The Eocene 5434 mya

1
The Eocene (54-34 mya)

• Global Warming and the Origin of Modern Primates
  (and many other modern mammals)

2
Middle Eocene Geography
3
Paleogeography during the Eocene

• South America Antarctica, Africa, and Australia
  remain as island continents
• North America connected to Europe and Asia until
  middle or late Eocene
• Tethys Sea separates Africa from Eurasia
• Eocene climate was generally warmer and more
  equable than Paleocene

4
PETM and Global Warming

• Paleocene-Eocene Thermal Maximum
• Huge release of methane into atmosphere from
  frozen methane hydrate deposits in sea
• Methane has 20X heat retaining ability as that
  other greenhouse gas, carbon dioxide
• Warming effects last 100,000 years and increase
  high latitude temperature by 7 degrees Celsius
• Negative carbon isotope excursion, benthic
  extinction, and land mammal turnovers and
  migrations
• Warmest period of entire Cenozoic Era

5
Faunal Turnover at PE Boundary

• Wasatchian NALMA
• First appearance of Euprimates, Perissodactyls
  and Artiodactyls signals beginning of Eocene
• High latitude dispersal from Asia to North
  America and Europe
• Turnover from archaic to modern orders of
  mammals throughout northern hemisphere
• Result of global warming???

6
The First Euprimates

• First creatures that share major synapomorphies
  of modern primates
• Post orbital bars, orbital frontation, and short
  snouts
• Nails and grasping thumbs and big toes
• Larger brains, changes in cranial blood supply,
  and petrosal bulla
• Dental and cranial similarities
• Two major groups of prosimians in the Eocene
• Adapoidea and Omomyoidea

7
Distribution of Eocene Primates

• Very common in North America and Europe, very
  rare in Asia and Africa
• N America and Europe still connected across N
  Atlantic during early Eocene
• Unknown from S. America and Antarctica and
  Madagascar
• First appear at very beginning of Eocene, mostly
  gone by the end of the Eocene
• Probably NOT descendants of any known
  plesiadapiformes (they were all too specialized)

8
Adapoidea

• Most primitive of all known primates
• Large body size, 2-1-4-3 DF, small vertically
  implanted incisors, large and sexually dimorphic
  canines, grasp-climbing adaptations in
  limbs,post-orbital bars, inflated petrosal bulla
  with suspended tympanic ring, molars often with
  lots of shearing crests (folivory?), mostly
  diurnal, mostly quadrupedal, no evidence of
  dental comb.

9
Subfamilies of Adapidae

• Notharctinae
• Cantius from E Eocene of N America Europe
• Notharctus Smilodectes from M Eocene of N
  America
• Pelycodus Copelemur from E Eocene of N America
• Large bodied, frugivores folivores, sexually
  dimorphic, grasp climbing arboreal quadrupeds
  with some leaping adaptations
• Similarities to modern prosimians like lemurs

10
Subfamilies of Adapidae

• Adapinae
• Adapis and Leptadapis from Late Eocene - Late
  Oligocene of Europe
• Medium to large body size with folivorous molars
• Slow arboreal quadrupedal locomotion, with no
  evidence of leaping, like modern lorises
• Adapoids from China suggests Asian origin
• Cercamoniinae or Protoadapinae
• Early to Late Eocene of Europe, Africa, Asia,
  N. America
• Closely related to Notharctines, but more diverse
• Most known only from dental remains

11
Are Adapoids Strepsirhines?

• They are lemur-like in many respects, but these
  similarities are all symplesiomorphies
• Cheek teeth
• Skull shape (postorbital bar long snout)
• Inflated bulla free ectotympanic ring
• Carotid circulation blood supply to brain
• Adapoids lack the dental comb but share a few
  synapomorphies with strepsirhines
• Grooming claw on pedal digit 2
• Flaring fibular surface on talus
• Arrangement of cuneiform facets on navicular

12
Omomyoids

• Generally tarsier-like in many respects
• Large, procumbent lower incisor, small canines,
  unfused mandibular symphysis, large eyes reflect
  nocturnality w/ tapetum lucidum, inflated
  petrosal auditory bulla with attached tympanic
  ring that forms a bony tube, moderately elongated
  calcaneus in some, and partially fused tibia and
  fibula in some, small to tiny body size in most
  (some late forms are large).

13
Omomyidae

• Mostly North American Eocene forms, include 2
  subfamilies
• Anaptomorphinae are most primitive group, most
  abundant in early Eocene
• Teilhardina is earliest form and is found in both
  Europe and North America during early Eocene
• Skulls are known from Shoshonius and Tetonius
• Postcrania are known from Shoshonius and
  Absarokius
• Both cranial and postcranial similarities to
  modern Tarsius are found in these anaptomorphines
• Nocturnal, leaping, insectivorous and frugivorous

14
Omomyidae

• Mostly N American forms, include 2 subfamilies
• Omomyinae are the 2nd group of N American
  omomyids, most abundant in middle and late Eocene
• Lower taxonomic diversity but greater dental
  diversity than anaptomorphines, 100g to 2 kg in
  body size
• Skull is only known from Rooneyia, from late
  Eocene of Texas
• Postcrania known from Hemiacodon and Omomys
• Both show leaping and quadrupedalism, similar to
  cheirogaleids or galagos, less specialized than
  tarsiers

15
Michrochoeridae

• Four genera from middle to late Eocene of W
  Europe, 50g to 1.8kg body size range
• All nocturnal with large eyes with tapetum
• Postcranials show partial tibia-fibular fusion
  and some calcaneal elongation, suggest leaping
• Recent suggestions of omomyoid presence in China,
  Pakistan, and Egypt (Fayum)
• Fossil tarsiids have been recovered from
  Oligocene of Egypt and the Eocene of China
• Suggest that tarsier lineage is at least 50 my old

16
Haplorhines and Strepsirhines

• Prosimian-Anthropoid dichotomy is a horizontal,
  non-phylogenetic, grade-based distinction
• Haplorhine-Strepsirhine is a vertical,
  phylogenetic, cladistic distinction
• Haplorhines include all living anthropoids plus
  tarsiers
• Strepsirhines include all living prosimians
  except tarsiers

17
Phylogenetic Relations

• Many omomyoid-tarsiid similarities seem to be
  homoplasies or symplesiomorphies
• Older idea that omomyoids are ancestors to
  tarsiers is fading, especially with evidence of
  middle Eocene tarsiids in China and Africa
• Omomyoids may be basal to haplorhines
• Adapoids may be basal to strepsirhines
• Tarsiids may be an independent lineage for 50my
• Anthropoid origins must be sought elsewhere

18
Adaptive Radiation of Eocene Euprimates

• Contrasting (complementary?) ecological patterns
  distinguish between adapoids and omomyoids
  throughout the Eocene in Europe N. America
• Body size
• Activity patterns
• Diet
• Locomotion
• Diversity
• By the end of the Eocene, the reign of these
  early Euprimates is over, and primates virtually
  disappear from Europe N. America