Pita Moon of Tikipuna School asks :-

What makes a dinosaur different from a lizard?

Christine Thomson, of Massey University's Institute of Veterinary, Animal and Biomedical Sciences, responded.

In evolutionary terms, the more anatomical features animals share, the more closely related they are. Dinosaurs and lizards both belong to the Class Sauropsida (‘lizard-faced’) and ‘dinosaur’ means ‘terrible lizard’. However, although dinosaurs and lizards share some anatomical similarities, they are quite different in many ways.

Generally speaking, dinosaur anatomy is characterised by hip joints in which the top of the femur (thigh bone) is directed inwards toward the pelvis, while the long shaft of the femur is rotated, so the stifle (knee joint) faces forward. With this design of the pelvic limb, dinosaurs could stand erect and run fast and efficiently on just the two back legs (bipedal locomotion). By comparison, lizards have pelvic limbs that are directed to the side rather than forward, giving them a more sprawled posture with slower, less efficient movement. Typically, they use all four limbs for running (quadrupedal locomotion).

Are lizards the descendents of dinosaurs? No. Birds are the evolutionary descendents of dinosaurs, specifically theropod dinosaurs. Like theropods, birds also have an erect stance, bipedal locomotion and do not use their thoracic limbs for walking. Dinosaurs and birds share a skeletal similarity that is unique amongst animals – the presence of a hole in the socket of the hip joint (perforated acetabulum). Modern birds and theropod dinosaurs also share respiratory (air sacs), gastrointestinal and behavioural similarities.

Lizards are cold-blooded (poikilothermic) animals; they rely on absorbing heat from external sources, like the sun. Were dinosaurs cold-blooded, too? Evidence suggests that dinosaurs may have been homeothermic, able to regulate their body temperature by internal means; again, this is just like modern day birds. So the next time you see a bird pause and consider its impressive ancestor – the dinosaur.