Friday, 30 January 2015

Size Matters

Ten years ago a gay fossil hunter, a professional palaeontologist, Edwin Cadena, uncovered a new species of giant turtle which helps to explain how such creatures could grow so large and what ecological environment could have led to its evolution. Edwin was a member of an expedition from the Smithsonian Tropical Research Institute in Panama and the University of Florida.

They had been alerted to a potentially rich seam of fossils in a huge open-cast coal mine in Cerrejón in northern Colombia by a fossil plant in a display case at a coal company. It was only when a professor from the University of Florida recognised it as part of an unusual jawbone and not a leaf that fossil-hunters began to get excited about what else they’d find at the mine.

Studying for an MSc in Geology at the University of Florida, Edwin Cadena was invited to join the expedition team that went to Cerrejón. Being a native of Colombia Edwin was an ideal choice. In 2004 the expedition collected as many fossils from the coal mine as it could.

They came back several more years and the specimens were sent to the University of Florida for cleaning and identification. Three years later a graduate student unpacked one fossil vertebrae labelled “crocodile”. After it was cleaned up it was obvious to him that it was too big for a crocodile (specimens aren’t usually examined in detail on site). When a specialist in fossil snakes saw it he was amazed at its size and began research into the bone and others bagged up from the same site in the coal mine. With only an incomplete snake skeleton to go on it took a couple of years of comparing other known giant snake fossils before palaeontologists finally revealed that the Cerrejón fossil belonged to the biggest snake ever known. They gave it the scientific name of Titanoboa cerrejonensis – literally “titanic boa from Cerrejón”. Later discoveries of other Titanoboa fossils have confirmed their findings.

Titanoboa was so big that it could swallow a fully-grown adult crocodile whole. It weighed over a ton, and about 42 feet long. If you own a car think about this next time you open any one of the car doors. It doesn’t matter what make of car it is, Titanoboa would find it a bit of a squeeze getting through that open door, if at all!

Titanoboa was discovered in rock strata that were formed between 58 and 60 million years ago in what is called the Palaeocene epoch. That was long after the extinction of the big dinosaurs.

Other giant fossils were discovered at the Cerrejón mines, and that brings us back to Edwin Cadena. While research was still being carried out on Titanoboa Edwin was back in that coal mine chipping away at the rock. It was ten years ago this month that he discovered that brand new species of giant turtle. It wasn’t the largest ever found, but he was the first human to set eyes on this new animal. It must have felt like his birthday. Considering he discovered the first bone a couple of days after his actual birthday, that’s probably true!

In fact there were two discoveries. First Edwin found a huge fossil turtle shell. It was about 5 feet 7 inches from front to back – just about the same at Edwin’s height. About 200 meters away he found a huge turtle skull. It was of a species previously unknown to science and Edwin eventually proved it was a new species. He gave it the scientific name Carbonemys cofrinii (literally “fresh-water turtle in coal, named after Dr. David Cofrin” – Cofrin funded Edwin’s expedition). Although there was nothing to link the shell and the skull together directly, and because no other skulls have been found in the vicinity, it is assumed that they belong to the same animal.

The Cerrejón mine has revealed other examples of giant fossils. Why did Titanoboa and Carbonemys grow so big? The mine used to be a hot swampy environment, hotter than any jungle today, and palaeontologists believe this may have been the reason. Cold-blooded reptiles need heat to enable them to move. The bigger the animal the more heat it requires, so in the hot swamp the reptiles were able to evolve into bigger species.

The illustration below gives a better idea of the relative size of these giant reptiles compared to a human, Edwin Cadena himself. (The reptile silhouettes are representative of a snake and turtle and are not actual silhouettes of the species named).

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