Vertebrates
3 November 2025: Origins of vertebrates
Features of a fish
Paraphyletic
A convenient desccirption, not taxonomic ranking
Poikilothermic, aquatic chordate
Tends to swim, uses gills as main respiratory fins, be bony, be covered in scales, be ectothermic (MANY EXCEPTIONS)
Taxnomoic evolution
Major chordate subphyla
Urochordata
Crainata
Chordates with cephalization and bone/cartilage
Essentially vertebrates but may lack vertebrate
8 superclasses
Conodonta (extinct)
Pteraspidomorphi (extinct)
General small (10 – 20cm), but some up to 1.5m
Benthic filter feeders
Evolved reduced armour, narrower head shield, lateral projections
Anaspida (extinct)
Small (<15cm), fusiform, compressed
Benthic parasitic/detrital feeders: marine → freshwater
Overlapping tuberculate scales
Fin-like projections + muscles + internal skeleton → manoeuvrability
Thelodonti (extinct)
Small (10 – 20cm), fusiform, depressed, large head, horizontal mouth
Hypocercal tail, dorsal & anal fins: benthic
Forktail form - supra-benthic!
Covered with characteristic scales or denticles (like sharks)
Stomach
Lateral line (first appearance???)
Osteostracomorph (extinct)
Abundant and diverse
Large, anterior, bony shield with eye, nose & pineal openings
Ossification of endoskeleton
Epicercal tail, body form and paired fins: creates lift
Complex brain
Myxinomorphi (extant)
70 living species in 1 class: Myxini
Temperate / cold temperate oceans, below 30m
Restricted to seawater: isosmotic!
Sister group to vertebrates: lack even primitive vertebrae
No true eyes
Mud-burrowing species extremely hypoxia tolerant
Predators of benthic inverts and scavengers (burrow into prey)
70 – 200 pairs of slime glands: exude mucous and thread cells
Petromyzontomorphi (extant)
38 living species in one class: Petromyzontida
Functional eyes, cerebellum, separate ventral & dorsal roots of the spinal nerves (a vertebrate feature)
Olfactory and respiratory pathways are separated
Freshwater species: may be parasitic
Anadromous species: all are parasitic
Migrate to upper streams for spawning
Gnathostomata (extant)
Cephalochordata
Overviw of extant vertebrates
55k known living species
27k tetrapods
0.5k marine
28k fishes
16k marine
Hagfish versus lampreys
Similarities, now thought to be convergent evolution:
Eel-like, scale-less, jawless forms
Produce pathogen-specific defensive substances: “variable lymphocyte receptors” (vs. antibody proteins in gnathostomes)
Tongues posses keratinous, replaceable teeth
No stomach
Differences
Origin of bone in vertebrates
Cartilage:
Tough, semitransparent, elastic, flexible
Glycoprotein strengthened by collagen
Mineralized skeleton can be:
External (dermal bone) OR internal, derived from cartilage precursors (endochondral)
Solid support for attachment of muscles
Fast, efficient locomotion → avoid predators and catch prey
Storehouse of chemicals (e.g. phosphates) for metabolism
Protection
3 November 2025: The arrival of jaws
Ancestors of gnathostomes
Thelodonts?
Stomachs, unlike extant agnathans
Scales like teeth and modern shark placoid scales
Broad based pectoral fins
Osteostracomorphs?
Ossified bones around eye
Cellular bone
Slit shaped gill openings
Paired fin structure
2 dorsal fins
Epicercal tail
Gnathostomata (extant superclass) (5 classes below)
Placodermi (extinct)
Bony, ornamented plates over 30–50% of body
Big jaws, teeth and large gape: “craniovertebral joint”
Quite diverse (200 genera)
Dunkleosteus: 1m x 6m or larger!
Antiarchs: pectoral fins enclosed in bone-like arms
Evolved towards reduced body armour
Limitations
No replacement dentition
Jaw could not generate suction forces
Chondrichthyes (extant)
970 living species
Defining features:
Prismatic calcification of endoskeletal cartilage
Pelvic claspers
Specialized as marine predators
Dominated ancient seas
Acanthodii (extinctt)
“Spiny sharks”
Small and stout
Large head and eyes
Bony spines before all fins
Cartilaginous skeleton
Body covered in small scales
Water column feeders:
Streamlined, round bodies
Reduced armour
Sarcopterygii (extant)
Fleshy, lobed fins
Enamelled teeth
Cosmoid scales
Only 8 extant fishes
26,742 extant species
Actinopterygii (extant)
26,891 living species
Sister group to Sarcopterygii
Monophyletic but no strong derived characters
Scales: ganoid, cycloid, ctenoid or absent
Spiracle absent
Gular plate absent
Fish scales
4 main types
Placoid
Found in Chondrichthyes
Dentine covered in vitrodentine (enamel)
Richly supplied with blood capillaries
Increase in number, not size, as fish grows
Ganoid
Found in ancestral Actinopterygii
Modified cosmoid scales
Dentine covered in ganoine
Often rhomboid, articulating peg & socket joint
Cosmoid
Found in Sarcopterygii
Probably a fusion of two placoid scales
Cosmine covered in vitrodentine
Supplied with blood capillaries
Grow from addition of bone underneath
Elasmoid
Found in Actinopterygii
Evolved from ganoid scales: loss of ganoine
Fibrous layer (collagen) covered in bony outer
Almost completely dermal and grow with fish
2 types: cycloid and ctenoid (with teeth)
Ossification of placoderms in skull cases
Chondrichthyans lost the bony skeleton
6 November 2025: Long in the tooth
Class Chondrichthyes
970 living species
Defining features:
Prismatic calcification of endoskeletal cartilage
Pelvic claspers
Specialized as marine predators
Dominated ancient seas
Subclasses
Holocephali (chimeras)
33 spp.
Deep water, weird!
Gill chamber further forward, no spiracle
1 opercular opening covering 4 gill openings
Upper jaw fused to cranium, not protrusable
Teeth:
Continuous growth, not replacement
Naked skin (modern forms)
Claspers on head (also pelvic claspers)
Venomous spine in front of 1 st dorsal fin
No stomach or ribs
Tail often “diphycercal” (pointed)
Elasmobranchii
5 – 7 gill openings
Dermal, placoid scales
Replacement dentition (derived from placoid scales?)
Upper jaw not fused to cranium
Ribs
Spiracle
Several radiations, all extinct except
Division = Neoselachii
Overhanging mouth – several jaw modifications
Calcified vertebral centra replace unconstricted notochord
Basal fin supports: fused, flexible, horny rays support fin
Developed sexual dimorphism and internal fertilisation
•Electroreception
Oil accumulation (buoyancy)
2 subdivisions:
Selachii (sharks: 8 orders, 403 spp)
Batoidea (rays/skates: 5 orders 534 spp)
Differences between the two:
Gill slits lateral / ventral?
Pectoral fin attached to head?
Presence of anal fin?
Size and position of spiracle?
Subdivision Selachii orders
Carcharhiniformes (Requiem sharks)
224 spp.
Tropical & subtropical
Nearshore
Order Lamniformes (Mackerel sharks)
15 spp.
Offshore, pelagic
Examples
Mako
White
Thresher
Basking
Order Squaliformes (Dogfish sharks)
97 spp.
Successful in North Atlantic, North Pacific & deep sea
Subdivison Batoidea orders
Rajiformes (skates)
285 spp.
Deep water
High latitude
2 dorsal fins
Long slender claspers
Dorsally depressed
Myliobatiformes (stingrays, eagle rays)
183 spp.
Inshore
Tropical
0 dorsal fins, tail spine
Short, stout, cylindrical claspers
Dorsally depressed
Body size
Relatively large
Smallest (17cm): Etmopterus perryi
Largest (>12m): Rhincodon typus
Habitats
Shallow temperate & tropical waters
Mainly coastal marine
5% of species in open ocean
5% in freshwater
Shallow waters, seldom >3,000m
Generally outside environmental extremes
Movement and bouyancy in sharks
Efficiencies through
Integument
Fins
Swimming type
Efficient buoyancy devices
No gas bladder
…but see Hussain 1989 Indian J. Fish., 36 (3): 266-268!
Lightweight skeleton
Oil-filled liver
Heterocercal tail → creates lift
Pectorals to adjust pitch
Movement and home ranges
Highly mobile, often large home ranges
Home range increases with age
Different movement patterns:
Local
Coastal
Oceanic
Metabolism and growth rates
Low metabolic rates
Low aerobic scope
Low food requirements
Variation among species depends on activity
Slow growth, long life spans
Feeding habits
Almost all carnivorous, many apex predators
Live prey
Scavengers
Planktivorous
Often nocturnal feeders
Strong bite: underslung jaw
Teeth for piercing, slicing, crushing
Dentition replacement
Other key feeding features
Tailfin (Thresher sharks: herding & stunning)
“Saws” (Sawsharks: slashing).
Electricity (Torpedo rays: stunning)
Cephalic horns (Manta rays: guiding)
Suction in some species
From enlarging orobranchial cavity
Protrusion of palatoquadrate
Improves bites speed and strength
Sensory physiology
Often nocturnal: rely on non-visual senses
High olfactory sensitivity
Good vision (esp at night)
Mechanoreception
Acoustic sensitivity
Electroreception
Large brain: integration
Reproduction
Older age at reproduction than actinopterygians
Typically mature at 6 – 18 years
Internal fertilisation
Produce few, successful offspring
Low fecundity
Large, precocial young
Large energetic cost for females
Embryonic development & nutrition
All nutrition from yolk sac:
Yolk sac oviparity
Yolk sac viviparity
Some additional nutrition from mother:
Eating unfertilized eggs or embryos (oophagy or embryophagy)
Placenta (placental viviparity)
Uterine secretions (uterine viviparity)
7 November 2025: Radiation of ray-finned fishes
Class Actinopterygii
26,891 living species
Sister group to Sarcopterygii
Monophyletic but no strong derived characters
Scales: ganoid, cycloid, ctenoid or absent
Spiracle absent
Gular plate absent
3 subclasses
Cladistia (bichirs; 16 spp)
Chondrostei (inc. Acipenseridae, sturgeons & paddelfishes; 27 spp)
Neopterygii
Equal numbers of fin rays as supports in dorsal and anal fins
Two types of fin types
Orders
Lepisosteiformes (Gars): 7 spp.
Order Lepisosteiformes (Gars): 7 spp.
Division Teleostei (everything else):
26,840 spp.
Mobile premaxilla
Neural arches on dorsal side of tail base → uroneural bones
Ventral pharnygeal toothplates unpaired
Particular arrangement of skull bones
Subdivision Osteoglossomorpha (220)
Subdivision Elopomorpha (804)
Subdivision Otocephala (8344)
Superorder Clupeomorpha (364)
Superorder Ostariophysi (7980)
Subdivision Euteleostei (17422)
Superorder Protacanthopterygii (356)
Superorder Esociformes (10)
Superorder Stenopterygii (391)
Superorder Ateleopodomorpha (12)
Superorder Cyclosquamata (236)
Superorder Scopelomorpha (246)
Superorder Lampriomorpha (21)
Superorder Polymixiomorpha (10)
Superorder Paracanthopterygii (1340)
Superorder Acanthopterygii (14,800)
Trends in teleostean phylogeny
Reduction in bony elements
Shifts in position /use of the dorsal fin
Shifts in placement and function of paired fins
Evolved/advanced caudal fin
Gas bladder
Arose either as a breathing or buoyancy device
Living preteleosts (e.g. gar) and basal teleosts (e.g. herring) are
Physostomous:
Gas released through Pneumatic duct
Derived teleosts (e.g. seabass) are Physoclistous:
Gas exchanged across Rete mirable
Loss of dependence on fins for buoyancy → diversification of swimming types
A suite of interrelated trends:
Increased speed, manoeuvrability and feeding capability
No significant loss of defensive structures
Diversity of swimming types and morphology
Similar (independent) trends in other groups of fish
Skeletal features and scales
10 November 2025: Functional morphology + anatomy of fish
Senses in fish
Sight
Eyes: similar to other vertebrates
Hearing
Good in chondrichthyans and actinopterygians
Sound transmits well in water
Detection in inner ear
Detection based on density differences among tissues
Otoliths (in actinopterygians)
Hair cells, stereocillia
Gas bladder
Sensory epithelium = macula
Mechanoreception/neuromasts
Gelatinous cupula displaced by water motion →
Cupula moves cilia of hair cells →
Hair cell initiates a change in signals to brain →
Able to filter out background “noise”
Two main types of neuromasts
Ones that detect slow moving water, located on surface of skin, very easily stimulated
Ones that sit inside canals that go down the body, better for fast moving water
Lateral line
Sensory input/electroreception
“Ampullae of Lorenzini”
Specialized electroreceptors which detect weak electrical fields.
Visible as tiny pores on the skin, enable the animals to find prey buried under sand
Navigate using Earth's magnetic field, and follow water currents
Two main types
Ampullary receptors - receptive to electrical fields produced by biological activity (ex. prey movement) and the environment, can also be used for socail communication and navigation
Tuberous receptors - detcted high frequency electric fields, used by fish to detect their own electric discharge
Smell
Olfactory chambers
Often ventilated by cili
Taste
Receptors on:
Mouth, lips, barbels
…also fins and trunk
Often clustered into taste buds
Maintaining water/salt balance (osmosis let’s goooo)
Hagfish
Isosmotic, simple kidneys
Lamprey
Similarities with teleosts (later)
Sarcopterygians
Similarities with sharks & rays (convergent evolution?)
Sharks and rays
Slightly hyperosmotic to seawater
Excrete salt using rectal gland
Concentrate urea and TMAO to maintain high osmolarity
Excrete dilute urea
Marine teleosts
Hypo-osmotic
Problem:
Water loss + salt gain
Drink water
Excrete salt (gills and gut)
Excrete scant urine
Freshwater teleosts
Hyperosmotic
Problem:
Water gain + salt loss
Avoid drinking
Uptake salt (gills)
Excrete copious urine
Respiration
The buccal pump: chondrichthyes
Expand volume of the mouth (buccal) cavity
Lower floor of mouth
Expand pharynx
Sucks water in through the spiracles & mouth
Close mouth and force buccal cavity smaller (contract pharynx and raise floor of mouth)
Water forced over gills, out through gill slits
Water flow is unidirectional and pulsatile
Also: RAM VENTILATION
A breathing method in sharks where they swim forward with their mouths open, forcing oxygen-rich water over their gills
Buccal + opercular pumps: teleosts
2 pumps (give almost continuous flow)
At higher speeds: RAM VENTILATION
Gills: teleosts
Brachiostegal rays/membrane
Concurrent exchange
Countercurrent exchange
Blood along the capillary is always in contact with water that has a higher PO2
Circulation
Myxinomorphi
Partially open circulatory system
Arteries → Sinuses → Veins
4 rudimentary hearts
Primary 3-chambered heart
1) Near gills: branchial heart
Auxiliary 1-chambered hearts
2) Behind mouth: paired cardinal heart
Re-establish flow
3) Mid-body: portal heart
Cardinal vein + intestine → liver
4) End of tail: paired caudal heart
Re-establish flow
Branchial & portal powered by intrinsic muscle
Paired heart powered by extrinsic, skeletal muscle
Petromyzontomorphi
Partially open circulation, more closed than hagfish
Main sinus in branchial region: for blood-gas exchange
1 heart, posterior to gills
Cutaneous respiration (CO2 and O2 exchange happens through skin)
Chondrichthyes & Actinopterygii
Positioned behind gills
4 chambers in series
1. Sinus venosus
A reservoir to collect blood
Assures easy filling
2. Atrium
3. Ventricle (pump)
4. Conus / bulbus arteriosus
Conus, muscular in sharks
Bulbus, elastic in bony fish
Sinoatrial and atrioventricular valves maintain unidirectional flow
10 November 2025: Tetrapod invasion of land
Challenges of moving onto land
Features central to the evolution of tetrapods
Pectoral (and pelvic) fins
Respiratory system
Circulatory system
Also: Reproduction, digestive system, sensory system
Main view
Alternative views
Movement not limiting
Many extant teleosts can move over land
Crutching (like mudskippers) may have been the common method
Respiration not limiting
Some advantages of air breathing
Air was higher in O2 at the time
Terrestrial reproduction can be a strategy to avoid predation
A force driving fish out of water?
Feeding in air requires much morphological modification
Fish remained tied to water by need to feed?
Class Sarcopterygii
Key traits
Enamelled teeth
Fleshy, lobed fins
Cosmoid scales
26,742 extant species
Only 8 extant fishes
Subclass: Coelacanthimorpha
Appeared in the Devonian, max diversity in the triassic
2 living species (considered extinct until 1938)
3-lobed tail supported by hollow spine
Unconstricted, unossified notochord
Double gular plate
Spiny dorsal fin
Cranio-vertebral joint!
Subclass: Dipnotetrapodomorpha
Dipnomorpha (includes lungfish: 6 living species, all freshwater)
All living spp. are FW: 1 Australian, 1 S. American, 4 African
Once considered origin of tetrapods
Tetrapodomorpha (all extinct except infraclass tetrapoda)
Large predatory fishes
Symmetrical tails (functioning swim bladder?)
Peaked in late Devonian, extinct in Permian...except tetrapods
Robust limb skeleton: hip / shoulder girdles and rotational shoulders
Could be large: up to 6m in Rhizodontiformes!
Dorsally placed eyes
1 pair of external nostrils (incurrent)
Choana (excurrent nostrils moved to palate)
Many thought to be ambush predators
Water versus air as a respiratory medium
Breathing frequency
1 per 3 -10 mins in obligate air breathers
1 per HOUR for water breathers with lungs
Fewer breaths = fewer trips to the surface
Water
High density (heavy)
High viscosity
Low O2 areas
Available everywhere
Easy to expel metabolic wastes
Air
Low density (1/800th water)
Low viscosity (1/30th water)
O2 always available
Requires surface access
Hard to expel metabolic wastes
Bimodal breathing the best of both worlds
Air is more O2 rich: 21% O2 in air vs <1% in water
Diffusion from air to blood is also faster
Air breathing fish
> 370 known spp (49 families): capacity to obtain O 2 from air
Has evolved many (~50?) times
Aquatic vs. amphibious
Facultative vs. obligate
Air-breathing organs:
Derived from gut (lungs, gas bladder, stomach, intestine)
Head & pharynx (gills, mouth, pharynx, opercles)
Skin
In higher actinopterygians, lung → gas bladder
Origins of lungs
Air breathing
To cope with seasonal dryness?
Exploit new habitats / release competition?
To survive low O2 waters?
Lungs probably evolved in marine species- not usually hypoxic
Habitats of lungfish not necessarily hypoxic
Farmer (1999): To avoid myocardial hypoxia?
Exercise stimulates air breathing more than aquatic hypoxia
Death from exercise results from heart failure
O2 sensors afferent to gill
Early fish active, high O2 environment
Secondary loss of lung?
Air access not possible at depth
Aerial predation
Origins of separate circulation
Separation of circulation
To survive low O2 waters?
Atrium fully divided
Ventricle functionally divided
Oxygenated blood → reduced gills
Systemic blood → gills then lung
13 November 2025: Return to the ocean I
Amphibian respiratory system
Amphibians: Tetrapods with aquatic eggs
Permeable skin and gills
Lungs (?)
Simple sacs divided by ridges
May simply supplement cutaneous respiration
Positive pressure breathing: buccal pump + elastic recoil
Marine reptiles
Successful in the mesozoic
Sauropterygians (plesiosaurs)
Ichthyopterygians
Mosasaurs
Sea Turtles
<70 extant spp
Tropical / subtropical
Three orders
Squamata (snakes/iguanas)
Snakes
True sea snakes (~50 spp.): fully marine
Ovoviviparity
Sea kraits (~5 spp.): some terrestrial needs
Digestion on land
Ovoparity
Highly venomous
Coastal tropical, Indian & Pacific Oceans
Excellent swimmers and divers
Iguana
1 sp. (Galapagos)
Testudines (sea turtles)
7 or 8* spp:
Green
Flatback
Loggerhead
Hawksbill
Olive Ridley
Kemp’s Ridley
Leatherback
* Some suggest black sea turtle as an 8th species
Distinguish spp. by head & shell
Circumglobal, tropical
Mainly coastal (except leatherback)
Good swimmers: foreleg paddles
Come ashore to lay eggs
Crocodylia (crocs)
2 species:
Crocodylus acutus (American Crocodile)
Crocodylus porosus (Saltwater Crocodile)
Reptile respiratory system
Skin is nearly impermeable to O2
But… cutaneous respiration in seasnakes
Increased reliance on lung as respiratory surface
Lung volume constant
Subdivision increases
Negative pressure breathing (aspiration pump):
Uncouples feeding and breathing
Requires thoracic cavity
TIDAL VENTILATION
Left to right shunt
Adaptations
Usually v. good swimmers
Good divers (esp. turtles)
Cutaneous respiration (seasnakes)
Do not become anaerobic despite up to 2h long dives
Lung extends full length of body
Posterior portion oxygen store
Small, thin scales and flattened body
Cuticle impermeable, but…
Salty foods
Accidental ingestion of seawater
Kidney cannot produce urine more concentrated than seawater
Salt glands- to excrete excess salt
In marine lizards:
On head
Empties into nasal cavity
Ridge prevents re-swallowing
Sudden exhalation to expel (sneeze)
In sea snake:
Base of the tongue
Empties into the oral cavity
In turtles:
In orbit of eye
Empties into posterior corner of orbit
In Crocodiles:
Distributed over the surface of the tongue
Sea birds
5 orders
Sphenisciformes
17 spp.
Penguins
All seabirds
Southern hemisphere*
*Galapagos penguin just north of the equator
Flightless
Feet → rudder
Wings → fins
Procellariiformes
125 spp.
Albatrosses, petrels, storm-petrels, fulmars and shearwaters
All seabirds
Tubular nostrils
Good sense of smell
Pelecaniformes
65 spp.
Pelicans, frigatebirds, gannets, boobies, cormorants, anhingas
All waterbirds
All seabirds, except anhingas, some pelicans and some cormorants
All four toes are webbed
Salt gland enclosed within orbit
Nostrils are slit like, nearly closed or absent
Charadriiformes
128 spp. + ~200 shorebirds
Skuas, jaegers, gulls, terns, auks, guillemots, puffins, shorebirds & skimmers
Mostly seabirds except shorebirds
Ciconiiformes
Herons, egrets, storks, ibis, spoonbills
May feed along the shoreline, but not ‘seabirds’
Bird respiratory system
Flight + endothermy
High metabolic demands
Insulation
HIGH O2 DEMAND!
Tidal ventilation of air sacs → Unidirectional ventilation of “PARABONCHUS” (lung)
Cross-current blood flow
Adaptations to life at sea
Energy management
Weight reducing adaptations
High MR and endothermy
Specialised lungs
Salt management
Feed in salt water
May avoid saltwater ingestion
Nasal salt glands- above eye
Connects to nasal cavity
Preening gland / waterproofing
Locomotion and feeding
Wings for:
Underwater swimming
E.g. penguins, cormorants
Flying vast distances
E.g. albatrosses
Flying fast and agile, close to shore
E.g. auks and puffins
Bodies can be streamlined for swimming underwater
Webbed feet
Bills adapted to prey type and feeding mechanism
Colouration
Can be cryptic… or not
Life history
Form large colonies
Large, long life, deferred maturity, small clutch size, extended chick period… due to energy limitation?
13 November 2025: Return to the ocean II
Marine mammals evolution and taxonomy
Order Sirenia
Includes manatees & sea cows
4 sp.
Arose in the Eocene (50 mya) in the Sea of Tethys
Evolved from the Proboscideans (elephants)
Main features
Herbivores
Very low metabolic ratergrgthth
Tropical / warm shallow water
Heavy bones
Flipper like forelimbs
Reduced hindlimbs
Blubber and sparse hair
Fleshy, almost prehensile lips
2 families:
Trichechidae (manatees)
3 sp.
New World
Dugongidae (dugongs)
1 sp. (+ Steller’s Sea Cow (extinct))
Indo-Pacific
Order Carnivora
Includes seals, sea lions & walruses
Pinnipedia 33 sp.
From late Oligocene (27 – 25 MYA)
3 monophyletic families:
Otariidae (eared/fur seals & sea lions)
14 sp.
Ability to rotate pelvis (walking)
Small external ear flaps (pinnae)
Dense fur for insulation
Long coarse guard hairs
Thick under-fur to trap air
Large fore flippers for propulsion
Sexual dimorphism
Phocidae (true or earless seals)
18 sp.
Unable to rotate pelvis: move by undulating body
No external ear flaps
Blubber: insulation
Pelvic flippers: propulsion
Pectoral flippers: stability & steering
Excellent divers
Odobenidae (walruses, 1 sp.)
1 sp.
Previously diverse, two subspecies today
Otarioidea (O)
Phocomorpha (P)
Ability to rotate pelvis (O)
No external ears (P)
Blubber for insulation (virtually hairless) (P)
Pelvic / pectoral flippers for propulsion (O & P)
Large canine tusks (Neither)
Semi aquatic
Carnivores
Fur/ hair and blubber
Very sensitive whiskers (vibrissae)
Mobile neck
Swim side to side like fish (lateral undulations)
Ancestral origins of pinnpieds
Enaliarctos – the earliest known pinnipeds
Mid-Oligocene – late Miocene (~30 MYA) from California and Oregon
Aquatic features
Distinct, highly modified flippers
Streamlined
Reduced tail
Still retained many terrestrial features
Inner ears adapted for hearing in air
Heterodont dentition: must bring prey to shore to handle + chew it
A coastal species
Similar to sea otter
Ancestral to all pinnipeds?
Only in Pacific
Puijila darwini: Rybczynski et al. (2009)
Late Oligocene early Miocene, Canadian lakes
Similar to land dwelling arctoids
No flippers
Long tail
Proportionally long limbs like a skunk or marten
A swimmer
Its all in the muscle attachment sites
Long shoulder blades (extend down back)
Big shoulder muscles
Large muscle (teres) that allows rotation of shoulder
Robust forelimbs
Enlarged webbed (?) feet (flattened finger ends)
Not an otter
Hands & feet proportions are wrong: big hands unlike otters
Long first finger, long phalanges
Shorter, slimmer tail not used in swimming
Uses all four limbs to swim (otters use only back and tail)
Unspecialized! Arctic! Freshwater!
Marine otters 2 sp.
Polar bear 1 sp.
Superorder Certartiodactyla
Includes whales, dolphins & porpoises
Cetacea (Order) 90 sp.
Arose in Eocene (53- 54MYA) in Sea of Tethys
Entire life in water
Blubber, almost hairless
Shortened neck with fused vertebrae, no hind limbs, powerful tail (horizontal flukes), paddle-like forelimbs
Blow holes
Specialised ear bones and semicircular canals
2 major groups:
Mysticetes
Feeding
Mouth is flexible, capacious
Lack teeth: have baleen plates
Eat small fish or krill
2 blowholes
Small eyes point sideways
Major families:
Family Balaenopteridae: fin, humpback
Family Balaenidae: right, bowhead
Family Neobalaenidae: pigmy right
Family Eschrichtiidae: gray
Odontocetes
“Toothed whales”
Peg like, uniform teeth
Eat fish and mammals (fast)
High frequency sound:
Echolocation
Communication
Melon on skull
Fused nostrils → one blowhole
Evolutionary origins
Artiodactyls (even toed ungulates):
Deer
Antelope
Camels
Pigs
Giraffes
Hippos
Extinct groups
Desmostylia (related to elephants), Kolponomos (marine bear- like carnivoran), Thalassocnus natans (aquatic sloth)
Respiration in marine mammals
Similar to birds
Completely divided
No cutaneous respiration
Mammalian lungs
Back to tidal lungs again
Dead space = 1/3 – 1/20th tidal vol
5% body volume
Finely divided → V. high SA
Surfactants prevent bubbles
Negative pressure ventilation
Marine mammal adaptions
Diving
Record dive: 137.5 min, 2992m (Cuviers Beaked Whale)
Challenges: O2 decrease, lactate build-up, pressure change, changes in gas chemistry
Heart:
Similar size & structure to terrestrial
Glycogen stores
Aortic bulb
Retia mirabilia
Myoglobin-rich muscles
Increased haematocrit
Blowhole muscles
Respiratory system:
Collapsible chest
Reduced lobulation
Supported trachaea
Blood buffering
Diving response:
Decline in heart rate
Regional vasoconstriction
Reduction in core temperature
Regional reduction in metabolic rate
Senses
Sound travels quickly underwater, light readily attenuated
Sound used for communication & echolocation
Low freq: long distance
High freq: fine resolution
Sound production
Larynx (pinnipeds)
Inflatable throat pouches (pinnipeds)
Phonic lips + melon (cetaceans)
Sound reception
Auditory canal (pinnipeds)
Lower jaw and throat (cetaceans)
Salt management
Have lungs, but not immune to problems of high salt:
May ingest water accidentally
Diet is salty (esp. invertebrates and plants)
Internal fluids are hypoosmotic to seawater
Derive water from food-preformed and metabolic
Large, reniculate kidneys-excrete concentrated urine