Travel Reference
In-Depth Information
threads of insight afforded by the insular Canadian fossils with those from
the rest of the world. Perhaps better than anyone on earth, he was capable,
using fossils, of drawing the fine lines of time that relate the various geo-
graphic regions of this far-flung earth. He had trekked over the entire region
of Vancouver Island. Yet Sucia still remained an enigma. Some of its fossils
were unique in the world, or so it seemed. It was still not certain how the
shale of Sucia correlated not only with other Cretaceous-aged rocks in
Europe but even with rocks in California and some regions of Vancouver
Island.
The best fossils for determining ages for the latter parts of the Creta-
ceous are the curious, straight-shelled ammonites called
Baculites,
forms
found abundantly in the Vancouver Island region. Although the majority of
ammonites during their long, 360-million-year reign on earth were coiled
like a nautilus shell, some, in the Cretaceous, tried the new tack of uncoiling
their shells. The
Baculites
were one of the more extreme manifestations of
this uncoiling. Their shells were long tubes, and some became as large as a
human. Most, however, were small. Nearly all of the
Baculites
showed two
distinctive characteristics that made them especially useful for dating rocks.
First, they were extraordinarily abundant. On Sucia there are easily ten
times as many
Baculites
ammonites as any other kind, and this is the pattern
reported around the world. Second, for reasons still entirely unknown, the
Baculites
lineage showed very high rates of evolution and extinction. Each of
their species lasted on earth but a short time—often a million years or less.
Thus they are among the best of all time markers, tor their presence in sedi-
mentary strata pinpoints very short intervals of time. They can allow precise
correlation between distinct rock assemblages.
The western interior of the United States has been subdivided into
units of a half-million years or less, on the basis of the presence of
Baculites
species. New species of
Baculites
ammonites appeared to have been forming
in the vast western interior ocean at a prodigious rate between 90 and 65
million years ago, and thanks to their amazing abundance, paleontologists
for more than a century had been able to use these fossils to subdivide the
