Classification and Evolutionary Relationships
Why scientists classify organisms
Classification helps scientists understand how organisms are related through evolution.
Organisms that share a common ancestor are grouped together.
Vertebrates and limb structure
All vertebrates have:
A vertebral column (backbone)
A skull protecting the brain
Jaws (usually with teeth)
When scientists compare the front limbs of different vertebrates (e.g. humans, birds, whales):
The limbs have different functions (grasping, flying, running, swimming)
But the basic bone pattern is the same:
One upper bone → humerus
Two lower bones → radius and ulna
Wrist bones
Five groups of hand/finger bones (some reduced or missing in birds)
➡️ These are called homologous structures.
What this shows about evolution
If animals were not related, it would be strange to see the same bone plan used for different jobs.
Evolution explains this:
All these vertebrates evolved from a common ancestor
Over time, the same limb structure was modified for different uses
Pangolin vs Armadillo: looks can be misleading
At first glance, pangolins and armadillos look similar
Scientists once grouped them together, but later evidence showed they are not closely related
Pangolin
Covered in keratin scales (like human nails)
No teeth
Eats ants and termites using a long tongue
Rolls into a tight ball for protection
Armadillo
Covered in hard bony plates
Has small teeth (no enamel)
Uses strong claws for digging burrows
Eats grubs and insects
Some species can also roll into a ball