(Class Aves), with over 9,000 living species, are the most
vertebrates to have evolved on Earth. Birds range from
the Jurassic to recent times. Out of the 153 extant families
of birds, 134 have fossil representatives. Fossil specimens
reveal a further 77 families of extinct birds. As new fossil
specimens are discovered, especially in China and Spain,
our knowledge of bird evolution increases (Benton, 2005,
1861, two years after the publication of Charles Darwin’s
On the Origin of Species, a fossil filling the
role of “missing
link” between reptiles and birds was discovered in the
Upper Jurassic limestones of Solnhofen, Bavaria. In fact, what
had been found was the first known bird Archaeopteryx lithographica.
The fine grained limstone was excavated to produce limestone
slabs that could be etched with acid to make lithographic plates
used to print illustrations, thus the species name lithographica
(Prothero, 2007, p. 257). The Solnhofen limestone is a fossil
shallow, saline lagoon community situated in a subtropical
climate (Selden & Nudds, 2004, p. 107). Archaeopteryx is
perhaps the most famous fossil organism from this deposit and
represents an excellent transition fossil in time and structure
now known from eight skeletons and one feather impression
(Benton, 2005, p. 257). As an intermediate, Archaeopteryx exhibits
both reptilian and bird features. The reptilian features
include: thecodont teeth, a long bony tail, a dinosaurian hand
with three clawed fingers, and a dinosaurian foot. The bird-like
characteristics include a furcula (collarbones fused into a
wishbone) and the presence of asymmetric feathers (Prothero,
1998, pp. 374-375). Archaeopteryx was a pigeon-sized
bird that lived in a subtropical environment. These birds had
running and wings formed from forelimbs. Although Archaeopteryx did
not have a keeled sternum like modern birds reconstructions
of the flight muscles suggest that it possessed the power for
takeoff and sustained flapping flight (Benton, 2005, p. 264).
Many think that Archaeopteryx hunted for insects and
could glide and climb among the trees.
analyses favor that birds are derived theropod dinosaurs,
most closely related to dromaeosaurids or deinonychosaurs (Benton,
2005, p. 261). The difficulty encountered in determining the
proper taxonomic position of possible basal Cretaceous birds
seems to only reinforce the theropod/bird connection. Rahonavis was
a raven-sized dinosaur/bird from the Upper Cretaceous of Madagascar
that had a reversed hallux (backwards pointing first
digit) and papillae on the ulna for the insertion of wing feathers.
It still retained a long tail like Archaeopteryx and
possessed an enlarged sickle claw on the second toe like the
Velociraptor. Jeholornis from the Lower Cretaceous
of China is a turkey-sized bird that possessed a tail with
feathers arranged in
a fan. It had broad wings with asymmetrical wing feathers and
the structure of the hand was more advanced than Archaeopteryx.
The type specimen of Jeholornis has seeds of the conifer Carpolithus preserved
in its crop. Rahonavis and Jeholornis represent
the most basal Cretaceous birds.
a primitive crow-sized bird from the Early Cretaceous of
China. The genus was named for the Chinese philosopher
Confusius. Confuciusornithids may be the first birds to
have a toothless beak. Confuciusornis had
a slight keel and a more flexible wrist than Archaeopteryx.
The tail was modified with the caudal vertebrae fused forming
The wing retained the three long fingers with claws like those
order Enantiornithes represent the most
diverse bird clade of the Cretaceous. These primitive birds
and ranged form sparrow size to birds with wingspans of 1.5
meters. Enantiornithines were more advanced than Archaeopteryx and Confuciusornis but
more primitive than modern birds. Most birds in this clade
had teeth and retained
fingers on the hand. Sinornis of China was a sparrow-sized
bird with a larger ossified sternum and a pygostyle tailbone.
Sinornis was capable of sustained flight as it hunted
for insects. Sinornis had a toothed beak and retained
the three-clawed fingers
on its wing. Sinornis possessed a wrist joint that
allowed it to fold the wings against its body and an opposite
toe for perching. Enantiornthines went extinct at the end
of the Cretaceous.
second major clad of Mesozoic birds was the Ornithurines.
Ornithurines are a sister taxa to the radiation that gave rise
to the modern birds. Members of the order Hesperornithiformes
were strong swimming predatory birds. These birds were
themselves through the water by kicking their feet. Hesperornithiformes
had teeth lining their jaws, which helped secure the fish they
captured. Coprolites of these organisms show their diet consisted
of sea fish. Hesperornis and Baptornis are
found in the Upper Cretaceous Niobrara Chalk Formation of Kansas,
USA. Members of the order Ichthyornithiformes
were strong fliers that also fed on fish. Ichthyornis of
the Niobrara Chalk Formation of Kansas was a gull-sized bird.
modern birds Ichthyornis had a deeply keeled ossified
sternum, unlike modern birds it had jaws lined with teeth.
It is thought
that Ichthyornis caught fishes in the Great Interior
Seaway by diving into the water from the wing (Benson, 2005,
palaeognaths (Division Palaeognathae) are represented today
by the small tinamous birds of South and Cental America
and the ratites. Ratites are flightless birds including
the ostriches of Africa, rheas of South America, emus of
Australia, Cassowaries of New Guinea, and the kiwis of
New Zealand. All of these birds evolved from a flying ancestor.
The tinamous birds are the only living palaeognath representatives
that retain flight. Some
interesting extinct forms of the ratites, like the elephant
bird of Madagascar, and the various moas
of New Zealand are thought to have gone extinct due to human
majority of living birds are neognaths (Division Neognathae).
Most modern orders make their first appearance during
and swans date back to the Eocene. One unusual flightless
to ducks and game birds is the Diatryma, a flightless
ratite-like bird that may have been a flesh eater. Diatryma lived
in North American and Europe during the Palaeocene and Eocene.
and rails date back to the Eocene. Pelicans and their close
relatives date from the Eocene. Gulls and auks are known
from the Eocene. Flamingos are known from the Eocene, while
oldest grebe is Miocene in age. Falcons, eagles, and vultures
date back to the Eocene. Albatrosses are known from the Miocene,
while penguins date to the Eocene. Hummingbirds date to the
Pleistocene. Pigeons and doves are known from the Eocene.
The dodo bird is a famous pigeon from the island of Mauritius
sailors hunted to extinction during the 1600’s. Parrots
date back to the Eocene. Woodpeckers and toucans date to
the Miocene. Finally, songbirds make their first appearance
Fossil evidence suggests that modern birds underwent two major
adaptive radiations. The first, occurred during the early Paleogene,
especially in the
Eocene. Songbirds represent the second major radiation of
modern birds, which occurred during the Miocene (Benson, 2005,
Science Olympiad Fossil Event
2016 Science Olympiad Fossil List includes the genus Archaeopteryx under
the class Aves (Birds).