Birds are warm-blooded to obtain the maximum metabolic efficiency
needed for sustained flight but have retained the reptilian mode of reproduc-
tion by laying eggs. The bones of some Cretaceous birds show growth rings,
a feature common among cold-blooded reptiles.This suggests that early birds
might not have yet developed fully warm-blooded bodies. Birds’ ability to
maintain high body temperatures has sparked a controversy over whether
some dinosaur species with similar skeletons were warm-blooded as well.
Archaeopteryx(Fig. 146), from Greek meaning “ancient wing,” was the ear-
liest known fossil bird. It was about the size of a modern pigeon and appeared to
be a species in transition between reptiles and true birds. Unlike modern birds, it
lacked a keeled sternum for the attachment of flight muscles.Archaeopteryxwas
first thought to be a small dinosaur until fossils clearly showing impressions of
feathers were found in a unique limestone formation in Bavaria, Germany, in
- The discovery sparked a long-standing controversy. Prominent 19th-cen-
tury geologists claimed Archaeopteryxwas a hoax and that the feather impressions
were simply etched into the rock containing the fossil. However, an Archaeopteryx
fossil discov ered in 1950 from the same Bavarian formation produced a well-pre-
served specimen that clearly showed feather impressions.
Although Archaeopteryxhad many accoutrements necessary for flight, it
was likely a poor flyer. It might have flown only short distances, similar to
today’s domesticated birds. It probably achieved flight by running along the
ground with its wings outstretched and glided for a brief moment or leaped
from the ground while flapping its wings to catch an insect flying by. Their
Figure 146
Archaeopteryxis a
possible link between
reptiles and birds.JURASSIC BIRDS