Taphonomy

This week, we're going to talk about something that is arguably one of the most important things to understand in palaeontology: taphonomy. A basic definition of taphonomy is the study of everything that happens to an organism after it dies, and before we find the fossil millions of years later. 

Understanding taphonomy can give us many clues about the environment that an animal lived and died in. In particular, it can be very useful when it comes to studying bonebeds, geological deposits that are full of many bones. Here, I'll go through a step by step example of the things you can learn from bonebed taphonomy from the moment you find the bonebed, to the fine details you can find in a lab. 

When you first find a bonebed, there are several features that you notice first, like the number of bones, the number of taxa, how the bones are orientated, and how complete the skeletons are, which give us a wide range of information. The number of bones can obviously tell you how many animals are found there, while the number of taxa can tell you about how those animals came to be there. For example, bonebeds that consist of mainly one species, and all ranges of sizes are likely to be from a herd or pack of animals that all perished at one time in a catastrophic event. On the other hand, bonebeds with several taxa may be characteristic of something like a predator trap where many animals go (like a watering hole), and are then killed by predators, leaving several different kinds of bones over a long period of time. These are termed monotaxic (only one taxa present), multitaxic monodominant (more than one taxa, but there is primarily one), or multitaxic multidominant (more than one taxa, with more than one dominant taxa). 

The Edmontosaurus bonebed in Edmonton. An example of a multitaxic monodominant bonebed. Photo by Liz Martin.

Next, you might notice how the bones are orientated. Some bonebeds will show an obvious  orientation to the bones, which can tell us that the bones were transported by something like a river, that will orient the bones in the direction of the flow. By studying and mapping these bones, we can understand palaeoflow and something about the ancient rivers. Completeness and degree of articulation (whether the bones are joined together in the way that a skeleton normally is or jumbled up and separated) can tell us more about how those bones came to be in that place. A complete, articulated skeleton tells us that an animal died and was undisturbed after it died. Single, isolated bones mean that the skeleton was disturbed either during death (during an attack), or after death. Bonebeds full of disarticulated bones can tell us more about transport (as an animal carcass is transported by a river, it begins to come apart), or scavenging before fossilisation. 

Example of a map of a ceratopsian bonebed showing the orientation of different bones [1].

Finally, once all the bones have been mapped and palaeontologists have returned to the lab to look at the bones, they study another important aspect of taphonomy: the fine structure of the bone. Looking at the fine detail of the bone can reveal marks like insect borings, scratch marks, and bite marks, which can tell us more about how the animals came to be in that position. A devastating bite mark may show us how it died, or bites can show that the carcass was scavenged after it died, and in some cases, by what kind of animal. Scratches can show trample marks, or possible predatory marks with an animal scratching at a carcass to pull off meat. Insect borings can tell us about decomposers that may have infested the carcass after it died. All of these different pieces of information can be put together to understand more about how the animal(s) died, the environment that it lived in and much, much more. 

Possible beetle feeding traces on a Jurassic dinosaur Camptosaurus from the US [2].

Bite marks on a humerus of Saurolophus [3].

This has been a quick review of different aspects of taphonomy, and I hope you have learned a bit about what it can teach us. In the future, we'll talk more in detail about different aspects of taphonomy. Stay tuned!

References
1. Eberth, D. A., et al. 2007. A practical approach to the study of bonebeds. In Rogers, R. R. et al. (eds.) Bonebeds: Genetic Analysis, and Paleobiological Significance. pp 265-333.
2. Britt, B. B., et al. 2008. A suite of dermestid beetle traces on dinosaur bone from the Upper Jurassic Morisson Formation, Wyoming, USA. Ichnos 15: 59-71.
3. Hone, D. W. E., and Watabe, M. 2010. New information on scavenging and selective feeding behaviour of tyrannosaurids. Acta Palaeontologica Polonica 55: 627-634.
Background info:
Eberth, D. A., et al. 2007. A bonebeds database: classification, biases, and patterns of occurrence. In Rogers, R. R. et al. (eds.) Bonebeds: Genetic Analysis, and Paleobiological Significance. pp. 103-221.