Dinosaurs to Birds: A Few Key Fossils

Creationists routinely attack the idea that dinosaurs evolved into birds, generally with the typical accusation that there is no fossil evidence for this hypothesis. In fact, abundant evidence for it exists in the fossil record.

Juravenator

Juravenator was a genus of small coelurosaurian theropod dinosaurs, known from a single specimen, j. starki.

Fossil of j. starki, photographed Aug 2010 at Jura Museum Eichstaett

This one specimen was a juvenile. Juravenator appears to have been a small bipedal predator. The genus has undifferentiated hind limbs that display no climbing ability, the spine attaches to the back end of the skull, not the base, and it has a long and bony tail. The genus is evolutionarily important because proto-feathers cover parts of the body for insulation.

Anchiornis

Anchiornis is a genus of small, winged paravian dinosaurs, and it has only one known specimen, once again.

Fossil specimen of A. huxleyi at the Beijing Museum of Natural History, photographed by Jonathan Chen

Anchiornis is considered a basal troodontid. Troodontidae is a family of bird-like therapod dinosaurs. This particular genus has symmetrical feathers on all four limbs. The wings don’t appear to be suited for flight, but would serve well for insulation, mating displays, and any gliding. Once again the spine attaches to the skull’s back end, and it has a similar tail to Juravenator.

Archaeopteryx

This is probably the best-known intermediate fossil. It was also one of the earliest discovered.

Archaeopteryx lithographica, displayed at the Museum für Naturkunde in Berlin, photo by
H. Raab

Few fossils have been better preserved in all of history than this one. It is probably the best intermediate form between dinosaurs and birds. It was certainly capable of gliding, but it lacked alula and keel and so could not have sustained powered flight. (By the way, we’d expect birds to have first evolved as gliders before powered fliers.) Once again the spine attaches to the skull’s back end, and it has a similar tail to the other two genuses I mentioned. The forelimbs seem to have three unfused, clawed fingers. The flight feathers are fully developed and asymmetrical. The furcula, or wishbones, are fused.

Confuciusornis

This fossil was found in the Liaoning province and is the first primitive bird with a pygostyle.

Confuciusornis sanctus, Naturhistorisches Museum Wien, photo by Gyik Toma

The fossil has a short tail and toothless beak. The beak is however a case of a case of convergent evolution because more advanced birds retained their teeth. The bird had unfused clawed digits and no alula. The pygostyle is basically a short tail with fused vertebrae at the end. The sternum was large and it had a primitive keel.

Ichthyornis

The bird is a close relative to the ancestor of modern birds. It has many sharp teeth in the beak.

Ichthyornis yale

The bird is extremely similar to modern birds except that it had the teeth. It had no functional claws on its hand.

The evolution of dinosaurs into birds, then, is well-documented, and these are just a handful of the relevant fossils. Evolution is truly amazing. It’s a shame that nearly 15% of Americans still deny it.

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