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Food is an important part of any animal’s lifestyle, and also life, but when it comes
to extinct creatures like dinosaurs, it can be tough to know for sure what they actually
ate.
And we’d like to know, because what an animal eats tells you a lot about it: from how it
hunts, to what’s around for it to snack on, to how that animal fits into a larger
food web.
Over the decades, paleontologists have developed some handy scientific tricks for inferring
dino diets, such as analyzing the shape and chemistry of their teeth.
But every now and then, the fossil record gives us a gift: a fossilized meal -- sometimes
still inside the gut of a dinosaur skeleton -- that tells us exactly what that dino had
for dinner.
Here are five dinosaur dinners and what they tell us about how these animals lived.
One of the best places in the world for studying ancient dinosaur lifestyles is northeastern
China.
The region is famous for an array of fossil sites preserving past life from about 120
to 130 million years ago, corresponding to the Early Cretaceous Period.
Collectively, these ancient ecosystems are called the Jehol Biota, and they’ve produced
some truly exquisite dinosaur remains, including many with their last meals fossilized inside
their body.
A study published in 2012 looked into the guts of one of the largest dinosaurs in the
Jehol Biota, a two-meter-long predator named Sinocalliopteryx.
Amidst the bones of one Sinocalliopteryx specimen, they found the remains of not one, but three
of its meals: two skeletons of a small bird known as Confuciusornis, and a couple of other
bones from an unidentified small plant-eating dinosaur.
Now, the first challenge in studying dino dinners is figuring out if they are actually
preserved meals or just an accident of fossilization.
After all, it could be that these smaller animals were fossilized under or over the
predator, giving the false appearance of being in its stomach.
But in this case, not only do the bones appear to be encased within the predator’s body
cavity, but they also show signs of damage from stomach acid -- they were being partially
digested before they got fossilized.
But they were not all digested equally -- the bones of the small plant-eater were much more
degraded than the bird skeletons, suggesting this predator ate the birds more recently,
and shortly before its death.
And that leads us to another challenging question: how to tell if a dino dinner was the result
of hunting or of scavenging.
This can be very difficult, but in this case, scientists think the two birds are a clue.
Both bird skeletons are pretty equally digested, so they were probably eaten in quick succession.
While it’s possible the predator came upon two carcasses of the same species one right
after the other, the researchers think it’s more likely that it was specifically pursuing
and capturing a prefered type of prey.
And if they’re right, then Sinocalliopteryx must have been a skilled hunter -- it’s
no easy feat to catch a bird.
Our next dinosaur dinner also comes from the Jehol Biota, this time found inside the body
of a small predatory dinosaur named Microraptor.
Microraptor is famous for having feathery wings on both its arms and legs that allowed
it to glide through the air.
But it’s also famous for stomach contents.
Several specimens of Microraptor have been found with meals inside them, revealing a
diverse diet of fish, mammals, and small birds.
But one particularly amazing find was reported in a 2019 study that identified an ancient
lizard inside a Microraptor gut.
The lizard skeleton was not only well-preserved, but also articulated, meaning the bones hadn’t
become separated -- they were pretty much still in the shape of a lizard.
This allowed researchers to notice the position of the lizard, with its tail pointing back
toward the dinosaur’s throat, and its head aimed at… well, the end of the dinosaur’s
digestive tract.
Which makes it look like Microraptor swallowed this lizard whole and head-first.
That’s a strategy we still see today in living birds and reptiles, over a hundred
million years later.
And with such a well-preserved skeleton, the researchers were able to identify the lizard
as a new species.
Small animals can be tough to find in the fossil record, and if this one hadn’t been
conveniently tucked in the guts of the dinosaur, we may never have known this species existed.
The researchers named the lizard Indrasaurus, after the Hindu deity Indra, who was swallowed
by a dragon.
With so many fossilized meals in the Jehol Biota, paleontologists have the very rare
opportunity to understand the ancient food web.
Across the Jehol fossil sites, several small birds have been found fossilized with plant
remains in their guts.
And similar small birds -- along with lizards and fish -- have been seen in the stomachs
of dinosaurs like Microraptor.
And just to bring things back around, at the top of the food web were big predators like
Sinocalliopteryx, with bellies full of other dinosaurs.
Our next dinosaur dinner comes from the Late Triassic Period of what is now North America,
over 200 million years ago, the early days of the Age of Dinosaurs.
It’s the tale of a dinosaur falsely accused of cannibalism.
The dinosaur in question is a carnivore named Coelophysis, similar in size to our friend
Sinocalliopteryx from China.
Coelophysis fossils are found by the hundreds at a fossil site near Ghost Ranch, New Mexico,
revealing a lot about these early dinosaurs’ anatomy, growth, and diets.
But Coelophysis became infamous during the 1980s and 90s when two skeletons were found
to have small bones preserved in their guts… bones that were originally identified as baby
Coelophysis.
Just like that, this species became the poster child for dinosaur cannibalism.
This reputation lasted almost twenty years before another study finally cleared its name.
The story goes that a young paleontologist, a grad student at the time, was studying fossils
at New York’s Museum of Natural History when he saw a replica in a subway station
of one of the famous cannibal specimens of Coelophysis.
But looking closely, he didn’t think those “baby Coelophysis bones” looked very much
like baby Coelophysis.
He got permission to examine the original specimen in the New York museum, and a few
years later, in 2006, he and his colleagues published a re-analysis of the two accused
cannibals.
In one specimen, what had been identified as gut contents weren’t inside the guts
at all, just buried alongside the dinosaur -- remember, we mentioned that was a risk!
And in the other specimen, the bones were in the gut, surrounded by the partially intact
rib cage, but they didn’t belong to baby dinosaurs of any species.
Rather, they were small cousins of crocodiles -- much less sensational.
So there you have it - Coelophysis wasn’t a cannibal - or maybe it was, but we don’t
have any proof of it.
But that’s not to say no dinosaurs ever munched on members of their own species.
Cannibalism isn’t all that rare in nature.
Some living dinosaurs -- that is to say, birds -- do it today.
But in the fossil record, evidence of dinosaur cannibalism is very rare.
One dinosaur that is considered a cannibal is the large predator Majungasaurus from Madagascar.
In this case, the evidence comes not from stomach remains, but from Majungasaurus bite
marks left on Majungasaurus bones -- comparable to the bite marks predators leave on their
prey.
It might be that dinosaur cannibalism was truly rare, compared to other animals.
Or maybe there’s more evidence waiting to be found...
Speaking of unexpected dinosaur dinners, there is another North American fossil find that
reveals that not all plant eaters ate... all plants.
Hadrosaurs are herbivorous dinosaurs, as we’ve known for a long time from their teeth, skulls,
and even gut contents.
But a discovery published in 2017 broke this trend -- not with fossilized stomach contents,
but with fossilized poop.
Coprolites are the petrified remains of ancient turds, and this study focused on ten impressively-sized
specimens from Utah.
Based on their size and location, researchers suspect this dung was dropped by a hadrosaur.
As expected, the poops were full of plants, but there were some extra ingredients.
The plant material was mostly wood from coniferous trees or shrubs, but with a bunch of small,
hard objects mixed in.
These turned out to be pieces of crustacean shells.
Now, it’s not unusual to find invertebrates digging around in poop after it’s already
been pooped.
And these coprolites did contain evidence of dung beetles and snails that crawled inside
after the fact.
But the crustacean shells were different -- they had been crushed to bits by the dinosaur’s
digestive system.
This raises the question of why plant-eating dinosaurs were dining on animals.
And the answer seems to be that these critters were living down where the dinos wanted to
chow.
Close examination of the wood in the coprolites showed damage caused by white rot fungus,
the kind that decompose logs.
This rot must have attacked the wood before it was eaten, which means these dinosaurs
were chomping on rotten logs -- and in the process, they gobbled up the critters inside.
But this might not have been an accident.
Some herbivores today -- like cows, sheep and deer -- have been known to snack on baby
birds or other animals when their diets are running low on essential nutrients.
So these plant-eating hadrosaurs might have been dining on rotting logs to get a combined
dose of plant and animal nutrition.
As we’ve seen, sometimes dinosaurs make meals out of unexpected foods, but other times
they will eat things that are definitely not food.
A lot of dinosaurs are found with stomachs full of rocks.
For example, Caudipteryx is a small feathery dinosaur from China that is known from several
well-preserved skeletons with piles of rocks in their guts.
Similar rocky remains are also found frequently in the ostrich-like ornithomimids and the
parrot-faced Psittacosaurus.
These stomach rocks are so common that they have a name: gastroliths, which means, well,
stomach rocks.
And we see them in living dinosaurs all the time.
Many plant-eating birds intentionally swallow small stones, which then sit in a special
section of their digestive tract called the gizzard.
There, muscle contractions continuously move the stones around to act as a grinding mill
to break up tough plant material and help with digestion.
Finding so many stones in dinosaur guts suggests this behavior goes back many millions of years.
But just like with any stomach contents, it can be difficult to tell a pile of stomach
stones from a regular ol’ heap of rocks.
So a 2007 study looked for identifiable patterns in the gastroliths of modern-day birds.
They found that gastroliths of modern birds tend to be highly worn down, or abraded, from
the grinding action in the gizzard.
They’re also usually composed of hard minerals like quartz, and they typically come in piles
weighing about one percent the body mass of the bird.
Those same trends held for suspected dinosaur gastroliths, suggesting they were the real
McCoy.
But not all dinosaurs seem to have used gastroliths.
That same study also examined supposed gastrolith piles in the remains of several sauropod dinosaurs
-- the long-necked, long-tailed titans of the dinosaur world.
In those cases, even though there were clearly stones in their guts, the stones weren’t
abraded like true gastroliths, and the piles were too small to have done much plant-grinding.
It might be that these dinosaurs swallowed small rocks by accident while vacuuming up
as much vegetation as they could.
Or maybe they were eating rocks as dietary supplements, like the crustacean-eating dinosaurs
we discussed earlier.
Modern birds are also known to swallow rocks to get a healthy dose of essential minerals
like calcium.
The fossil record is fickle, and most of what dinosaurs ate will probably forever be a mystery
to us.
But these occasional glimpses into dinosaurs’ guts give us incredible insights into how
they behaved, and how -- when it came to dinner time -- they weren’t all that different
from animals today.
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