evolution of invertebrates and vertebrates

Question 1

what is an invertebrate

Answer 1

• lacks a spinal chord and backbone
• lacks bones

Question 2

6 evolutionary events led to the evolution of metazoa

Answer 2

1. multicellularity
2. extracellular digestion
3. nervous system
4. middle germ cell layer
5. bilateral symmetry
6. through-gut

Question 3

evolution of multicellularity

Answer 3

3 theories
- symbiotic theory, different protozoa join together as symbionts
- colonial theory, asexual reproduction of cells that remain together
- cellularisation, multinucleate protist evolves cell membranes around its nuclei

Question 4

evidence for colonial theory, evolution of mulitcellularity

Answer 4

• choaloflagellate is a protists very similar to collar cells
• proterospongia is accumulation of choaloflagellate cells
• sponge contains collar cells
• none of these are closely related to each other

Question 5

embryonic development

Answer 5

• embryology recapitulates phylogeny
• blastea = hollow ball of cells
• cells differentiate and rearrange
• blastula forms
• creation of multiple cell layers through invagination or ingression
• gastrula = multilayered embryo
• each cell layer becomes different cell types

Question 6

diploblastic organisms

Answer 6

• ectoderm = outer layer, differentiates into epithelium etc
• endoderm = inner layer, differentiates into gut lining etc

Question 7

triploblastic organisms

Answer 7

• ectoderm = outer layer, differentiates into epithelium etc
• endoderm = inner layer, differentiates into gut lining etc
• mesoderm = middle layer, forms muscles, organs etc

Question 8

non-bilateria properties

Answer 8

• asymmetrical invertebrates
• include basal groups like sponges
• primarily marine
• covered in microscopic pores
• cellular level of organisation, lack tissues and organs
• diploblastic
• sessile
• defensive chemicals

Question 9

structure of sponges

Answer 9

• pinacoderm = outer layer of cells, pinacocytes = wide and flattened
• choanocytes = collar cells, line central atrium
• gelatinous non-living matrix in central atrium
• totipotent archaeocytes/ameboid cells within matrix, involved in feeding
• spicules
• porocyte = pore cell

Question 10

sponges, spicules

Answer 10

• small SiO2 or CaCO3 structures
• skeleton-like structural support
• secreted by specialised sclerocytes which fuse, lay down spicules then pull apart
• megascleres support sponge
• microscleres support sporocytes

Question 11

sponges, digestion

Answer 11

• intracellular
• flagella of choanocytes beat, creating a current to draw in water through pore cell for filter feeding
• food particles trapped in mucous around microvili that make up collar of choanocytes
• water exits through osculum (larger pore)

Question 12

sponges, reproduction

Answer 12

• external fertilisation
• choanocytes can differentiate into gametes in breeding season, eggs often retained and larvae released
• planktonic larval form drift around in water column

Question 13

4 phyla in non-bilateria group

Answer 13

• poripheria (sponges)
• placozoa
• Cnidaria
• Ctenophora (comb jellies)

Question 14

placozoa

Answer 14

• arose from the evolution of extracellular digestion and true epithelium, advantageous for growth and predation

Question 15

evolution of the nervous system

Answer 15

• gave rise to neuralia clade
• gave rise to cnidaria
• organisms can swim and respond to the environment

Question 16

Cnidaria structure

Answer 16

• epidermis contains epithelialmuscular cells, totipotent interstitial cells, cnidocytes (stinging cells), mucous gland cells, sensory cells that make up nerve net
• mesoglea = gelatinous matrix in between
• gastrodermis lines gastrovascular cavity and contains enzymatic gland cells, nutritive muscular cells, mucous gland cells and some nerve cells
• 2 morphs

Question 17

cnidaria, 2 morphs

Answer 17

• polyp, sessile, tentacles pointing upwards
• medusoid, tentacles pointing downwards
• species often travel through both morphs in their life cycle

Question 18

phyla Cnidaria, class hydrozoa

Answer 18

• marine and freshwater
• colonial organisms
• polymorphic polyps
• cnidae only present on epidermis
• alternation of generations

Question 19

Cnidaria properties

Answer 19

• anemones, corals, hydroids, jellyfish etc
• once thought to be radially symmetrical but now thought to be bilaterally symmetrical (cilliated groove down middle of animal on inside), so possibly not in non-bilateris
• all have stinging cells, cnidocytes
• mostly marine
• tissue level of organisation

Question 20

phyla cnidaria, class scyphozoa (true jellyfish)

Answer 20

• all marine
• medusoid stage dominant in life cycle
• thick mesoglea

Question 21

scyphozoa (true jellyfish) life cycle

Answer 21

• adult medusa is dioecious (either male or female)
• external fertilisation forms ciliated planula larvae that swim around
• planula larva settle and develop into scyphistoma
• scyphistoma undergoes strobilation releasing young jellyfish (ephyrae)

Question 22

phyla cnidaria, subclass octocorallia

Answer 22

• soft octocorals
• 8 pinnate (feather like) tentacles
• 8 longitudinal septa
• thick mesoglea
• internal calcium skeleton

Question 23

phyla cnidaria, subclass hexacorallia

Answer 23

• 6 tentacles
• stony sclerotinia corals
• secrete calcium skeleton that the coral sits on top of
• have spriocysts (modified cnidocytes used to catch prey)

Question 24

Ctenophora phyla

Answer 24

• comb jellies
• younger lineage than placozoa and cnidaria but less complex, possibly shows secondary simplification

Question 25

characteristics of eubilateria

Answer 25

- bilateral symmetry - triploblastic - organs - centralised nervous system with 'brain' - cephalisation

Question 26

coelomate phyla

Answer 26

- vast majority of eubilateria - Spiralia, arthropoda, chordata etc - coelom = fluid filled cavity bounded on both sides with embryonic mesoderm

Question 27

acoelomate phyla

Answer 27

- lack coelomic cavity - e.g. Platyhelminthes

Question 28

Platyhelminthes

Answer 28

- basal phylum of eubilateria - acoelomate - varied group, no defining synapomorphies - incomplete gut, one hole (secondary simplification) - advanced osmoregulatory organs, protonephridia

Question 29

pseudocoelomate phyla

Answer 29

- lack true coelomic cavity, only bounded by embryonic mesoderm on one side - e.g. Rotifera, Nematoda, Priapula

Question 30

Protostomes

Answer 30

- determinate development, cell fate is fixed from embryo - presence of a coelom formed through schizocoely in development - includes spiralia, ecdysozoa etc

Question 31

Spiralia

Answer 31

- protostomes that undergo spiral cleavage, cell twists when it undergoes cell division - not a true ranked taxon - includes Mollusca, annelida, platyhelminates etc

Question 32

taxon ecdysozoa

Answer 32

- has an exoskeleton that is often calcified - moults cuticle at least once in life cycle to be able to grow (ecdysis) - e.g. Phylum arthropoda

Question 33

Phylum arthropoda

Answer 33

- non-calcified exoskeleton secreted by epidermis - procuticle made of chitin - epicutlicle, waxy lipoprotein kayer for protection - segmented body with a pair of jointed legs at each segment (tagmatisation) - complex gut with specialisation - compound eyes

Question 34

subphyla crustacea

Answer 34

- arthropods - e.g. crabs, lobsters - head and thorax fused (cephalathorax), covered with calcified carapcace - 2 pairs of antennae - nauplii larvae

Question 35

subphyla myriapods

Answer 35

- arthropods - e.g. millipedes, centipedes - cannot close spiracles so exclusively found in damp environments

Question 36

subphyla hexapoda

Answer 36

- arthropods - e.g. class insecta

Question 37

properties of class insectica

Answer 37

- wings (if present) on last 2 segments of thorax - thorax segments prothorax, mesothorax, metathorax - tympanal organs - tracheal system for gas exchange

Question 38

subphyla chelicerata

Answer 38

- arthropods - include arachnids

Question 39

lophotrochozoa taxa

Answer 39

- 5 phyla that produce a larvae type called tropophore and possess a lopophore - platyhelminthes, rotifera, nemertea, annelida, mollusca

Question 40

phylum annelida

Answer 40

- includes earthworms, leeches, ragworms, sipubunculans - most long and thin, adaptation for burrowing - specialised through gut with regionalisation - closed circulatory system with blood vessels (as long and thin) - defining feature is bristles, chaete - majority have metameric segmentation

Question 41

annelida, metameric segmentation

Answer 41

- body comprised of many repeating units - protostomium = first segment, contains sensory structures - peristomium = second, has mouth - metameric segments - pygmidium = fourth segment, contains anus, organism grows from here

Question 42

properties of phylum mollusca

Answer 42

- includes snails, slugs, cephalopods, bivalves - very diverse - open circulatory system, haelocoel - visceral mass, organs concentrated into hump - mantle = sheet of tissue covering visceral mass - metanephridia = complex kidney-like filtering organs - e.g. class gastropoda

Question 43

class gastropoda, shell

Answer 43

- vast majority have coiled (typically clockwise) shell containing visceral mass - useful for predator evasion - size constrain means they have lost duplicate organs - attached to shell via collumellar muscle, enables it to contract into shell - torsion, internal organs rotated 180 degrees, anus is next to head - some organisms such as nudibranchs have no shell, so have detorted

Question 44

class gastropoda

Answer 44

- molluscs 3 recognised groups - prosobranchs (marine) - opisthobranchs (marine) - pulmonates (terrestrial)

Question 45

gastropoda, radula

Answer 45

- radula = toothed tongue used for feeding - secreted from radula sac - rasping mechanism - supported by muscular odontophore -can be modified into harpoon drill etc - strongest biological material

Question 46

Deuterostomes

Answer 46

- undergo radial cleavage (cell does not twist during cell division) - development is indeterminate/regulative - coelom formed through enterocoely (pouches form coelom) - 1st pore formed anus, 2nd pore formed mouth - includes Echinodermata, hemichordata and chordata

Question 47

Phylum Echinodermata

Answer 47

- include starfish, brittle stars, sea urchins etc - majority marine - no head or circulatory system (secondary simplification) - photoreceptors - adults have pentaradial symmetry, larvae are bilaterally symmetrical - water vascular cavity with fluid-filled cavity derived from coelom

Question 48

Echinodermata anatomy

Answer 48

- dorsal anus, ventral mouth - 2 stomachs, cardiac and pyloric - pyloric stomach branches to the pyloric caeca, with papulae to increase surface area - madreporite = opening that filters water into vascular system - pedicellariae = extension of water vascular system to clean surface of animal

Question 49

Phylum hemichordata

Answer 49

- halfway between echinodermata and chordata - lack a notochord, but have a dorsal hollow nerve chord - bilaterally symmetrical - pharyngeal gill slits - open circulatory system - complete complex gut

Question 50

properties of phylum chordata

Answer 50

- non-vertebrates and vertebrates, all non-vertebrates are marine - notochord = dorsal flexible rod of tissue derived from embryonic mesoderm - dorsal hollow nerve chord - bilaterally symmetrical - pharyngeal gill slits - postanal tail - complex gut - Urochordata, cephalochordata and craniates

Question 51

paedomorphosis

Answer 51

- larvae become sexually mature before reaching adult form - neoteny = retention of larval/embryonic characteristics past reproductive maturity - progenesis = accelerated development of reproductive organs relative to somatic tissue - theory of how chordates evolved

Question 52

subphyla urochordata/tunicates

Answer 52

- colonial, solitary or pelagic - e.g. class Ascidacea

Question 53

class Ascidiacea

Answer 53

- urochordate - sea squirts, sessile filter feeders - heart - large ciliated pharynx with gill slits (stigmata) -endostyle (thyroid-like) secretes iodine rich mucous net that traps and digests particles - produces pelagic 'tadpole' larvae with notochord present in tail - notochord degenerates when larvae undergoes metamorphosis

Question 54

cephalochordates

Answer 54

- chordates that have all chordate features present in adults - e.g. branchiostoma

Question 55

properties of craniates

Answer 55

- chordates that have a cranium (skull) - neural crest - raised metabolism - heart with at least 2 chambers - haemoglobin in red blood cells - kidneys

Question 56

neural crest

Answer 56

- embryonic source of many unique craniate characteristics - pluripotent - forms peripheral nervous system and myelin sheath - migrates out of neural plate to form autonomic nervous system, skull, bones etc - neural plate fuses into neural tube, forms central nervous system

Question 57

fossil origins of vertebrates, conodonts

Answer 57

- 'cone teeth' - abundant over 300mya - no jaw - soft, slender bodies - probably hunters

Question 58

craniates, class myxini

Answer 58

- hagfish - least derived surviving craniate lineage - cartilage skull - lacks a jaw - lack vertebrae - snake like swimming through muscles pushing against notochord - small brain, eyes and ears - nasal opening connects with pharynx - keratinous tooth like formations - mostly bottom dwelling scavengers - water-absorbing slime glands, slime repulses/suffocates

Question 59

properties of vertebrates, vertebrae

Answer 59

- craniates that have a vertebral column - some vertebrates have vertebrae made of cartilage majority have vertebrae that enclose the spinal chord and take up role of notochord - supports body - protects nervous system and brain - can grow and repair

Question 60

origins of bones and teeth

Answer 60

- vertebrate skeleton originally evolved as a structure made out of unmineralised cartilage - mineralisation may have begun in mouth as feeding mechanisms transitioned from filter feeding to predation, as they then needed a way to break down particles - earliest mineralised structures found are conodont teeth - armour is then derived from dental mineralisation - the endoskeleton then becomes mineralised, starting from the skull

Question 61

fossil origins of craniates, haikouella

Answer 61

- emerged 530mya in the cambrian explosion - not a true craniate as no skull or ear organs - suspension feeders - large well formed brain - small eyes - muscle segments along body - respiratory gills in pharynx

Question 62

fossil organs of craniates, Myllokunmingia

Answer 62

- more advanced chordate - regarded at true craniate as has ear and eye capsules as part of skull

Question 63

other properties of vertebrates

Answer 63

- skull - well developed circulatory system - internal organs suspended in coelom - 3 part brain (forebrain, midbrain, hindbrain) - duplication of hox gene complex - neural crest cells - underwent another gene duplication after branching off from craniates, transcription factor (DIx genes), possibly lead to innovations in nervous system and skeleton - aquatic vertebrates have fins stiffened by fin rays

Question 64

class petromyzodontia

Answer 64

- lampreys - oldest living vertebrate lineage - majority freshwater - jawless (agnatha) - development of an oral hood with keratinous teeth - cartilage skeleton, no collagen, stiff protein matrix instead - notochord persists in adults - cartilagenous pipe around notochord, partially encloses nerve chord - pairs of cartilage projections related to vertebrae extend dorsally

Question 65

petromyzodontia feeding mechanisms

Answer 65

- larvae are freshwater suspension feeders - most adults are parasitic on fish - round jawless mouth with rasping tongue digests blood and tissues from rasping wound on fish - anti-coagulant secreted from oral gland

Question 66

later fossil vertebrates

Answer 66

- emerged during Ordovician, Silurian and Devonian - paired fins - inner ear, 2 semicircular canals for balance - no jaw but muscular pharynx to suck in other organisms/detritus - armoured, mineralised bone and spines

Question 67

Gnathostomes, properties

Answer 67

- vertebrates that have jaws - diverse, outnumber agnatha - additional replication of hox genes (4 clusters) - other gene clusters duplicate, increasing genetic and developmental complexity - enlarged forebrain, complex olfaction and vision - aquatic gnathostomes have a lateral line system ( sensitive to vibration, early versions in some jawless vertebrates)

Question 68

advantages of jaws

Answer 68

- active predation, can capture and bite prey - herbivory - gripping and slicing food, especially when paired with teeth - chewing facilitates breakdown and digestion of food - mouth brooding - nest building - mate grasping - improved gill ventilation

Question 69

evolution of jaws

Answer 69

- from branchial arches, skeletal rods that support gills - first gill arch evolves into upper and lower jaw - second gill arch supports/suspends jaw - evolution of hyoid bone that supports tongue

Question 70

gnathostomes, fossil history

Answer 70

- emerged mid-Ordovician ~470mya - paired fins and tail, jaws with large bite force - placoderms = earliest gnathostomes, plated/armoured, became extinct in early carboniferous E.g. Dunkleosteus - acanthodians = marine and freshwater organisms in Devonian era, probably sister group to the bony fish (dermal operculum, hyoid attachment, true dermal teeth)

Question 71

gnathostomes, Chondrichythyes class

Answer 71

- cartilage skeletons (secondarily derived, traces of bone found) - skeletons often impregnated with calcium - sharks , rays and skates - ratfish/rabbitfish

Question 72

shark properties

Answer 72

- fusiform streamlined body shape - forward propulsion from trunk and caudal fin - dorsal fin acts as stabiliser - paired pectoral and pelvic fins for tilt - no swim bladder - hylostylic jaw extension, upper jaw is only attached by ligaments so sharks can grip and pull back prey - cloaca

Question 73

cloaca

Answer 73

single external opening for reproduction and waste removal

Question 74

buoyancy in sharks

Answer 74

- have no swim bladder so buoyancy is maintained through combination of oil in their liver and continuous swimming - continuous swimming also forces water across gills, keeping them oxygenated - when sharks are resting on bottom of sea floor, they open and close jaws and use muscles in pharynx to squeeze and pump water across the gills

Question 75

sensory physiology of sharks

Answer 75

- sharp black and white vision - olfaction through nostrils (dead-end cups) - electrophysiology for detecting electrical fields around them such as muscle contraction of prey - no eardrums, entire body transmits sound to inner ear

Question 76

Feeding mechanisms of sharks

Answer 76

- The largest sharks and rays are suspension feeders e.g. basking sharks - Most are carniverous, so have several rows of teeth - Teeth move to anterior as old ones are lost - Have a shorter digestive tract than many vertebrates - Evolved spiral valve to help with digestion of meat, a corkscrew-shaped ridge in intestine that increases surface area and slows digestive transit

Question 77

reproductive strategies of sharks

Answer 77

- various reproductive strategies - oviparous, ovoviviparous or viviparous

Question 78

Oviparous

Answer 78

= eggs in protective coat hatch outside body

Question 79

Ovoviviparous

Answer 79

= fertilised egg retained in oviduct, nourished by yolk, offspring hatch in uterus

Question 80

Viviparous

Answer 80

= offspring develop in uterus, nourished by mother, birth live young

Question 81

Rays

Answer 81

- Different lifestyle to sharks - Mostly bottom dwellers, feed on molluscs and crustaceans - Flattened shape - Enlarged pectoral fins for propulsion - Whiplike tail, many have venomous barbs

Question 82

Osteichthyses

Answer 82

- Include bony fish and tetrapods - almost all have an ossified endoskeleton with a hard calcium phosphate matrix - 2 clades which evolved in the Devonian era, Actinoperygii and sarcopterygii

Question 83

properties of bony fish

Answer 83

- operculum - swim bladder - most have bony scales, different to tooth-like shark scales - mucus secreting glands reduce drag - lateral line system - diverse reproductive strategies

Question 84

operculum of bony fish

Answer 84

- Protective bony flap covering gill chamber - Movement of the operculum and contraction of the muscles surrounding the gill chamber draws water through the mouth and pharynx and out between the gills

Question 85

buoyancy of bony fish

Answer 85

- maintained by the movement of gases between the blood and the swim bladder - very efficient - swim bladder evolved from early lungs in some lineages

Question 86

Actinopterygii clade

Answer 86

- 'ray-finned fish' - Bony rays support fins, modified for manouvering and defence - Originated in freshwater then spread to seas - Many then returned to freshwater - Some species are both freshwater and sea e.g. salmon

Question 87

Sarcoptergyii

Answer 87

- 'lobe-finned fish' - Pectoral and pelvic fins have rod-shaped bones surrounded by a thick layer of muscle - Evolved in brackish water such as coastal wetlands, used lobe fins to swim and 'walk' across substrate 3 extant lineages - Coelacanths (actinistia) - Lungfish (dipnoi) - Tetrapods

Question 88

Coelacanths (actinistia)

Answer 88

- part of Sarcopterygii clade - Secondarily derived cartilagenous skeletons - 2 species, originally thought to have become extint ~65mya

Question 89

Lungfish (dipnoi)

Answer 89

- part of the Sarcopterygii clade - Evolved in ocean, now all 6 species are freshwater species in stagnant ponds and swamps - Have lungs connected to pharynx, come to surface to gulp air - Also have gills, main gas exchange organ - Adapted to dry seasons by burrowing in mud - closest living relatives to tetrapods

Question 90

Evolution of tetrapods

Answer 90

~360mya - Pectoral and pelvic fins evolved into limbs and feet in one lobe-fin lineage - Supports weight on land and transmits muscle generated forces to ground to allow for locomotion - Lineage also retained adaptations for aquatic life Devonian and Carboniferous - Greater diversity of tetrapods emerged, most still tied to water

Question 91

Acanthostega, evolution of tetrapods

Answer 91

~365mya - Fully formed legs, ankles and digits - Bones supporting gills - Tail-rays supporting fin - Weak pectoral and pelvic girdles - Possibly unable to support body, hypothesis that it slithered out of water occasionally

Question 92

Other changes to the tetrapod body plan

Answer 92

- Head separated from body by neck - Originally 1 vertebrae, can only move head up and down - Evolution of second vertebrae allowed side to side movement of head, useful for predator detection - Bones of pelvic girdle fused to backbone, forces from hind legs can be transferred to the whole body - Extant tetrapods have no gill slits, embryonic pharyngeal gill slits give rise to other structures

Question 93

class amphibia

Answer 93

3 orders - urodela (tailed) - anura (tailless) - apoda (legless)

Question 94

Urodela

Answer 94

- Tailed, e.g. newts, salamanders - Some entirely aquatic, others on land as adults or throughout life - Walk with a side-to-side bending body motion - Trot gait, diagonally opposed limbs - Paedomorphosis e.g. Mexican axolotl

Question 95

Anura

Answer 95

- Tailless e.g. frogs - More specialised for moving on land - Adults have powerful hind legs and elastic muscles - Tongue for prey capture and feeding - Often have distasteful/poisonous toxins for predator evasion - Colouration for defence, warning/mimicry, camouflage

Question 96

Apoda

Answer 96

- Legless e.g. caecelians - Secondarily derived - Nearly blind - Tropical - most burrow in moist forest soil - Some species are freshwater

Question 97

Life stages of amphibians

Answer 97

- Anuran larval stage = tadpole (aquatic herbivore) - Metamorphose into adults, legs, lungs, external eardrums develop, digestive system adapts to carnivory, gills (and lateral line system in may species) disappear - Urodele and apodan larvae are carniverous and look like the adults

Question 98

Habitats of amphibians

Answer 98

- Most live in damp habitats or burrow under vegetation - Keeps skin moist for gas exchange - Some terrestrial species lack lungs (breathe only through skin and through oral cavity

Question 99

Other adaptations of tetrapods for terrestrial life

Answer 99

- a ribcage to ventilate lungs - More efficient than throat based respiration - Amphibians supplement breathing through the skin with breathing with the buccal cavity - May have allowed amniotes to abandon respiration via their skin - They then could evolve less permeable skin, giving them more ability to conserve water and therefore live on land

Question 100

reproductive strategies of amphibians

Answer 100

- Most have external fertilisation - Lay shelless eggs in water/a moist environment - Won't lose water through dessication - Various types of parental care including mobile nurseries (back, mouth, stomach brooding) - Some ovoviviparous, some viviparous

Question 101

main characteristic shared by amniotes

Answer 101

- evolution of a terrestrially adapted egg = amniotic egg - 4 extraembryonic membranes: yolk sac, allantois, amnion, chorion - Most reptiles and some mammals also have a shell (leathery or calcified) - Unclear evolutionary reasons, but may have allowed size and strength of egg to increase

Question 102

properties of amniotic egg

Answer 102

- shell, protection against damage/ water loss, permeable for gas exchange - Amnion and chorion (surrounding embryo) are vascularised, allowing for gas exchange - allantois allows for excretion of waste and is also vascularised - albumen for nutrition and protection - yolk for nutrition

Question 103

Amniote fossils

Answer 103

- Ancestor ~370mya - Found in dry climates - Herbivores (grinding teeth) - Predators - no fossils of amniotic eggs found

Question 104

properties of reptilian clade

Answer 104

- Keratinous scales, protection against damage and dessication - Most lay shelled eggs on land, therefore have internal fertilisation - Many are viviparous - Most are ectothermic, behavioural thermoregulation - Birds are endothermic, metabolic thermoregulation

Question 105

Earliest living reptiles

Answer 105

- Oldest fossils ~310mya Parareptiles - Large, stocky, quadripedal - Plated for defence - Extinct by end of triassic ~200mya

Question 106

Diapsids

Answer 106

- Diversified as parareptiles were dwindling (Triassic) - Most obvious derived diapsid character = pair of holes each side of the skull behind eye socket (temporal fenestrae) - 2 main lineages, Lepidosaurs and Archosaurs

Question 107

extinct lepidosaurs

Answer 107

Marine reptiles e.g. giant mososaurs

Question 108

extant lepidosaurs

Answer 108

- Tuataras, lizards and snakes - Modified diapsid skull - 2 extant lineages, Sphenodontians and Squamates

Question 109

Sphenodontians

Answer 109

- Tuataras, 1 species - Lizard-like reptiles - Relatives ~220mya over many continents - Now only 30 islands off New Zealand, not found on main island due to rodent introduction - ~50cm - Eat insects, small lizards, bird eggs, chicks

Question 110

squamates

Answer 110

- lizards and snakes - ~7900 species

Question 111

Lizards

Answer 111

- Mostly small - Jaragua lizard is 16mm long - Komodo dragons ~3m (Indonesia) - Hunts deer and stalks wounded prey, toxins in bite

Question 112

snakes

Answer 112

- Legless (secondarily derived - Some species show remnants of pelvic girdle and limb bones

Question 113

movement of snakes

Answer 113

- Normal, lateral bending (Sidewinding, concertina) - Rectilinear, grips ground with belly scales and pushes self forward, useful for prey ambush

Question 114

Extinct archosaurs

Answer 114

- On land dinosaurs diversified into 2 main lineages - Ornithischians - Saurischians

Question 115

Ornithischians

Answer 115

- Herbivores - Many have anti-predator defences such as tail clubs and horned crests

Question 116

Saurischians

Answer 116

- Long necked giant tree browsers - Theropods = bipedal carnivores e.g. Tyrannosauras rex, bird ancestors

Question 117

Extant archosaurs

Answer 117

Crocodilians, 23 extant species (Alligators, crocodiles and gharials)

Question 118

evolution of crocodilians

Answer 118

- Emerged during Triassic - Early crocodilians were small, terrestrial quadripeds with long slender legs - Later adapted to aquatic habitats, evolution of upturned nostrils

Question 119

properties of tesdudines

Answer 119

- Turtles, terrestrial and aquatic species - Anapsid, no temporal fenestra - Box-like shell - Head retraction Earliest turtles could not retract heads Retraction mechanisms evolved independently Pleurodires Fold neck horizontally Cryptodires Fold neck vertically

Question 120

testudine shells

Answer 120

- Most are hard for defence - Clavicles and ribs fused to carapace (dorsal side of shell) - Plastron = ventral side of shell - Absence of transitional fossils to show evolution of shell - Molecular data suggests that testudines are related to crocodilians - Plates of archosaurs possibly became more extensive and started to form a shell - Other data suggests they are perhaps a sister group to birds

Question 121

Head retraction in testudines

Answer 121

- earliest turtles could not retract heads - Retraction mechanisms evolved independently - Pleurodires fold neck horizontally - Cryptodires fold neck vertically

Question 122

origin of birds

Answer 122

- Cladistic analysis from fossils shows they evolved from theropods - Feathered theropod fossils show feathers evolved before flight - Feathers possibly for insulation, mating or camouflage

Question 123

Evolutionary theories of flight in theropods

Answer 123

- Cursorial (ground-up): small running dinosaurs gained lift from feathers, aided predatory lifestyle - Arboreal (trees down): dinosaurs climbed trees and glided, aided by feathers

Question 124

Theropods evolved into birds by 150mya

Answer 124

Archaeopteryx: - Feathered wings - Ancestral characteristics (teeth, clawed digits in wings, long tail) Later Cretaceous bird fossils: - Lost teeth and clawed forelimbs - Acquired short feathered tail

Question 125

extant birds

Answer 125

- neornithese clade - 11000 species - 32 orders - variety of forms - most have similar fusiform body shape adapted to flight - beak shape highly adapted to diet - foot structure highly adapted to lifestyle

Question 126

neornithese clade, derived characteristics and modifications for flight

Answer 126

- wings with feathers made of beta keratin - no urinary bladder - females of most species have one ovary - males have small gonads apart from during breeding season - toothless (secondarily derived)

Question 127

Advantages of flight

Answer 127

- Enhances hunting and scavenging - Escape mechanism - Ability to migrate long distances

Question 128

birds, evolution of high metabolic rate

Answer 128

- as flight is energetically expensive - Evolution of endothermy - Feathers and fat for insulation - Lungs have tubes to elastic air sacs, improving respiration - 4 chambered heart

Question 129

Order Sphenisciformes

Answer 129

- Flightless penguins - powerful pectoral muscles

Question 130

Ratites

Answer 130

- In order Struthinioformes - Flightless, adaptations for cursorial locomotion include long legs - Sternal keel absent (attachment for flight muscles) - Small pectoral muscles E.g. ostrich, emu, kiwi etc

Question 131

synapsids

Answer 131

- evolutionary origin of mammals - one lowered temporal fenestra on either side of skull - 3 radiations of lineage

Question 132

1st radiation of synapsid lineage

Answer 132

- Palaeozoic era - evolution of pelycosoaurs (primitive) - include sailbacks and sphenacodontids - Beginning of 3 boned middle ear in sphenacodontids

Question 133

2nd radiation - Paleozoic

Answer 133

- evolution of therapsids (more derived) - Upright posture, limbs drawn in so they can be used like levers, also helps to free up respiratory muscles - Increased jaw musculature

Question 134

evolution of cynodonts

Answer 134

- Triassic - Most derived therapsid, but still not a true mammal - E.g. Triethelodon - Size reduction to rat sized - Evidence of endothermy - turbinate (nasal) bones, increases airflow, reduces water loss - Secondary palate, can swallow and breathe at the same time - Reduced ribcage restricted to anterior allowed evolution of diaphragm - Still conflict between hearing a chewing as jaw bone involved in channeling sound (mammalian inner ear bones evolved from synapsid jaw joint)

Question 135

3rd radiation of synapsids

Answer 135

- Cenozoic - Evolution of true mammals - Earliest mammals very small, shrew sized - Lived alongside dinosaurs until late Triassic

Question 136

Features of early mammals

Answer 136

- Small, <100mm - Nasolacrimal duct - Evolution of fur for insulation - Precise occlusion = molars fit together, helps with mastication - Diphyodonte = two sets of teeth - Not good at evaporative cooling - Ears lack pinna (outer part) - Low metabolism, suited to nocturnal lifestyle (cooler at night) - Probably insectivorous and solitary - Large olfactory lobes. more sophisticated sensory processing - start of evolution of lactation

Question 137

nasolacrimal duct

Answer 137

- Channel between tear ducts and nasal cavity - Important for pheromones, olfactory sensing and cleaning eyes/fur - characteristic anatomical feature of early mammals

Question 138

early mammals, evolution of lactation

Answer 138

- No nipples, secreted on to fur - Not yet a food source for young - Antimicrobial, possibly for protecting eggs laid in nest

Question 139

key features of mammals

Answer 139

- Hair/fur for insulation, communication, camouflage, sensation - lactation and suckling - variety of skin glands

Question 140

mammalian skin glands

Answer 140

- Variety of skin glands - Apocrine, eccrine and sebaceous - Functions include lubrication, waterproofing, olfactory communication and thermoregulation - Mammary glands evolved from skin glands

Question 141

Suckling

Answer 141

- Unique mammalian feature - reflex - Must be able to make a seal with mouth and breathe and swallow at the same time - Facial muscles required - evolution of mobile lips and cheeks, used for other functions like communication later in evolutionary history

Question 142

benefits of lactation and suckling

Answer 142

- Paternal care not required - Offspring do not rely on seasonal food supply - Provides care outside uterus (marsupials)

Question 143

evolution of lactation and suckling alongside precise occlusion and diphyodonty

Answer 143

- lactation and suckling evolved before precise occlusion and diphyodonty - Diphyodonty precedes precise occlusion - Feeding on milk requires no teeth so reduces number of sets of teeth needed - Having no teeth allows jaw growth and eruption of permanent teeth in an almost adult sized jaw

Question 144

major mammalian lineages

Answer 144

- Allotheria (extinct multituberculates) - prototheria - theria

Question 145

prototheria

Answer 145

- infraorder Ornithodelphia - order monotremata - oviparous (lay eggs) - cloaca - shoulder girdle has retained ventral elements, secondarily derived sprawling stance

Question 146

Platypus

Answer 146

- prototherian - 1 species - Semi-aquatic - Eat aquatic invertebrates - Australian - Venomous spurs - Leathery 'beak' with electrosensitive pores

Question 147

Echidna

Answer 147

- prototherian - Insectiverous, long sticky tongue - Short-nosed echidna 1 species Australian Eats ants and termites - Long-nosed echidna 3 species New Guinea Eats earthworms

Question 148

Metatheria

Answer 148

- Traditionally order marsupiala, now 4 recognised orders - Geographically split - 1 order in New World (Americas) - 3 orders in Australia - Inflected jaw - Epipubic bones retained - Primitive dental formula: I5/4 C1/1 P3/3 M4/4

Question 149

Australian methatherian orders

Answer 149

- Dasyurids, carnivores e.g. Tasmanian devil - Peramelids, insectivorous e.g. bandicoots and bilbies - Diprotodontians, modified lower incisors, 3 radiations: possums, koalas, kangaroos

Question 150

theria

Answer 150

- metatheria and eutheria - Viviparity = give birth to live young - Nipples - At least 2.5 coils of cochlea (improved hearing) - Pinna = external ears - Tribosphenic molars - Urogenital and alimentary openings - Derived shoulder girdle, ventral elements lost, scapula moves independently - increases stride lengths, allows for specialised gaits

Question 151

Eutheria

Answer 151

- May be referred to as placental mammals, but some metatheria have modified placentas - Rapid radiation so phylogeny obscure - Auditory bulla surrounds ear - Herbivores had a post-orbital bar that stabilises the jaw - Lost epipubic bones, possibly aiding the birth of larger offspring - Primitive dental formula: I3/3 C1/1 P4/4 M3/3 (usually fewer incisors and molars than metatherians, but more premolars)

Question 152

Biogeography of mammals

Answer 152

- Radiation peaked in cenozoic era as land masses separated - vicariance and dispersal

Question 153

Vicariance of mammals

Answer 153

- Populations separated by physical processes - Distinct mammalian faunas on each continent

Question 154

Dispersal of mammals

Answer 154

- Active movement of populations - Mammalian faunas mixed when continents rejoined

Question 155

Convergent evolution of therians

Answer 155

- Eutherian and metatherian mammals share body forms and habits - Evolved similar characteristics to suit similar environmental conditions, no common shared ancestors

Question 156

Humans, evolution of bipedal locomotion

Answer 156

- Frees up upper limbs - Energy efficient running - Ideal head position to scan horizon