The Evolution of Whales

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The Evolution of Whales

• Natalie Steckler
• Evolution
• Spring 2005

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Introduction

• Scientists currently know that modern whales
  evolved from terrestrial mammals.
• Some scientists link them to ungulates.
• Many transitional fossils have been found,
  forming a possible lineage.
• Evidence also exists in the areas of molecular
  biology, embryology, morphology, and geology.

http//upload.wikimedia.org/wikipedia/en/1/14/Blue
WhaleSkeleton.jpg
3
Modern Whales

• Classification Kingdom Animalia Phylum
  Chordata Subphylum Vertebrata Class
  Mammalia Order Cetacea
• Includes whales, dolphins, porpoises
• Give birth to live young that are nursed
• Adults have no body hair, but some newborns
  exhibit temporary body hair
• Over 80 species, in two suborders

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Defining Characteristics

• Streamlined body
• Horizontal flukes and a dorsal
• fin
• Shortened neck vertebrae
• Pectoral flippers composed of short arm bones,
  flat wrist bones, and five fingers
• Some species have a vestigial pelvis with small
  nonfunctional hind limbs
• Mobile rib cage with ribs separated from
  vertebral column in some species
• Lengthened skull shape, nostrils on top of head,
• No tear glands, no olfactory sense, no external
  opening to ear

http//www.ftexploring.com/askdrg/fbones.gif
http//images.encarta.msn.com/xrefmedia/sharemed/t
argets/images/pho/t025/T025799A.jpg
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http//webnetworkone.com/zoobooks/images/whalebone
.gif
http//www.mbayaq.org/efc/living_species/organism_
images/lsl_mammal_m229.jpg
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Early Speculations

• 1693- John Ray was the first to record that
  whales are mammals.
• 1859- Charles Darwin believed they descended
  from bears (not a popular idea).
• 1883- William Flower linked whales to
  ungulates.
• 1960s- Van Valen and Szalay used dental fossils
  to link early whales to mesonychid
  condylarths (extinct carnivorous
  ungulates).

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Sinonyx (60 mya)

• Primitive ungulate mesonychid in order
  Condylartha
• Elongated muzzle (used by whales today to hunt
  fish)
• Enlarged jugular foramen
• Short cranial cavity
• 44 heterodont teeth including molars with several
  cusps

http//www.researchcasting.ca/images/sinonyx.jpg
http//www.talkorigins.org/features/whales/
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Pakicetus (52 mya)

• Only fragments of the skull have been found
• Upper and lower molars have multiple cusps
  premolars are triangular with a single cusp (seen
  in later whales)
• Narrow braincase, high narrow sagittal crest,
  prominent lambdoidal crests
• No vascularization in inner ear which is needed
  today for deep diving
• Not a land dweller but unable to swim in deep
  water

http//www.talkorigins.org/features/whales/
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http//critters.pixel-shack.com/WebImages/critters
gallery/Pakicetus.jpg
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Ambulocetus (50 mya)

• the walking whale that swims
• 2 meters in length
• Capable of both land and sea travel
• Probably moved like sea lions on land
• Strong femur bones but only small attachment
  points for leg muscles
• Radius and ulna able to support weight, strong
  elbows
• Swam by moving spine up and down, and had large
  back feet for propulsion
• Toes of back feet were
• hooves
• Long tail and long
• flexible neck
• Skull had long muzzle
• No blowhole yet

http//idd02mb7.eresmas.net/images/Professional_po
rtfolio/2001/EAA/EAA_Ambulocetus_natans004.jpg
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Rodhocetus (46 mya)

• Likely had a strong tail for swimming (spine very
  flexible with large attachment points for
  muscles) may have had a tail fluke
• Smaller pelvis, still connected to sacral
  vertebrae
• Shorter femur
• Very large enlongated skull
• Teeth less differentiated than in earlier whales
• Nostrils moved back along the snout

http//www.talkorigins.org/features/whales/
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http//www.cas.cz/ziva/cisla/0405/17.jpg
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Basilosaurus (35-45 mya)

• Dont know if it was part of lineage that led to
  modern whales
• 21 meters in length
• Pelvis completely separated from spine (made
  weight-bearing impossible)
• Vertebral column similar to that of modern
  whales may have had flukes
• Nostril moved back to top of the head

http//www.dinooption.com/img06/Basilosaurus.jpg
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http//www.mheine.com/jpeg/basilo.jpg
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Dorudon (40 mybp)

• 5 meters in length
• Lived completely in water
• Short neck vertebrae but no apparatus for
  echolocation yet
• Tiny hind limbs (therefore no land travel)

http//www-personal.umich.edu/gingeric/PDGwhales/
Whales.htm
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Overall Results of Whale Evolution

• Elongation of the skull
• Teeth became more conical
• Nostrils migrated to top of skull
• Hind limbs and pelvis became smaller and
  non-functional
• Hearing devices developed for underwater use

http//www.talkorigins.org/features/whales/
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DNA Analysis

• 1985- Goodman et al. studied myoglobin, lens
  alpha-crystallin A, and cytochrome sequences
  from 46 species of animals
• 1986- Miyamoto and Goodman studied a- and
  ß-hemoglobins and ribonuclease from 72 mammal
  species
• Results whales are included among ungulates

http//www.ks.uiuc.edu/Research/pro_DNA/dna_w_anal
og/dna-wat.big.gif
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Interesting Facts

• Modern whales still possess vestigial limbs such
  as pelvic bones, femurs, and tibias
• Modern whales develop body hair as fetuses but
  dont retain that feature after birth
• Whale embryos begin with nostrils at the end of
  the snout which later migrate to the top of the
  head
• Some baleen whales have teeth in the embryonic
  stage

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References

• Hoelzel, A. Rus, ed. Marine Mammal Biology an
  Evolutionary Approach. Malden, Mass Blackwell
  Science, 2002.
• Berta, Annalisa and James L. Sumich. Marine
  Mammals Evolutionary Biology. San Diego
  Academic Press, 1999.
• Sarfati, Jonathan. Whale evolution? Answers
  in Genesis. 2005. 17 April 2005.
  http//www.answersingenesis.org/home/area/re1/chap
  ter5.asp
• Gingerich, Philip D. Research on the Origin and
  Early Evolution of Whales (Cetacea). 2004. 17
  April 2005. http//www-personal.umich.edu/
  gingeric/PDGwhales/Whales.htm
• Evolution of Cetaceans. Wikipedia, the free
  encyclopedia. 2005. 20 January 2005.
  http//en.wikipedia.org/wiki/Evolution_of_cetacean
  s
• Sutera, Raymond. The Origin of Whales and the
  Power of Independent Evidence. The Talk
  Origins Archive. 2001. 15 April 2005.
  http//www. talkorigins.org/features/whales/