What is the modern day dinosaur bird?

The modern day living relative of dinosaurs that is most closely related to ancient dinosaurs like Velociraptor and Archaeopteryx is the bird. Birds are literally modern-day flying dinosaurs. They evolved from small feathered theropod dinosaurs over 150 million years ago during the Jurassic Period and still retain many features that connect them to their dinosaur ancestors.

How are birds the modern day version of dinosaurs?

There is overwhelming evidence that birds evolved from small feathered theropod dinosaurs, and are in fact a subset of dinosaurs that survived the Cretaceous-Paleogene mass extinction event 66 million years ago. Here are some of the key pieces of evidence linking birds to dinosaurs:

• Birds share over 100 distinct anatomical features with theropod dinosaurs, indicating they evolved from a common ancestor. This includes details of their skeletons, lungs, skulls, teeth, claws, and feathers.
• Some dinosaurs from the late Jurassic and Cretaceous Periods like Archaeopteryx, Microraptor, and Rahonavis show a clear transition from dinosaurs to early birds. They have feathers, wings, and wishbones like modern birds but retain dinosaur-like teeth and claws.
• Molecular evidence indicates birds evolved from within the theropod group of dinosaurs. Comparison of protein sequences confirms their close evolutionary relationship.
• The discovery of many feathered dinosaur fossils, including some with complex feather structures like modern flight feathers, supports birds inheriting feathers from dinosaurs.
• The fossil record shows a slow transition from early feathered dinosaurs to primitive birds over tens of millions of years, revealing how birds gradually evolved flight abilities.
• We can observe similarities between dinosaur and bird embryos, including how their tails develop. This indicates they share a common ancestral developmental path.
• Birds still retain dinosaur-like features such as claws, eggs with hard mineralized shells, certain wrist and ankle bones, and in some cases teeth.

With so many shared physical and genetic traits linking them to dinosaurs like Velociraptor and other theropods, there can be no doubt that birds are literally just a subset of dinosaurs that managed to survive mass extinction at the end of the Cretaceous Period. They are the direct descendants of dinosaurs.

What key features show the dinosaur connection?

Birds share a variety of anatomical, skeletal, and genetic features with theropod dinosaurs that confirm their evolutionary connection. Some of the most important dinosaur-like features still seen in modern birds include:

• Feathers – Feathers are a unique evolutionary innovation of dinosaurs and birds inherited complex, modified feathers from dinosaur ancestors. Feathers likely started out as simple filaments.
• Skeleton – Birds have lightweight skeletons with many hollow bones, similar to those of theropod dinosaurs. Bone cells in birds and dinosaurs are also microscopically similar.
• Skulls/Teeth – Bird skulls retain similarities to those of dinosaurs like Velociraptor, with the same number and position of skull openings. Some early birds retained teeth while modern birds have beaks.
• Claws – Raptor-like claws on the toes and fingers are a bird feature inherited directly from dinosaurs.
• Lungs – Birds have a complex system of air sacs and lungs similar to what we find in theropods and other dinosaurs.
• Eggs – Hard eggshells with pores are shared by dinosaurs and birds, unlike reptile eggs.
• Tails – Birds and dinosaurs share a similar pattern of tail vertebrae development as embryos.
• Wings – Bird wings evolved from forelimbs and feathered arms of dinosaurs.

The widespread sharing of all these specialized features indicates birds and theropod dinosaurs share a relatively recent common ancestor.

What fossil evidence links birds to dinosaurs?

A number of important transitional fossils have been found that link birds to their dinosaur ancestors. Some of the most notable include:

• Archaeopteryx – This famous 150 million year old fossil has feathers and wings like a bird but teeth and a long bony tail like a dinosaur.
• Confuciusornis – This crow-sized primitive bird from 125 million years ago retains dinosaur-like claws and teeth.
• Microraptor – With four wings, this dinosaur shows an intermediate stage between dinosaurs and birds.
• Anchiornis – Full-body feathers and perching feet reveal this dinosaur’s relationship to birds.
• Sinornithosaurus – This raptor-like dinosaur had primitive feathers covering its body.

These fossils represent just a few examples of the many feathered dinosaurs and early birds with transitional features that link birds to theropods. They fill in the fossil gap between non-avian dinosaurs and modern terrestrial birds.

How do bird and dinosaur embryos support their connection?

Experts have compared dinosaur and bird embryos and identified similarities that indicate they share a close evolutionary relationship. Some of the embryonic similarities include:

• Tail development – As embryos, birds and dinosaurs develop tail vertebrae in the same order and pattern.
• Limb development – Birds and dinosaurs develop forelimbs at an earlier stage than hind limbs.
• Claw development – The three-clawed hands of theropods develop the same way in bird embryos.
• Egg tooth – Bird and dinosaur embryos develop an egg tooth for breaking the egg shell.
• Skull development – Major skull bones harden at similar stages in dinosaur and bird embryos.

These precise matches between dinosaur and bird embryo development provide more evidence they share a common ancestral path. Birds evolved from within the theropod dinosaur group.

What dinosaur behaviors do birds still exhibit?

In addition to anatomical and genetic similarities, birds retain a number of behaviors characteristic of their theropod dinosaur ancestors, including:

• Nesting – Birds build nests and incubate their eggs just as dinosaurs did.
• Brooding – Sitting on eggs to provide warmth and protection is seen in both birds and dinosaurs like Citipati.
• Social flocking – Many theropods likely lived in social groups similar to modern bird flocks.
• Parenting – Primitive birds fed and cared for chicks, as some dinosaurs also did.
• Migrating – Seasonal migration may have first evolved in feathered dinosaurs before birds.
• Perching – Raptors like Microraptor could grip branches like modern birds.

The continuity of these and other types of complex behaviors provides additional evidence for the close evolutionary relationship between theropod dinosaurs and birds.

How does radial flow in lungs connect birds and dinosaurs?

One of the most striking similarities linking birds to theropod dinosaurs is the design of their lungs and air sac respiratory system. Birds have a flow-through lung ventilation system driven by air sacs that is also seen in theropods. Air flows in a one-way loop through specialized chambers and air sacs in both birds and dinosaurs. This radial flow of air is vastly more efficient for oxygen absorption than the simpler in-and-out breathing of mammals and other reptiles. The complex lung structure shared by theropods and birds provides evidence they evolved from a common ancestor.

What genetic evidence links birds and dinosaurs?

In addition to physical features, scientists have found genetic evidence that confirms the evolutionary relationship between birds and theropod dinosaurs. Some key genetic similarities include:

• Mitochondrial DNA – Analysis of mtDNA sequences demonstrates birds fall within the genetic diversity of theropods.
• Keratin – Birds and theropods share versions of keratin genes related to claws and beaks.
• Limb development – The PAX6 gene involved in limb/wing development is shared by birds and dinosaurs.
• Egg proteins – Egg white proteins like ovotransferrin are nearly identical in both birds and dinosaurs.
• Skull development – Genes controlling skull development like BMP4 are present in both groups.

The many genetic parallels between birds and theropods reflect their relatively recent shared ancestry around 150 to 200 million years ago.

How does Archaeopteryx represent a missing link?

The 150 million year old fossil Archaeopteryx is considered one of the most important transitional fossils ever discovered. This crow-sized animal shares distinct characteristics with both dinosaurs and modern birds. Features linking it to theropods include:

• Teeth – Unlike modern birds, Archaeopteryx had a full set of small pointed teeth in both jaws.
• Claws – It had three large curving claws on each hand, similar to raptors.
• Bony tail – Its tail was long like a dinosaur’s, not short like modern birds.
• Pelvis – The pelvis was dinosaur-like, not fused into a single unit like in birds.

But Archaeopteryx also shows some critical hallmarks of birds, including:

• Feathers – Large flight feathers form a clear wing outline and fan tail.
• Wishbone – It had a furcula wishbone like modern birds.
• Light skeleton – The skeleton was lightened by air spaces and hollow bones.
• Wings – The arms/hands formed wings capable of flapping flight.

With this precise mosaic mixture of traditional dinosaur and bird anatomy, Archaeopteryx represents a transitional fossil filling the evolutionary gap between non-avian dinosaurs and early birds. It shows birds evolved flight from small feathered, raptor-like theropod dinosaurs.

How did the discovery of feathered dinosaurs impact bird origins?

Starting in the 1990s, paleontologists in China began unearthing numerous feathered dinosaur fossils. These discoveries had a tremendous impact on our understanding of bird origins and reinforced their direct descent from theropod dinosaurs. Some key points include:

• Over 30 feathered dinosaur species are now known, most from the Cretaceous of China. Feathers were widespread among theropods.
• Feathers likely first evolved for insulation, only later adapting for flight. Colorful feathers may have served for display.
• Non-avian dinosaurs like Sinosauropteryx had simple filament-like feathers covering their body.
• Advanced species like Microraptor had fully formed wing feathers specialized for aerodynamic flight.
• Fossils showing the transition from dinosaurs to birds are no longer missing.

The feathers found on so many theropod dinosaurs provides definitive evidence that birds evolved feathers from dinosaurs before adapting them for flight. Birds are just one lineage within the greater theropod group that gained the ability to fly through feather modifications.

How similar are dinosaur and bird bones?

This table summarizes some of the major skeletal similarities between theropod dinosaurs and birds. Both share hollow air spaces, lightweight and often fused bones, reduced fingers, and in some cases a wishbone. The many parallels indicate they evolved from common dinosaur ancestors.

Conclusion

From shared physical features and genetics to behavioral continuity and transitional fossils, an overwhelming body of evidence conclusively demonstrates that birds evolved from maniraptoran theropod dinosaurs starting over 150 million years ago in the Jurassic Period. After surviving the extinction of non-avian dinosaurs 66 million years ago, birds still retain many key dinosaur-like features that connect them to raptor dinosaurs like Velociraptor. While other dinosaur lineages perished, birds live on as the only surviving dinosaur group, making them the modern-day equivalent of dinosaurs.