What overall characteristics are seemingly shared by dinosaurs and modern birds?
Not all dinosaur characteristics are similar to those of modern birds, but there are many similarities. For example, some dinosaurs had features such as bony tails, claws on the fingers, beaks, and on some, feathers.
Birds share over 130 physical traits with dinosaurs, and some species look remarkably like dinosaurs with feathers for example, birds in the ratite family, including ostriches, emus, rheas, and this cassowary from New Zealand. The cassowary even sports a head crest reminiscent of animals like the Dilaphosaurus (Big Stock Photo).
Feathers are only one major characteristic that links dinosaurs to birds, including such feathered dinosaur fossils as the Archaeopteryx lithographica, and specimens found in other parts of the world, such as the Sinosauropteryx prima from northeast China. All these fossils exhibit feather-like impressions in the sedimentary rock in which they were found.
Other characteristic links between dinosaurs and birds involve certain skeletal similarities. For example, fossils of the dinosaur Deinonychus have many bird-like characteristics: the large head was balanced on a slender, almost birdlike neck; and the chest was short, with the arms folding inward in a resting position, similar to the wings of a bird at rest. The creatures foot had a huge claw on the second toe. In many ways, the feet of the Deinonychus resembled an enlarged representation of a birds foot.
How did feathers evolve?
Scientists really dont know yet how feathers evolved. Some scientists believe feathers probably began as modified scales. These changed scales were not intended for flight, but rather for insulation to preserve the reptiles body heat. Eventually, they evolved into feathers. Other scientists believe feathers evolved from scutes similar to the thick scales on the top of a birds foot. Analysis shows that the bird scutes, scuttelae, claw sheathes, beak sheathes, and scales around a birds eyes have the same chemical composition as feathers, and they are controlled by the same genes. Crocodiles, a sister group of the dinosaurs, also have scutes, with a similar (but not identical) chemical composition to bird scutes. Scientists also know that dinosaurs had scutes, too, but they dont know the composition. Of course, to confuse matters even more, some scientists speculate that scutes evolved from feathers.
What dinosaurs are thought to have evolved into birds?
Paleontologists who believe birds evolved from dinosaurs think that the most likely bird ancestors were the small, carnivorous theropods. At least one fossil finding seems to indicate that dromaeosaurs, a subgroup of the theropods, eventually branched into many lines, including birds. This subgroup line also included such dinosaur species as Velociraptor, Deinonychus, and Utahraptor.
Do scientists believe the Microraptor could fly?
The recently discovered Microraptor gui a feathered dinosaur found in northeastern China that lived about 125 million years ago was only 30 inches (77 centimeters) long. These creatures had not one, but two sets of wings, one on top of the other, making them look like a kind of early animal biplane. Because of this, scientists believe that the Microraptor could not fly, but would glide from tree to tree, or even hop and glide from place to place. Unlike many birds today, the Microraptor probably could not land on the ground after jumping from a tree. Based on its structure, its wings did not act like a parachute, so they would have crashed to the ground.
What is the latest theory stating birds are truly dinosaurs?
One recent theory goes one step further than birds are descendants of dinosaurs. Some paleontologists now think modern birds are truly dinosaurs. This theory states that birds are dinosaurs that evolved certain bird-like characteristics, such as light weight, agility, wings, feathers, and beaks. These specialized characteristics enabled the animals to somehow survive the extinction at the end of the Mesozoic era and continue evolving into modern birds.
Do all paleontologists believe that birds and dinosaurs are related?
No, not all paleontologists believe that birds are dinosaurs or even that birds evolved directly from dinosaurs. Many suggest that birds and dinosaurs descended from a common, older ancestor, and developed many superficial similarities over millions of years due to convergent evolution; because they both developed body designs for bipedal motion, they eventually started to resemble each other.
This Scelidosaurus harrisonii had a birdlike beak instead of teeth. Beaks in some dinosaurs are one reason some paleontologists see parallels between dinosaurs and modern birds (Big Stock Photo).
There are four major reasons why some scientists think there is not a direct dinosaur-bird link: the timing problem, body size differences, skeletal variations, and the mismatch in finger evolution. First, with regard to timing, there is some fossil evidence that bird-like dinosaurs evolved 30 to 80 million years after the Archaeopteryx lithographica, which seems to put the cart before the horse, or the bird before the bird-like dinosaur. This is the opposite of what you would expect if birds descended from dinosaurs.
Second, some scientists suggest it was nearly impossible for theropods to give rise to birds because of differences in body size. They point out that these carnivorous dinosaurs were relatively large, ground-dwelling animals, with heavy balancing tails and short forelimbs, not the sort of body that could evolve into a lightweight, flying creature.
Third, although birds and dinosaurs have skeletons that appear similar at a macroscopic level, there are really many variations on a smaller scale. The teeth of theropods were curved and serrated, but early birds had straight, unserrated, peglike teeth; dinosaurs had a major lower jaw joint that early birds did not; the bone girdle of each animal was very different; and birds have a reversed rear toe for perching, while no dinosaur had a reversed toe.
Fourth, there is a discrepancy between the fingers of dinosaurs and birds. Dinosaurs developed hands with three digits, or fingers, labeled one, two, and three, and corresponding to the thumb, index, and middle fingers of humans. The fourth and fifth digits, corresponding to the ring and little fingers, remained tiny vestigial bumps, which have been found on early dinosaur skeletons. However, as recent studies of embryos have shown, birds developed hands with fingers two, three, and four, corresponding to the index, middle, and ring fingers of humans. Fingers one and five, corresponding to the thumb and little finger, were lost. Some paleontologists wonder how a bird hand with fingers two, three, and four could have evolved from a dinosaur hand with fingers one, two and three. And they say the answer is: Its impossible.