct genus of short-faced bear endemic to North America from the Late Miocene to the Pliocene.

Taxonomy

Described by Childs Frick in 1926,[1] Plionarctos is the oldest known genus within the subfamily of the short-faced bears (Tremarctinae),[2] and is believed to be ancestral to Arctodus, Arctotherium and Tremarctos.[3] Plionarctos probably evolved from Ursavus which emigrated into North America from Eurasia during the Miocene,[4] or possibly Protarctos.[5] A new species, Plionarctos harroldum, was described in 2001 from the White Bluffs Fauna in Washington from remains previously attributed to Protarctos abstrusus.[3] Middle Pleistocene remains from France were reported but have since been reassigned to Ursus.[6]

Evolution

Tremarctinae within Ursidae

Script error: No such module "Clade".

Script error: No such module "Check for unknown parameters".Plionarctos first appeared in North America during the late Miocene epoch, being recorded from the Rattlesnake Formation of Oregon circa 7Ma.[7] Plionarctos was the sole representative of the Tremarctinae subfamily of bears during its existence, with P. edensis being thought to be ancestral to P. harroldorum.[3] Both Plionarctos edensis and Plionarctos harroldorum coexisted in the Late Hemphillian faunal stage of the Late Miocene, although only P. harroldorum is confirmed from the Blancan faunal stage.[3]

Plionarctos is last recorded ca. 2.9Ma from Taunton, Washington, from a specimen which appears to be evolutionarily intermediate between Plionarctos harroldum and Tremarctos floridanus.[8][9] Plionarctos was followed by three new genera of short-faced bear around the Plio-Pleistocene boundary.[10] These were Arctodus (pristinus), Tremarctos (floridanus) and Arctotherium sp., which emerged in the Late Blancan age of North America circa 2.6Ma.[11][12][13]

An investigation into the mitochondrial DNA of bear species indicates that the short-faced bears diverged from the Ursinae subfamily approximately 5.7 million years ago.[14][15] Around the Miocene-Pliocene boundary (~5.3 Ma) short-faced bears, along with other ursids, experienced an explosive radiation in diversity, as C4 vegetation (grasses) and open habitats dominated, the world experienced a major temperature drop and increased seasonality, and a faunal turnover which extinguished 60–70% of all Eurasian faunal genera, and 70–80% of North American genera.[16][17] Correspondingly, the three succeeding genera appear to genetically diverge around this time, with Arctodus splitting from Arctotherium and Tremarctos at between 5.5Ma and 4.8Ma,[10][18] and Arctotherium and Tremarctos branching off at 4.1Ma.[10]

Description

Plionarctos is thought to have weighed around the size of a smaller spectacled bear (60-150kg), and a skull length of 20cm.[7] Postcranial skeletons of Plionarctos are unknown.[7]

Diagnostics

Unlike other tremarctine bears, Plionarctos did not posses a premasseteric fossa. Although tooth sizes are similar, they also be differentiated from Tremarctos by the slightly shorter M2 molar.[7]

Paleobiology

Plionarctos existed between the middle Hemphillian faunal stage to the early Blancan faunal stage (7Mya - 2.9Mya).[7] Present on the coasts but rare in the Great Plains, Plionarctos is thought to have preferred more humid forested habitats.[7]

Like other tremarctine bears, Plionarctos is believed to have been sexually dimorphic.[7] A Plionarctos harroldum specimen from Taunton (Washington, 2.9Ma)[19] appears evolutionarily intermediate between P. harroldum and T. floridanus, such as being the size of T. floridanus.[20]

Fossil distribution

P. edensis

P. harroldorum

References

<templatestyles src="Reflist/styles.css" />

  1. ↑ Script error: No such module "Citation/CS1".
  2. ↑ Script error: No such module "Citation/CS1".
  3. ↑ a b c d e f g h i Script error: No such module "Citation/CS1".
  4. ↑ Script error: No such module "Citation/CS1".
  5. ↑ Script error: No such module "Citation/CS1".
  6. ↑ Script error: No such module "Citation/CS1".
  7. ↑ a b c d e f g h i j k l m Script error: No such module "citation/CS1".
  8. ↑ Script error: No such module "Citation/CS1".
  9. ↑ Script error: No such module "Citation/CS1".
  10. ↑ a b c Script error: No such module "Citation/CS1".
  11. ↑ Script error: No such module "Citation/CS1".
  12. ↑ Script error: No such module "Citation/CS1".
  13. ↑ Script error: No such module "Citation/CS1".
  14. ↑ Script error: No such module "Citation/CS1".
  15. ↑ Script error: No such module "Citation/CS1".
  16. ↑ Script error: No such module "Citation/CS1".
  17. ↑ Script error: No such module "Citation/CS1".
  18. ↑ Script error: No such module "Citation/CS1".
  19. ↑ Script error: No such module "Citation/CS1".
  20. ↑ Script error: No such module "Citation/CS1".
  21. ↑ Script error: No such module "citation/CS1".
  22. ↑ Script error: No such module "Citation/CS1".
  23. ↑ Script error: No such module "Citation/CS1".
  24. ↑ Script error: No such module "Citation/CS1".
  25. ↑ Script error: No such module "citation/CS1".
  26. ↑ Script error: No such module "Citation/CS1".
  27. ↑ Script error: No such module "Citation/CS1".
  28. ↑ Script error: No such module "Citation/CS1".

Script error: No such module "Check for unknown parameters".

Template:Ursidae extinct nav Template:Taxonbar

Retrieved from "http://debianws.lexgopc.com/wiki143/index.php?title=Plionarctos&oldid=9106085"