An introduction to taphonomy

Think back to the last time you were at a natural history museum. Do you remember seeing fossils? Perhaps you were excited by the dinosaurs, from the long necked Apatosaurus (the real name of the beloved Brontosaurus) to the quick and vicious Velociraptor. Or maybe you were awed by the ichthyosaurs and mosasaurs, the marine reptiles that ruled the oceans while the dinosaurs ruled the land. My friends always ask me about the creatures – “What were they? What did they eat? How fast could that Velociraptor run – would I be able to escape?“. When I walk through a museum, I see the fossil remains of ancient organisms and wonder “how did they get here?“.

A series of wonderful bird fossils from the Royal Ontario Museum in Toronto.

A series of wonderful bird fossils from the Royal Ontario Museum in Toronto.

My main focus in paleontological is taphonomy, the study of how fossils form. As a taphonomist, I try to piece together the myriad of processes that result in the transformation of a once living organism to the very fossils you see in a museum. Without understanding how the fossil formed, we cannot fully understand the organism or its ancient environment. Most importantly, without studying these processes, we cannot know what information is lost from the fossil record or how the record is biased towards or against certain groups of organisms.

For some types of fossils, like the bones of dinosaurs and the shells of ancient molluscs, this information loss may be minor – we are still able to understand the animal quite well through the mineralized hard parts. However, think of the world around you – many important organisms like insects and plants do not have mineralized hard parts. Fossils of these ‘soft bodied’ organisms are much more uncommon and the processes, such as decay, that leave bones intact may completely break down a leaf before it has a chance to be preserved. When soft bodied fossils are found, they are often referred to as exceptional – for indeed, exceptional circumstances are required for them to exist! I study how these exceptional, soft bodied fossils are preserved and how our view of the ancient earth is affected by processes that form them.

A 40 million year old beetle from Eckfield, Germany with color preserved. McNamara et al. 2011

A 40 million year old beetle from Eckfield, Germany with color preserved. McNamara et al. 2011

The processes that are involved in fossilization are often referred to as ‘taphonomic filters’ – with each step, some part of the original biological community (the ‘biosphere’) may be removed or changed. These include processes that occur both before and after burial – transport, scavenging, decay, mineralization, and compaction to name a few. The majority of organisms – both plants and animals – do not survive all of these filters to become a fossil in the rock realm (part of the ‘lithosphere’). Think of it as a “Chutes and Ladders” scenario.

The goal is to make it to becoming a fossil, and to get to that goal the remains of an organism must navigate a dangerous path to get there. There is one ladder that goes almost all the way to the top – this might be rapid burial, perhaps even before the organism has died. However, there are chutes that block the path to fossilization – perhaps the organism decays away despite the burial. Unlike the much loved board game, the chutes often end the game entirely – fossils normally get only one chance to make it to the top. If they catch a chute on the way down, they are out of the game!

This chutes and ladders scenario is further complicated by an organism’s preservation potential – a starting probability of fossilization. The preservation potential is related to the structure of the animal or plant. Things with mineralized hard parts – like the bones and shells of many animals – have a higher preservation potential than totally soft bodied organisms, like slugs and flowers. Some organisms or parts of organisms, such as the hard exterior of a beetle or wood of a tree, fall somewhere in between on this spectrum. Bony or shelly organisms may have fewer chutes to avoid, while the soft bodied animals and plants may have a more treacherous route.

This may seem like a bleak outlook – that many organisms do not make survive to becoming a fossil! However, the fossil record is remarkable. Over the past 100 years, paleontologists have found deposits all over the world that contain fossils of the most soft and squishy animals (yes, there are jellyfish fossils!), and new fossils are being discovered each year. In addition, parts of animals once believed to be absent from the fossil record, like the feathers of dinosaurs and birds, have been found – it’s not just their bones anymore!

A fossil jellyfish, complete with tentacles! From

A fossil jellyfish, complete with tentacles! From

By studying how these fossils formed, we are better able to understand the environment in which they were preserved and changes to the organism that may affect our understanding of what it is or how it lived. My research has explored the preservation of color in fossils, why land crabs have a poor fossil record, and how fossil plants form. In upcoming posts, I’ll discuss my research in greater detail. In the mean time, take a look at some exceptional fossils, visit your local natural history museum, and think about how each fossil has made it through the fossil game and survived millions of years against all odds- it’s incredible!

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