List of Transitional Fossils - Dinosaurs To Birds

Dinosaurs To Birds

Further information: Origin of birds Further information: Evolution of birds

*The Dinosaurs* → birds Evolutionary Series**
Appearance	Taxa	Relationships	Status	Description	Image
152-151 Ma	Genus: Juravenator			Primitive traits Undifferentiated hind digits displaying no specialties for climbing Spine attaches to the back end of the skull rather than the base Moderately long, bony tail Derived traits Basic proto-feathers cover parts of the body for insulation
168-152 Ma	Genus: Pedopenna			The find is represented only by a hind leg, but one that is very bird-like. It belonged to a small maniraptoran dinosaur with long, pennaceous feathers on its hind legs and (in all likelihood) arms.
161-151 Ma	Genus: Anchiornis	Basal troodontid	Although once classified as a bird, Anchiornis is now considered a basal troodontid which bears pennaceous, symmetrical feathers on all four limbs.	Primitive traits Wings symmetrical and rounded, probably not used for flight but instead insulation, mating displays, and gliding Long legs overall morphology similar to that of other troodontids Spine attaches to the back end of the skull rather than the base Moderately long, bony tail Derived traits Flexible wrists which are more similar to aves than other theropods Like birds and unlike troodontids, Anchiornis had arms nearly the same length as the hind legs Bore primary and secondary pennaceous symmetrical wings on both arms, legs, toes, and wrist
150–145 Ma	Genus: Archaeopteryx	Known for its mosaic of avian and theropod characteristics Archaeopteryx is both the first primitive bird in the fossil record and one of the first transitional fossils discovered.	Traditionally seen as the first proper bird, though it is not directly ancestral to modern birds. An excellent intermediate form between dinosaurs and birds. Capable of gliding, but lacking alula and keel, it could likely not sustain powered flight.	Primitive traits Slower dinosaur-like growth rate No keel Spine attaches to the back end of the skull rather than the base Forelimbs have three unfused, clawed fingers, no alula Maxilla and premaxilla bore unserrated teeth Moderately long, bony tail Derived traits Fully developed asymmetrical flight feathers Fused furcula from two joined clavicles Backward and elongated pubis similar to maniraptors, but not found in more primitive theropods
120 Ma	Genus: Confuciusornis	Found in the famous Liaoning province Confuciusornis is the first primitive bird with a pygostyle.	With its short tail and toothless beak, Confuciusornis is very modern looking compared to Archaeopteryx. The toothless beak is however a case of convergent evolution, as more advanced birds retained teeth, illustration the sometimes confusing mosaic evolution of the dinosaur-bird transition.	Primitive traits Retained unfused clawed digits, no alula Sideways-facing glenoid joint Derived traits Short tail with fused vertebrae at the end (pygostyle) Larger sternum with a low primitive keel Unlike other early birds Confuciusornis had a toothless beak
115 Ma	Genus: Eoalulavis	Primitive bird and possibly a descendant of "urvogels" like Archaeopteryx. First bird to possess an alula.		Plesiomophic traits Two unfused, functional digits remain on second and third digit Derived traits First digit bearing an alula rather than claw
93.5-75 Ma	Genus: Ichthyornis	Considered a close relative to the ancestor to modern birds	A flying bird found in several epochs in the late Cretaceous which still bore teeth, but in most respects very similar to Neornithes.	Primitive traits Numerous sharp teeth in much of the beak Derived traits Fused bones (metacarpals) II & III of the hand Rigid ribcage with a well developed carina No functional claws on the hand Short childhood with distinct adult stage.

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