The marine predators, the marine monsters

coprolite ZPAL Tf.6 Cretaceous Poland, from Bajdek 2013
Coprolite of a marine carnivore with bivalve shell fragments, Upper Cretaceous, Poland (reproduced from Bajdek, 2013)

Marine food chains

The ichthyosaurs were an extraordinarily adapted to life in water group of reptiles of the Mesozoic Era. Due to the hydrodynamic body shape, it’s commonly believed that the ichthyosaurs preyed on agile and fast animals. Indeed, the ichthyosaur gastric contents described from the Lower Jurassic of Lyme Regis and Charmouth, England, as well as Holzmaden, Germany, contain remains of belemnites, which were generally slim cephalopods resembling modern squids.

Certain accumulations of belemnite rostra are interpreted as ichthyosaur regurgitalites (fossilized vomit). For instance, such an accumulation from the Jurassic of Peterborough, England, was presented in 2001 by Peter Doyle and Jason Wood. Because it seems improbable that the strong and sharp rostra passed through the entire gastrointestinal tract and were excreted in the form of feces, the find was interpreted as a regurgitate of an ichthyosaur. This interpretation is supported by the etching marks on the surfaces of the rostra, and also the fact that they belonged mostly to juvenile individuals.

It was surprising the stomach content of an ichthyosaur from the Upper Albian (Lower Cretaceous) of the Toolebuc Formation, Queensland, described in 2003 by a team of researchers led by Benjamin P. Kear. Apart from fish bones, in the stomach there were present remains of a turtle, and a bird. Turtle fossils are common in those rocks; it also seems that the turtle was an easy prey. The bird was most likely consumed in the form of carrion. Possibly, the dietary habits of ichthyosaurs were much more flexible than previously thought. The finding is also interesting because it’s one of the latest ichthyosaurs – at the end of the Cenomanian, 10 million years later, the ichthyosaurs went extinct. Some speculated that the dietary specialization of ichthyosaurs were a contributing factor in their extinction. This explanation seems however inconsistent with the discovery from the Toolebuc Formation.

What did the turtles cf. Notochelone, which the ichthyosaurs preyed on, eat? The Cretaceous turtles of the family Protostegidae are an extinct group whose diet was unknown. However, three years later Benjamin P. Kear described stomach contents and coprolites (fossilized feces) of the turtles from the Toolebuc Formation. They contained crushed shells of bivalves belonging to the family Inoceramidae. As the bivalves were benthic organisms, it means living on the seafloor, the conclusions one more time were inconsistent with the expectations. Some supposed that these turtles were pelagic predators and fed on ammonites in the water column.

Taken together, the findings from the Australian Toolebuc Formation give an unusual opportunity to take a look at ancient food chains, which encompassed the turtles feeding on bivalves, and the ichthyosaurs feeding on turtles, fishes, and even the carrion of birds.

The marine depths

In 2013, I described a little younger coprolite from the Upper Cretaceous of the Carpathian Mountains, Poland. Similarly to the coprolites from Australia, the putative coprolite from Poland contains crushed shells of bivalves belonging to the family Inoceramidae. Unfortunately, it’s not easy to determine what animal it was produced by: although a reptile cannot be ruled out as the producer, a teleost fish seems the most simple explanation. In contrast to the specimens from Australia, which come from shallow-marine sediments, the coprolite from the flysch of the Carpathians was found in rocks formed in the marine depths. Its geologic context is indeed interesting. The feces were buried beneath sediments of a so-called turbidity current, i.e. a submarine avalanche transporting sediments to the oceanic depths. The specimen is also interesting because it contains numerous shells, whereas the host rocks are extremely poor in body macrofossils of animals. Feces constitute an exceptional accumulation of remains. The dietary residues can be moreover transported in the gastrointestinal tract of the fecal producer far away, even to a different environment.

The juvenile prey

In 2015, a team of researchers led by David R. Schwimmer described an interesting find from the Upper Cretaceous of South Carolina. The spiral bromalite, i.e. feces or an intestinal cast, contains partially articulated vertebrae of a baby freshwater turtle. Due to the small size of the bromalite, the researchers suggest that the shark itself was juvenile as well. These observations might carry interesting ecologic implications showing that the shark fed closely to a freshwater river environment and the breeding sites of the turtles. The researchers consider even the possibility that juvenile sharks migrated far upstream.

Gastric contents of plesiosaurs reveal remains of ammonites, belemnites, bivalves, and fishes. An unusual find from Wyoming was described in 2009. The stomach of a Late Jurassic plesiosaur contained ichthyosaur remains. Strictly speaking, it was an embryo of an unborn ichthyosaur!

Piotr Bajdek

References

Bajdek, P. 2013. Coprolite of a durophagous carnivore from the Upper Cretaceous Godula Beds, Outer Western Carpathians, Poland. Geological Quarterly 57 (2): 361–364. doi: 10.7306/gq.1094

Kear, B.P. 2006. First gut contents in a Cretaceous sea turtle. Biology Letters 2: 113–115. doi: 10.1098/rsbl.2005.0374

Kear, B.P., Boles, W.E., and Smith, E.T. 2003. Unusual gut contents in a Cretaceous ichthyosaur. Proc. R. Soc. Lond. B (Suppl.) 270: 206–208. doi: 10.1098/rsbl.2003.0050

Lomax, D.R. 2010. An Ichthyosaurus (Reptilia, Ichthyosauria) with gastric contents from Charmouth, England: first report of the genus from the Pliensbachian. Paludicola 8 (1): 22–36.

Nature News, 12 February 2002. Jurassic vomit comes up at meeting. doi: 10.1038/news020211-3

O’Keefe, F.R., Street, H.P., Cavigelli, J.P., Socha, J.J., and O’Keefe, R.D. 2009. A plesiosaur containing an ichthyosaur embryo as stomach contents from the Sundance Formation of the Bighorn basin, Wyoming. Journal of Vertebrate Paleontology 29 (4): 1306–1310.

Schwimmer, D.R., Weems, R.E., and Sanders, A.E. 2015. A Late Cretaceous shark coprolite with baby freshwater turtle vertebrae inclusions. Palaios 30: 707–713. doi: 10.2110/palo.2015.019
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