Saturday, January 26, 2013

The Ecological Importance and Awesomely Gigantic Reptiles of the Cerrejon Formation

We all know the story: 65.5Ma, the dinosaurs became extinct (except for the ones that survived), and the world was at last liberated from the cold, scaly monarchy of reptiles. Hooray!

This wasn’t the case. At all. First of all, dinosaurs are warm-blooded, and secondly, in the ten-million-year period following the extinction of the non-avian dinosaurs, the world was still, in some areas, home to truly enormous reptiles. The Cerrejon Formation of Colombia, dating back to the Paleocene epoch, preserves an otherworldly environment in which giant snakes, turtles, and crocodilians ruled the landscape, and this formation has drawn much attention from its abundance of tremendous scaly beasts.

While the wildlife of the Cerrejon Formation is no doubt amazing, the ecological importance of the 58-million-year-old formation is often overlooked. The various fossilized plants, leaves, and evidence of herbivorous insects represent the earliest known record of modern Neotropical rainforests. The families of plants that have been found, including various palms and legumes, can still be found in the Amazon Basin. Though they were present in the Paleocene, they are far more diverse today; this may be due to the fact that the earth was still in recovery from the latest mass extinction at the time the Cerrejon was formed. It may also be due to the fact that the Cerrejon represents a wetland, rather than a rainforest, environment; wetlands generally host a lower diversity of plants than forests. (Gomez-Navarro et. al, 2005)

Titanoboa cerrejonensis, a dyrosaurid, and a giant turtle: the scaly, cold-blooded overlords of the Cerrejon Formation. Reconstruction by Jason Bourque.
Mean annual temperature (MAT) and mean annual precipitation (MAP) estimates are somewhat varied. Some authors suggest a balmy temperature of greater than 28C (~82F), with an average of 2,500mm (~8ft) of rainfall annually. (Gomez-Navarro et. al, 2005) Others suggest a slightly cooler MAT of 24C (~75F) and still higher rainfall levels of 3240mm (~11ft). (Herrera et. al, 2005) These figures were calculated using a method known as leaf-margin analysis: the number of angiosperm species with toothed leaves is inversely proportional to the MAT. Therefore, the greater percentage of untoothed leaves that are present in any environment, the higher the temperature is likely to be. (Niinemets et. al, 2012) Untoothed angiosperms make up anywhere from 74-78% of fossilized leaves recovered from Cerrejon, implying a high MAT for the local environment.

Scaly Monsters and Serpent Freaks
These early Neotropical wetlands of Colombia, at the northern tip of the ancient island of South America, were home to a host of reptiles. The high temperatures and humid environment favored the cold-blooded creatures and, because no large mammalian or avian predators had evolved yet, some of these grew to outrageous sizes.

A life-sized model of T. cerrejonensis swallowing an unfortunate dyrosaurid, with artist Kevin Hockley. Photo by Robert Clark.
In 2009, one particular species made headlines, breaking all kinds of records as the world’s largest, longest, and heaviest snake: Titanoboa cerrejonensis, a name that needs no explanation. Twenty-eight specimens of T. cerrejonensis were uncovered from the coal mines of the Cerrejon Formation, and the largest of these measured up to 15m (~50ft) long and tipped the scales at 1,135kg (~2,500lb).

This huge serpent was the apex predator of its environment, and, like the closely-related anacondas, hunted a variety of animals, including fish and crocodilians. As a boid, the family of snakes which includes boa constrictors and anacondas, T. cerrejonensis used its bulk and muscle to subdue its prey. With an abundance of large-bodied reptiles in the area, it was likely a specialist in hunting local dyrosaurids, as well as various species of lungfish and other large fish in the waterways.

Check back soon for the next installment of this small series, in which we will take a look at the specialized dyrosaurids of the Cerrejon. 

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