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
