Q.List the unique features of bird’s endoskeleton.

Step 1. The bird endoskeleton is fully ossified (bony), like other vertebrates, but its long bones are hollow and contain air cavities connected to the respiratory air-sac system — these are the pneumatic bones, which significantly reduce the skeleton's weight without sacrificing strength.

Step 2. The skeleton is also built to support powerful flight: the well-developed pectoralis major and pectoralis minor muscles, which power the wing's downstroke and upstroke respectively, anchor onto an enlarged breastbone (keel/sternum) — a specialisation not needed by non-flying vertebrates. …

Identify the skeletal features that specifically serve flight — bone lightening (pneumatic bones) and …

• Describing the bones only as 'hollow' without connecting this to weight reduction for flight. …