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Taphonomic Processes: Not Just Destructive by Nature

Taphonomy is broadly defined the study of those processes that act on an organism between death and fossilization. Such processes might include breakage and disarticulation due to weathering, scavenging, and trampling, and transportation due to water currents, among many others. Turner (2007) characterized taphonomic processes as information-destroying by nature, and I can certainly understand where he’s coming from. If you’re trying to reconstruct the anatomy of an individual whose fossil bones were once subjected to all the above processes, it’s going to a frustrating job.

      But as Wilson (1988) points out, depending on your point of view, taphonomic processes can also create information. He provides an example from his own work on bromalites (which are fossils derived from the digestive systems of ancient organisms) containing the disarticulated, partly dissolved bones of fishes. Many fish-bearing bromalites of Eocene age (56–34 million years ago) were once thought to represent fossilized dung deposits but, using a series of nuanced criteria, Wilson (1987) showed that many are instead regurgitated bird pellets. This finding is significant because birds are quite rare as fossils (owing to those information-destroying taphonomic processes that act on their delicate bones), yet we can still infer their existence in the fossil record from their fossilized pellets (thanks to those information-creating taphonomic processes). In some fossil-bearing rocks, we know that ancient birds were around strictly from their fossil pellets, and not from any other preserved remains.

Fossilized bird pellets like these can tell us that there were once prehistoric birds living in the area, even when their bones are nowhere to be found. (Image source: Wilson, 1987)
 
      An example from my own work might drive the point further home. Back in 1970, palaeontologist Charlie Sternberg noted that most of the pachycephalosaur skull domes he had collected over his lifetime were rounded and worn, as though they had tumbled along the bottom of a river bed for many miles. Sternberg concluded that the dome-headed pachycephalosaurs must therefore have lived in mountainous upland palaeoenvironments, and not in the lowland coastal palaeoenvironments where their remains are typically found. A couple of years ago, I co-authored a study (Mallon and Evans, 2014) that revisited Sternberg’s claims, and found that, in fact, pachycephalosaur domes aren’t typically worn, and that their degree of wear does not correlate with the distance from their presumed origin in those ancient mountains. It seems instead that pachycephalosaurs really did live in the coastal lowlands. Again, it’s thanks to the differential action of information-creating taphonomic processes that we’re able to know this.

 

The differential weathering of bones like these pachycephalosaur domes can actually teach us something about where these animals once lived. (Image source: Mallon and Evans, 2014).

 
      There’s a saying that if life gives you lemons, make lemonade. I think maybe we can take a similar lesson from the fossil record: If you’re left with a scattered mess of disarticulated fossil bones to interpret, look to those information-creating taphonomic processes to help you get the most out of them.
 
Posted by Jordan Mallon, Canadian Museum of Nature
 
Literature cited:

Mallon, J. C., and D. C. Evans. 2014. Taphonomy and habitat preference of North American pachycephalosaurids (Dinosauria, Ornithischia). Lethaia 47:567–578.

Sternberg, C. M. 1970. Comments on dinosaurian preservation in the Cretaceous of Alberta and Wyoming. National Museums of Canada Publications in Palaeontology 4:1–9.

Turner, D. 2007. Making Prehistory: Historical Science and the Scientific Realism Debate. Cambridge University Press, Cambridge.

Wilson, M. V. 1987. Predation as a source of fish fossils in Eocene lake sediments. Palaios 2:497–504.

Wilson, M. V. 1988. Paleoscene #9. Taphonomic processes: Information loss and information gain. Geoscience Canada 15:131–148.
 
Posted: 7/4/2016 11:47:56 AM by mallonjordanadmin | with 0 comments
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