Dinosaurs Without Bones (35 page)

Based on other stomach contents, another feathered theropod, the Early Cretaceous
Sinocalliopteryx
of China, also ate birds and non-avian dinosaurs. One skeleton had two specimens of the bird
Confuciusornis
in its body cavity, as well as acid-etched bones of an unidentified ornithischian dinosaur. In this instance, two birds in the gut was worth one neat hypothesis, as the birds were nearly complete and in the same digested state, meaning they were likely caught and gulped quickly, one after the other. Yet
Sinocalliopteryx
had no apparent adaptations for climbing trees, and at more than 2 m (6.6 ft) long, it was likely too big to scale a tree trunk anyway. A different specimen of the same species also contained a “drumstick” (leg) of another theropod—probably
Sinornithosaurus
—an example of theropod-on-theropod action that did not end well for one of them. All in all, these body fossils of
Sinocalliopteryx
and their enclosed trace fossils tell us that
Sinocalliopteryx
was probably a formidable ground-hunter.

Luckily, not all Cretaceous theropods with stomach contents were magically restricted to China. Ably representing North American theropods and their meals, David Varricchio—introduced in a previous chapter—discovered a Late Cretaceous tyrannosaurid (
Daspletosaurus
) in Montana with a few anomalous bones in its abdominal region. These consisted of four tail (caudal) vertebrae and part of a lower jaw (dentary) from unidentified juvenile hadrosaurs. Notice the plural: the vertebrae belonged to a hadrosaur that was likely about 3 m (10 ft) long, whereas the dentary came from one that was about 1 m (3.3 ft) long. Juvenile hadrosaurs typically had a thin layer of outer (cortical) bone on their caudal vertebrae, but this was missing; the spongy bone underneath was exposed
and pitted. Low-pH stomach acids in the theropod’s proventriculus probably dissolved cortical bone on the caudal vertebrae, and the dentary was likewise in bad shape. So based on their identity as juvenile hadrosaurs, appearance, and location inside a
Daspletosaurus
skeleton, Varricchio concluded that both hadrosaurs used to be food. Although this was not enough evidence to say whether this
Daspletosaurus
actively preyed on these two differently aged hadrosaurs or munched on already-dead ones, the close proximity of these bones as gut contents implies that the theropod must have eaten one immediately after the other.

The Early Cretaceous theropod
Baryonyx walkeri
of England is yet another large theropod with stomach contents, but surprising ones. The first specimen of this dinosaur was discovered in a clay pit mine in 1983; paleontologists Alan Charig and Angela Milner named it several years later, in 1986. It died before growing to full adult size, but was still an impressively large theropod at about 10 m (33 ft) long, or half the length of a healthy tapeworm. Yet its most noteworthy features were: a snout shaped more like that of a crocodile; a kink in its jaw also like that of a crocodile; nearly a hundred teeth in its jaws; robust arms; huge claws on its “thumbs”; and leg proportions that suggested it could walk on all fours. This was a big predatory dinosaur but built unlike most known at that time, thus provoking a good question: With adaptations like these, what did it eat?

In a more detailed study of this specimen published in 1997, Charig and Milner concluded that all of these traits made
Baryonyx
well suited for grabbing, handling, chomping on, and eating fish. In other words, it acted like a grizzly bear, albeit a massively up-scaled one. Preposterous? Not when the same specimen also had acid-etched fish bones and scales in the area of its former stomach. These bits belonged to a bony fish identified as
Scheenstia
, a common fossil in Early Cretaceous rocks in England, France, and Germany. Consequently, Charig and Milner speculated that
Baryonyx
was comfortable wading into and swimming in lakes and streams to find food. So thanks to this combination of body and trace fossil
evidence, paleontologists began to think more often of some theropods as
piscivorous
(fish-eating), whether as a main part of their diet or whenever they felt like having fish. (As learned previously, paleontologists were further encouraged to adopt this formerly strange idea of fish-eating theropods when they found thousands of theropod swim tracks in Early Jurassic rocks of Utah.)

This same specimen of
Baryonyx
included lots of other ichnological extras, such as the remains of a juvenile ornithopod (identified as
Iguanodon
), gastroliths, and its own broken bones. The
Iguanodon
remains included neck, back, and tail vertebrae as well as arm, leg, finger, and toe bones. Thus the “grizzly bear” analogy holds up well for
Baryonyx
in this respect, as these modern carnivores are not just restricted to eating fish but also deer, elk, caribou, moose, and other animals. The
Iguanodon
bones were eroded, probably by stomach acids, just like the hadrosaur bones in
Daspletosaurus
.

Charig and Milner also mentioned gastroliths as being present and associated with the skeleton; sadly, they gave no other description of these trace fossils. Oddly enough, they mention “gastroliths” in their 1986 paper, but only “an apparent gastrolith” in the 1997 one. Did the others get misplaced during that eleven-year gap? However, if
Baryonyx
only had one or a few gastroliths, such rocks could have been accidentally grasped and swallowed as it scooped up a slippery fish. Lastly, a few broken bones in
Baryonyx
were explained as the trace fossils of other dinosaurs that irreverently stepped on its body after it had already died and been buried.

Nearly all of the trace fossils mentioned thus far were enterolites, food items that only made it down as far as the proventriculus, gizzard, or whatever else functioned as a stomach in a dinosaur. What about cololites, in which this food was more digested, passing through the intestines for further nutritive absorption, and almost ready to explode from a dinosaur’s other end but never quite made it?

Only a few such trace fossils are known in dinosaurs, but one of the best is also in the most complete dinosaur from an entire continent,
Minmi paravertebrata
. This Early Cretaceous dinosaur lived about 115
mya
in Queensland, Australia, and was an ankylosaur;
recall that ankylosaurs were armored dinosaurs that lived throughout much of the Jurassic and all of the Cretaceous periods. I have seen a cast of this specimen displayed at a small museum in Richmond, Queensland, and it is incredible. Although flattened so that it looks like Cretaceous road kill and about the size of an adult sheep, nearly every hard part of its body is intact and articulated.

Fortunately, this exceptional preservation included its gut contents, which consisted of a compacted mixture of leaves, seeds, small fruits, and other parts from a variety of plants inside the area of its hip. All of these plant remains were the size of coarse coffee grounds, measuring only a few millimeters across. “Then it must have had gastroliths!” you shout excitedly. In response, I smile, nod, and thank you for outwardly expressing such enthusiasm for those trace fossils, but then gently inform you that this ankylosaur had no gastroliths. This means that it more likely chewed its food thoroughly in its mouth before swallowing, rather than relying on its stomach to reduce food to a more digestible texture.

Okay, time to get skeptical. Dinosaurs, like other vertebrates, probably spilled their guts after dying, whether from decomposition, scavengers, or a combination of the two. Once opened, a dead dinosaur’s body cavity would have invited the outside world to intrude on its inner spaces. This means river currents could have carried in the finely ground and varied plant material and deposited it in the open body cavity of this
Minmi
after it died. Therefore, these plants might not represent its final meal after all.

Good thinking, but in my preceding description of
Minmi
and its cololite, I omitted a key piece of information, one that crushes that hypothesis like ankylosaur jaws would a Cretaceous plant. It turns out this specimen of
Minmi
was deposited in a Cretaceous sea, and no river was anywhere near its body when it was laid to rest in a shallow marine grave. Central Queensland abounds in fossils from this Cretaceous seaway that divided Australia then. In the same museum where I stared at the cast of
Minmi
, hundreds of fossils of ichthyosaurs, plesiosaurs, ammonites, squid, clams, and other sea life surrounded it, all from the same rocks.

No serious paleontologist suggests that the heavily armored ankylosaurs paddled out to sea, just as medieval knights were not likely keen about going for a swim in full armor. So this
Minmi
must have been a “bloat-and-float” dinosaur. It died on land with a belly full of terrestrial plants and was filled with enough gas from decomposition to buoy it into the ocean. Once out there, it somehow escaped scavenging by marine carnivores; no toothmarks or other signs of nibbling were on its body. Once it sank, it also must have made quite an impression on any sea life living on the bottom before burial. Most amazing of all, this is an example of a dinosaur that carried its trace fossil with it after death and on a long journey to sea.

Dinosaur Puke

So how about food that a dinosaur’s gastrointestinal tract rejected instead of passing through, or more quiescently as gastric pellets like those emitted by predatory birds today? Tragically, examples of dinosaur regurgitalites are either extremely rare or unrecognized from the fossil record. One regurgitalite inferred from Late Triassic rocks contains pterosaur remains, but is thought to have come from a large fish rather than a land-dwelling animal. I also mentioned one example interpreted in 2009, which was apparently fossilized beside the mouth of a
Coelophysis
. As much as I want to believe this is Triassic puke, the coincidence of vomiter and vomit seems a little too fortuitous. For instance, how did this former meal stay put while river currents buried its supposed producer?

Nonetheless, I am hopeful that dinosaur regurgitalites are more common than previously supposed, and paleontologists just need a combination of training and imagination to find them. So here are some criteria for finding dino-barf. For one, because the contents of regurgitalites only spent a short amount of time in an animal’s gut, they will be noticeably less digested than anything coming out its other end. Still, any solid items, such as bones, may have some acid etching, while also being more broken, poorly sorted, and chaotically arranged than if they had not been chewed, swallowed, and partially digested by a dinosaur.

Unless preserved as a pellet, like a tightly packed modern-day owl pellet, vomit should have contained enough liquids to cause it to spread, especially if delivered from a great height. For a moment, just imagine the Late Jurassic sauropod
Brachiosaurus
puking its guts out, with its mouth as much as 14 m (46 ft) above the ground. This likely would have caused immediate panic amongst any animals in the vicinity, which would have tried to escape such a harrowing aerial bombardment, or at least been spooked by the unusual noises accompanying a purging sauropod. Trace fossils would thus show the following:

• Large sauropod footprints at a standing position, and behind a crater with splatter marks radiating several meters around its center;
  
• A concentration of bigger, more solid items in the middle;
  
• Run-off marks from included fluids, especially if influenced by slopes on the former ground surface;
  
• Trackways of other animals with ratios between footprint lengths and stride lengths showing they were moving at high speeds and fleeing in directions away from the crater;
  
• The remains of one or two small unlucky theropods knocked out and drowned by the initial shower of debris;
  
• Thousands of trackways of the “cleanup” crew, such as insects specialized at eating dinosaur throw-up. Just as there are insects that specialize in eating dinosaur poop, there may have been some that enjoyed a pre-digested (but totally vegan) meal.
  

Only one instance of fossilized dinosaur vomit, containing a mix of dinosaur and turtle bones in Early Cretaceous rocks of Mongolia, is inferred to have come from an actual dinosaur. Another possible dinosaurian up-chuck is embodied in a mass of four birds from the Early Cretaceous of Spain. However, the paleontologists reporting
it thought it also may have been from a pterosaur. Otherwise, most Mesozoic regurgitalites are credited to marine-reptile contemporaries of dinosaurs: ichthyosaurs. These deposits, found in Late Jurassic rocks of the U.K., consist of concentrated collections of belemnite shells. Belemnites, which were squid-like animals that shared the seas with ichthyosaurs, also show up as stomach contents. However, these masses of cigar-shaped shells were found by themselves and were acid-etched. This suggested they spent time bathed in low-pH stomach acids, but because they were not inside an ichthyosaur skeleton, they were either regurgitalites or coprolites.

Coprolites were quickly eliminated as an explanation, though, because belemnite shells are pointy on one end. Now imagine being an ichthyosaur that swallowed several dozen pointy-ended shells and passed those out its other end: no, thanks. The risk of internal injury also would have been too high to pass such shells all the way through intestines too sensitive to handle such a payload. Hence these were the marine version of gastric pellets, in which ichthyosaurs snapped up lots of belemnites, kept them down long enough to digest their useful nutrients from the soft parts, and then coughed up their shells.

Other than gastric pellets or illness, what would have been other reasons for a dinosaur to barf? One would have been from the desire to feed their children warm meals. And if it were regurgitated as meals for hungry youngsters and puked right into their waiting little mouths, a trace of this in the fossil record would be very rare indeed. As mentioned earlier, though, bird parents commonly seek out food, ingest it, partially digest it, and then egest it into their chicks’ mouths. Keep this in mind for later, and how other trace fossils opened our eyes to this particular nurturing behavior as a possibility in dinosaurs.