the evolution of cetaceans evolutionary phylogeny, fossil records and evolutionary novelties

8/4/2019 The Evolution of Cetaceans Evolutionary Phylogeny, Fossil Records and Evolutionary Novelties

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The Evolution of Cetaceans:

Evolutionary Phylogeny, Fossil

Records and Evolutionary Novelties

Jayson Garcia

Abigail Larios

Jacob Labios



Cetaceans

From Latin cetus = “a large sea animal” and Greek ketos = “sea

monster”

Uncharacteristic of the Class Mammalia due to modifications of

the basic mammalian structure adaptation to transition from

terrestrial to aquatic habitat

Isolated from primitive eutherian ancestors leads to rapid

evolutionary changes

Include whales, dolphins and porpoises in about 87 species,

14 families and 2 sub-orders

I

Main Groupsof Cetaceans



CLASSIFICATION

Kingdom Animalia

Class Mammalia

Order CetaceaSuborder Odontoceti

Suborder Mysticeti



Suborder Odontoceti

toothed whales

with teeth for feeding and a single blowhole for

respiration

asymmetrical skull

include more species and aresmaller than the other

subgroup



Suborder Mysticeti

baleen whales

with baleen plates for filter feeding and to

blowholes for respiration

symmetrical skull



warm-blooded

no hairs in the body uses blubber, a heavy fat layer underneath the skin,

for insulating or warming of the body torpedo shaped body with no distinct neck

streamlined body and horizontal end fin (flukes) for efficient swimming

paddles for balancing their bodies

blowholes for exchange of gases

poor sense of smell

good sense of hearing for sensing vibrations underwater for echolocation

highly developed brains

give birth to live and well-developed young and nourish their offspring

through their mammary glands

II

Unifying Characteristics

/Features



Transition to Toothlessness

baleen plates of mysticetes evolved gradually through time

early baleen whales such as Janjucetus and Mammalodon still

had fully developed enamel-covered teeth

whale embryos also show that their distant ancestors once boreteeth. They still grow tooth buds that disappear before the

young whale is born

through time, proteins needed to encode enamel on teeth of

whales are impaired via mutation

all species of baleen whales have a different set of at least three

tooth genes that mutated into pseudogenes

III

Evolutionary ChangesMicroevolution



Possible explanation: baleen whales lost enamel

independent from each other or their common ancestor

lost enamel once

Evidence: fossil records show a modification in the

MMP20 gene (gene involved in processing tooth proteinssuch as enamelin and ameloblastin) which lead to the

permanent lost of teeth of baleen whales



gradual evolution from fully terrestrial to fully marine

lifestyle with corresponding adaptations (elongatedbodies, webbed feet, blowholes, etc.) at various key

intervals along the way

order Cetacea are believed to have evolved from

smaller terrestrial hoofed mammals like cows, camels

and sheep some 45 million years

they are a good example of adaptive radiation in

mammals

III

Evolutionary Changes

Macroevolution and

Evolutionary Novelties



Their body became streamlined; forelimbs modified into

flippers; limbs lost; tail broadened horizontally all for

efficient motility in water

blubbers, in place of hair, for buoyancy and insulation

nostrils shifted to the top of the head to create blowholes foreffective respiration when they reach the surface of the water

their sensory organs have been modified to adapt to the

differences in the life on land and the life on sea

hearing is highly developed

sensory and reproductive organs have been

internalized to reduce drag while swimming



Changes in their reproductive and parental behaviors

have also taken place, enabling whales to provide

optimum care for their young in the cold, large ocean

Since renal urea transporters are highly conserved

among mammals inhabiting terrestrial and pelagic

environments, urea-based concentrating mechanism,presumably evolved to meet the demands of an arid

terrestrial environment



whales share brain cells with humans suggesting that

certain cetaceans and hominids may have evolvedside by side

there is substantial variability between the cell

structures of the cortex in humpback whalescompared to toothed whales like dolphins

spindle cells in the humpback cortex and in other

areas of the whale brain is comparable to that of the

spindle cells of hominids.



fossil cetaceans are classified based on skeletons

(other fossil parts have not yet produced

biomolecules useful in molecular taxonomy)

teeth and, rarely, other bones (vertebrae, limb

elements) have been used at times

IV

Fossil Records



Modes of Fossil Preservation

fossil cetaceans occur in sedimentary rocks

from strata including sandstone, mudstone, limestone,greensand, and phosphorite, most of which are marine

rocks now exposed on land

rare fossils have been recovered from the sea floor



Center of Fossil Distribution

oldest known cetaceans

from coastal and fluvial deposits inthe Indo-Pakistan region of South Asia, dating to approximately

55 Ma, by Philip Gingerich

Hans Thewissen found Ambolectus later in 1995

Archaeoceti

Early cetacean fossils with four limbs, heterodont dentitions,

and shared basicranial, facial, vertebral, and forelimb

characters with modern cetaceansfrom Pakistan, India, Egypt and USA

later separated into protocetids and basilosaurids and then

dispersed Jordan, Egypt, and the southeastern United States



Ambolectus

Rhodhocetus

Pakicetus



Range in Geologic Time Scale

Eocene, Oligocene, Miocene, Pliocene, and Pleistocene

the early Oligocene reduction in archaeotes and first

appearances of echolating and baleen-bearing cetaceans

(odontocetes and mysticetes)

Miocene diversification of cetaceans

middle Miocenemost representatives of extant familiesappear



increasing volume of CO2 emissions through the years

Global Warming

increase in temp of the waters

alterations in the migration pattern of some species of whales

lower capacity of holding O2 dead zones

decrease in the population of phytoplankton main

diet of baleen whales

V

The Cetacean

Future



water pollution

11 of 9 genera of mysticetes are endangered

odontocetes are being hunted for tourism (e.g.

amusement parks)

insufficient conservation efforts (e.g. IWC) due to

unstoppable problem in whaling

After a million years EXTINCTION!



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