Again, birds are different. Sometimes not all food makes its way through a bird gut, but instead returns from where it came. Probably the most well known of such deposits are cough pellets, also known as gastric pellets. Owls and some other predatory birds produce these regularly, and it is perfectly normal and healthy. Owls or hawks start these pellets by: grabbing a mouse, chipmunk, or squirrel; eating it whole or in chunks, with fur, bones, muscle, and organs mostly intact; and digesting most of the protein in the proventriculus and gizzard. These birds then eject the undigested parts from the proventriculus, all packaged in a neat little cylindrical mass consisting of fur and bones. For smaller mammals swallowed whole, its entire skeleton might be extractable from this pellet.
Gastric pellets vary according to the size of the bird turning its head and coughing, as well as what it ate. For instance, I have seen candy-bar sized pellets made by wading birds, such as herons and egrets; these are filled with fish scales and bones, or sometimes crayfish parts. For seagulls, their much smaller pellets include lots of molluscan or crustacean body parts, the latter reflecting bountiful fiddler crabs that might be living in nearby coastal environments. Tracks associated with these cough pellets normally show the coughers with their feet together (side by side) and a pellet in front of the tracks.
Birds have yet another reason for purposeful vomiting, and that is out of a sense of parental responsibility. Most people know about this behavior after watching heart-warming (and foot-chilling) documentary films about penguins in the Antarctic. In these films, dutiful adult penguins go out to sea, swim around, eat lots of crustaceans, some get eaten by leopard seals, and the survivors go back on land to hurl crustacean-flavored goo into the mouths of their appreciative young ones. However disgusting this behavior might sound to us, it is a perfectly fine method for ensuring that hungry chicks get fed and fed well, particularly for those chicks that require extended parental care in or near their nests.
How about urine and feces in other vertebrates that live on land, such as some amphibians and reptiles? Frogs, toads, and salamanders certainly leave scat, but also excrete urine. I have seen toad trackways accompanied by central grooves—caused by a toad turd that stubbornly clung onto a rear end before finally detaching—as well as toad urination marks. Naturally, for those amphibians and reptiles that spend most or all of their time in lakes, streams, or other water bodies, their world is also their toilet, with urine fulfilling a “dilute and disperse” strategy, and with feces falling to the bottom and contributing to the nutrient cycling of these ecosystems.
Among those aquatic reptiles voiding in their environments are crocodilians, which are most readily compared to dinosaurs in many people’s minds. Crocodilians have extremely thorough digestion, which is achieved by a combination of strong stomach acids and a long residence time for food once down the hatch. This digestion causes their feces to emerge as homogenous white or gray rounded cylinders, bearing little evidence of what might have contributed to them: fish, frogs, birds, raccoons, or cocker spaniels. Alligator feces have always impressed me in this respect, and whenever I encounter these traces, my field dissections of them reveal no visible bits of bones, feathers, or fur. These traits contrast greatly with what I have experienced with large mammalian carnivore scat, such as those from cats, canids, or bears. For instance, scat I have seen by mountain lions (Puma concolor) or wolves typically contains lots of hair and macerated bone. For black bears (Ursus americanus) that have eaten elk or other protein-rich meals, their scat is large, flattened, and composed of pinkish masses of digested flesh and bits of bone or fur, or if they ate plants, it will emit grassy or fruity scents. Scat from grizzly bear (Ursus arctos) is similar to that of black bear scat, only much larger, occasionally containing little bells, and smelling like pepper spray.
As mentioned before, urine is a big deal in mammals for scent marking, but not so much in birds, reptiles, and amphibians. In ratites, they “urinate” (get rid of liquid waste) first, and then defecate; meaning for them, #1 is indeed followed by #2. But remember that birds use just their cloacas for waste disposal. So even though male ratites and some other birds, such as ducks and geese, have penises—some of which, incidentally, are worthy of applause or dread—these lack an enclosed urethra. In fact, these birds must first get their lengthy penises out of the way so they can urinate and defecate out their cloacas.
Describing feces, whether from mammals, birds, crocodilians, or other vertebrates, can be enjoyable, using terms that evoke instant search images: for instance, pelletal, cord-like, tapered, or blocky. For humans, the standard descriptive method for feces is the Bristol scale, used in clinical situations. In this scale, stools are rated from 1 to 7, with 1 as separate, hard, rounded nuggets and 7 as completely fluid. In between these two extremes, most of the weight of a stool (about 75%) comes from water, and of the ~25% solid stuff, almost a third of this can be from dead bacteria, whereas the rest can be undigested food, which if recognizable also enters into a description. These proportions vary with all sorts of factors, such as what was eaten or overall health. Speaking of health, feces also can contain living or dead remains of parasites, ranging from one-celled protozoans to tapeworms, the latter reaching lengths more than twice that of a stretch limousine.
All of these fun facts about feces and other by-products of digestion would go to waste if it were not for also realizing how feces have changed the world. This is the fault of plants, which as we all know by now are organisms completely unencumbered by morals and ethics and thus are free to advance their evolutionary agendas by directing animals to carry out their wishes. This tyranny started with seed plants, which developed in the Devonian Period (about 400 million years ago), then escalated into outright slavery with the evolution of flowering plants in the Late Jurassic Period, about 145 to 150 million years ago. Flowering plants were particularly crafty, developing soft, delicious, juicy, sugary fruit that surrounded seeds. It was evolutionary bribery at its best: I give you food, you bear my children, and oh, by the way, give them a ride while you’re at it. You see, while the fruits are digestible, the seeds are not. Hence, these pass through animal digestive tracts unscathed and come out the other end, covered in warm fertilizer.
What flowering plants started, then, was a combination of seed dispersal and seed planting, which non-avian and avian dinosaurs likely helped throughout the end of the Mesozoic. Today, birds and mammals have shaped entire landscapes by eating fruit, carrying seeds in their guts, and pooping. This is a topic we will revisit toward the end of this book as we consider how dinosaur traces molded our modern world and will continue to affect it.
Last Suppers and Permanent Constipation: Dinosaur Stomach and Intestine Contents as Trace Fossils
If put in the same order as an alimentary canal, trace fossils related to dinosaur feeding typically start with toothmarks and end in coprolites. So what trace fossils are between these two end members? Gastroliths certainly qualify, and as discussed before, enough of these are preserved in dinosaur abdominal cavities to inform us about dinosaur behavior. But what about the digested food itself? Does any of this get preserved? Yes, indeed. Preserved contents of stomachs, intestines, and anything else that resided in a dinosaur’s gut—but did not make it out in one form or another before that dinosaur died—are also trace fossils. What about dinosaur hurling? In ichnology, this counts too; it just needs to have been preserved in the fossil record, and then ichnologists would very happily label these as trace fossils.
Before going on any further, a little more jargon is needed to know how paleontologists name such trace fossils. Most broadly, any former food item associated with the digestive tract of a dinosaur (or any other fossil animal, for that matter) is called a bromalite. Bromalites include enterolites (fossil stomach contents), cololites (fossil intestinal contents), gastroliths, regurgitalites (fossil puke), and coprolites (fossil poop). Emetolite is yet another term proposed for a regularly regurgitated deposit, such as a cough pellet.
For now, we will focus on enterolites and cololites. Paleontologists are always very excited whenever they find such trace fossils, considering the amount of information these provide about a specific dinosaur’s diet. Of course, paleontologists also must take care whenever interpreting possible dinosaur last meals. After all, fossils stacked on top of one another or otherwise jumbled together can give the illusion that plant or animal remains are inside an animal’s body cavity. Add compression from a few tons of overlying rock, and formerly three-dimensional and separate body fossils can get squished together into flattened masses. Thus paleontologists must make sure that the suspected food items are actually in between the ribs or pelvis of the dinosaur, rather than above or underneath it.
This situation applies to the Late Triassic theropod Coelophysis bauri which, based on supposed stomach contents, was once falsely accused as the Hannibal Lecter of dinosaurs. Coelophysis was a slender, greyhound-sized theropod and is one of the most abundantly represented dinosaurs in the fossil record, with hundreds of complete specimens in former river deposits in northern New Mexico. Among these were a few skeletons of adult Coelophysis that apparently contained the remains of juveniles between their ribs. The “cannibalism” hypothesis was originally interpreted and promoted by noted paleontologist Ned Colbert, who had excavated and studied Coelophysis since the late 1940s. “Eating children” thus became one of the most commonly told Tales from the Crypt for Coelophysis, and for decades most people accepted it because it came from Colbert. Its plausibility was further supported by how many modern carnivores eat their rivals’ offspring. In terms of Mesozoic grim fairy tales, also recall those Tyrannosaurus and Majungasaurus toothmarks in bones of their own species, confirming that at least a few theropods made daily specials out of their relatives.
Great story, but too bad it was wrong. In 2002, paleontologist Robert Gay took a closer look at these Coelophysis specimens and found that the “juvenile Coelophysis” bones were misidentified. Instead, they belonged to Hesperosuchus, a small crocodile-like animal that lived at the same time as Coelophysis. Another study done by Sterling Nesbitt and others in 2006 confirmed that it was Hesperosuchus in the belly of the beast, not another Coelophysis. In yet another study in 2010, Gay pointed out that supposed “stomach contents” in one Coelophysis made up a larger volume than its original stomach, so this was not an enterolite, either. Still, the idea that Coelophysis looked to its kin for an occasional meal did not go away, as another adult specimen was found with juvenile bones next to its mouth. Interestingly, this deposit, because of its position and jumble of bones, was interpreted as a regurgitalite. If so, did this Coelophysis purge itself just before dying and entombing, or did this digestive rejection reflect some sort of remorse? It probably was not the latter, as hungry dinosaurs surely lacked any such taboos.
Fortunately, paleontologists did not have to fixate solely on Coelophysis for examples of theropods with stomach contents, as many more were uncovered from the 1990s on. For instance, in 2011, Jingmai O’Connor and two other paleontologists reported a specimen of Microraptor—a small feathered theropod from the Early Cretaceous of China—with bird bones between its ribs. The bones, consisting of a left wing and both feet, were undigested, without toothmarks, and the feet were closer to the front of the Microraptor’s body cavity. All of this implied that the bird, which was an adult, was snatched headfirst and eaten whole or in chunks. These contents comprised a wonderful find, as they confirmed that Microraptor—which had feathers on all four limbs—was likely a tree-dwelling dinosaur, hunting fully grown birds far above the ground. However, this did not mean Microraptor ate only birds, as another specimen also had a mammal bone in it.
A couple of Early Cretaceous theropods from China, Sinosauropteryx and Sinocalliopteryx, also have intriguing enterolites. Sinosauropteryx, a fuzzy theropod covered by a thin coat of down, is famous as the first of many feathered theropods discovered in China starting in the 1990s. As a special bonus, the first specimen also had a lizard in its gut, but farther down—closer to its hips—were two eggs. Did this dinosaur die after attempting to reenact a scene from the movie Cool Hand Luke (1967)? No, as any swallowed eggs would have never made it intact to the intestines. That meant this Sinosauropteryx was female, pregnant, probably had dual oviducts (remember Troodon and the paired eggs in its nest?), and had just gained some needed sustenance before giving birth, but instead died and became part of the fossil record; its loss, our gain.
Another Sinosauropteryx contained jaws from three different small mammals. These remains demonstrated how this dinosaur terrorized mammals more than a hundred million years before dinosaur-worshipping humans made movies depicting similar scenarios, perhaps reflecting an ancestral memory. Fortunately for Mesozoic mammals, at least one struck a blow against its dinosaurian oppressors: stomach contents of the Early Cretaceous Repenomamus, a badger-sized mammal that also lived in China, included the bones of a baby Psittacosaurus, and thus started a long-time tradition of mammals eating dinosaurs.
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 the
se, 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.
Dinosaurs Without Bones Page 26
