limbs – Forelimbs of Vertebrate
omologous Organs – Forelimbs of Vertebrates(Whale, Bat, Lizard, Bird, Human)
Definition
Homologous organs are organs that have the same basic structure and origin but are modified to perform different functions in different organisms.
The forelimbs of vertebrates are the best example of homologous organs.
Common Basic Skeletal Plan (Same in All)
All five vertebrates have the same arrangement of bones in their forelimbs:
Scapula – shoulder bone
Humerus – upper arm bone
Radius and Ulna – forearm bones
Carpals – wrist bones
Metacarpals – palm bones
Phalanges – finger bones
This shows they all evolved from a common ancestor.
Detailed Explanation of Each Forelimb
1. Whale (Flipper) 🐋
The forelimb is modified into a broad, flat flipper.
Humerus is short and thick, giving strength.
Phalanges are numerous and elongated, making the flipper wide.
Covered with skin and blubber for smooth movement.
Function:✔ Swimming, steering, and balance in water.
2. Bat (Wing) 🦇
The forelimb is modified into a wing for flight.
Radius is very long and strong.
Ulna is reduced.
Phalanges are extremely long and support a thin wing membrane.
Function:✔ Flying and gliding in air.
3. Lizard (Forelimb) 🦎
Forelimb is used for movement on land.
Bones are well-developed and separate.
Digits are short and strong for support.
Function:✔ Walking, crawling, and climbing.
4. Bird (Wing) 🐦
Forelimb is modified into a wing.
Carpals and metacarpals are fused to make the wing strong but light.
Phalanges are reduced to decrease weight.
Function:✔ Flying.
5. Human (Forelimb / Arm) 🧍
Forelimb is adapted for skilled movements.
Wrist has 8 carpals, palm has 5 metacarpals.
Fingers have 14 phalanges, allowing precision.
Function:✔ Grasping, lifting, writing, tool use.
Why They Are Called Homologous Organs
Same basic skeletal structure
Same embryonic origin
Different functions
Modified due to different needs and environments
Evolutionary Significance (Very Important)
Homologous organs are evidence of divergent evolution.
They prove that different vertebrates evolved from a common ancestor but adapted to different lifestyles.
The forelimbs of whale, bat, lizard, bird, and human are homologous organs because they have the same basic skeletal structure but perform different functions. This proves divergent evolution and common ancestry among vertebrates.