Mammalian Form

Question 1

Mammalian Ancestors

Answer 1

Mammals are synapsids

Early synapsids were reptile-like with long tails, had “full” sets of ribs, and legs on the horizontal

Question 2

The Mammalian Skeleton

Answer 2

All mammalian skeletal features have been modified from reptilian(ish) ancestors

Compared to synapsids there are a number of important changes:

• jaw joint/dentition
• stance - change in gait requires fundamental redesign
• adaption of limbs

Question 3

Mammalian Jaw

Answer 3

Mammals possess a simplified jaw and a new jaw joint - different to reptiles

Significant lateral movement as well as a vertical hinge - mammalian herbivores can chew

Question 4

Mammalian Dentition

Answer 4

Differentiation/specialisation of teeth into: incisors, canines, molars & premolars

Specialisation of teeth according to diet, multiple functions - killing, slicing, chewing, grinding, etc

For grinding jaw changes to L-shape - hinge moved out of line with jaws

Question 5

Mammalian Stance

Answer 5

Mammals have an “enhanced” gait over amphibians and reptiles - the parasagittal gait is better for bearing weight

the abdominal spine flexes vertically (especially in carnivores) which increases stride length in gallops and keeps the legs below the body - the thoractic spine is stiff

the ribs are restricted (not a “full set”) to the thorax, protecting the heart and lungs but not the abdomen

Question 6

Mammalian Limbs

Answer 6

Mammalian limbs became specialised for various modes of locomotion

All vertebrates have a standardised pentadactyl limb

Bats use elongated metacarpals and phalanges as “umbrella”

cetaceans have greatly reduced upper limbs with flattened 2D shapes with extended phalanges and reduced digits

Femurs are relatively short in fast runners

the tibia/fibula are shorter in plantigrades and longer in fast runners

as are the wrist/hand