Encyclopedia of Evolution.pdf - Online Reading Center

Because the DNA of many archaebacteria is associated
with histone proteins, just like the DNA of eukaryotes, some
evolutionary scientists have suggested that the eukaryotic
nucleus originated from an archaebacterium (see eukaryotes,
evolution of). In this scenario, an archaebacterium
invaded a eubacterium and formed a mutually beneficial
association with it. The archaebacterium acquired much of
the DNA of the eubacterial host and became its nucleus.
This would have been the first step in a series of mutually
beneficial bacterial invasions that has produced the modern
eukaryotic cells of plants and animals (see symbiogenesis).
If this is true, then archaebacteria are not an evolutionary
sideshow or mere leftover from the distant past but are
the partial ancestors of all complex life on Earth, including
humans.
Further Reading
Museum of Paleontology, University of California, Berkeley. “Introduction
to the Archaea.” Available online. URL: http://www.ucmp.
berkeley.edu/archaea/archaea.html. Accessed March 22, 2005.
Archaeopteryx Archaeopteryx is the earliest undisputed
bird fossil, intermediate between reptiles and modern birds.
Archaeopteryx
This is one of the original Archaeopteryx fossils found in the limestone deposits of Solnhofen, in what is now Germany. The skeleton is very reptilian; the
impressions of feathers are clearly visible. (Courtesy of James L. Amos/Photo Researchers, Inc.)
When it was first discovered, Archaeopteryx looked like
just another skeleton of a coelurosaurian dinosaur, until the discoverers
saw the imprint of feathers in the rock. The discovery
of the first fossil of Archaeopteryx lithographica by paleontologist
Hermann von Mayer in a limestone quarry at Solnhofen,
Bavaria, in 1861 could not have been more auspicious. Like the
discovery of the first Neandertal skull, it was just in time for
Charles Darwin to use it in some editions of his famous book
(see Darwin, Charles; origin of species [book]). Named
after the Greek for “ancient wing,” Archaeopteryx was just the
kind of intermediate species that Darwin needed as evidence
that entire modern groups of organisms (such as birds) had
come into existence by evolution. One hundred and fifty million
years ago, a bird fell into a shallow anaerobic pool and died.
The anaerobic conditions inhibited decomposition, and microscopic
marine organisms produced lime sediments, resulting in
a vast number of fossils preserved in the limestone of what is
today Solnhofen. The bones had transformed into stone; the
feathers had decomposed but left their detailed imprint (see
photo above) (see fossils and fossilization). Six other fossilized
Archaeopteryx individuals have been found in the same
quarry. Some authorities recognize some of the specimens as a
different species, Archaeoptemx bavarica.