History (T1): Origin Of Dinosurs

ORIGIN OF DINOSURS




The ancestry of dinosaurs can be traced back some 230 million years ago to the Late Triassic. At this time, all landmasses were united into a gigantic continent called Pangea. The breakup of this enormous landmass together with significant changes in global climate, and the disappearance of primitive lineages of archosaurs provided impetus for the divergence of dinosaurs. Afterwards, the rapid evolution of critical physical innovations equipped these animals with the specializations required to rule over all Mesozoic terrestrial ecosystems.

All dinosaurs belong to a group of reptiles called archosaurs-a group that also includes crocodiles and a variety of Mesozoic reptiles (pterodactyls and others) that are often misinterpreted as dinosaurs. The anatomical characteristics of both the earliest known dinosaurs and their archosaurian relatives suggest that the common ancestor of all dinosaurs was a small bipedal predator, which had forelimbs shorter than hind limbs. This ancestor was probably similar to the 235-million-year-old Lagosuchus from Argentina, pictured below.

From the most primitive Triassic forms to the most advanced ones of the latest Cretaceous, all dinosaurs share defining traits that distinguish them from their closest archosaurian relatives. Among these innovations, the femur (or upper leg bone) developed a distinct head for a tied attachment into a hollow hip socket. These and other changes resulted in a hind limb that was tucked directly underneath the body, providing upright, pillar-like support of the body and also enhancing locomotive abilities. The changes that led to the erect posture of dinosaurs from the sprawling posture of their reptilian predecessors had a profound effect on the evolutionary success of these animals. These transformations may have also been coupled with the evolution of a higher metabolism (a step towards warm bloodedness) that endowed them with a greater capacity for sustained activities such as running.