Predation is a pretty big topic in palaeontology, but not as straight forward as you might expect. We all have this image in our head of the T. rex from Jurassic Park feasting on another dinosaur (or perhaps the lawyer on the toilet), but where does that information come from? Unlike in Jurassic Park, humans were never alive to actually witness a T. rex eating a Triceratops, so how can we be certain those interactions ever occurred?
Anti-predatory adaptations, such as armour, spikes, frills, are a good first clue that something is trying not to be eaten. Even better, though, is the actual evidence of an interaction preserved on the hard parts of either predator, or (more often) prey. For example, there is a really nice specimen of a Triceratops at the T. rex Discovery Centre in Eastend, SK, where you can see tooth marks from a predator.
Unfortunately for vertebrate palaeontologists, bigger animals are not as abundant, so the occurrence of such fossils is really special and rare. With invertebrate palaeontology, we have a bit of an easier time. One type of predation trace preserved on invertebrate prey is called a drill hole, which is a hole in the shell of a prey animal created by predatory gastropods (snails).
If you remember my post about cone snails, I mentioned that gastropods have a special feeding organ called a radula, which is usually rough like a cat’s tongue and used for scraping food. In the case of drilling gastropods, they have another organ called an accessory boring organ (ABO), which secretes material to soften the shell of their prey as they scrape with their radula. One of the more common predatory snails is called a naticid (moon snail). They can get to be very large (bigger than a softball), and have a giant foot that they use for both moving, and grappling their prey.
Drill holes can be used to study many aspects of predation and predator-prey dynamics. For example, we can look at how often prey are being attacked and see if there are predator preferences (Yanes and Tyler 2009). Or perhaps there is evidence of anti-predatory adaptations, such as spines (Leighton 2001), or a lack of edible parts (Tyler et al 2013). Drill holes can even be used for taphonomic studies (everything that happens from the moment an animal dies to the time the fossil is discovered), such as how drill holes affect the transportation and deposition of shells (Molinaro et al. 2013).
Predators are not always successful, and will sometimes get interrupted, perhaps even by a predator of their own. Such interruptions produce incomplete drill holes, which can also be used to determine the success rates of predators, or the intensity of predation upon the drillers themselves (Chattopadhyay and Baumiller 2010).
Some predators will even recognize different prey types and attack each in a particular manner, producing sterotypic drill holes that are in a consistent location unique to that prey (Leighton 2001). Not only that, but they can be highly cannibalistic, and will often eat smaller members of their own species (Chattopadhyay et al. 2014). Basically, if they are able to grapple you with that huge foot, you are in trouble.
TL,DR: Drill holes have an extensive fossil history, and are very useful for studying predator-prey dynamics and how predation has evolved. Stay tuned for a future blog post on another type of predation trace: repair scars…
Chattopadhyay, D., and Baumiller, T. K. 2010. Effect of durophagy on drilling predation: a case study of Cenozoic molluscs from North America. Historical Biology. 22:367-379.
Chattopadhyay, D. Sarkar, D., Dutta, S., Prasanjit, S. R. 2014. What controls cannibalism in drilling gastropods? A case study on Natica tigrina. Palaeogeography, Palaeoclimatology, Palaeoecology. 410:126-133.
Leighton, L. R. 2001. New example of Devonian predatory boreholes and the influence of brachiopod spines on predator success. Palaeogeography, Palaeoclimatology, Palaeoecology. 165:54-69.
Molinaro, D.J., Collins, B.M.J., Burns, M.E., Stafford, E.S., Leighton, L.R. 2013. Do
predatory drill holes influence the transport and deposition of gastropod shells?
Tyler, C. L., Leighton, L. R., Carlson, S. J., Huntley, J. W., Kowalewski, M. 2013. Predation on modern and fossil brachiopods: assessing chemical defenses and palatability. Palaios 28:724-735.
Yanes, Y., and Tyler, C. L. 2009. Drilling predation intensity and feeding preferences by Nucella (Muricidae) on limpets inferred from a dead-shell assemblage. Palaios 24:280-289.