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Huge meat-eating, land-living dinosaurs evolved into birds by constantly shrinking for over 50 million years, scientists have revealed.

Previous work has shown that theropod dinosaurs, the dinosaur group which included Tyrannosaurus rex and Velociraptor and gave rise to modern birds, must have decreased in size at some point in their evolution into small, agile flyers.

But size changes frequently occurred in dinosaur evolution, so the research team members, led by Mike Lee, from the University of Adelaide, Australia, wanted to find out if the dramatic size reduction associated with the origin of birds was unique. They also wanted to measure the rate of evolution in dinosaurs using a large data set

"Dinosaurs became ever more 'birdy' over time," Brusatte said, but there was no single missing link, he added. Birds and dinosaurs are like two colors in a rainbow, he said — you can recognize each, but they bleed into each other at their borders.

The new pedigree of carnivorous dinosaur evolution is the most comprehensive one ever assembled, the researchers say. The findings show that birdlike features such as wings and feathers developed slowly over tens of millions of years.

The label of "bird" is somewhat arbitrary, but scientists consider the feathered fossil Archaeopteryx to be the first of the group, Brusatte said. "What probably distinguishes birds is the ability to have powered flight," he said, though it's possible that other dinosaurs could fly too.

Shrinking success

Dolphins are cetacean mammals closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from 1.2 m (4 ft) and 40 kg (90 lb) (Maui's dolphin), up to 9.5 m (30 ft) and 10 tonnes (9.8 long tons; 11 short tons) (the orca or killer whale). They are found worldwide, mostly in the shallower seas of the continental shelves and are carnivores, eating mostly fish and squid. The family Delphinidae, the largest in the order Cetacea, evolved relatively recently, about ten million years ago during the Miocene.

Zoos are premises for the captivity of animals, often in urban areas where many of the animals would not otherwise be found, with the intention of studying the animals and displaying them to the public at large. The predecessor of the zoo was the menagerie, which involved the captivity of birds typically for the entertainment of the aristocracy, and has a long history running back to ancient times. The first modern zoo evolved out of an aristocratic menagerie in Vienna in 1765. Many types of zoo now exist, from the petting zoos that encourage the public to get up and close with the animals to the large nature reserves that provide space for the animals to roam around within and most famously the large, urban zoos like the London Zoo which include elephants, lions and penguins and are usually notable tourist drawcards for the cities concerned. Proponents argue that zoos are beneficial both to the animals themselves, protecting endangered species with specific breeding programs, and the public, as an educational tool to increase both awareness and understanding. Opponents respond that the removal of wild animals from their habitat is wrong, that they should be left in their natural surroundings and not used as tools for public entertainment. Show less

Zoos are premises for the captivity of animals, often in urban areas where many of the animals would not otherwise be found, with the intention of studying the animals and displaying them to the public at large. The predecessor of the zoo was the menagerie, which involved the captivity of birds typically for the entertainment of the aristocracy, and has a long history running back to ancient times. The first modern zoo evolved out of an aristocratic menagerie in Vienna in 1765. Many types of zoo now exist, from the petting zoos that encourage the public to get up and close with the animals to the large nature reserves that provide space for the animals to roam around within and most famously the large, urban zoos like the London Zoo which include elephants, lions and penguins and are usually notable tourist drawcards for the cities concerned. Proponents argue that zoos are beneficial both to the animals themselves, protecting endangered species with specific breeding programs, and the public, as an educational tool to increase both awareness and understanding. Opponents respond that the removal of wild animals from their habitat is wrong, that they should be left in their natural surroundings and not used as tools for public entertainment. (shamelessly taken from our sister site idebate.org)

Today, we can safely declare that birds evolved from a group of dinosaurs known as maniraptoran theropods-generally small meat-eating dinosaurs that include Velociraptor of Jurassic Park fame.