The “origin of birds” is the term used to refer to the scientific subject of where the evolution of birds took place within a bigger animal species. The current scientific consensus holds that birds are a clade of Mesozoic-era maniraptoran theropod dinosaurs.
Following the discovery of the early bird Archaeopteryx in Germany in the nineteenth century, the idea that dinosaurs and birds had a close connection was initially proposed. Many distinctive skeletal features of prehistoric non-avian dinosaurs and birds are similar.
More than thirty species of non-avian dinosaur fossils with intact feathers have also been discovered. There are even extremely tiny dinosaurs with long, vaned arm and leg feathers that function as wings, such as Microraptor and Anchiornis.
The basic avian Pedopenna from the Jurassic period also has similar lengthy foot feathers. This evidence is adequate to show that the evolution of birds passed through a four-winged stage, according to a 2009 analysis by paleontologist Lawrence Witmer.
Additionally, fossil evidence shows that dinosaurs and birds shared traits including hollow, pneumatized bones, gastroliths in the digestive tract, nest-building habits, and raising young.
Similar Features Between Birds and Theropods
As they studied animal bones, paleontologists saw connections between dinosaurs and birds. Theropods and birds have a lot of similar anatomical characteristics.
The first reliable evidence of a type of “feathered dinosaur,” Archaeopteryx, was found in 1861 in southern Germany’s Solnhofen limestone. It had characteristics that are unmistakably in-between non-avian theropods and modern birds.
Its finding sparked the early discussion between believers in creationism and evolutionary biology. Without a distinct imprint of feather shapes in surrounding rock formations, a specimen of this early bird was mistaken as a Compsognathus because of how dinosaur-like it looked.
More dinosaurs with feathers were discovered during the 1990s, adding to the mounting evidence that shows the tight connection between therapod dinosaurs and contemporary birds that we see today.
The first was thought to be straightforward filamentous protofeathers, and examples of them have been found in lineages of dinosaurs as ancient as tyrannosauroids and compsognathids. Soon later, however, paleontologists also discovered non-avian dinosaurs with feathers that they could not distinguish from contemporary birds.
A few scientists have argued that species with undeniable feathers, such as oviraptorosaurs and dromaeosaurs, are not dinosaurs but rather actual birds unrelated to dinosaurs. They claim that the filamentous structures (called “protofeathers”) result from collagen fibers decomposing underneath the dinosaurs’ fins or skin along their backs.
The bulk of scientists, however, have concluded that the filaments of undisputed theropods are simply feathers and that dinosaurs with feathers are, in fact, dinosaurs. Researchers have found melanin bearing different colors, but not collagen fibers, in the arrangements that we would anticipate in feathers.
Others have shown that even robust feathers seem filamentous when they’re subjected to crushing forces that occur during fossilization, and the purported “protofeathers” could be more complicated than previously believed using studies of current bird decomposition.
A thorough investigation of Sinosauropteryx prima’s “protofeathers” revealed that each feather was made up of a core quill (rachis) and thinner barbs coming out of it, similar to yet made more simply than modern bird feathers.
Dinosaurs with feathers are frequently referred to as a “missing link” in the study of dinosaurs and birds since feathers are frequently linked with birds. However, the most significant evidence for paleontologists is the variety of skeletal traits that both groups share.
Cladistic analysis and skeletal comparisons of dinosaurs and birds support the hypothesis, especially for the Maniraptora clade of theropods. Maniraptorans that are not birds exhibit almost all of Archaeopteryx’s skeletal characteristics.
Bird skulls can be descended from therapod skulls through paedomorphosis that resulted in the retention of their forebears’ juvenile traits, according to research comparing embryonic, juvenile, and adult archosaur skulls.
What was hitherto thought to be only found in birds was, in some way, present in the progenitors of birds. Paleontologists have discovered evidence that dinosaurs possessed air sacs, like modern birds, which have air sacs extending from their lungs and letting them take in oxygen during both inhalation and expiration.
The sophisticated system of air sacs in giant carnivorous dinosaurs was comparable to that in current birds. Flexible soft tissue air sacs, comparable to those seen in birds, most likely circulated air through the stiff lungs of theropod dinosaurs which were carnivores that moved on two legs and had feet that resembled birds).
Thescelosaurus specimens’ chest cavities were subjected to computed tomography (CT) scans in 2000. The results revealed what seemed to be the remains of a sophisticated, four-chambered heart, similar to those found in modern mammals and birds. The theory is debatable among scientists, who accuse it of wishful thinking or poor anatomical research.
Dinosaurs slept with their heads curled beneath their arms, as evidenced by the fossils of the Troodontidae – Mei, and Sinornithoides. Modern birds also exhibit this habit, which they may have used to keep their heads warm.
Female birds develop a particular kind of bone in their limbs during egg-laying. Eggshells are made from the calcium found in this medullary bone, which develops as a calcium-rich layer inside the hard outer bone.
Parts of a Tyrannosaurus rex specimen’s hind leg had endosteally produced bone tissues lining the inside marrow cavities, which indicated that T. rex utilized comparable reproductive techniques and proved that the specimen is female.
According to further study, medullary bones have been discovered in the theropod Tenontosaurus and ornithopod Allosaurus. This shows that all dinosaurs formed medullary tissue since the line of dinosaurs that gave rise to Allosaurus and Tyrannosaurus separated from the line that produced Tenontosaurus relatively early in the history of dinosaurs.
Numerous Citipati specimens have been seen in its nest, leaning over the eggs in a manner that most closely resembles brooding. Many dinosaur species, including Maiasaura, have been discovered in herds that contain both young and adult individuals, indicating that they interacted richly.
The discovery of a dinosaur embryo without teeth shows that parental care was needed to feed the young dinosaur, and it’s possible that the adult dinosaur regurgitated food into the mouth of the young dinosaur. Numerous bird species exhibit this behavior; the adult bird regurgitates food into the mouth of the hatchling.
Gizzard stones are used by dinosaurs and birds alike. Animals ingest these stones to help digestion and to break down food and tough fibers once they reach the stomach. Gastroliths are the name for gizzard stones that are discovered alongside fossils. Additionally, certain fish and crocodiles have gizzard stones.
It has been said on several occasions that proteins and DNA may be extracted from the fossilized remains of Mesozoic dinosaurs, allowing for a comparison with birds. Hemoglobin is one of the proteins that may have been found in dinosaur remains.
When seven collagen types from T. rex bone pieces are matched to collagen information from extant birds, the two groups of dinosaurs – older theropods and birds – are closely connected. The soft tissue made it possible to do molecular analyses of collagen tissue’s protein sequence and cellular architecture, which were reported in 2007.
These analyses revealed that T. rex and birds are more closely related to one another than either is to alligators. Although a second molecular analysis did not place birds in the Theropoda as was anticipated, it strongly confirmed the link between birds and birds.
Eight more collagen sequences that were taken from the “mummified” femur of Brachylophosaurus canadensi were used in this investigation. Both theories could not be validated after closer examination and peer review.
Despite these revelations, skepticism persisted. The idea that birds descended from dinosaurs didn’t truly gain traction until the late 1900s when paleontologists discovered a Velociraptor skeleton in Mongolia with a wishbone (a bone often found in birds).
Since then, more finds have been found, including many feathered dinosaurs. Now, it is known that birds are descended from tiny theropod dinosaurs, who were carnivorous dinosaurs. Dr. Currie continues that throughout time, feathers offered them an “aerodynamic edge,” presumably enabling them to glide, make short leaps, and climb trees.
Some theropod groups’ body sizes steadily shrank throughout the course of their evolutionary history, and this development, along with several other skeletal alterations, eventually gave rise to the avian phylum.
Birds’ Dinosaurian Origin
Early in the nineteenth century, dinosaurs were first discovered. Initially, people imagined dinosaurs to be massive, hundreds of feet long creatures that resembled giant lizards. We must continuously revise our theories about dinosaurs’ looks, behavior, and lifestyle in light of new discoveries.
Only a few scientists currently contest the dinosaurian origin of birds, arguing that they descended from other kinds of archosaurian reptiles, even though the origin of birds has traditionally been a contested issue within evolutionary biology.
The precise order of the evolutionary processes that gave birth to the early birds within maniraptoran theropods is debated within the body of evidence that supports dinosaurian origins.