| Name: Lophorhothon atopus Etymology: From the Greek 'lopho' (crest) and 'thon' (snout); and the Greek 'atopus' (strange/out of place) Distribution: Late Cretaceous (Campanian) of North America Type Specimen: Disarticulated skull and postcranial skeleton - juvenile Estimated size: Approximately 4.5 metres in length (for juvenile) First described by: Langston, Jr. (1960) | 
Image courtesy NHM |
Interesting fact: L. atopus went for a swim, then a sink
Although Lophorhothon atopus was a terrestrial hadrosaurid, its remains were found in a marine chalk deposit (the Mooreville Chalk Formation). Various taphonomic scenarios have been suggested for how it ended up in the middle of the ocean, including the bloat-and-float model. This model suggests that:
So the idea behind the location of L. atopus in marine sediment is that after it died, it was washed into the ocean, floated for a period of time, and then sank onto, and was buried by, marine chalk sediments. It would be difficult to tell whether it was washed out to sea while still alive, or whether it had already died. Although modern experiments involving carcasses lying on the ocean floor suggest that if had died at sea, it would likely be completely obliterated before it had a chance to float! (As per this pig decay experiment - WARNING - some may find these images disturbing). And the paucity of fossil material recovered from this specimen and others preserved in the eastern United States marine formations suggests that these oceans were very taphonomically active zones (TAZ), with lots of micro- and macro-scavengers consuming soft and hard tissue.
- As a carcass undergoes initial decay, internal bacteria in the digestive tract produce gases which cause the carcass to swell up and 'bloat'.
- If the carcass is laying at the bottom of a lake, river, or ocean, the gases causing bloating overcome the carcass's weight and negative buoyancy in water, and will therefore allow it to 'float' to the surface.
- The carcass may then drift for some time until decay advances enough for the internal gases to escape, resulting in the carcass sinking.
So the idea behind the location of L. atopus in marine sediment is that after it died, it was washed into the ocean, floated for a period of time, and then sank onto, and was buried by, marine chalk sediments. It would be difficult to tell whether it was washed out to sea while still alive, or whether it had already died. Although modern experiments involving carcasses lying on the ocean floor suggest that if had died at sea, it would likely be completely obliterated before it had a chance to float! (As per this pig decay experiment - WARNING - some may find these images disturbing). And the paucity of fossil material recovered from this specimen and others preserved in the eastern United States marine formations suggests that these oceans were very taphonomically active zones (TAZ), with lots of micro- and macro-scavengers consuming soft and hard tissue.
Representation of L. atopus floating in the taphonomically active zone (TAZ) of the eastern United States Cretaceous oceans. Courtesy of James T. Hays, copyright 2009, and the Encyclopedia of Alabama
This float-and-bloat model is exactly what I've been testing for my PhD: looking at the buoyancy of juvenile salt-water crocodiles and native fish in fresh water. This will help add to the body of knowledge regarding what sort of time frame different animals bloat-and-float over, and the potential distances they could travel in that time, including floating into the middle of an ocean!
Simplified cladogram of all non-avian dinosaurs. L. atopus was a hadrosaurid, within ornithopoda.
References
Langston, W. Jr. 1960. The vertebrate fauna of the Selma Formation of Alabama. Part VI. The dinosaurs . Fieldiana: Geology Memoirs 3(6): 315-361
Schwimmer, D. R., Dent Williams, G., Dobie, J. L., and Siesser, W. G., 1993. Late Cretaceous Dinosaurs from the Blufftown Formation in Western Georgia and Eastern Alabama. Journal of Paleontology 67(2): 288-296
Schwimmer, D. R. 2010. Lophorhothon. The Encyclopedia of Alabama TM & © 2012, accessed 7 December 2012.
Langston, W. Jr. 1960. The vertebrate fauna of the Selma Formation of Alabama. Part VI. The dinosaurs . Fieldiana: Geology Memoirs 3(6): 315-361
Schwimmer, D. R., Dent Williams, G., Dobie, J. L., and Siesser, W. G., 1993. Late Cretaceous Dinosaurs from the Blufftown Formation in Western Georgia and Eastern Alabama. Journal of Paleontology 67(2): 288-296
Schwimmer, D. R. 2010. Lophorhothon. The Encyclopedia of Alabama TM & © 2012, accessed 7 December 2012.
