The oldest known prehistoric birds were found in lithographic stone of Upper Jurassic age. _Archaeopterix_ was discovered in 1861 at Solenhofen, Germany. Sixteen years later a similar bird in a better state of preservation was found in Bavaria. The latter was named _Archaeornis_. These Jurassic fossils are regarded as true birds by some authorities, while others believe them to be more nearly related to the reptiles, the opinions being based on careful studies of the skulls and other skeletal features. Both birds had teeth of reptilian character, and it is evident that there was no beak, for the jaws were covered with scaly skin. The bony construction of the long tail would suggest lizards rather than birds, were it not for the presence of feathers which were attached at each side. Head, neck, and parts of the body were covered with scales. Wings were well provided with stout feathers but the skeletal framework indicates that the birds were gliders rather than true flyers. Claws on the wings served like fingers to aid in climbing among the branches of trees, a practice which is occasionally noted among the young of living birds. In adult birds of today, however, the claw-like appendages of the fore limbs are greatly reduced and of little service. The next fossil birds of importance have been found in Cretaceous rocks of Kansas, both of them fishers of the seas instead of forest inhabitants. _Ichthyornis_ was a small bird, standing about eight inches in height, a powerful flyer with reptilian jaws and teeth. _Hesperornis_ was built for diving and swimming, like the loon, but was somewhat larger and provided with teeth. Its wings were too poorly developed to be of use in flying. Toothed birds became extinct with the close of Cretaceous time, and the ancestors of modern types were in existence before the Age of Mammals, but fossil remains are few and poorly preserved. Large ostrich-like birds, however, are known to have lived in North America during the Eocene period. One of these, named _Diatryma_, stands nearly seven feet tall in the reconstructed skeleton. Its legs are heavy, wings greatly reduced, beak massive. In its relation to modern birds it is possibly nearer to the cranes than the ostriches. Flightless birds of large size are known from many parts of the world and seem to have been prominent throughout the Cenozoic era, as they are today in the southern hemisphere. _Aepyornis_ lived in Madagascar during the Pleistocene period and may have become extinct quite recently. Its eggs are the largest known among fossils, several times the size of an ostrich egg. Also in this period the moas were living in New Zealand where their remains are still abundant. One of the largest, known as _Dinornis_, had about the same form as _Diatryma_ but the neck was longer, head and beak smaller, legs better fitted for running, height about eleven feet.