Dinosaurs Without Bones (54 page)

• Ceratopsian and pachycephalosaur trackways that confirm these big-headed dinosaurs really did smash into one another with their bony accouterments. Or, more interesting, show that they did not, and instead got along famously and that those big heads and accompanying horns and shields were there for some other purpose.
  
• More examples of dinosaur urolites. After all, they all had to go some time.
  
• Clear, definitive dinosaur regurgitalites, ideally with partially digested food directly associated with a probable regurgitator nearby.
  
• Long, continuous trackways made by really big theropods. I’m talking about trackways made by 7–9 ton Cretaceous theropods like
  Spinosaurus
  or
  Carcharodontosaurus
  of northern Africa,
  Gigantosaurus
  of South America, or
  Tyrannosaurus
  of North America. Such trackways would give us much more information on how these dinosaurs really moved, while also reeking of awesomeness.
  
• Sauropod trackways that demonstrate whether or not these animals traveled in family structures like modern elephants, with mixtures of young and old.
  
• More detailed studies of microwear on ornithopod teeth, illuminating how these dinosaurs ate, and in some instances what they ate.
  
• Dinosaur toothmarks preserved in unusual substrates, like molluscan shells or eggshells, and not just bones.
  
• Closer looks at broken and healed lower limb bones in theropods to see if these were the marks of cranky stegosaurs and angry ankylosaurs who objected to unwanted attention from those theropods. Likewise, more healed tail spikes and clubs of these dinosaurs, further showing how they disciplined their oppressors.
  
• Dig marks in fossil termite or ant nests that match the dimensions of therizinosaur hands or the limbs of other unusual dinosaurs.
  
• More dinosaur ground nests and nesting grounds. So few of these are known as trace fossils, yet more must be out there, waiting to be recognized.
  
• Burrows made by small theropods or other dinosaurs. Why restrict all of the underground fun to small ornithopods?
  
• More gastroliths, whether in or out of their dinosaur hosts: who really had them, who really lacked them?
  
• Enterolites or coprolites that show clear evidence of insectivory or omnivory in dinosaurs. They weren’t just all “meat eaters” or “plant eaters” (how boring).
  
• Dinosaur sex traces. (Need I say more?)
  

Although paleontologists may find none of these, or only stumble upon a few of them, if any are found we should all celebrate their success with alacrity. What is also gratifying to know is that some of the people who find these may not even be professional paleontologists, but people who happened to be looking in the right place at the right time and with the right search image in mind. Paleontology, archaeology, and astronomy are among the few sciences in which amateurs regularly make important contributions
through their numerous eyes on the ground (or on the stars). Let the games begin.

Nevertheless, we should describe and interpret these trace fossils with care.
One of the best facets of the fossil record is that it gets better every day, and trace fossils are a big part of this daily improvement. Yet of the dinosaur trace fossils found, many either remain undescribed or (far worse) have been under-described, without enough meaningful attention to detail to be faithful records of dinosaur behavior. If dinosaur trace fossils are treated like curios that are simply named “track,” “toothmark,” or “coprolite,” for instance, and linked to a possible dinosaur, they will become as dead as their makers. Technology will certainly play a part in better describing trace fossils. For example, 3-D images and 3-D printers of dinosaur tracks have already allowed researchers on other sides of the globe to work cooperatively, or to add to one another’s observations.

Remember that dinosaurs are still making traces.
With 10,000 species of extant birds, all of which are making traces, we have no shortage of modern analogs for dinosaur behaviors. Granted, these dinosaurs are limited to avian theropods, but their tracks, nests, burrows, gastroliths, feces, and other traces supply many opportunities to think about how dinosaurs both avian and non-avian might have behaved, and whether they made similar traces. Furthermore, although crocodilians are only distant relatives of dinosaurs, these big archosaurs are wonderful examples of big scaly four-legged toothy tracemakers that fit as tracemaking surrogates for a few dinosaurs and their Mesozoic relatives.

Become ichnologically imaginative.
As one might have intimated from the wish list given above, I am encouraging everyone interested in dinosaurs to speculate about behaviors dinosaurs may have done and the traces that resulted from these behaviors. In the spirit of leading by example, I’ve done a few flights of reasonable fancy in this respect throughout the book, with the hope that more people will do the same. As a result, I fully expect dinosaur enthusiasts, armed with a heightened awareness of trace fossils and their
importance in our understanding of dinosaurs, to make and share a surfeit of their own creative traces, both whimsical and serious.

So as we all make our own traces in our everyday lives, also imagine which ones will outlast us all. Will any of our traces also survive longer than the tracks, nests, burrows, and toothmarks of dinosaurs? Or will dinosaur trace fossils somehow surpass our own meager ichnological record? They already have had a 230-million-year head start, and with thousands of living descendants sharing the earth now, the odds are stacked against us. But no matter. This renewed appreciation for dinosaurs is now permanent, and one that recognizes another dimension of them beyond their bones. Place your hand on a dinosaur track, and you connect with the breathing essence of its maker, leaving your own fingerprints on it: life traces intersecting through time.

CHAPTER 1
:
SLEUTHING DINOSAUR

p. 10
   “It turns out a good number of
Triceratops
head shields, which are composed of paired parietal and squamosal bones, bear deformities in the squamosals.” Farke, A.A., Wolff, E.D.S., and Tanke, D.H. 2009. Evidence of combat in
Triceratops
.
PLoS One
, 4(1): e4252. doi:10.1371/ journal.pone.0004252.

p. 10
   “Ceratopsians, a group of dinosaurs that includes
Triceratops
and related horned dinosaurs, also made tracks, which are preserved in Cretaceous rocks from about 70 million years ago… .” Ceratopsian tracks are still quite rare, but a few are known from Colorado, Utah, and Alaska: (1) Lockley, M.G., and Hunt, A.P. 1995. Ceratopsid tracks and associated ichnofauna from the Laramie Formation (Upper Cretaceous: Maastrichtian) of Colorado.
Journal of Vertebrate Paleontology
, 15: 592-614; (2) Milner, A.C., Vice, B.S., Harris, J.D., and Lockley, M.G. 2006. Dinosaur tracks from the Upper Cretaceous Iron Springs Formation, Iron County, Utah.
In
Lucas, S.G. and Sullivan, R.M. (editors). 2006 Late Cretaceous vertebrates from the Western Interior.
New Mexico Museum of Natural History and Science Bulletin
, 35: 105-113.

p. 10
   “In the Cretaceous Period, about 95 million years ago and on a lake-shore in what is now Queensland, Australia, nearly a hundred small, two-legged dinosaurs ran in the same direction and at high speed.” Although this interpretation has been disputed in the past few years (see Chapter 3), the original study of these tracks is: Thulborn, R.A., and Wade, M., 1979. Dinosaur stampede in the Cretaceous of Queensland.
Lethaia
12: 275-279.

p. 11
   “One grouping of swim tracks, made by seven separate theropods, is preserved in Early Cretaceous rocks (110 million years ago) of Spain. Many more swim tracks are in Early Jurassic rocks from about 190 million years ago in southwestern Utah.” Two articles on dinosaur swim tracks came out in quick succession in 2006 and 2007: (1) Ezquerra, R., Doublet, S., Costeur, L., Galton, P.M., and Pérez-Lorente, F., 2007. Were non-avian theropod dinosaurs able to swim? Supportive evidence from an Early Cretaceous trackway, Cameros Basin (La Rioja, Spain). Geology, 35, 507-510. (2) Milner, A.R.C., Lockley, M.R., and Kirkland, J.I. 2006. A large collection of well-preserved theropod dinosaur swim tracks from the Moenave Formation, St. George, Utah. In Harris, J.D., et al. (editors), The Triassic-Jurassic Terrestrial Transition. New Mexico Museum of Natural History and Science Bulletin 37: 315-328.

p. 11
   “In 2007, I helped two other paleontologists document the first known burrowing dinosaur (Oryctodromeus cubicularis, a small ornithopod) from Cretaceous rocks (95 million years old) in Montana.” Varricchio, D.J., Martin, A.J., and Katsura, Y. 2007. First trace and body fossil evidence of a burrowing, denning dinosaur. Proceedings of the Royal Society of London, B, 274: 1361-1368.

p. 12
   “Two years later, I interpreted similar burrows in older Cretaceous rocks (105 million years old) of Victoria, Australia.” Martin, A.J., 2009. Dinosaur burrows in the Otway Group (Albian) of Victoria, Australia, and their relation to Cretaceous polar environments. Cretaceous Research, 30: 1223-1237.

p. 12
   “A different type of digging by other dinosaurs also has been inspired by unusual trace fossils found in Late Cretaceous rocks (about 75 million years ago) of Utah in 2010.” Simpson, E.L., Hilbert-Wolf, H.L., Wizevich, M.C., Tindall, S.E., Fasinski, B.R., Storm, L.P., and Needle, M.D. 2010. Predatory digging behavior by dinosaurs. Geology, 38: 699-702.

p. 12
   “These nests also contained clutches of paired eggs, which were arranged vertically in the nests by one or both of the parents after egg-laying.” (1) Varricchio, D.J., Jackson, F., Borkowski, J., and Horner, J.R. 1997. Nest and egg clutches of the dinosaur Troodon formosus and the evolution of avian reproductive traits. Nature, 385: 247-250. (2) Varricchio, D.J., Jackson, F., and Trueman, C.N. 1999. A nesting trace with eggs for the Cretaceous theropod dinosaur Troodon formosus. Journal of Vertebrate Paleontology, 19: 91-100.

p. 12
   “Similarly, a spectacular find of Late Cretaceous nests in Argentina from 70 to 80 million years ago and attributed to gigantic sauropods called titanosaurs shows that dinosaurs other than Troodon made ring-like enclosures for their eggs.” (1) Chiappe, L.M., Coria, R.A., Dingus, L., Jackson, F., Chinsamy, A., and Fox, M. 1998. Sauropod dinosaur (2) Chiappe, L.M., Schmitt, J.G., Jackson, F., Dingus, L., and Grellet-Tinner, G. 2004. Nest structure for sauropods: sedimentary criteria for recognition of dinosaur nesting traces. Palaios, 19: 89-95.

p. 13
   “What has surprised paleontologists in recent years, though, is the realization that a few theropods, a group of dinosaurs once assumed to have been exclusively carnivorous, also have these ‘stomach stones.’” Wings, O. 2007. A review of gastrolith function with implications for fossil vertebrates and a revised classification. Acta Palaeontologica Polonica, 52: 1-16.

p. 13
   “Although no one has yet found gastroliths directly associated with Struthiomimus, some of its relatives, collectively called ornithomimids (‘ostrich mimics’), do have them.” Kobayashi, Y., Lu, J.-C., Dong, Z.-M., Barsbold, R., Azuma, Y., and Tomida, Y. 1999. Herbivorous diet in an ornithomimid dinosaur. Nature, 402: 480.

p. 13
   “This is backed by healed toothmarks caused by a large predatory theropod preserved in a few bones of Edmontosaurus, including at least one with a smoking gun (or tooth, as it were) linking it to Tyrannosaurus or its close relatives.” Carpenter, K. 2000. Evidence of predatory behavior by carnivorous dinosaurs. Gaia, 15: 135-144.

p. 14
   “Triceratops bones also bear toothmarks that could only have been made by tyrannosaurs, including those that mark the front of the face… .” At the time of this writing, this research had only been reported through an abstract, so hopefully a paper is out now: Fowler, D., Scannella, J., Goodwin, M., and Horner, J. 2012. How to eat a Triceratops: large sample of toothmarks provides new insight into the feeding behavior of Tyrannosaurus. Journal of Vertebrate Paleontology [Supplement to 3], Society of Vertebrate Program and Abstracts, October 2012, p. 60.

p. 14
   “Amazingly, not one but two colossal coprolites attributed to tyrannosaurs have been documented, each with finely ground bone and one containing fossilized muscle tissue.” (1) Chin, K., Tokaryk, T.T., Erickson, G.M., and Calk, L.C. 1998. A king-sized theropod coprolite. Nature, 393: 680-682. (2) Chin, K., Eberth, D.A., Schweitzer, M.H., Rando, T.A., Sloboda, W.J., and Horner, J.R. 2003. Remarkable preservation of undigested muscle tissue within a Late Cretaceous Tyrannosaurus coprolite from Alberta, Canada. Palaios, 18: 286-294.

p. 14
   “From coprolites, we also suspect that at least some Late Cretaceous hadrosaurs ate rotten wood.” Chin, K. 2007. The paleobiological implications of herbivorous dinosaur coprolites from the Upper Cretaceous Two Medicine Formation of Montana: why eat wood? Palaios, 22: 554-566.

p. 14
   “We even figured out from dinosaur coprolites that at least a few animals—namely, dung beatles—depended on dinosaur feces as ‘manna from heaven’ to ensure their survival.” Chin, K., and Gill, B.D. 1996. Dinosaurs, dung beetles, and conifers: participants in a Cretaceous food web. Palaios, 11: 280-285.

p. 14
   “Trace fossils, such as dinosaur tracks and burrows in sedimentary rocks from formerly polar environments, tell us that they likely stayed put during the winters.” (1) Martin, A.J., 2009. Dinosaur burrows in the Otway Group (Albian) of Victoria, Australia, and their relation to Cretaceous polar environments. Cretaceous Research, 30: 1223-1237. (2) Martin, A.J., Rich, T.H., Hall, M., Vickers-Rich, P., and Vasquez-Prokopec, G. 2012. A polar dinosaur-track assemblage from the Eumeralla Formation (Albian), Victoria, Australia. Alcheringa: An Australasian Journal of Palaeontology, 36, 171-188.

p. 14
   “In one recent study, the earliest ancestors of dinosaurs were proposed on the basis of not-quite-dinosaur tracks in 245-million-year-old rocks in Poland from the earliest part of the Triassic Period.” Brussatte, S.L., Niedźwiedzki, G., and Butler, R.J. 2010. Footprints pull origin and diversification of dinosaur stem lineage deep into the Early Triassic. Proceedings of the Royal Society of London, B, 278: 1107-1113.