Alberta is of course, one of the most drilled places on earth. For
that reason we have a detailed mapping of the original landforms.
Thus it is possible to make these interpretations.
The apparent diversity strongly reminds me of general bird diversity
in a plant species rich environment. That the herbivores did the
same is a little unexpected only so much as we see little of that
among the present population of herbivores. This may merely reflect
the comparable youth of the mammalian lineage.
In any event it is certainly instructive regarding the march of the
evolutionary imperative to penetrate of optimize prospective niches.
Many species of
ancient Canada’s plant-eating dinosaurs survived because they
‘divvied up’ veggies
Randy Boswell,
Postmedia News | 13/07/1
Two Canadian
scientists who examined the fossilized skulls of 82 individual
dinosaurs from ancient Alberta have gathered powerful new evidence
about how such a startling variety of enormous, plant-eating species
were able to survive in the same geographically restricted habitat
about 75 million years ago.
It turns out that
evolution produced a respectful sharing of limited resources among
the huge vegetarian beasts that lived together there during the Late
Cretaceous era, a time when much of today’s Western Canada was part
of a narrow, swampy island continent — Laramidia — separated from
the rest of the future Canada by a vast inland sea.
In a paper published
Wednesday in the journal PLOS ONE, Canadian Museum of Nature and
University of Calgary paleontologist Jordan Mallon and fellow U of C
scientist Jason Anderson argue that subtle differences in the skulls
of 16 species of big herbivorous dinosaurs show that they must have
survived by “niche partitioning” — a delicate ecological
balance in which each animal specialized in munching plants of
certain types and heights to avoid competing directly with others for
food.
“At any one time you
can get six, seven or even eight of these giant herbivore species
living together at once,” Mallon told Postmedia News. “The
western continent, where all of these animals inhabited, was
extremely narrow, and there just wasn’t very much space for them to
live. So how do you support all that diversity, which we know
existed, on such a small land mass?”
Paleontologists, he
said, have been puzzling over the issue for a long time because there
wouldn’t seem to have been enough plant resources to feed the large
populations and multiple species of dinosaurs — including several
horned, armoured and duck-billed varieties — known to exist at the
same time and place.
“It’s a mystery
that keeps rearing its head in the last 10 or 20 years,” added
Mallon. “How do you support that many species? There’s nowhere on
Earth today where we can see that many large herbivores living at the
same time, coexisting.”
There were several
possibilities, he said, including a theory that vegetation growth was
so phenomenal in the dinosaur age that food supplies were essentially
“unlimited.” Another theory suggested that the metabolism rates
of the so-called “mega-herbivores” might have been so low that
relatively little plant material was required to sustain their
massive bodies.
But Mallon and
Anderson reached a different conclusion based on skull differences
among species that cohabited the Alberta portion of Laramidia between
76.5 million and 75 million years ago.
“We found pretty
good evidence for niche partitioning in these animals,” Mallon
said, noting that traits such as jaw structure, tooth shape, beak
width and other characteristics point to significant specialization
in terms of what types of plants different dinosaurs would have been
eating, how low they were from the ground and the quality of
nutrients they provided.
Analyzing the
dinosaurs’ skull morphology allowed the researchers to “tease
apart” details about the likely diets of different species and
determine that they were probably “coexisting by specializing on
different resources, divvying up the resources that way.”
The telltale
differences, he said, could be seen even among different species
within the same sub-groups of dinosaurs.
He compared the
phenomenon to how the wide-muzzled white rhinoceros and its
narrow-snouted cousin, the black rhino, feed on different types of
plants in the same African ranges, thus avoiding a dietary overlap
that would otherwise have them competing for the same limited,
life-sustaining resources.
Mallon, who examined
dinosaur fossils among research holdings in Ottawa, Toronto, Alberta,
Chicago, New York and Britain, also said the study “really
highlights the importance of fossil collections at museums” —
particularly the maintenance of specimens stored on backroom shelves
rather than on public display.
“Any one institution
wouldn’t have done,” he noted, describing the challenge faced in
amassing enough data to draw reliable conclusions. “I had to go
everywhere.
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