Lec 15 and 16 Flashcards
Cetaceans are in superorder ___________________
Laurasiatheria
Evolution of whales
Fossils found in India
Cetaceans had a walking ancestor (called a “walking whale”)
Early Miocene 52Mya
Superorders diverged ~100Mya
Subcontinent of India was still attached to Africa
Afrotheria strictly from continental Africa
Laurasiatheria from attached European countries
Show transition from quadrupedal terrestrial animals to whales
Cetacea is a monophyletic group
Archeoceti descended from ancestral artiodactyls
Hippos sister to ancestral cetaceans
Eocene cetaceans appeared in region of coastal Tethys Sea 53-45Mya
Transitional forms from terrestrial to fully aquatic
Note transitions in:
- Limbs
- External nares
- Development of flukes
Nares moved from apex (front) to top of head
Tail flukes start to develop around Dorudon
One of the best transitional series in the fossil record
Cetacean Characters
Streamlining:
- Body fusiform
- Nearly hairless
- -Have some whiskers
- Thick layer of blubber
- Testes remain abdominal
- Teats enclosed within slits next to urogenital opening
Blubber used for thermoregulation AND decreasing wrinkles or other non-hydrodynamic features of the body wall, results in a smoothing of the animal
Vertebrae with high neural spines
-Supporting structures for long straps of muscles
Hypaxial muscles contract: Tail goes down
Epaxial muscles contract: Tail goes up
Cervical vertebrae compressed
- Still 7 present
- 6 and 7 fused; atlas (one articulating with skull) enlarged
Clavicle absent
Forelimbs (flippers) paddle-shaped
Digits long and with hyperphalangy
- Hyper = more than; more than usual number of phalanges comprise a digit
- Lengthens the paddle-like flipper
Fused neck vertebrae = restrict head movement
-Allows for faster locomotion, head moving around would decrease hydrodynamic shape
Hind limbs vestigial (not visible externally)
Pelvic girdle reduced to 2 rod-like bones
Flukes horizontal
-Provide propulsive force from the tail end
Skull highly modified
- Posterior migration of nares
- Lengthening of maxillaries and premaxillaries
- Nasals and frontals telescoped
- -Premaxilla and maxilla elongated, run parallel; nasal and frontal pushed together (telescoped)
In what other groups of mammals have we seen fusiform shape?
Moles, gophers, seals, sea lions, otters
Cetacean Characters: Physiological adaptations
Able to alternate between periods of EUPNEA and APNEA
- Eupnea = breathing
- Apnea = controlled stop of breathing
Rapid rates of gas exchange in lungs
-Red blood cells have hemoglobin which binds to oxygen; more red blood cells = more hemoglobin = more oxygen
2x number of red blood cells
2-9x as much myoglobin (higher for deep diving species)
-Whale meat is a very deep red/purple color due to more myoglobin
Many ribs lack connection to sternum - lungs collapse at depth
Lungs dorsal to diaphragm
Vasoconstriction = constriction of blood vessels
Reduced amount of blood going to external parts
Diving reflex:
- Bradycardia = slowing of heart rate
- Peripheral vasoconstriction = constrict blood cells
- Splenic contraction = red blood cells in spleen pushed out into blood
Order Artiodactyla
Infraorder Cetacea
Parvorder Mysticeti
The baleen whales
Evolution:
Early mysticetes appear in early Oligocene
-Lacked baleen, had teeth
-Large eyes - suggests they hunted fish
–Earliest baleen whales did NOT have baleen, they had teeth
Later forms likely had both teeth and baleen
-Limited filter feeding
By middle Miocene mysticetes lost teeth, only used baleen
- Elongate rostrum to support more baleen
- Bulk filter feeding possible
Baleen is a neomorph = a recent attribute
Large eyes = likely hunted fish
Later forms had both baleen AND teeth; baleen doesn’t preserve in fossils, teeth spacing indicated presence
Transition to filter feeding corresponds to opening of Antarctic Circumpolar Current
- Explosion in marine plankton productivity
- Provided new resource for mammals to exploit
Antarctic Circumpolar current = mixing brings up nutrients from ocean floor; oceans around Antarctica are very nutrient-rich
Mysticeti Traits
Symmetric Skull
Lack bony mandibular symphysis
External nares paired (i.e. two blowholes)
Adults lack teeth, have baleen
-Baleen composed of keratin
Order Artiodactyla
Infraorder Cetacea
Parvorder Mysticeti
Family Balaenopteridae
Engulfers/lunge-feeders
Actively chase food; throat grooves (extend from lower jaw to naval) expand
Includes humpback whales and rorquals
9 species
Vary widely in size
- Minke whale 11m and 4000kg
- Blue whale at 31m and 160,000kg
Baleen plates short and broad
Longitudinal pleats on throat
May migrate long distances
Humpbacks especially known for long migrations
Order Artiodactyla
Infraorder Cetacea
Parvorder Mysticeti
Family Balaenidae
Right whales and bowhead whales
2 genera, 4 species
18m long, up to 67000kg
Huge head and tongue
350 long baleen plates per side
Flippers short and rounded
Dorsal fin usually absent
Highly arched skull
Right whales: The “right whales to catch” by early commercial whaling
These are skim feeders, don’t move fast, able to harpoon easily from wind-powered boats; due to lots of blubber, didn’t sink quickly
Distribution: Typically found in arctic and antarctic waters
Very overhunted by yankee whalers in the 19th century; rarely seen off the coast of California anymore
Life history
Populations decimated by 19th century whaling
-The “right” whales to catch
Still among the most endangered marine mammals
Among the oldest living mammals (~200 years)
Skim feeders
Order Artiodactyla
Infraorder Cetacea
Parvorder Mysticeti
Family Eschrichtiidae
Gray whales
Monotypic family = gray whale
Distribution = North Pacific Ocean
-Eastern and Western North Pacific populations
up to 15 meters and 31,500kg
Small head, short baleen plates
Blotched gray with white spots
Migrate annually up to 22,000 km
-Cold Arctic waters to equatorial breeding lagoons of Baja California and back again
Western population endangered, Eastern population recovered
Gray whale baleen is small and tan
Life History
Life expectancy = 55-70y, sex mature at 8
Breeding and calving occurs during late November - early December in breedin lagoons of Baja Califonria
Biennial births most common
13.5 month gestation period and lactation occurs for 7 months afterward
2010 sighting in Israel suggests that grey whales are revisiting breeding grounds abandoned for centuries
2013 sighting in Namibia was the first ever in the Southern hemisphere
Order Artiodactyla
Infraorder Cetacea
Parvorder Odontoceti
Toothed whales
8 families, 34 genera, about 76 species
- Sperm whales
- Beaked whales
- Dolphins, porpoises
Occur in all oceans and seas, also some river systems
Polydont = having more than typical number of mammal teeth
Homodont = same size and shape
Monophyodont = only 1 set of teeth, never replaced
Asymmetric skull
Single external nare (i.e. one blowhole)
Fatty melon present
Echolocate using complex nasal passages
Piston-like tongue used to capture prey
Some may stun prey acoustically
Echolocation in Odonticeti
Sound production: Sounds produced in nasal sac system
- Series of muscular valves and sacs associated with the blowhole
- Muscles contract in synchrony with clicks
- Sounds bounce off parabolic dish-shaped skull and reflected outward
Lens-shaped melon
-Acoustic lens: Directs the soundwaves
Sound reception: Returning echoes received via small, thin mandible
- “Pan bone” of the dentary is an oil-filled sinus that channels sound to auditory bullae
- Bullae not fused to skull: insulated by sinuses containing fat and air
- So refined that they can distinguish the type of fish
Order Artiodactyla
Infraorder Cetacea
Parvorder Odontoceti
Family Monodontidae
Diversity and Distribution
2 species
- Narwhal
- -Long, straight, forward-directed
