Geological Time and Vertebrate Evolution

[I] Geological Time and Vertebrate Evolution #

Tuesday, February 11, 2020 — 12:56 PM

Vertebrate Evolution #

• Chordates (Cambrian Period, 560 Ma)
  • earliest vertebrate traits

Cambrian Explosion: Adaptive Radiation of Chordates (~5 my) #

• Organisms with the earliest vertebrate traits

  • Notochord (stiff rod)
  • nerve cord (precursor to brain and spinal cord)
  • pharyngeal slits (respiration)
  • muscular tail (aid in digestion)

• Organisms with the earliest vertebrate traits

  • Notochord (stiff rod)
  • nerve cord (precursor to brain and spinal cord)
  • pharyngeal slits (respiration)
  • muscular tail (aid in digestion)

Upper Cambrian: 510 mya #

• heads
• endoskeleton
• true vertebral column
• closed circulatory system

Lower Silurian: 430 mya #

• Gnathostomata
  • jaws
  • pairs of appendages — ex. placoderms
  • early fish
• lots of niches filled

Middle Devonian: 400 mya #

• Cartilaginous and bony fish
  • chondrichthyes / osteichthyes
  • ↳ leads to mammals
• lobe-finned fish
  • ↳ leads to amphibians

Upper Devonian: 370 mya #

• True amphibians: tetrapods
  • arms, legs
  • 5 digits
  • air breathing
  • live on land — but still laid eggs in water

Environment: new environment outside of water; better support for life

Lower Carboniferous: 320 mya #

• amniotic egg: shelled egg with a hard shell
  • all required nutrients included
  • allows for eggs to develop outside of water

Permian: 270 mya #

• Last part of Paleozoic Era

• Synapsids

• Last part of Paleozoic Era

• Synapsids

  • powerful jaws
  • heterodont dentition (variety of teeth)

• temperature regulation

Later Permian: 260 mya #

• efficient, complex limbs
• higher metabolism
  • give rise to the mammals

Cynodonts: #

• successful in Mesozoic Era
• relied on sense of hearing/smell
• nocturnal
• ruled at night (dinosaurs lived during day)

K-Pg Boundary #

The end of the dinosaurs #

• Plants died out, so dinosaurs lost food source
• Little mammals were used to living in dark, underground conditions
  • flourished, expanded

Middle Triassic: 230 mya #

• Pre mammals (mammaliformes)
• rodent-like
• fur
• bigger brains
• better hearing/ear structures + bones
• mammary glands (lactation)

Mammals #

3 Groups #

• Monotremes (egg laying) — non-therian — mix of amphibian, mammal traits (early branch) — Mid. Triassic
  • ex. Platypus
• Marsupial (pouches) — metatherian — don’t fully gestate babies — Upper Triassic
  • ex. Opossum, kangaroos, koalas
• Placental Mammals — eutherian — mature offspring, large brains, high metabolism (endothermic), heterodont — Cretaceous
  • ex. Pigs, humans

Lots of adaptive radiation over 100 my — evolved all modern mammals

First primate fossils: Eocene

First Primate #

• Arboreal

• Nocturnal

• Insectivore

• Arboreal

• Nocturnal

• Insectivore

• Large forward eyes

• Clinging leaping

Eocene Primates #

• First strepsirhines
  • Adapids (Ida)
  • Omomyids (Necrolemur) — lemur-like
• First haplorhines

Features (Adapids/Omomyids):

• Snout (olfaction)
• Post-orbital bar
• Forward eyes = diurnal
• Grasping hands
• Ectotympanic tube
• Small incisors

Oldest Primate Fossil: Archicebus #

• China
• 55 mya
• Smallest primate
• Similar to tarsiers

Clear haplorhines (anthropoids): #

• Catopithecus
• Proteopithecus
• Found in Egypt
• Enclosed bony orbits
• Fused mandible
• Sexually dimorphic
• Early traits: snout, small brain

New World Monkey Ancestors #

• Continental drift: stock of monkeys already in new world
• Very few fossils due to poor conditions

First Catarrhines: Oligocene #

• Fayum Depression, Egypt
• Aegyptopithecus
  • Long snout, small brain
  • 2.1.2.3 dental, frugivorous (like macaque), Y-5 molar
  • Arboreal quadruped
• Possible ancestors to OWM, hominoids
• Mosaic fossil: mix of primitive/derived traits
• 23–25 mya

True Hominoids: Miocene #

• 5–23 mya

The Miocene: The Age of the Hominoids #

• Late Miocene (11.5–5.2 mya)
  • True Hominoids
  • Mostly Eurasian
    • Pierolapithecus catalunicus — Spain, 13 mya
    • Dryopithecus — Europe, 12.5–9.5 mya
      • Four species, Spain to Georgia

True Hominoids: Miocene #

• 5-23 mya
• Adaptive radiation of hominoids
• Sivapithecus
  • looks like modern orangutan
  • concave face, projecting incisors, tall eye orbits
  • small crania

Did the first ape ancestor evolve in Africa or Eurasia? #

• Gigantopithecus: huge primate

Mostly Eurasian #

• Pierolapithecus catalunicus — Spain, 13 mya
• Dryopithecus — Europe, 12.5-9.5 mya
  • Four species, Spain to Georgia
• Ouranopithecus — Greece, 9.5 mya
• Sivapithecus — South Asia, 12.5-7 mya
  • Three species, Pakistan to Nepal
• Ankarapithecus — Turkey, 10 mya
• Lufengpithecus — China, Thailand, 9 mya