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Re: New dinosaur diversity articles
Tim Donovan (firstname.lastname@example.org) wrote:
<The point is that diversity did decline prior to the end, indicating that
other factors* were at work causing extinction.>
Tim has yet to prove this, or even show it's likely, without using a
small set of a lineage (only lambeosaurs? why not use hadrosaurs? Do not
climate shifts cause population shifts?). Say the biota of a forest JUST
destroyed by a family of elephants over a 20 year period suffers from
attrition and must adapt, move, or die. Their disappearance "proves"
extinction how? Tim cannot prove his gradual reduction in species without
using a small group of dinosaurs from ONE continent, as I have yet to see
a globally correllated example from him.
<Btw, I don't think the hadrosaurines and chasmosaurines etc eclipsed the
other taxa, they just proved less vulnerable in the face of something
Huh, interesting. Which scapegoat? This does not show, however, how
hadrosaurines were not MORE diverse than lambeosaurines at the time,
demonstrating almost equivalent diversity given what could be a selection
bias (there are more species of dinosaur described from the Late Campanian
of southern Alberta than the entirety of Late Campanian Montana, wow)
<Someone suggested the edmontosaurs/anatotitan "mastered" the lambeosaurs
by the late Maastrichtian.>
Yah, me. Why? Because there are fewer lambeosaurs and more hadrosaurines
in the Maastrichtian, and to use Tim's favored model for pterosaur
extinction, they were "outcompeted" by their longer-jawed, larger, more
efficient hadrosaurine relatives. I do not think they were, as I think
Marjanovic used the flavor of competition, I simply attempted to explain
how more hadrosaurines are known from Maastrichtian NA than
lambeosaurines, as a refutation that diversity was shrinking. Rather, one
group is replaced by another in the selected area of investrigation (there
were plenty of Maastrichtian lambeosaurs in Asia, and likely in Europe as
well, but it appears fewer hadrosaurines given the brevity in the Nemegt
and the materials further north and west). Read work by Lehman on the
subject; his chapter in _Mesozoic Vertebrate Life_ shows an extensive
array of papers on the subject, as the chapter itself attempts to
summarize. One of the major problems with Tim's theory is that to support
it, one has to start ignoring data.
<I doubt it. Edmontosaurus already existed in the late Campanian,
apparently in near coastal environments which excluded lambeosaurs.
Farther inland, Hypacrosaurus was still abundant about 3 million years
later. Ankylosaurids and nodosaurs also appear ecologically separated.>
This proves very little. Prior occurance of hadrosaurines to
lambeosaurine diminishment is simply a factor of lineages of sister-taxa
occupying the same strata and altering geography together. Take the
changing climate: in the Maastrichtian, we see the climate shift from the
"bayou"-like wetlands into a drier, less-bushy Okavango-like floodplain.
Suddenly, animals used to browsing must make way for grazers. Smaller size
for travelling dense vegetation at times makes way for huge size for open
areas, high-browsing shifts to low-browsing and the Late Cretaceous
version of grazing: fern-munching. Even a Savuti lion still pauses at a
bull elephant, so a *Triceratops* would make a formidible foe to even an
animal 1.5 times bigger than it (I am, of course, speaking of
So as climate shifts, we will SEE animals change, populations shift, and
new animals take precedence over the old. Using the old population for the
underlying strata to prove diversity issues for the whole ignores the rest
of the biome.
Jaime A. Headden
Little steps are often the hardest to take. We are too used to making leaps
in the face of adversity, that a simple skip is so hard to do. We should all
learn to walk soft, walk small, see the world around us rather than zoom by it.
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
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