Paleontologists discovered in the 1970s that Archaeopteryx and theropods, a small class of carnivorous dinosaurs, shared certain distinctive characteristics. With the exception of the ornithischian dinosaurs, every group of dinosaurs on this evogram is a theropod. Scientists hypothesized that birds could have descended from theropods based on the similarities between their features. Paleontologists were even more persuaded when they constructed evolutionary trees to investigate the issue. On the dinosaurs’ branch of the tree of life, the birds are merely a twig.
Variations in the dinosaurs’ digits that led to the development of birds provide additional evidence. Small fifth and fourth digits and a long second digit were present in the hands of the earliest theropod dinosaurs. In the theropod lineage that would eventually give rise to birds, as the evogram demonstrates, the fifth digit (e g. , as seen in Coelophysoids) and then the fourth (e. g. , as seen in Allosaurids) were completely lost. The wrist bones that supported the first and second fingers coalesced into a semicircular shape, enabling sideways rotation of the hand against the forearm. Eventually, this made it possible for the wing joints of birds to move in a way that produces thrust for flight.
The finding that birds descended from Late Jurassic small carnivorous dinosaurs was made possible by newly found fossils from China, South America, and other regions, as well as by using innovative techniques and new perspectives to examine historical museum specimens. An early 1860s discovery of a specimen of Archaeopteryx, the first known bird, marked the start of the search for the ancestors of modern birds. It had feathers on its arms and tail, just like birds do, but it also had teeth and a long, bony tail, unlike living birds. Moreover, unlike many bones in living birds, many of the bones in Archaeopteryx’s hands, shoulder girdles, pelvis, and feet were distinct rather than fused and reduced. These traits led to the recognition of Archaeopteryx as a transitional species between birds and reptiles, but which reptiles?
There has long been discussion regarding the evolutionary roles of feathers. It is evident that the initial, most basic feathers resembled hairs had an insulating purpose. However, even though the forelimbs of later theropods, like some oviraptorosaurs, are short, the arms and hands have long feathers. One theory regarding the function of these animals with long feathers on short arms comes from some amazing fossils of oviraptorosaurs found in the Cretaceous sediments of the Gobi Desert. The animal’s skeleton is hunched over an egg nest, resembling a protective chicken. The hands are positioned so that they appear to be protecting the eggs. It is possible that these feathers provided warmth and protection for the eggs.
We find several new types of feathers in theropods even more closely related to birds, such as the oviraptorosaurs. One is branched and downy, as pictured below. Others have developed an unstructured base and a central stalk with branches branching off of it. Others (such as the Archaeopteryx and Dromaeosauridae) have a structure resembling a vane, with barbules holding the well-organized barbs together. This is identical to the feather structure of living birds.
How Birds and Reptiles are Related
We specialize in reptiles and amphibians here at the zoo, and that includes exhibits with emus and parakeets. [av_textblock size=” font_color=” color=” av-medium-font-size=” av-small-font-size=” av-mini-font-size=” admin_preview_bg=” av_uid=’av-vutdal’] As a result, we frequently receive feedback from guests who question why, exactly, there are birds at a reptile zoo. The short answer is that birds are reptiles, but it wasn’t always so. Let us explain. [/av_textblock].
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Av_textblock size=” font_color=” color=” av-medium-font-size=” av-small-font-size=” av-mini-font-size=” admin_preview_bg=” av_uid=’av-7pq8rwt’] The four main categories of reptiles that exist today are: crocodilians, dinosaurs, turtles and tortoises, and lizards and snakes. The final two groups are the living reptiles most closely related to birds, the archosaurs, a highly specialized group of reptiles that have existed for 225 million years.
Heres a more detailed explanation from Arizona State Universitys Ask a Biologist:
© Arizona Board of Regents / ASU Ask A Biologist.
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Source: http://www.ucmp.berkeley.edu/museum/events/bigdinos2005/turkey.html
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Due to anatomical similarities, many scientists have long assumed that birds and reptiles are related, but there is no concrete evidence to support this theory. [av_textblock size=” font_color=” color=” av-medium-font-size=” av-small-font-size=” av-mini-font-size=” admin_preview_bg=” av_uid=’av-4t893sd’] However, in 1860, a highly detailed fossil of the dinosaur Archaropteryx lithographica, which resembled a bird, was found by archaeologists. This fossil filled the gap left by the absence of the “transitional species” that scientists needed to connect reptiles and birds. Since then, many fossils of feathered dinosaurs have been found. [/av_textblock].
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[av_textblock size=” font_color=” color=” av-medium-font-size=” av-small-font-size=” av-mini-font-size=” admin_preview_bg=” av_uid=’av-2ge1jm5?] Birds may be most closely related to living reptiles, but they descended from theropod dinosaurs when it comes to their relationship with dinosaurs. These theropods share over 100 traits with modern birds. Here are a few:
- Three forward-facing toes
- Fused collarbone, called a wishbone (yes, that kind of wishbone!)
- Hollow bones
- Feathers
Granted, not every theropod dinosaur was able to soarimagine a Tyrannosaurus Rex on the air!but some did have inadequate skeletal adaptations or primitive feathers. Feathers are believed to have been used for mating displays in the past, and birds today continue to do so.
As was previously mentioned, 65 million years ago, a mass extinction event caused swift worldwide events like volcanic eruptions and tsunamis. Larger animals were at a disadvantage when resources became scarce, and all dinosaurs other than birds perished. Ultimately, birds evolved because they had to adapt to a changing environment, which is what made them successful. There are between 9,000 and 10,000 species of birds today, deriving directly from dinosaurs! [/av_textblock]
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