the evolution of baleen from the ancient toothed whale amber fitzgerald morgan hinson tom lesinski

The Evolution of Baleen from the Ancient Toothed

Whale

Amber FitzgeraldMorgan Hinson

Tom Lesinski

Our Smithsonian Adventure

• We were drawn to the ocean area of the museum

• We noticed whales have a huge evolutionary background so we chose whales as a topic

• We were interested as to why some had teeth and why some had baleen

Question: Why did whales diverge from toothed to

baleen?

Cetacean family tree

Whales• Order: Cetacea• Most specious living

group of aquatic mammals

• First found in fossil record approximately 52.5 million years ago

• Earliest whales were terrestrial

• Probably moved to ocean in search of food

Whales• Cetaceans are divided into two

distinct groups based on their morphology: – Mysticeti (baleen whales) – Odontoceti (toothed whales)

• Evidence suggests that Odontoceti and Mysticeti are derived from the archaeocete family Basilosauridae

Baleen Whales

Wait a minute, what is baleen?

What is baleen?

• Baleen is a keratinous sieve that continuously grows from a whale’s palate that is used to filter food from the water

• Its strong but flexible• Hair-like fringe

Baleen Whales(Mysticeti)

• Use baleen to filter feed• Some had both teeth and baleen (intermediate

species)• Today all mysticetes have baleen and lack teeth• Huge head and jaw allow baleen whales to hold

long baleen plates– A Right whale’s head takes up about 1/4 of it’s

length

Baleen Whales (cont.)

• Baleen whales lunge through schools of fish filtering plankton as they swim with their mouths wide open

• The whale closes its mouth and forces water out through the baleen strainers

• This traps food and the whale swallows• http://www.youtube.com/watch?v=H0yyRi

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Toothed Whales(Odontoceti)

• Generally smaller than baleen whales

Toothed Whales (cont.)

• Use echolocation to find prey– Produce specialized sounds and receive and

process these echoes to navigate, find food and avoid predators

– Take individual prey, which consists mainly of fishes and squids

An Intermediate: Llanocetus denticrenatus

• Known as an intermediate step in the evolution of baleen whales

• Oldest known filter feeder• Its teeth and baleen formed a sieve that kept

plankton in while letting water out

Why did some whales lose their teeth?

• About 38 million years ago, whales developed baleen as a new way to eat

• Decreased ocean temperatures• Upwelling of nutrients• Increase in plankton• Increase in krillBaleen whales may have evolved to take advantage of this rich new food supply

Evidence

Lateral view of mysticete fetus (Balaenoptera physalus - fin whale) with dissection showing tooth buds in the upper jaw

New Avenues…

• Evolution will continue to occur, will another method of feeding eventually develop for whales?

• Will one morph become extinct?