Vert Bio Flashcards
past this bs exam
1
Q
Define systematics
A
the study of biological diversity using phylogeny
2
Q
Define taxonomy
A
the description, identification and classification of spp
3
Q
Define nomenclature
A
the standardised system of naming taxa
4
Q
Define classification
A
the arrangement and hierarchy of taxa (Kingdom, Phylum, Class etc…)
5
Q
Define phylogenetic systematics/cladistics
A
the shared derived character states constitutes evidence that the spp possessing these features share a common ancestry
6
Q
Define monophyletic groups
A
groups of taxa that consist of a common ancestor plus all descendants of that ancestor
7
Q
Define paraphyletic and polyphyletic groups
A
include a common ancestor and some, but not all, descendants of that ancestor (eg. recent molecular evidence data supports river dolphins as a polyphyletic group as Indian river dolphins do not share the smae common ancestor as other river dolphins)
8
Q
Purpose of phylogenetic tree
A
- other name being cladogram
- shows relatedness of animals
9
Q
What are common features of chordates?
A
- bilateral symmetry
- notochord: dorsal rod of specialised cells
- dorsal nerve chord: hollow tube just above the notochord
- pharyngeal pouches: gill slits
10
Q
What are the three subphyla of chordates?
A
- Urochordata (eg. tunicates)
- Cephalochordata (eg. lancelets)
- Vertebrata
11
Q
Why are vertebrates used as a model for studying evolution?
A
- monophyletic group
- free living
- basic anatomy and development in common
- diversity of form and function can be related to adaptation and evolution
- best-studied eukaryotic group
- good fossil record
12
Q
What are the modern (extant) lower vertebrates?
A
- Myxinoidea & Petromyzontoidea (jawless fish)
> hagfishes and lampreys - Elasmobranchii & Holocephali (cartilaginous fish)
> sharks, rays, skates and ratfishes - Actinopterygii (ray-finned fish)
> bichirs, bowfins, gars, sturgeons, teleosts - Sarcopterygii (lobe-finned fish)
> coelacanths and lungfishes - Lissamphibia (amphibians)
> frogs, salamanders, caecilians
13
Q
What are the extant higher vertebrates: amniotes
A
- Testudines > turtles, tortoises, terrapins - Lepidosauria > tuatara, lizards, snakes - Crocodilia > alligators, crocodiles, caymans Aves > birds - Amniotes arose from a tetrapod amphibian ancestor in the late Devonian period (~370mya)
14
Q
What are common features of vertebrates?
A
- vertebrae: series of bones that make up the backbone, protect the spinal chord and act as attachments for muscles
- postnatal tail: for movement in some vertebrates
- pharyngeal pouches in chordates evolved into:
> gill slits in fish and amphibians
> structures in throat and ears in mammals - vertebral column (backbone; developed from notochord)
- specialised sensory organs
- brain at anterior end of nerve chord
- closed-loop circulatory system (heart, arteries, veins and capillaries)
- myomeres (muscle segments)
- vertebrates are craniates ie. they have a head. Origin of head opened up a completely new way of feeding for chordates - active predation
- cranium: outer shell protecting the brain
- skeleton: made up of backbone, skull etc.
15
Q
What ten systems are vertebrate organs organised into?
A
- skeletal - circulatory
- muscular - excretory
- integumentary - immune
- digestive - nervous
- respiratory - reproductive
16
Q
Class - Agnatha (jawless fish): features and facts
A
- originated around 500mya
- two extant groups: lampreys and hangfish (90-100 spp in total)
- features:
> cartilaginous skeleton
> characterised by absence or paired fins
> seven or more paired gill pouches
> no identifiable stomach or any appendages
> fertilisation and development are external
17
Q
Class - Osteichthyes (bony fish): features and facts
A
- originated 500mya, first appeared around 410mya
- bony fish are an extremely diverse and abundant group with ~25,000 (100 new described each year) spp alive of which 60% are marine
- the largest class of vertebrates in existence today, divided into:
> Actinopterygii (ray-finned fish)
> Sarcopterygii (lobe-finned fish) - all bony fish have scales, gills for respiration and are ectotherms, however some members of the family Scombridae (swordfish and tuna) have some level of endothermy
18
Q
Class - Chondrichthys (cartilaginous fish, sharks, rays, skates and ghost sharks): features and facts
A
- first appeared around 420mya
- ~1200 spp: ~500 sharks and ~600 rays and skates
- jawed fish with paired fins, denticles (scales), skeletons made of cartilage not bone
- gills for respiration
- no gas bladder - will sink if they stop swimming
- fertilisation is internal
- development:
> usually through live birth (ovoviviparous spp)
> can be through eggs (oviparous) - two subclasses:
> Elasmobranchii (sharks, rays and skates): upper jaw not fused to braincase, separate gill slit openings (5-7 gillslits)
> Holocephali (chimaeras/ghost sharks): upper jaw fused to braincase, one gill slit with operculum cover (4 pairs of gills)
19
Q
Elasmobranchs - feshwater + skates and rays
A
- almost all are marine, but:
> 43 spp can tolerate brackish or freshwater
> stingrays, sawfishes and the bull sharks are more tolerant than others and can penetrate far up freshwater rives - the bull shark has been recorded 4,200km from the mouth of the Amazon river
> there are a few (~23) spp of South American river stingrays (Potamotrygonidae) that are entirely feshwater - Batoids (skates and rays)
> flat-bodied with pectoral fins developed into broad flat wang-like appendages
> major difference between skates and rays is how they reproduce:
+ rays are viviparous (live bearing)
+ skates are oviparous (egg-laying), eggs in rectangular cases sometimes called ‘mermaids purses’
> skates normally have prominent dorsal fins while rays have reduced or absent fins
20
Q
What are the various Pelagic zones in the ocean?
A
- Epipelagic: 0-200m. Continental shelf. Lots of light, where most organisms are found
- Mesopelagic: 200-1000m. Twilight zone. Little light but enough for phtosynthesis. Together, epipelagic + mesopelagic = Photic zone
- Bethypelagic: 1000-4000m. Pitch black. Deepest recorded Chondrichthyan: great lantern shark
- Abyssopelagic: 4000m-seafloor
- Hadopelagic: Ocean tenches
21
Q
Shark diagram - refer to notes
A
Shark diagram - refer to notes
22
Q
What is the ideal shape for aquatic locomotion
A
- fusiform, length:depth ratio = 4.5 (spindle-like shape that is wide in the middle and tapers at both ends)
- sharks have ratios between 3 and 8, optimum is 3-7
23
Q
What are the purpose of fins?
A
- used for stabilising, steering, lift and propulsion
- one or two dorsal fins = anti-roll stabilising fins, may have spines or skin glands that produce irritating substance for defence
- pectoral fins for steering and lift
- pelvic fins are also stabilisers, so are anal fins (if present)
- tail region = caudle peduncle + caudal fin. Peduncle may be flattened into lateral keels. Caudal fins provide thrust.
24
Q
Tail types?
A
- heterocercal: vertebrae extend into larger lobe, tail is asymmetrical
- homocercal: vertebrae do not extend into lope, tail more or less symmetrical
- epicercal: upper lobe is bigger (sharks)
- hypocercal: lower lobe is bigger (flying fish)
25
Q
Shark skin features?
A
- rough due to small rough placoid scales called dermal denticles
- denticles consist of bony plate buried in skin and a raised portion that is exposed
- dermal denticles are homologous in structure to teeth
- form a protective barrier and aid in swimming
- the low sharp-edged ridges of the denticles are parallel to the direction of movement and reduce drag by delaying turbulence
26
Q
Shark teeth features?
A
- not lodged permanently in jaw, instead attached to a membrane called a tooth bed
- tooth bed membrane works like a conveyor belt, teeth move forward as shark grows, replacing damaged, lost or worn teeth infront
- Cookie Cutter sharks (order: Squaliformes; two spp, small: 40-50cm) attach themselves to prey and spin to cut out ‘cookie’ of flesh
27
Q
How do you determine a sharks age?
A
- vertebrae examined - growth rings
- spine growth (not uniform, greater areas of growth can indicate year quality/season)
- oldest shark: Greenland shark, 392 +/- 120 years old
28
Q
Why study elasmobranchs
A
- protect biodiversity
- top predators - indicator spp
- threatened by:
> fisheries (mainly for fins). Last UK Basking shark fishery closed in 1995, protected in UK since 1999
> shark nets
> incidental catch (bycatch) in fisheries - little information on abundance and status for most spp
- tourism: swimming with basking, whale and great white sharks
29
Q
What factors are used to model growth and survival?
A
- distribution
- abundance
- population structure
- biology
- mortality
- ecology
- behaviour
- human impact
30
Q
Swimming and buoyancy - Dynamic lift? (shark related)
A
- fish denser than water will sink - must generate dynamic/static lift
- can create dynamic lift by using their (airplane wing-like) pectoral fins or inclining their bodies at an angle of attack
- they need to move forward to create the lift, but this increases drag, increasing energy expenditure
- may be energetically ‘cheaper’ to be a bottom-dwelling spp, however most hover just above the sea floor
- degree of dynamic lift decided by size and shape of pectoral fins
31
Q
Swimming and buoyancy - Static lift? (shark related)
A
- storing light materials creates static lift
- most (bony) fish create static lift with their swimbladder
- sharks don’t have a swim bladder, so:
> they use low density cartilage
> low density lipids (fat and oil eg. squalene: 860g/l)
> oil is bulkier than air but is easier to use to regulate buoyancy, Lift provided by oil varies a little with depth as changes in ambient pressure have little effect on volume of oil - more consistent buoyancy
> oil is stored in liver and muscles, but have to trade-off as oil is also a food store for adult and embryo
> sharks regulate oil to balance their weight in water (however exact process not know)
32
Q
Elasmobranch gills
A
- all sharks have 5-7 paired gills
- gas exchange occurs at gills, oxygenated water must flow over the gills for respiration to occur
- water enters through the mouth (or the spiracle), into the pharynx, over the gills and exits through the gill slits
- respiratory gas exchange takes place on the surface of the gill filaments as the water passes over the gills and out
33
Q
Spiracle
A
- essentially a first gill slit
- opening behind the eye
- provides oxygenated blood directly to the eye and brain through a separate blood vessel, and/or to pump water through the gills
- absent in many sharks eg. front swimming sharks
- larger in bottom dwelling sharks
- in rays the spiracle is larger and more developed and is used to actively pump water over the gill, allowing the ray to breathe whilst buried in the sand
34
Q
Elasmobranch senses: Ampullae of Lorenzini
A
- they are small vesicles and pore (electroreceptors), that form part of an extensive subcutaneous sensory network system
- found around the head and appear as dark spots
- each ampullae contains multiple nerve fibres that are enclosed in a gel-filled tubule (glycoprotein with electrical properties) which has a direct opening to the surface through a pore
- the ampullae detect weak magnetic fields produced by other fish
- since all living creatures produce magnetic fields by muscle contraction, sharks may pick up electrical stimuli from their prey
- this allows sharks to detect eg. prey hidden in the sand
- ampullae may also be used to navigate to the electric fields of the ocean currents and earths magnetic field
- (REFER TO DIAGRAM)
35
Q
Elasmobranch senses: Lateral line
A
- the lateral line along with the ampullae of Lorenzini comprise the electrosensory component of the sharks sensory system
- the lateral line allows the shark to orient to particle movement or sound
- it consists of structures called neuromasts that are located in canals that lie just beneath the surface of the skin or the scales
- similar to the ampullae of Lorenzini there are pores that open to the outside and movement caused by prey can be detected by the neuromasts
- there are also ‘Pit organs’ - surface neuromasts
- the lateral line canal lies just beneath the lateral line which is open to seawater by tubules connected to the surface by pores, bundles of neuromasts lie in a gelatinous dome which is partially exposed to the lateral line canal
36
Q
Elasmobranch Senses: Hearing
A
- sharks have a sharp sense of hearing, possibly being able to hear prey many miles away
- a small opening on each side of their heads (not the spiracle) leads directly to the inner ear through a thin canal
- the lateral line shows a similar arrangement, which is open to the environment via a series of openings called lateral line pores
- this a reminder of the common origin of these two vibration- and sound-sensing organs that are grouped together as the acoustico-lateralis system
- in bony fish and tetrapods the external opening to the inner ear has been lost
37
Q
Elasmobranch Senses: Smell and taste
A
- sharks have sophisticated olfactory senses, located in the short duct between the anterior and posterior nasal openings, with some spp able to detect as little as one part per million of blood in seawater
- sharks are are attracted to the chemicals found in the guts of many spp, and are often found near sewage outfalls
- some spp eg. nurse sharks, have barbels (whisker-like tactile organ near their mouth) that increase their ability to sense prey
38
Q
Why the hammer in hammerhead sharks?
A
there are two basic thoughts:
- hydrodynamic advantages (head is flattened on lower surface and rounded on upper and therefore may increase lift)
- sensory enhancement:
> nostrils of most spp are located near the tips of the hammer and have specialised grooves which channel scent-bearing water to the nostrils
> by having nostrils mounted far apart they can sample the water column in stereo
> the ampullae of Lorenzini are distributed over the entire under surface of the hammer, and the width of the head may work as a ‘metal prey detector’
39
Q
Elasmobranch osmosregulation
A
- the blood and other tissue of sharks and Chondrichthyes in general is isotonic (same or similar salt concentration) to their marine environment
- due to the high concentration of urea and trimethylamine N-oxide (TMAO), allowing them to be in osmotic balance with the seawater
- this adaptation prevents most sharks from surviving in freshwater
40
Q
Elasmobranch osmoregulation: Bull shark
A
- the bull shark is an exception to normal osmoregulation, it has developed a way to changes its kidney function to excrete large amounts of urea and allow it to move far up rivers
- despite this reduced solute concentration in freshwater, Lake Nicaragua Bull sharks still have body fluids more than twice as ‘salty’ as typical freshwater fish
- they must, therefore, experience a massive influx of water. The water influx is almost certainly dealt with by the kidneys, resulting in copious excretion of dilute urine.
- an early measurement of urine production by a freshwater sawfish indicated a daily flow rate of 250ml/kg of body mass - more than 20x that of a normal Elasmobranch
41
Q
Elasmobranch thermoregulation
A
- most sharks are ectotherms - their internal body temperature matches that of their environment
- members of the family Lamnidae, such as the shortfin mako shark and the great white shark, are endothermic and maintain a higher body temperature than the surrounding water
- in these sharks, a strip of aerobic red muscle located near the centre of the body generates the heat, which the body then retains via a countercurrent exchange mechanism a by system of blood vessels called the rete mirabile
42
Q
Elasmobranch thermoregulation: rete mirabile
A
- lateral artery carrying blood from heart
- lateral vein coming out carrying warm blood
- they are in close proximity, heat exchange, blood in lateral vein artery up
- core remains warm - more efficient muscles
43
Q
Elasmobranch reproduction example: Porbeagle
A
- sharks are sexually dimorphic
- males (have):
> pelvic claspers which are modified pelvic fins used for sperm delivery
> claspers are rolls of cartilage that become stiffened with calcium in adults
> paired testes, the right one is more developed than the left, which even be absent - females (have):
> no claspers but a cloacal opening (as do the males) between the pelvic fins
> paired ovaries, left side is often reduced and releases very few or no eggs - mating (ex. porbeagle)
> during copulation males meet face to face
> the male inserts one of his claspers into the cloaca of the female
> the spermatosphores are forcefully ejected by contracting organs known as siphon sacs which use seawater to carry the spermatophore
44
Q
How to access data? (samples)
A
- samples from dead animals (fossils, fisheries catch and bycatch)
- samples from living animals:
> catching live animals
> field work:
+observations (behaviour, ID)
+tagging (mark-recapture, and various radio/acoustic-data tags, tissue samples)
45
Q
Patterns in Elasmobranch distribution
A
- some spp have very limited distribution eg. northern river shark is a spp of requiem shark found in tidal rivers in northern Australia
- others range across ocean basins (eg. whale, basking, blue, salmon and great white sharks)
46
Q
How to investigate population structure
A
- morphometrics (some skeleton structure that is selected for and shows measurable differences between non-interbreeding populations)
- genetics and DNA forensics:
> using polymerase chain reaction (PCR) amplification of mitochondrial DNA (mtDNA) and nuclear DNA followed by restriction enzyme analysis to generate a form of DNA fingerprint (for spp, individuals or populations)
> using or a combination of direct sequence comparison and clustering approach to determine similarities between DNA sequences from samples of unknown origin to reference spp (phylogenetic approach) - ecological: stable isotopes, contaminants and parasites
47
Q
Life history of Elasmobranchs
A
- shark lifespans vary by species:
> most live to 20 to 30 years
> Greenland shark: 392 years old - unlike most bony fish, sharks are K-selected reproducers, meaning they produce a small amount of well-developed young as opposed to a large number of poorly developed young
- fecundity in sharks ranges from 2 to over 100 young per reproductive cycle (every 1-3 years)
- sharks mature slowly compared to other fish, eg. lemon sharks reach sexual maturity at around 13-15 years old
- annual rate of increase between (
48
Q
Conservation of Elasmobranchs
A
- by January 2014, 1041 of all chondrichthyans had been evaluated at a global scale and only 23% of the spp are categorised as being safe, or of “least concerned”
- it is estimated that 40-100 million sharks are killed each year due to commercial and recreational fishing. Sharks are eaten around the world and in many places regarded as a delicacy (eg. fins in China and Japan). Icelanders ferment Greenland sharks to produce hakarl (sharks buried in the ground for months to ferment)
- shark fins is a big business. In 2010, CITES rejected proposals from the US and Palau that would have required countries to strictly regulate trade in several spp of sharks. Majority of delegates (but not the needed 2/3), approved the proposal. China and Japan led the opposition
- 2013: CITES added a variety of sharks to Appendix 2
49
Q
Conservation ecosystem effects: what happens to the ecosystems if large-scale apex predators are removed?
A
- lack of prey regulation - ecological instability
- ecosystem shift
- possible cascading effects
- loss of important indicator spp on the health of the marine system
50
Q
Actinopterygii - ray-finned fish: Facts and features
A
- have “fin rays”, their fins being webs of skin supported by bony or horny spines (“rays”), as opposed to the fleshy, lobed fins that characterise the class: lobe-finned sarcopterygii
- actinopterygians are the dominant class of vertebrates, comprising nearly 99% of the 30,000 spp of fish
- they are distributed throughout freshwater and marine environments from the deep sea to the highest mountain streams
- extant spp range in size from 8mm to massive Ocean Sunfish at 2,300kg and the long-bodied oarfish a 11m
51
Q
Teleosts (Actinopterygii): facts and features
A
- by far the most dominant living fish are the teleosti
- most advanced of all the living bony fishes
- teleosts account for 96% of all living fish
- exhibit the greatest variation in habitat types, body plans, foraging and reproductive habits of any fishes
- first arose around 200mya (early Mesozoic)
- only group to utilise plant material in all its forms
- (can) produce light and electricity
- > 24,000 spp (to date)
52
Q
What are otoliths?
A
- stony concentrations situated in part of the ear system at the base of the brain
- carry a complete record of fish growth as they are deposited gradually throughout life
- shape of large otoliths is spp dependent (diagnostic)
53
Q
Fish scales: Placoid
A
- primarily for protection
- placoid is comprised of dentine and enamel
- sharks
54
Q
Fish scales: Cosmoid
A
- probably evolved from fusion of placoid scales
- consist of two layers of bone:
> inner layer of dentine-like cosmine
> outer layer of vitrodentine
55
Q
Fish scales: Ganoid
A
- usually rhomboid in shape
- have articulating peg and socket joint between them
- modified cosmoid scales
- consists of a bony basal layer, a layer of dentine, and an outer layer of ganoine (an inorganic bone salt)
56
Q
Fish scales: Cycloid/Ctenoid
A
- in the majority of teleost fish
- ctenoid found in eg. trout and herring
- cycloid found in eg. sole and perch
- two main regions:
> a surface ‘bony’ layer, comprised of an organic framework impregnated with calcium based salts
> a deeper fibrous layer comprised mainly of collagen - they grow throughout the fishes life
- they provide a growth record of the fish and may also show spawning
57
Q
Respiration in teleosts
A
- gills covered by bony plate - operculum
> provides protection
> space between gill and operculum - opercular chamber - less gills
58
Q
Gas bladder
A
- gas filled sac located in the dorsal region of the body cavity
- volume can be increased/decreased
- there are two types: physostomous and physoclistous
- in both swimbladders there is a gas gland with a rete mirabile, counter-current multiplier arrangement of capillaries, which allows gas to be trapped in the swimbladder
59
Q
Gas bladder: Physostomous
A
- more primitive
- connection retained between swim bladder and gut
- allows fish to fill up the swim bladder by “gulping air”, gas can be removed similarly
60
Q
Gas bladder: Physoclistous
A
- connection to the digestive tract is lost
- fish have to either rise to the surface to fill their bladders or introduce gas (usually oxygen) to increase buoyancy (via the bloodstream)
61
Q
Gas secretion in swim bladders
A
- amount of gas that blood can carry depends on pH
- more pH (alkaline), more oxygen can be stored
- lower pH (acidic), haemoglobin has to give up oxygen, less O2 stored
- counter-current system between closely associated artery and vein:
> CO2 taken up by arterial blood coming in
> CO2 dissociates to carbonic acid
> proteins released which lowers pH
> so oxygen is given up - swim bladder wall embedded by guanine crystals making it impermeable to gas (so all oxygen lost enters swim bladder)
- rate of secretion can be altered by blood flow (therefore gas flow)
62
Q
Locomotory types
A
- fish move by a variety of means, simplest are positive drifters
- four types of locomotion, characterised by how much of and what body parts are involved in propulsion
- whether the fins undulate or oscillate (snake vs caterpillar)
63
Q
Anguilliform
A
- involves sinusoidal undulations
- seen in most eels, dogfish and may fish larvae
- occurs in fish with very flexible bodies
- all but head contributes to propulsion
- as the wave moves more posteriorly it increases in amplitude
- speed (freq) of the wave remains constant - always exceeds speed of forward movement
- faster waves –> faster swimming
- slow because of long bodies and involvement of anterior regions in propulsion
- segments creating push force also waste energy by pushing laterally causing drag
64
Q
Carangiform (sub carangiform)
A
- only posterior propels to avoid ‘self braking’
- use ligaments to transfer force from muscle to tail
- functional hinge: connecting tail to peduncle maintains tail at ideal angle of attack (10-20 degrees) during powerstroke
- advanced thunniform swimmers have originating from narrow peduncle and have lateral keels to create a more streamlines shape - less drag
- within the carangiform swimmers tail deign varies as fish become more advanced (subcarangiform –> thunniform):
> thunniform - high aspect ratio, minimal drag, sustained swimming, stiff
> subcarangiform - low aspect ratio, for rapid acceleration and can aid hovering, tail has intrinsic musculature to help control shape
65
Q
Ostraciform
A
- only body moves while whole body stays rigid
- contract muscle on one side then the other
- this type of fish relies on armour not speed
- the caudal fin is small and not differentiated into distinct lobes - isocercal
66
Q
Swimming with fins: oscillatory
A
- tetraodontiforms - flap their dorsal and anal fins synchronously (sunfish)
- labriform - row their pectoral fins, pushing it with the broad blade then feathering it in the recovery phase (parrot fish)
67
Q
Swimming with fins: undulatory
A
- amiiforms - undulations pass along dorsal fins (seahorses)
- balistiform - both dorsal and anal fins undulate
68
Q
Colonising the land: obtaining oxygen from the air
A
- the evolution of lunglike sacs in response to the inadequacy of gills for respiration in the oxygen-poor waters set the stage for the invasion of land
- some bony fishes were able to supplement their gills with lung sacs when oxygen levels were low
- this ability allowed them to breathe air and leave the water temporarily
- the lobe-finned fish (class: sacropterygii) were the first lineage to evolve jointed fins
69
Q
Sarcopterygii - lobe-finned fish: facts and features
A
- fleshy, lobed, paired fins, joined to the body by a single bone
- the fins differ from other fish - attached on a fleshy, lobe-like, scaly stalk extending from the body
- the scales consisting of dentine-like cosmine and keratin
- pectoral and pelvic fins resemble tetrapod limbs. These evolved into legs of the first tetrapod land vertebrates; amphibians
- they have two dorsal fins with separate bases, as opposed to the single dorsal fin actinopterygians (ray-finned fish)
- many early sarcopterygians have a symmetrical tail
- all possess teeth covered with enamel
70
Q
Colonising the land`
A
- the lungfishes (class Dipnoi) were important predators in shallow-water habitats in the Devonian, but most lineages died out
- the six surviving spp live in stagnant swamps and muddy waters in the southern hemisphere
- they have lungs and gills; can burrow in mud when ponds dry up, and survive many months in an inactive state while breathing air
- some descendants of early fish with jointed fins began to use terrestrial food sources and over time fully adapted to life on land
- this lineage is believed to have given rise to the tetrapods: the four-legged amphibians, reptiles, birds and mammals of today
71
Q
Origin of Tetrapods
A
- the proto-tetrapod evolved from a sarcopterygian, with Dipnoans (lungfish) as closest extant relatives
- most likely ancestor was an Elpistostegid (extinct group):
> crocodile-like flattened body
> no dorsal or anal fin
> dorsal eyes
> reduced tail
> pectoral girdle and fins attached to opercular bones over gills
72
Q
The closest relative of Tetrapods?
A
- a Devonian fossil found on Ellesmere Island (arctic Canada) in 2006 may represent an intermediate between a finned fish and a limbed tetrapod
- pectoral girdle and fins separated from opercular bones and skull
73
Q
Feeding advantages of separating the pectoral girdle from skull
A
- once the pectoral girdle is free from the skull greater mobility is possible in the skull
- this is enhanced by the architecture of the two occipital condyls and the presence of the atlas
- the snout and jaws became elongated (seen as relative shortening of otic-occipital region)
- there is improved articulation of the jaw, and expansion of the primary palate
74
Q
Advantages of terrestrial life - why did lobe-fins evolve into limbs?
A
- adaptation to temporary and shallow pools
- foraging above water surface (insects, plants)
- juvenile dispersal movements
- escape from predatory fish
- new semi-terrestrial (amphibious) foraging niches available
75
Q
Consequences of terrestrialisation
A
- smell
- reproduction
- circulation with multiple respiratory structures
- skeletal solutions to terrestrialisation:
> pectoral girdle is divorced from back of skull (implications for sound conduction)
> undulatory locomotion
> suspension of vertebral column
> regionalisation of vertebral column
> organisation of amphibian vertebrae
> suspension of internal organs
> reorganisation of the skull
76
Q
Adaptations to transition to life on land?
A
- no buoyancy in air, so weight-bearing is crucial
- movement facilitated by limbs, to apply force to the land surface for propulsion
- gills collapse in air, so lungs are required for gas exchange (symplesiomorphy: already present in a common ancestor with Dipnio)
- water loss as evaporation in air required production of concentrated urine in kidneys (also providing a route for nitrogen excretion as insoluble uric acid salts)
77
Q
Buccal pump - extracting oxygen from air
A
- opens mouth, depresses buccal floor drawing in air, closes opercular
- closes mouth, air held in buccal cavity
- presses buccal cavity (becomes smaller), air is pumped into lungs - positive pressure system
- elastic recoil causes air to move back into buccal cavity
- air then exits via mouth and operculum
