Large Theropods Shrank to Bird-size

Published: 1st Aug 2014

Scientists have described how a group of fierce predtory dinosaurs evolved and downsized to the likes of robins and hummingbirds. 120 different dinosaur species were studied and 1,500 skeletal features, in particular the thigh bones. The first theropds lived about 225 million years ago and were large – about 272kg (600lbs). By 200 million years ago this group of dinosaurs had shrunk to 163kg (3600lbs). Then the shrinking with evolution became faster and in just 25 million years the dinosaurs were slimmed down to barely 45kg (100lbs). By 167 million years ago, 2.5kg (6lb) paravians, the more direct ancestor of birds, were around. Finally 163 million years ago the first birds, weighing less than 1kg (2lbs), probably evolved.

Not all of the dinosaurs in this group of theropods shrunk through evolution. One noteable exception was T rex, which did not evolve until the late Cretaceous and weighed about 5.5 tonnes. By downsizing and evolving into birds it meant that the remainder of this group of coelurosaurs were much better able to adapt to the mass extinction that happened 65 million years ago. So if you feed the birds in your garden you are infact feeding the modern-day direct descendents of dinosaurs.

---