A Colombian coal mine where scientists found the largest known snake species has offered up another gem: A new species of 20-foot-long (6-meter-long) prehistoric croc. (See pictures of Titanoboa, the biggest snake ever found.)

The 60-million-year-old Acherontisuchus guajiraensis lived alongside the snake and a bevy of other reptiles in an Amazon-like river system, which wove through one of Earth's earliest rain forests before eventually emptying into what's now the Caribbean Sea.

Within this wide, flat river, A. guajiraensis would've used its long snout to capture fish—also the favorite prey of Titanoboa. That meant the two heavyweights likely duked it out over food, with young crocs sometimes becoming dinner for the snake, experts say.

In fact, one of the problems a growing croc "would have had to deal with is trying to get fish without irritating Titanoboa to the point where, rather than going for the fish, it'd go for a croc," quipped study leader Alex Hastings, a University of Florida graduate student in vertebrate paleontology who works with the school's Florida Museum of Natural History. (Read about another prehistoric crocodile that may have been eaten by Titanoboa.)

Fossils Shed Light on Croc Evolution

Fossils of the prehistoric croc were first collected in 1994 by a geologist at the Cerrejón mine—one of the world's largest open-pit coal mines—and stored in the mine's offices until 2004.

Field expeditions between 2004 and 2007 uncovered more remains from the site, allowing researchers to piece together an adult specimen, according to the study, published recently in the journal Palaeontology.

Analysis of the fossils revealed that A. guajiranesis belonged to a family called the dyrosaurids, crocodilyforms that inhabited coastal and marine habitats. A crocodilyform is a reptile that belongs to the order Crocodilia, which includes crocodiles, alligators, caimans (picture), and gavials, among other species.

The newfound species may give scientists several insights into the evolution and eventual fate of the dyrosaurids, whose history is still somewhat fuzzy, noted Christopher Brochu, a paleontologist at the University of Iowa.

For instance, it's known that the hardy creatures arrived in South America about 75 million years ago by literally swimming across the Atlantic Ocean from Africa. Dyrosaurids are also one of the few groups of big animals that survived the mass extinction that largely killed off the dinosaurs about 65.5 million years ago. The family later flourished into many sizes and shapes, said Brochu, who wasn't involved in the research. (Related: "5 'Oddball' Crocs Discovered, Including Dinosaur-Eater.")

Yet environmental factors such as climate may have finally done them in, Brochu said. According to the fossil record, dyrosaurids dwindled as Earth grew chillier during the Eocene period (56 million to 49 million years ago).

"Getting a better understanding of the diversity and relationships of these animals enhances our ability to use these fossils to explore environmental change over time," he said.

New Croc Retreated to Rivers to Survive Mass Extinction

A. guajiranesis's discovery may lay to rest a theory that only young dyrosaurids spent time inland, before eventually returning to the sea to continue their life cycles.

Two features of the new species strengthen the idea that A. guajiranesis crocs spent their whole lives in rivers: The sheer size of the adult specimen, and the animal's long, slender pelvis, study leader Hastings said. Such a bone structure suggests the reptile had adapted over time to placid waters that did not require the bigger, flaring pelvis characteristic of marine crocodyliforms, which would've dealt with strong ocean currents.

Hastings also suspects A. guajiranesis initially retreated to rivers as a strategy to survive the extinction that killed off most life on Earth.