Marine mammal evolution notes

Ring Species

• There are several ring species, but the most famous example is the herring gull. In Britain, these are white. They breed with the herring gulls of eastern America, which are also white. American herring gulls breed with those of Alaska, and Alaskan ones breed with those of Siberia. But as you go to Alaska and Siberia, you find that herring gulls are getting smaller, and picking up some black markings. And when you get all the way back to Britain, they have become Lesser Black-Backed Gulls.

• So, the situation is that there is a big circle around the world. As you travel this circle, you find a series of gull populations, each of which interbreeds with the populations to each side. But in Britain, the two ends of the circle are two different species of bird. The two ends do not interbreed: they think that they are two different species.

Evolution and Systematics

Convergence, Divergence and Parallel Evolution

– Distantly related taxa can come to resemble one another through the process of convergence (wings)

– Closely related taxa may quickly develop very different morpholgies through divergence

– Species may have diverged in the distant past can maintain similar morphologies through parallel

evolution

Adaptations

• An adaptation is a character or suite of characters that helps an organism cope with its environment

• A preadaptation (or exaptation) is an adaptation that performs a function other than previously held

– e.g. the lower jaw of odontocetes is used to transmit high frequency sounds underwater but first

evolved to transmit low frequency sounds from the ground

Adaptive Radiation

• Rapid diversification of a lineage into many forms

• Can obscure relationships due to rapid evolutionary change if in distant past

• If recent, may be hard to detect differences: what is a species??

What is diphyly, with regards to monophyly vs diphyly?

• If whales are monophyletic, that means a single common ancestor gave rise to all whales. If it is diphyletic, that means the whales have two different ancestors and that they are only similar because of convergent evolution. There are 2 great groups of whales: toothed whales and baleen whales. There is strong evidence that baleen whales evolved from a toothed whale, therefore there is strong evidence that whales form a monophyletic group

– Biological Species Concept

– Inability to interbreed

Studying evolutionary relationships

• Systematics – the study of defining evolutionary relationships among organisms both extinct and extant

• A phylogeny is a hypothesis about evolutionary relationships

– Often shown on a tree

– Can never be “proven” only strongly supported!!!

Phylogenetic Trees(Cladograms)

• Tree representing best estimate of phylogenetic lineages

– Lines are clades or lineages (groups of related taxa from a common ancestor)

– Nodes = branch points = speciation events

Cladistics

• Organisms can be deemed related based on shared derived characters (synapomorphies)

• Characters

– any feature useful in phylogenetic analysis

– May be ancestral (primitive) or derived (apomorphy)

– Characters may be primitive or derived but taxa are not

• Taxa are all endpoints of evolution

• Character State

– Condition of the character

Homology and Analogy

• Cladistics relies on finding synapomorphies

• Homology

– Characters that arise from similar ancestry

– Bats’ wing bones and human fingers

• Analogy

– Similar characters that do not share evolutionary history

• Bird wing and bat wing

• Do analogies help in resolving evolutionary relationships?

Determining Character States

• It is critical to determine which character states are ancestral and which derived

– Can use outgroups or closely related lineages; often use sister group – the most closely related

lineage

– Character states shared with outgroup likely are ancestral

Types of groups on cladograms

• Monoplyletic

– includes hypothetical ancestor and all descendents

• Paraphyletic

– does not include all descendants of an ancestor

• Polyphyletic

– Collection of descendants from >1 ancestor not including all ancestors

Types of characters

• Behavioral

• Physiological

• Mophological

• Molecular

Molecular vs Morphological Characters

• Molecular

– Huge number of possible characters (down to each nucleotide)

– Can find parts of genome not under environmental selection

– Long time periods can obscure due to saturation (problems with parallel evolution)

– Time to saturation depends on rate of evolution at each locus

• Morphological

– Evolve more slowly (little saturation)

– Can include extinct taxa

– Can have problems with convergence

– Defining characters can be difficult

• Use of both types of data best!

Fossil Taxa

• Contribute most when they help plug holes in long divergent lineages

• Can complete morphological series, help determine homologies

• Can help determine earliest occurences

• Can’t Use many characters – results in poloytomy (unresolved nodes)

Constructing a Cladogram

• Select group, define all taxa

• Select and define characters and character states

• Create data matrix

• Use outgroup comparison to determine ancestral and derived states

• Construct all possible cladograms

• Select best cladogram using parsimony

• Principle of Parsimony – the best cladogram is the one involving the fewest evolutionary transitions

(steps)

Uses of phylogenies

• Character mapping

Pinniped Evolution and Systematics

The pinnipeds

• Monophyletic group with 3 monphyletic families

• 18 phocids, 14 otariids, walrus

• Diversity was once much greater (13 species of walrus are extinct)

• First pinnipeds arose in Oligocene (27-25mya)

• Much speciation in last 2-5 million years

• Poor fossil record generally

Major pinniped synapomorphies

• Large infraorbital foramen (hole below eye to allow vessel and nerve passage) (1)

• Short, robust humerous (6)

• Digit I on hand emphasized (7)

• Digit I and V on foot emphasized (8)

Mono or diphyly?

• Evidence for diphyly

– Biogeorgaphy and morphology

– Otarrids (eared seals) and odobenids (walrus)close to bears; phocids (earless seals) close to mustelids (otters, weasels)

• Evidence for monophyly: the best explanation

– Molecular, karyological, morphology

– All support close ties to ursids (bear), mustelids, otters (sister group unclear)

– Diving behavior and breeding patterns suggest eared seals evolved first (Costa 1993)

• Phocids are most aquatically adapted (diving, breeding, body plan)

Early Pinnipeds

– Find describe in 2009 sheds new light on early evolution

– Pujila darmwini was “walking seal” ~24 mya

– Otter-like body, webbed feet, lived in freshwater lakes of Canadian Arctic

– Suggests pinnipeds went through a freshwater phase

– High productivity associated with cold water upwelling probably supported prey base early pinnipeds

exploited

– First found from cool waters and rocky coasts of eastern N. Pacific during late Oligocene

– Pinnipedimorpha clade

– Show ancestral, heterodont (having teeth of different shapes, such as the molars and incisors of humans), dentition

– Many similarities to archaic bears

– Later forms show derived homodont dentition

Early Pinnipeds

• • Pinnipedimorpha clade

• – Lateral and vertical movement of vertebral column possible

• – Both sets of flippers modified for aquatic locomotion

• – Still very capable on land, probably spent more time there than modern forms

• Modern Pinnipeds: Otariidae

• • Seal lions and fur seals

• • Shallow divers often targeting fast-swimming fish

• • Monophyletic group first appeared late Miocene (11 mya) but all modern forms in last 2-3 my

• • Two subfamilies

• – Otariinae (seal lions)

• – Arctocephalinae (fur seals)

• In cladistics, a synapomorphy or synapomorphic character is a trait that is shared ("symmorphy") by two or more taxa and their most recent common ancestor, whose own ancestor in turn does not possess the trait.

• Some Otariid synapomorphies

• – Frontals extend anterior between nasals (9)

• – Uniformly spaced pelage units (primary and secondary hair)

• – Trachea subdivides close to voicebox (13)

• – Secondary spine on scapula (11)

• – External ear flaps “pinnae”

• – Can turn hindflippers forward; use to walk

• Otariid systematics

• – Otariinae (sea lions) monophyletic (single stock) , not Arctocephalinae (fur seals) which are still poorly resolved

• – Hybridization and Introgression may cause problems

• – aggressive sexual behavior of male sea lions directed at other species

• Modern Pinnipeds: Odobenidae

• • Current 2 subspecies relicts of once diverse group

• – Modern walrus large-bodied, shallow diving mollusk feeder

• • Monophyletic family, origin middle Miocene (16-9 mya) eastern North Pacific

• Odobenid synapomorphies

• • Five synapomorphies

• • Modern walrus distinguished by squirt-suction feeding

• • TUSKS ARE NOT A SYNAPOMORPHY

• – They evolved in only one lineage leading to modern walrus

• – Many ancient odobenids did not have tusks

• Where do the odobenids fit?

• • Molecular evidence points to otariids, but morphological data suggests a close association with phocids

• – Middle earbone enlarged

• – No pinnae

• – Well-developed thick subcutaneous fat

• – Abdominal testes

• – Similarities in hair and venous system

• • What gives?

• – Still unclear where walrus fit in pinniped clade

• – Odobenids probably branched off from basal pinnipeds very early leading to a long branch

• – Subsequent long-branch attraction causes molecular similarities

• Odobenid movements

• • Origin in eastern North Pacific

• • Invaded Atlantic through Carribean

• • 600,000 ya modern walrus reinvades Pacific through Arctic and diverge into subspecies

• – Middle earbone enlarged

• – No pinnae

• – Well-developed thick subcutaneous fat

• – Abdominal testes

• – Similarities in hair and venous system

• • What gives?

• – Still unclear where walrus fit in pinniped clade

• –Modern Pinnipeds: Phocidae

• – “True” seals, lack ear flaps

• – Generally larger than otariids

• – Some fantastic divers

• – Weddell and elephant seals over 1000m

• – Late Oligocene origin (29-23mya) in N. Atlantic

• – Monphyletic family with two subgroups

• – monoachines and phocines

• Some phocid synapomorphies

• • Unable to turn hindflippers forward

• • Inflated entotympanic bone (21)

• • No supraorbital process (10)

• Subspecies, hybridization and a misplaced genus

• – Five subspecies of harbor seal recognized based on morphological, molecular, behavioral differences

• – Eastern and western sides of Atlantic and Pacific, lakes of northern Quebec

• – Harp seal Phagophilus groenlandicus x hooded seal Cystophora cristanta hybird – what does this mean

• for biological species concept

• – What is the status of the gray seal genus?

• Phocid systematics

• • Are traditional subgroups monophyletic?

• • Monk seals Monachus often considered most basal of phocids due to ancestral characters (some moreso

• than fossil taxa)

• Pinniped Evolution: Summary

• • Morphologic and molecular data support monophyly

• • Derived from arctoid carnivores, probably close relatives of bears

• • Earliest appear 27-25mya in north Pacific

• • Modern lineages diverged quickly

• • Position of the walrus unclear

• Cetacean Evolution and Systematics

• Cetaceans

• • Monophyletic group with 3 suborders

• – Archaeoceti (extinct)

• – Odontoceti (~76 species)

• – Mysticeti (11 species)

• • Earliest marine mammals (with sireneans) 53-54 mya

• Cetacean Origins

• • Currently some questions about origins: several competing hypotheses

• • Evolved from small primitive ungulate group

• – Could share common ancestor with hippos

• – Could be sister group of other artiodactyls (even-toed; hippos, camels, antelope, pigs, giraffes, etc)

Archaeoceti (extinct)

• – Could be another ancestor not closely related to moder artiodactyls

• Cetacean Origins: The old favorite

• • 1. Decendent of Order Condylartha, Family Mesonychidae

• • Wolf-like with digitigrade stance (walk on toes), possibly hoofed

• • Massive crushing dentition; early skulls suggest similarity

• Cetacean Origins: close to hippos?

• • 2. Some molecular data points to close affinity with hippos; recent skull finds disagree – more like

• mesonychids

• Cetacean Origins

• 3. Sister group to clade including hippos and artiodatyls; not particularly close to mesonychids

• –

• – Probably all derived from mouse-deer like ancestor

• Cetacean Origins: Indohyus brings us closer to an answer

• • 4. Sister group to cetaceans more primitive than other artiodactlys

• – Recent finds in India suggest cetaceans closest ancestor is an ancient artiodactyl group (raoellids)

• – Similarity to cetaceans based on morphology of inner ear, the arrangement of incisors, and

• morphology of premolars

• – Indohyus was an aquatic wader based on bone density and oxygen isotopes

• – Carbon isotopes suggest feeding on terrestrial vegetation or omnivores on land but escaped to water

when in danger like modern African mouse deer

• – Adaptation to aquatic habitats did not occur first in early cetaceans, but more basal species –

• cetacean branch probably driven by switching to aquatic prey (unique dentition and oral skeleton)

• – Early cetacean ancestors went through a hippo-like stage

• – Study published in 2009 suggests that hippos are, in fact, closest living relatives of cetaceans.

• Archaeocete cetaceans

• • Paraphyletic group of ancient whales that gave rise to modern whales

• – lack telescoped bones of the skull

• – Elongate snout

• – Narrow braincase

• – Large temporal fossa

• – Well defined sagital and lambdoidal crests

• • Earliest from Early Eocene (>50 mya)

• • Extinct by end of Eocene

• • Pakecetoids are most ancient group (50 my)

• – Pakecetus – earliest whale; India and Pakistan

• – Ear morphology gives them away as cetaceans

• – Lived in an arid environment with ephemeral streams and floodplains

• • Always found in river deposits

• • At best site, 60% of mammal remains are pakicetids!

• •– Quadropedal and probably mainly terrestrial but not swift runners (dense bones that may have

• been for ballast)

• – Long thin legs and short hands and feet suggest they were poor swimmers (quadropedal

• paddling) and many deposits were rivers that were too shallow for swimming

• – Teeth vary greatly – some hyena-like

• • may have been scavengers or predators

• • Probably ate freshwater aquatic organisms and land animals near water

• • Ambulocetids

• – Found in middle Eocene rocks of India and Pakistan

• – Most basal amphibious marine cetaceans

• • Nearshore marine (estuaries and bays) but tied to freshwater for drinking

• – Abulocetus natans and others close to size of male sea lion

• – Show first signs of hearing adaptations

• – Eyes above profile of skull

• • Ambulocetids

• – Likely slow on land

• – Elongated hind feet and tail that would aid in locomotion

• • Probably swam like modern otter swinging tail and feet

• – Probably ambush hunter like modern crocodiles

• • Remingtonocetidae

• – Short-lived group from Middle Eocene of India and Pakistan

• – Nearshore tidal environments, but more aquatic than ambulocetids

• – Long narrow jaws

• – Probably swam with tail like Amazonian giant otter

• – Captured fast-swimming aquatic prey

• •– Protocetids

• – Globally distributed during the middle Eocene

• • First group to leave South Asia

• – Expanding niches inhabited including deep offshore waters but probably restricted to tropics

• – Nasal openings more caudal than earlier species

• • Could breath with much of head underwater

• – No fluke

• •– Lifestyle probably very similar to modern pinnipeds

• – Hindlimbs may not have been able to support weight in some species

• • Basilosaurids

• – Middle to late Eocene/early Oligocene

• – large-bodied family with elongated vertebral bodies (Basilosaurinae)

• – Very reduced hind limbs – fully aquatic

• – Basilosaurus grew to 25m

• – Throughout the tropics and subtropics

• – Had fluke, but back undulations rather than the fluke provided propulsion

• – Piscivorous

• • Dorudontids

• •– Lifestyle probably very similar to modern pinnipeds

• – Hindlimbs may not have been able to support weight in some species

• • Basilosaurids

• – Middle to late Eocene/early Oligocene

• – large-bodied family with elongated vertebral bodies (Basilosaurinae)

• – Very reduced hind limbs – fully aquatic

• – Basilosaurus grew to 25m

• – Throughout the tropics and subtropics

• – Had fluke, but back undulations

rather than the fluke provided

propulsion

• Archaeocete trends

• – Rapid evolution (few million years) from

• – Quadropedal to flukes (hindlimb reduction)

• – Freshwater dringing to seawater drinking

• – Land animal to not able to move on land and giving birth in water

• – Movement of nostrils to the top of the head

• – Extinction probably tied to changes in food supply driven by oceanographic change

• Modern Cetaceans

• – Diverged from Archaeocetes about 37 mya

• – Monophyletic clade derived from dorudontids

• – Split between mysticetes and odontocetes probably 35 mya

• – Synapomorphies

• – Telescoping of skull: movement of blowholes to the top of skull

• • Migration of premaxillary and maxillary bones forms a rostrum (beak)

• – Fixed elbow joint not present in archaeocetes

• Mysticetes (Baleen whales)

• – Modern forms distinguished by baleen plates, but early mysticetes had teeth

• – Origin probably tied to Oligocene development of Circum-Antarctic current and generation of nutrientrich

• upwelling that led to huge zooplankton shoals

• – Early mysticetes were small 4-5 m

• – Major evolutionary transition is from raptorial predation (single prey item at a time) with teeth to batch

• or filter feeding with no teeth (baleen present by Oligocene, but decomposes so record poor)

• – Other trends include increased body and head size, shortening of the neck

• Mysticete Synapomorphies

• • Maxilla extends posteriorly to form infraorbital process

• • Mandibular symphysis (lower jaw connection) unfused

• Modern Mysticete Relationships

• – Four extant families?

• – Balaenopteridae,

• – Balaenidae

• – Eschrichtiidae

• – Neobalaenidae

• – Taxonomy not well-resolved

• Mysticetes: in order of divergence

• – Balaenidae

• – Right whales and Bowhead

• – First appear in early Miocene (23 mya)

• – Heavy body, cavernous mouth, no throat grooves

• – Head 1/3 of length

• – Long baleen plates

• – Only mysticetes with 5 digits on forelimb

• – Monopyletic

• • Support for two separate genera poor

• – Neoalaenidae

• – Anatomical data places as separate family outside Balaenidae

• – More anteriorally thrust occipital shield

• – Shorter, wider mouth for shorter baleen

• – Separate from balaenids due to presence of dorsal fin, throat furrows, different type of baleen,

• relatively smaller heard, four digits on hand, shorter humerous)

• – Eschrichtiidae-grey

• – Current species has 100,000 year fossil record (only one for family)

• – North Atlantic population extinct in 17th or 18th century

• • No dorsal fin

• • 2-4 throat grooves

• • Baleen is thicker, fewer in # and whiter than rorquals

• – Balaenopteridae

• – Fossil record extends 10-12 mya from Americas, Europe, Asia, Australia

• – Hybrids occur

• – Dorsal fin

• – 14-22 (humpback) to 56-100 (fin) throat grooves extend beyond gular (cooling)region

• – Short baleen

• Odontocetes

• • Diverse array of toothed forms from freshwater rivers to deep-diving in pelagic habitats

• • First appear in fossil record 28-29 mya

• • Major Miocene radiation of pelagic forms appears to be linked to changes in currents and thermal

• gradients

• • Monophyly well supported despite well-publicized argument against with early genetic data

• Are odontocetes monophyletic?

• • Most morphological characters argue that they are, but one of the supposed synapomorphies has come

• been disputed: presence of a single blowhole

• – Odontocete facial structure serves a number of functions

• – Respiration cause of much skull rearrangement

• – Sound production (echolocation) and detection another major force

• – Buoyancy control, at least in sperm whales

• – Some of the 20 Synapomorphies

• – Concave facial plane

• – Asymmetric cranial vertex

• – Premaxillary foramen present

• – Maxilla overlays supraorbital process (frontal bone)

• – Antorbital notch present

• – Asymmetric skulls (except possibly most primitive)

• – Asymmetric soft tissues in modern forms due to enlargement on right side

• – Fatty melon in front of nasal passages for echolocation

• Ziphiidae

• • More than 20 species in 5-6 genera extant

• – Found in Mocene and Pliocene, including one freshwater form; extant species mainly pelagic

• – Trend towards loss of teeth with exception of 1-2 pairs anteriorly which become enlarged (only

• Shepard’s beaked whale has full functional dentition)

• • Possible sexual display/weapons

• – Pair of throat grooves that converge anteriorly

• – Phylogeny unclear; no rigorous cladistic review

• Physeteridae

• • Long fossil record (29-21 mya), once diverse but only one extant species

• • Loss of one or both nasal bones

• • Deepest known divers

• • Have spermaceti organ

• – in supracranial basin

• – may occupy 30% of length and

• 20% of weight

• – May control buoyancy but still unclear

• Kogiidae

• • Linked into a superfamily with sperm whales because of supercranial basin and spermaceti organ

• • Lack both nasal bones

• • Have short rostrum and are much smaller than sperm whales (<4m; <2.7m)

• • Oldest known from late Miocene (8.8 mya)

• “River Dolphins”

• • Once put into a single family, but similarities (reduced eyes, elongated snouts) are due to convergent

evolution

• – freshwater/estuaries have

• been invaded at least 4 times

• Platanistidae

• • Asiatic river dolphins

• – Ganges and Indus Rivers

• – Reduced eyes in Ganges form

• – Long narrow beak with numerous narrow pointed teeth

• – Broad paddle-like flippers

• – No known fossil record, time

• of freshwater invasion unknown

• – Bony facial crest

• Pontoporiidae • Fransiscana

• – Coastal waters of western S. Atlantic

• – Long rostra, tiny teeth – Close relative of Iniidae

• Iniidae

• • Amazon river (botu)

• – Reduced eyes

• – Extremely elongated rostrum and mandible

• – Conical front teeth, molariform rear teeth

• – Greatly reduced orbital region

• – Maxilla forms crest

• – Fossils from late Miocene originated in Amazonian basin

• Lipotidae

• • Yangtze Tiver (baiji)

• – Narrow, upturned beak

• – Triangular dorsal fin

• – Broad round flippers

• – Reduced eyes

• – One fossil, one extant species from China

Delphinidae

• – Most diverse cetacean family 36 sp, 17 gen

• – Open ocean to some into freshwater (Orcella brevirostris, Sotalia fluvatilis)

• – Most small to medium 1.5-4.5m, killer whale to 9.5m

• – Loss of posterior sac of nasal passage

• – Reduction of posterior end of left premaxilla: does not contact the nasal

• – Oldest from late Miocene (11 Ma)

• • Systematics are still a mess

• – Some genera are not monophyletic

• – Diversity likely to increase (e.g. Tursiops)

• – Stenella is polyphyletic

• Phocenidae

• – Six small extant species

• – Synapomorphies

• – Raised rounded protuberances on premaxillae

• – Premaxillae do not extend beyond anterior half of nares

• – Spatualte (not conical) teeth

• – Sister taxa of delphinids

• – First appeared in late Miocene, eastern Pacific

• Monodontidae

• • Delphinoids with flat or convex facial planes in profile

• • Extant species in Arcitc

• • Miocene/Pliocene some species found in E. Pacific to Baja California

• Sirenians, Sea otters, Polar Bears, and other marine mammals: Evolution

• Sirenians

• • Monophyletic group with two extant familes

• – Trichechidae (manatees)

• – Dugongidae (dugongs)

• • Unique in strictly herbivorous diet

• • First appear in early Eocene (50 mya)

• Sirenian Origins

• – Monophyly strongly supported

• – Syapomorphies

• – External nares retracted and enlarged reaching beyond the level of the anterior margin of the orbit

• – Premaxilla contacts frontal

• – Lacks sagital crest

• – Bones dense and compact (for buoyancy regulation)

• – Closest living relatives are proboscideans (elephants)

• – Teeth and skull morphology unite the groups

• – Extinct Desmostylians form clade with sirenians and elephants (monophyletic “Tethytheria”)

• – First arose in Old World, but quickly spread to New World 50 mya

• Ancient Sirenians

• • Prorastomus (50mya) first (Jamaica)

• – Had functional hindlimbs

• – Dense bones, swollen ribs and presence in marine deposits suggest partially aquatic; riverine and

• estuarine selective browser

• • Protosiren (middle Eocene) (Egypt)

• – Functional terrestrial locomotion but auditory, olfactory, and visual systems appear modified for

• aquatic lifestyles

• • Much of the spread of sirenians tied to the spread of seagrasses in the temperate Pacific

• Modern Sirenians: Trichechidae

• – Appear to be derived in late Eocene/early Oligocene, possibly from dugongids

• – Monophyletic, united by features of the skull and reduction of neural spines on vertebrae

• – Mainly freshwater/estuarine

• – Ability to produce new teeth as old ones are worn down

• • 3 modern species

• – West Indian manatee (Trichechus manatus)

• • 2 subspecies: Antillean (T.m. manatus); Florida (T.m. latirostris)

• – Amazon manatee (Trichechus inunguis); freshwater only

• – West African manatee (Trichechus senegalensus)

• Modern Sirenians: Dugongidae

• • Paraphyletic family with Caribbean/W. Atlantic origins spreading to Pacific

• • More marine than manatees

• • Two extinct subfamilies and one extant

• – Hydrodamalinae (includes Steller’s sea cow) appears to have split from Dugonginae (dugong) in

• late Eocene

• • Includes Stellar’s sea cow (extant into historical times)

• • Some temperate species

• • Large body size

• • Loss of tusks

• • May have fed on kelp high in the water column

• Steller’s sea cow

• • Named after Georg Steller

• • 7.6m long, 4-10 tons

• • Lacked teeth, had bark-like skin

• • Cold waters near islands of the Bering Sea

• – Prehistorically from Japan to Baja California (to Montery 19,000 years ago)

• • Extinct by 1768 (27 years after discovery)

• – Mainly Russian hunting, but possibly exacerbated by aboriginal hunting

• Dugonginae

• • Currently one species, but once many genera

• • Tropical and subtropical

• • Once widespread; 15 mya from North and South America, Caribbean, Mediterranean, Indian Ocean,

• North Pacific

• • Some extinct species used tusks to dig up seagrasses

• • Modern dugongs use tusks socially, not for feeding

• Sirenian evolution in the Caribbean (Domning 2001)

• • From Oligocene onwards, there was a great diversity of sirenians in the Caribbean, especially dugongids

• • Seagrass communities were similar to extant ones but were more diverse

• • Habitat could be partitioned along several axes

• – Rhizome size

• – Location of feeding in water column

• • Morphology of sirenians reflects partitioning of seagrass resources

• – Body size differences lead to differences in access to shallow waters and ability to consume more

• fibrous seagrasses (bigger are better)

• – Rostral deflection influences ability to feed on the bottom or on midwater or surface plants and

• ability to dig

• – Tusk size influences ability to dig out largest rhizomes

• – Interaction of tusk size and defection can be complex

• • Why so few species today?

• • Close of Central American Seaway about 3 mya led to major shifts in habitats

• – Dugongids died out along with large rhizome seagrasses

• – Manatees were able to disperse into open marine habitats to move into North America and to West

• Africa

• Desmostylia: Sirenian Relatives

• • Only extinct Order of marine mammals

• • Confined to North Pacific (Japan through N. America)

• • Late Oligocene to Middle Miocene (33-10mya)

• • Hippo-like amphibious quadropeds

• • More closely related to elephants than sirenians

• • Probably fed on algae and seagrasses in subtropical and cool-temperate waters

• • Locomotion probably like polar bears

• –Thalassocnus

• • Aquatic ground sloth!

• • Pliocene marine rocks of Peru

• • Medium to giant sized herbivores

• • Aquatic or semi-aquatic grazer on seagrasses or seaweeds (well developed lip for grazing)

• • Probably swam with tail

• Kolponomos

• • Bear-like carnivore (early Miocene)

• • Massive skull, down-turned snout, broad crushing teeth

• • Coastal habitat feeding on marine invertebrates on rocks and crushed their shells

• • Sea otter only marine mammal that may be similar in habitat

• • Relationships problematic

• – Appears to be closely related to basal ursids and forms leading to pinnipedimorphs

• Sea otter Enhydra lutris

• • Smallest marine mammal but largest mustelids

• • Three subspecies across northern Pacific

• • E. lutris arose in North Pacific early Pleistocene (1-3mya)

• • Several extinct species from Africa, Europe, and Eastern United States that appear to have

• consumed extremely hard prey items like modern otters

• Polar Bear Ursus maritimus

• • Most recently derived marine mammals

• • Descended from lineage of brown bears during middle Pleistocene (300,000-400,000 ya)

• • Brown bears of southeast Alaskan islands closest relatives

• This phylogenetic tree for the sea otter contains all the sea otter genera. The sea otter is the only member of the genus Enhydra. Each genus is a monophyletic group, meaning that the organisms in each genus share a common ancestor. The sea otter is sister to the speckle-throated otter (Hydrictis maculicollis) and is by far the closest relative to the sea otter. This also shows that the sea otter shares a common ancestor with the Eurasian otter (Lutra Lutra), African clawless otter (Aonyx capensis), small-clawed otter (Aonyx cinerea), and the speckle-throated otter (Hydrictis maculicollis).

MARINE MAMMAL DISTRIBUTION

Zoogeography

Zoogeography

• Study of the distribution of extant species

• Water temperature critical for marine mammals

– Directly on animals physiology

– Indirectly on prey

– Species often occur in latitudinal bands

• Shape of nearby land/shelf

• History is Critical

– When did lineages arise and diversify?

– Continental Drift and Climate Change

– The early and middle

Miocene

Basic Climatic Zones

• Polar

• Subpolar/Cold Temperate

• Temperate

• Subtropical

• Tropical

Basic Types of Distribution

• Cosmopolitan- a taxon is said to have

a cosmopolitan distribution if its range extends across all or most of the world in appropriate habitats. For instance, the killer whale has a cosmopolitan distribution, extending over most of the world's oceans.

• unknown for many species

–• Pan Tropical In biogeography, a pantropical ("across the tropics") distribution is one which covers tropical regions of all of the major continents, i.e. in Africa, in Asia and in the Americas

• Temperate/Subpolar

• Circumpolar

• Anti-tropical

• Regional (Endemic)

• still unknown for many species

Horizontal Habitats

• Nearshore

– Lakes and Rivers

– Estuaries

– Freshwater and saltwater mix, high productivity and low visibility

– Bays

– Relatively protected waters

– Coastal

– Shallow waters, often high energy (wave action)

• Offshore

– Continental Shelf

• Relatively shallow but deeper than nearshore habitats

• Light usually penetrates to bottom over much of this habitat

– Continental Slope

• Depth changes rapidly, light penetration begins to diminish

• Often associated with high productivity

– Pelagic

• Extremely deep, no light at depth

• Generally low productivity except in areas of relief (seamounts, etc)

• Frontal dynamics and current features may be very important

Vertical Marine Habitats

• Vertical Distribution of Habitats

– Light, temperature, pressure, salinity, and water density change considerably as depth increases

– Deep-water habitats can be divided into photic and aphotic zones

– Depth where these start varies considerably with water visibility

Ice Habitats

• Many pinnipeds rely on ice as habitat

– Haul outs

– Breeding

• Polar bears use the ice to stalk seals

• Cetaceans must navigate the ice to access many polar habitats

– Fast ice

– Ice attached to shore that does not move

– Pack ice

– Ice that forms at sea and moves with currents

– Covers central Arctic, surrounds Antarctica

– Largely melts in summer, especially in Antarctica

– Ice floes

– Large pieces of sea ice broken by wind or waves

– Leads

– Open water formed when floes move apart

Current Distributions: Mysticetes

• Typified by seasonal shifts from high latitudes (feeding in summer) to low latitudes (breeding in winter)

• Bowhead: arctic

• Right whales: temperate

• Gray whale: warm temperate

• Rorquals: cosmopolitan

– B. edeni, B. brydei pantropical (<40°)

Current Distributions: Odontocetes

• Not limited by temperature in general

• Sperm whales – pelagic, cosmopolitan

– 2 smaller species more tropical

• Narwhal and Beluga – coastal, arctic

– Move with sea ice

• Beaked whales – pelagic, regional or antitropical

– In general, very poorly known

• Delphinidae – coastal and pelagic forms; tropical, anti-tropical, cosmopolitan, regional all found

• Porpoises – coastal, sometimes freshwater, regional/endemic

• “River Dolphins” – large tropical river drainages; one coastal species in SA

– Indus, Ganges, Yangtze, Orinoco, Amazon

Current Distributions: Sirenians

• Tropical/Subtropical; Regional

– Recently extinct Stellar’s Sea Cow was cold temperate

• Dugongs: fully marine

– Limited by marine plant distributions

– Prefer >18°C, <6m depth

• Manatees (Trichechids): tend towards freshwater sources

– Amazon manatee: obligate fresh water

Current Distributions: Pinnipeds

• Cetaceans more successful in low latitudes, pinnipeds more successful at high latitudes

• Odobenids

– disjunct circumpolar

• Otariids

– cool temperate/subpolar (except N. Atlantic)

– lower latitudes where cold currents occur

•– Arctopcephalus (fur seals) have 6 species only in southern ocean

– Distributions highly influenced by sealing

– Some species highly endemic, but others widespread

– Zalophus (sea lions) mainly in north with California sea lion most widespread

• Phocids

– Most widespread pinnipeds

– Northern group Phocinae

• Many give birth on ice or in ice lairs

• Temperate, Arctic, subarctic, some landlocked lake seals

– Monachinae

• Warm water seals, elephant seals, Antarctic ice seals

– Some ice seals can maintain holes (Ringed seal) in ice, others must stay near ice edge (Bearded seal)

– Monk seals only true warm water seals

Current Distributions: Sea otters and Polar Bear

• Sea Otter

– North Pacific

– Tied to shallow waters

– Poor dispersal ability

• Polar Bear

– Circumpolar

– Track seal distribution (mainly ringed seals)

Current and historical distributions

• May have been modified greatly by human activities both ancient and modern

• Pinnipeds in central and northern California are a perfect example

Pinnipeds of central California

• Currently dominated by CA sea lions and N elephant seals with northern fur seals (NFS) rare and only

breeding in recent and small colonies on offshore islands

• Most NFS breeding is in Alaska and may forage in pelagic waters as far south as Baja

• A strange observation: remains of NFS extremely common in archeological sites in California.

Explanations of NFS abundance in ancient times

• Always had northern rookeries and foraged closer to shore where they were available or were hunted

more commonly

• More abundant on offshore rookeries of California

• Were historically more abundant and had mainland rookeries

Burton et al (2001)

• Used archeological data, stable isotopes to address these hypotheses: what did they find?

– Differences in hunting or foraging location did not explain remains

– NFS were mainland breeders in CA during mid-late Holocene

– NFS were extremely abundant historically compared to other pinnipeds and may have limited the

abundance of other pinnipeds

Range of Polar bears

River Dolphins