Pinnipeds

There is a continuing debate about pinniped phylogeny - some suggest Phocids and Odobenidae should be 1 grouping

All Pinnipeds capable of sustained diving and can survive/live in water

Otariidae (eared/walking seals), Phocidae (earless/true seals) and Odobenidae families

Pinnipedia - sister relationship w/ Ursids or Mustelids

Disovery of nearly complete skeleton of new semi-aquatic carnivore form early Miocene

• Morphological link in early Pinniped evolution

Retains long tail and proportions of fore/hindlimbs - similar to modern terrestrial carnivores compared to modern npinnipeds

Traits indicative of semi-aquatic adaptation

• Pelvis w/ short ilium
• Shortened femur
• Flattened phalanges - webbing?

Pinniped evolution included a freshwater transitional stage

Found in high Arctic - early centre of Pinniped evolution?

Enaliarctos 

Marine 'bear-like' creatures from Early Miocene

First member of Pinniped lineage to have flippers

Larger than Puijla w/ shorter tail and streamlined

Characteristic horizontal structure w/ fore/hindlimbs

Expansion of hindlimbs = asymmetry of skeleton

Still had carnassials - modern Pinnipeds have simple, conical cheek teeth (to grab fish)

Found NW N. America

1 extant species - Odobenus rosmarus 

• 6 distinct populations
• Some considered sub-species
• 4 in Atlantic - Odobenus rosmarus rosmarus
• 1 in Pacific - Odobenus rosmarus divergens
  • Evidence for distinct sub species
• 1 in Laptev Sea - Odobenus rosmarus laptevi

Pacific wlarus larrge - weighs <1,900kg

Atlantic males largests - weighs <1,600kg

Wild walruses life span 20-30yrs

Males reach sexual maturity 7-10yrs

• Rarely mate till 15yrs
• Sufficient bulk to compete in rutting displays and control harem of females
• Males rut Jan-April
• Mate in water
• Have baculum (bone) in penis to hold it

Females start ovulating 4-6yrs

• Polyoestrous - heat both in lare summer and Feb
• Functionally monoestrous though - females receptive to males only in same locality and timeframe
• Peak conception is Feb
• 4-5 month delayed implantation (April-June following year) = calves feed in escess on land/ice floes and are well advanced before next winter
  • Swim and weaned at 8-11 months but spend <5yrs w/ mother
• Actual gestation 15-16 months

Sometimes catch fish - generally feed on bivalves

Pacific walruses feed on >60 marine genra including shrimp, crabs, tube worms, soft coral, tunicates, sea cucumbers and echinoderms, molluscs, other pinnipeds

Not fussy

Abrasion patterns on tusks = tusks dragged through sediment and stir it up

Upper edge of snout used to dig up prey

Can spit jets of water to reveal buried bivalves

Large male walruses attack seals if no other food source

• Often don't kill and eat them though

Both sexes - tusks for feeding

• Males larger = secondary fighting use

Need to dive to reach their food - various adaptations seen in all pinnipeds

Mystacial vibrissae (moustache)

• Highly sensitive tactile receptors - feel buried prey in sediment
• Sensitive to sound ~100Hz

ALL PINNIPEDS = near-spherical eye lens and highly muscular iris

• Compensate for refractive indices of air and water by lens
• Well-defined iris = compensate for differences in light levels
• Otters less well adapted 
• Tapetum (layer of eye tissue) - most well developed 
  • Formed with intracellular reflective rodlets - line back of retina and reflect any potentially lost light back into retine
  • Maximises visual acuity at low light levels

Eared/walking seals

Retention of visible pinnae (ears) and ability to bring hind limbs under body to aid land movement

Divided into fur seals (Sub-Fam Arctocephalinae) and sea lions (Sub-Fam Otariinae)

Male otariid size between 70kg (Galapagos fur seal) and over 1000kg (Stellar sea lion)

Mature males weight 2-6x more than females

• Proportionally larger heads, necks and chests
• Most sexually dimophic of all mammals
• Males often kill pups by accidentally squashing them

All species covered in thick body fur and blubber = retain heat via insulation

Appeared late Early Miocene (20-15mya) in N. Pacific

Moved S and diversified in S. Hemisphere - most species live here

Arctocephalinae appeared before the Otariids

• Arctocephalus pusillus cape fur seal (Afro-Australian) has behavioural and anatomical characteristics of both sub-families

7 living genera divided into 15 species

• Bering sea, N. & S. Pacific ocean, S. Atlantic, S. Indian ocean, S. Ocean
• Occupy subpolar, temperate and equatorial waters

Strongly polygynous - highly territorial male mating in harem system

Usually mating on land but 4 species mate in water

Prefer islands - avoid land predators and proximity of offshore feeding areas

Nurse pups for long phase - several months = protracted lactation

• Otariid milk is lower fat content 25%-50%
• Leads to social bond formation

Complex vocalisastion patterns compared to other Pinnipeds = great social intteraction

Elephant seas have calls that differ - more in next slide

Rhythm perception in non-human mammals found through behavioural training but not in wild

• No evidence to indicate biological function

Performed playbacks to seals w/ natural and modified vocalisations

Elephant seals naturally recognise/memories rhythmic patterns and timbre of rivals' calls 

• Calls = series of pulses characterised by tempo and timbre

Breeding colonies of <4000 individuals - need to identify others

Use rhytmic information to:

• Identify competitors (including subordinates avoiding lethal contatcs w/ beachmasters) 
• Identify local social grouping of 20-30 individuals (social networks)

First experimental demonstration of temp perception in a wild mammal

High density of fur in Otariids (~57,000pcm3) 

• Hunted to near extinction for this

Phocids rely on blubber (~18,000pcm3)

More and longer underhairs in Otariid fur compared to Phocids

• Underhairs stop guard hairs from flattening - increases insulation

Harbour seals - Erdsack et al, 2016

• Vibrissal system for orientation and foraging - needs to be heated up intensely
• High hair densities at vibrissal pads to reduce heat loss
• Unique fur structure of hair bundles
  • Broad guard hairs
  • Smaller underhairs
  • Small and broad intermediate hairs
• Intermediate hairs may serve for thermal insulation and drag reduction

Otariid postcainine teeth for series of intermeshing points

• Adapted for seizing prey, not shearing/chewing

Crabeater seals, leopard seals and antarcitc fur seals:

• Filter-feed for megaplankton using teeth
• Also attack larger prey

Otariids - better land movers

• Enlarged, muscular forelimb to swim
  • Combination of rowing/flying action
• Hind limbs act as rudders
• Move easily over land

Phocids - better swimmers

• Propel with alternate strokes of massive webbed hind feet
• Forelimbs for sculling (propel) and steering 
• Sharp claws on forelimbs for terrestrial locomotion
• Not good at propping body up on land
  • Use vertical wriggling motion = galumphing
• Propulsive tail = more agile and fast swimming

Otariids - better land movers

• Enlarged, muscular forelimb to swim
  • Combination of rowing/flying action
• Hind limbs act as rudders
• Move easily over land

Phocids - better swimmers

• Propel with alternate strokes of massive webbed hind feet
• Forelimbs for sculling (propel) and steering 
• Sharp claws on forelimbs for terrestrial locomotion
• Not good at propping body up on land
  • Use vertical wriggling motion = galumphing
• Propulsive tail = more agile and fast swimming

More sensitive tactile vibrical systems

Lower cavernous sinus and ring sinus highly innervated (lots of nerves)

Detect slight changes in water

Upper cavernous sinus - blood vessel in centre to heat main sensory areas

• Maintain optimal tactile sensitivity, indpendent of ambient temp

Varies with species - some solitary groups, some colonial

Polygynous phocids

• Dominance hierachies
• Strong sexual dimorphism
• Male otariids defend territory but male phocids defend harems
  • Strategies may reflect different levels of mobility on land

Strong courtship behaviours - Hooded seals w/ loud noises and red display pouch

Phocid females nurse short periods between offshore feeding forays

• Short lactation period of 4-50days
• Fat content in milk is highest of all marine mammals (45-60%) = pups grow rapidly
• = seals on land for little peiods of time, reducing predation risk
• Minimal maternal boding = lack of complex social groupings
• Most females mate during late lactation or after weaning pup
• EXCEPTION - common seal, similar to Otariids w/ short foraging trips