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The Dinosaurs Weren't Alone
Dinosaurs may have ruled the earth, but they were never alone on it. A
colorful cast of characters, including pump-headed insects, gigantic amphibian
reptiles and tiny woodland mammals, coexisted with dinosaurs throughout the
Mesozoic age. Supporting this ancient ecosystem was an equally fascinating
array of plants. "If we want to understand the environment dinosaurs came from
and why they succeeded, we have to use all the information available to us,"
says Kevin Padian, professor of Integrative Biology at the University of
California at Berkeley. Richard Stucky of the Denver Museum of Natural History
agrees. "We want to know what dinosaurs were like, how they interacted with
one another and what kinds of communities they lived in. Studying the
environment can give us important clues." But finding and piecing together
these clues is tricky.
It is the rare living thing that become a fossil in death. The vast majority
of organisms, whether they be plants, animals or insects, simply decompose.
But sometimes, if conditions are just right, an organism can be preserved for
millions of years. Find out how some ancient organisms beat the clock—and
what role they may have played in the lives of the dinosaurs.
The first step towards fossilization for vertebrates, or animals with
backbones, is rapid burial in sediment. One scenario might be a drowned
 animal that washes downstream and lodges into a riverbank, where it quickly
becomes covered in sand or mud. The animal's soft parts, namely its flesh and
organs, rot away, while sediments surround and protect the animal's hard parts—its bones and teeth. Over time, mineral-rich water percolates through the
bone's tiny pores and, gradually, the bones absorb these minerals and turn to
stone. But this is only the beginning. For a fossil to survive through time,
the surrounding rock must withstand the forces of erosion and tectonic activity
as well.
The fossil record reveals that dinosaurs first appeared in the Triassic period,
between 250 to 213 million years ago. It also reveals that the first turtle,
the first salamander, and the first frog appeared in the Triassic, as did the
first crocodilian reptile, the phytosaur. On land, mammals also made their
debut during this period, in the form of small insect-and-seed eating critters
that scurried around the forest underbrush. Knowing the vertebrate players is
important, according to Kevin Padian, professor of Integrative Biology at the
University of California at Berkeley, because it gives insight into how
 dinosaurs may have gotten their first toehold in their climb to supremacy.
"It's pretty clear that the first dinosaurs weren't directly competing with
other animals for food. Phytosaurs were in the water eating mainly fish and
there were reptilian herbivores on land, like some of the aetosaurs. But early
dinosaurs were small bipedal carnivores—meaning they had their hands free
and ate meat. So they did very well."
Figuring out the relationship between plants and dinosaurs can be revealing,
but is difficult to do. The problem is not for a lack of specimens. Plant
fossils easily outnumber bone fossils and they come in many more forms. The
 billions and billions of tons of coal in the world are ancient plant remains,
as are compressed leaves, leaf imprints, pollen grains and pieces of fossilized
wood. The difficulty is that bone fossils and plant fossils are rarely found
at the same site. "It has to do with the chemical conditions that favor
preservation of bones as opposed to those that favor the preservation of plant
matter," explains Scott Wing, Curator in the Department of Paleobiology at the
Smithsonian's Museum of Natural History. "Plant matter is preserved best in an
acidic environment, like in a peat bog. Whereas bones, having a lot of calcium
in them, are essentially demineralized by acidic conditions. If you drop a
bone in a bog, it gets rubbery, loses its calcium and it's difficult for it to
be preserved. Conversely, if you take a piece of plant and drop it in a nice
alkaline soil where a bone would likely be preserved, the plant is going to be
degraded, not only by the chemical conditions, but also by all organisms that
live in the soil."
Despite this wrinkle, plant groups of the Mesozoic are well known. The major
players were; conifers, a tree similar to today's Norfolk Island Pines;
 cycads, a palm-like tree with leathery leaves and great big cones that still
grow in some tropical areas; bennettitales, a wholly extinct group of plants
that had leaves like cycads, but were more closely related to flowering plants;
and ferns, which were more varied and abundant than they are today. Flowering
plants, or angiosperms, first appeared near the end of the Mesozoic, around 144
million years ago, and quickly took hold, constituting nine-tenths of all known
plant species by the end of the period. Grass, so common today, was completely
non-existent.
If plant fossils and dinosaur fossils tend to avoid one another, how do
paleontologist answer questions like, "What did herbivorous dinosaurs eat?"
"You use some manner of correlation," explains Peter Dodson, Professor of
Anatomy in Geology, at the University of Pennsylvania. "Some of the large,
important fossil deposits of the American and Canadian west are geographically
quite widespread. So you find bones and skeletons in one place and maybe a few
miles away you find rich plant deposits. You build up a picture from all the
material that's available from different geographical localities." Richard
Stucky, Curator of Paleontology at the Denver Museum of Natural History,
agrees. "Oftentimes you get sites with specimens above and below the time
period you're looking at and you can extrapolate that a particular critter or
plant lived through the period you're interested in."
Another source of information on dinosaur diets, albeit a rare one, are
coprolites, or fossilized dung. "Coprolites give information about what one
 particular individual was eating, but you don't usually know what genus or even
what species was producing the coprolite unless you find it inside a dinosaur
skeleton," explains Scott Wing. "In general, it's a pretty speculative
endeavor. You've got your plant fossils and you've got your dinosaur fossils—and they're often not from the same places or even from the same times. We
can track changes in plants through time and we can track changes in dinosaurs
through time, but we don't have any very good way of establishing cause and
effect. So the real answer to 'What did dinosaurs eat?' is that, most of the
time, we don't know."
Insects are perhaps the least understood organisms of the Mesozoic. Conrad
Labandiera, a research scientist specializing in fossil insects at the National
Museum of Natural History, explains that this is due, in part, to their sheer
number. "Estimates of modern insect species range from about 5 million to 30
million. For vertebrates, including fish, it's about 80 or 90 thousand. One
of the consequences of there being so many more insects living today is that
their proportional know-ability in the past is less. The other issue is that
there are so few people studying them." Aside from a colleague in Canada and a
small cadre of scientists in Russia, Labandeira is alone in his work.
Ideal conditions for preserving insects are different from those that preserve
plants or bones. An insect's exoskeleton is made out of a substance called
chitin. "You know when you step on a cockroach or beetle? That snap is
chitin," explains Labandiera. "And chitin is best preserved when it's entombed
in very fine-grained sediments." Typically, insects destined for fossilization
were ones that got washed into a stagnant body of water like a lake or pond,
where they quickly became buried. Mummification in tree resin or amber,
popularized in Steven Spielberg's film "Jurassic Park," is a less common method
of preservation and only appears in the fossil record after 125 million years
ago. "I don't know why that is," says Labandiera. "One possibility is that
wood boring insects really didn't savage trees until then, but it's really a
mystery."
The story of ancient insects really begins in the period preceding dinosaurs—in the Paleozoic Age, between 590 to 248 million years ago. Insects with
piercing and sucking mouth parts, primitive grasshopper-like bugs and giant
dragon flies flourished, as did the primitive ancestors of modern insects. But
an episode at the end of the Paleozoic Age called the Permian Extinction wiped
out most of these insects, not to mention a number of other life forms. The
insects that survived into the Mesozoic Age are basically the insects that we
know today. "If you were plopped down into the Cretaceous by a time machine,
and you had a basic entomology textbook with the keys to the families, you
probably wouldn't have much trouble finding your way around," states
Labandeira. "There'd be a few things you'd have trouble with—a few extinct
groups like the Kalligrafmatidae that had butterfly-like wings—or the
flea-sized Saurophthirius which had small antennae and a pump on top if its
head that inflated like a balloon to create negative suction to pull up, we
think, blood." Labandeira is quick to point out that these creatures may still
exist today somewhere in the tropics, but because of our poor knowledge of
insects, they may have gone undetected.
Despite their relatively small size, there is evidence that insects played a
very big role in the lives of dinosaurs. Insects may have competed directly
with herbivorous dinosaurs for food. "That's certainly been an important
question in modern ecosystems," says Labandeira. "In grasslands, vertebrates
probably outperform insects in terms of consumption of plant material—but in
all other ecosystems, it looks like it's the other way around." Insects may
have played a role in recycling dinosaur waste. A researcher named Karen Chin
recently looked at cross-sections of dinosaur coprolites and found structures
within that indicated the presence of scarab beetles that were probably feeding
on the dung. Insect also may have been responsible for transporting diseases
like malaria and dysentery, but Labandeira admits this
possibility is purely speculative.
Photos (1-3), (5), Painting (1): Photo Archives, Denver Museum of Natural History
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