Evolution of mammals and mammalian diversity Flashcards
Describe the origins of mammals
Pelycosaurs and therapsids
Describe the Pelycosaurs
- Pelycosaurs more primitive than therapsids
- mainly in Laurasia (N. hemisphere)
- sailbacks; not all had sails
- generalised amniotes
- no evidence of high locomotor capacity or metabolic rate
- non-mammalian synapsid
Describe Archeothyris
- earliest pelycosaur
Describe the Synapsids
- temporal fenestra
Describe fenestral implications
- larger temporal fenestra indicates greater volume of jaw muscles
- implies more food eaten per day
Describe Dimetrodon
- carnivorous pelycosaur
- most derived pelycosaur
- arched palate: first step towards separation of mouth and nasal passages
- elongation of neural spines into sail: evolved in dependently in two groups of
dimetrodon - no sexual dimorphism
Describe therapsids
- more derived than pelycosaurs
- Gondwana
- increased metabolic rate
- trough in roof of mouth: airway separate from rest of oral cavity
- differentiation of teeth types
- flexible neck
List some therapsids
- Titanophoneus
- Gorgonopsian
Describe Massetognathus
- advanced cynodont
- enlarged infraorbital foramen: highly innervated face and maybe sensitive muzzle
- whiskers
List the evolutionary trends of the Synapsida
- Larger temporal fenestra
- Greater teeth specialisation
- Development of bony secondary palate
- Limb position
- Dual gait locomotion
- Loss of lumbar ribs suggests diaphragm – higher rate of
respiration - Increasing ability to regulate internal temps and
chemical environments accurately
Summarise the origin of the mammals
- pelycosaurs and therapsids
- radiation of Mesozoic mammals
- Dinosauria ascendancy
- Tertiary radiation
- Quaternary Megafaunal extinction
Cenozoic
age of mammals
Mesozoic mammals
= diverse taxonomically, homogenous in body form
Most of mammal history is characterised by (2/3)
radiation in the Mesozoic
Describe Mesozoic mammals
- tiny
- derived features: skull;
larger brain and inner ear - evolution of lactation and suckling
- hair
- special Harderian gland insulates fur (important for size)
Give an example of a Mesozoic mammals
Megazostrodon, one of the earliest mammals
After extinction of dinosaurs mammals
diversify into larger, more specialised forms
List some Tertiary mammals:
- Moeritherium (Proboscidea)
- Brontotherium
- Phenacodus ‘condylarthran’
- Eocene whales
Give some megafauna
- Megaceros (giant Irish elk)
- Smilodon
- Megatherium
- Phoberomys
- Procoptodon
Describe Phoberomys
- 700kg
- 3 metres
- rodent
- South America, Miocene of Venezuela
Describe Procoptodon
- 3m
- Pleistocene
- giant short-faced grazing kangaroo
List some mammalian characteristics
- endothermy
- reproduction
- lactation
- hair
- high blood pressure
- high oxygen uptake
- high metabolic rate,
- water regulation (loops of Henle)
- improved locomotion
- improved sensory systems
Describe lactation
- early innovation
- milk: antimicrobial, immunity; nutrition later
- young can be born at relatively undeveloped stage and cared for outside uterus
- reproduction at any time of year (not linked to food supply)
- complex teeth
Describe lactation and teeth
- newborn mammals do not need teeth
- shift from continual replacement of teeth to diphyodonty
- occlusion
- diversified to exploit a
greater range of food and feeding strategies than seen in any group of vertebrate
Describe suckling
- uniquely mammalian
- fleshy seals formed against the bony hard palate with the tongue and the epiglottis
- isolates functions of breathing and swallowing
- changes in bony anatomy of palate and surrounding areas occurred in only the most derived cynodonts
- facial muscles = characteristic
Describe mammalian hair functions
- insulation
- camouflage
- communication
- sensation via vibrissae
Describe mammalian hair
- epidermis
- dermal papillae
- nerve endings
- capillaries
- arrestor pili muscle
- sebaceous gland
- hair root
- sweat gland
- group of fat cells
- dermis
- hair shaft
- free length of hair exterior to skin
Discuss mammalian sensory systems
- exceptionally large brain: neocortex
- reliant on hearing and olfaction (less on vision than other amniotes)
- evolved as nocturnal animals; visual sensitivity more important than acuity
- retinas largely rod cells (high sensitivity to light but poor acuity)
- cone fovea allows acute vision
Describe the Anthropoid primates
unique in having a brain specialised for visual sensory mode
Describe primitive, non-cursorial mammals
- basic mode of mammalian locomotion
- small body size over bumpy ground
- neither faster nor more efficient than in a similar sized reptile
- increased agility and an ability to keep breathing while running
- e.g. tree shrew
Describe the morphology of primitive, non-cursorial mammals
- cervical
- thoracic
- lumbar
- sacral
- caudal
- pelvis
- fibula
- tibia
- femur
- ulna
- radius
- humorous
- scapular
Describe the forelimb
- smaller than hindlimb
- rotation of loosely attached scapula on the rib cage
- no net thrust
scapula
shoulder girdle
Describe the hindlimb
- larger, pelvic girdle fixed rigidly to the sacral vertebrae
- foot: extra extensible unit
- provides all the thrust
Describe the morphology of fossorial mammals - the basics
- short limb bones
- stout
- muscle attachments well away from the joints
- powerful (slow) movement of the limbs
- e.g. European mole
Describe the morphology of fossorial mammals - the specifics
- origin of teres major
- insertion of teres major
- keeled manubrium
- groove and tunnel for bicep tendon
- origin of deep flexor
- olecranon
- falciform sesamoid broadens foot
- phalanges: short, broad
keeled manubrium
origin of pectoralis
Describe Echidna morphology
- sesamoids under distal phalanges
- carpus and metacarpus short
- large median epicondyle: origin of pronators and flexors
Describe cursorial mammal morphology
…
fossorial
digging
cursorial
running
Describe horse morphology
- tendon stretched as body moves forward over the leg
- shortens as foot leaves the ground
- springing action: additional propulsive force
- fetlock joint
- coffin joint
Describe cheetah locomotion
- hind leg rotation
- spine extension
- bounding action (body unsupported)
Who locomotes saltatorially
- kangaroo (Macropus)
- kangaroo rat (Dipodomys)
- springhare (Pedetes)
Who uses aerial locomotion?
- Coluga; flying lemur (Cynocephalus, Dermoptera)
Who uses aquatic locomotion
- eared seal (colonies)
- Pygmy Killer Whales
Describe some specialised forms of locomotion
- aquatic
- arboreal
Who uses arboreal locomotion?
- sloth: below the branches
- gibbon
How do gorilla locomote?
knuckle walking
Describe human bipedalism morphology
- ventral position of occipital condyles and foramen magnum
- S-shaped spinal curvature
- relatively short arms
- shorter iliac blade
- relatively long legs
- more compact feet
Discuss mammalian diversity
- reflects isolation of different groups on different land masses
- changing climates of higher latitudes in Cenozoic
- different habitats and associated adaptations (grassland etc)
List the 3 mammalian Subclasses
- Monotremata
- Marsupialia (Metatherians)
- Placentalia
Gives example of Monotremata
- Ornithorhynchus (duck-billed platypus)
Give an example of Marsupialia
- Didelphis virginiana (Virgin opossum)
Give an example of Placentalia
- Chrysochlorida (Golden Mole)
Describe the Monotremes
- egg-laying mammals
Give the two Monotremata Families
- platypus, Family Ornithorhynchidae
- echidna; spiny anteater: Family Tachyglossidae
- occur only in Australia and New Guinea.
Describe Monotreme reproduction
- cloaca
- lay eggs (ancestral)
- young have reptile-like egg tooth to escape
cloaca
single posterior opening for excretion and reproduction
Monotreme literally means
one holed
Describe Monotreme development
- small egg develops to form a rapidly dividing outer layer (envelops the egg)
- uterus secretes double-layered porous shell
- grows
- meroblastic cleavage
Monotreme egg
- amnion
- shell
- allantois
- yolk sac
- embryo
- mesoderm
- bilaminar yolk sac
Describe sex determination in the platypus
- multiple sex chromosomes
- male has 5X and 5Y
Describe the Platypus genome
large expansion of natural killer receptor proteins, certain antimicrobial peptides, and other components of the innate immune system
Describe Platypus venom
- venom spur on the heels of their hindlegs
- premating, defence
- gene duplication, divergence and neofunctionalisation
Describe the morphology that facilitates Platypus venom
- curved and hollow spur
- connected by ducts to venom gland under thigh muscles
Describe Platypus electrolocation
- determine the direction of an electric source by comparing differences in signal strength across the sheet of electroreceptors
- cortical convergence of electrosensory and tactile inputs: determining the distance of prey items
Describe Marsupials - the basics
- c.500 spp.
– South America (didelphid oppossums, caenolesdid shrew-opposums)
– Australasia (carnivore - Tasmanian devil, bandicoots (Peramelines), a single marsupial mole and many diprotontid herbivores (kangaroos, wallabies, possums, koalas etc)
Describe Marsupial development
- chorio-vitelline “placenta”
- allantois
- bilaminar yolk sac
- foetal membranes of wallaby
- mesoderm
- amnion
- uterus
- cervix
- bilaminar blastocyst
- e.g. wallaby
Describe Marsupial reproduction
- egg size intermediate between montremes and placentals
- development of jaws, facial muscles and tongue advanced
- CNS retarded
Describe Marsupial neonate girdles
- novel
- shoulder: allows them to get to nipple
- front claws holdfast
- shoulder arch brace
- crawling locomotion
- limits subsequent development
Describe Marsupial lactation
- complex
- lasts much longer
- oligosaccharides, proteins, fats, monosaccharides
List some South American marsupials (opossums)
- woolly opossum
- yapok, or water opossum
- Sarcophilus: the Tasmanian devil (carnivore)
- Phascolarctos: Koala (herbivore)
- Notoryctes: marsupial mole
- Burramys: the pygmy possum
- Petaurus: sugar glider
- Petauroides volans – better glider
- Petauroides - best glider
Describe Placetalia (Eutheria)
- Laurasiatheria
- Euarchontoglires
- Xenarthra
- Afrotheria
List some Afrotheria
- Hyracoidea (roch hyraxes)
- Sirenia (dugongs and manatees)
- Proboscidea (elephants)
- Chrysochlorida (golden mole)
- Tenrecida (tenrecs)
- Tubulidentata (aardvark)
- Macroscelidea (elephant shrews)
Which Placentalia have a Northern Hemisphere origin?
- Laurasiatheria
- Euarchontoglires
Which Placentalia have a South American origin?
Xenarthra
Which Placentalia have an African origin
Afrotheria
Describe Placentalia development
- placental bilaminar trophoblast
- inner cell mass -> embryo
- allantois
- placental foetal membranes
- amnion
- uterine epithelium
- choric-allantoic placenta
Describe Placentalia reproduction
- larger opening at base of pelvis than other mammals
- large live young
Describe the Placentalia return to water
- denser, more viscous than air
- light readily absorbed, suspended particles (turbidity); visibility poorer
- sound travels further, faster
Describe elephant seal vision
- 300–700 m
- adapt to poor light faster (6 mins to 20: humans)
Describe touch in harbour seals (Phoca vitulina)
- vibrissae
- rely solely whiskers to track hydrodynamic trails left by fish
Describe echolocation in bottlenosed dolphin (Tursiops truncatus)
- blow-hole
- melon
- auditory bulla
- oil-filled cavity in lower jaw
- sound in
- click out
Describe humpback whale communication (Megaptera novaeangliae)
- song structure
- local dialects in different populations
Describe mechanoreceptors
- sub- terrestrial adaptation
- Star nosed mole (Condylura cristata)
- 11 rays moved by tendons attached to facial muscles
- each ray contains hundreds of mechanoreceptive Elmer’s organs innervated by infraorbital nerve
Describe bat echolocation
- independent evolution
- frequency, bandwidth, duration and pulse interval
Where has echolocation evolved?
- bats
- shrews
- toothed aquatic mammals
Describe the long-eared bat (Plecotus auritus) and moth coevolution
ong-eared bat , listens for moth movement. Filters out other sounds.
* Uses echolocation to navigate obstacles, and then “stealth mode” to catch moth.
