( CNN ) -- To get through the long , tedious hours sitting in the fossil archives at the University of California-Berkeley , Jason Head would listen to the hypnotic sounds of The Doors . So when he happened upon one of the biggest lizards that ever walked on land , he found it fitting to name it after the band 's frontman , Jim Morrison -- the original Lizard King . But that 's not what makes this find interesting . It 's what the existence of the `` Bearded King Morrison '' tells us about the effects of climate change that 's intriguing . The climate connection . Lizards , like snakes and turtles , are cold-blooded animals . They depend on warmth from their surroundings to heat their bodies . And when the environment warms up , they become more active , get hungrier , eat more and grow . For six years , Head sifted through fossils of animals that lived 40 million years ago , looking for clues on climate change . Then it jumped out at him : The Bearded King Morrison , as Head named his now-extinct lizard . Head and his team introduced it in a study to be published Wednesday by research journal Proceedings of the Royal Society B . `` It struck me that we had something here that was quite large and quite unique , '' he said . The find was striking , because when it comes to climate trends , bigger reptiles point to a warmer climate , Head said . `` One of the things you can actually do is estimate past temperatures by looking at the body size of fossil reptiles , '' said Head , a paleontologist who studies the Earth and its atmosphere at the University of Nebraska-Lincoln . The lizard 's hefty size helped confirm the elevated global temperature during a period known as the Paleocene greenhouse . `` This would be a globally warmed time in Earth 's history , where there 's no ice at the poles , '' Head said . There was a lot of carbon dioxide in the atmosphere back then . Sound familiar ? Man-made global warming in the 21st century is pushing temperatures back up in that direction , he said . Current average temperatures are only about 2.5 degrees Celsius shy of where they were 40 million years ago , Head said , when the Bearded King Morrison grazed in the forests of what is now Myanmar . The Doors connection . The lizard 's proper scientific name is Barbarurex morrisioni , and there is a backstory to how Head arrived at it . The Doors is Head 's favorite 60 's rock band . The Doors ' founder Ray Manzarek dies at 74 . `` I had their albums going on kind of endless loop while we were writing and doing the analysis on the lizard , '' he said . The size of the lizard took him by surprise . It reminded him of the nickname of now deceased Doors singer Morrison , also known as the Lizard King . Morrison also had a reputation for standing up for the environment . The king-size lizard , the ecological connection . For Head , the name fit . The Bearded King Morrison was no dinosaur . It was smaller than today 's crocodiles and Komodo dragons . But those are carnivorous reptiles . This was an herbivore . It ate plants . It was six feet long and weighed as much as a German shepherd , pretty sizable for a lizard . Head says he has n't found fossil records that show why the creature eventually went extinct . The big deal . The evolution of such a large reptile shows what a huge effect a slight warming bump can have , Head said . With the ice caps gone , Earth 's climate became warm and muggy , and forest covered the planet . There was plenty of greenery for the chubby lizard to munch through . As man-made climate change progresses , existing reptiles will spread out into new territory , Head predicts . So can we see another spurt of such giant lizards ? Unlikely . For them to evolve to the size of the Bearded King Morrison , they would require global temperatures to slowly rise a few degrees and then remain stable for a very long time . Today 's climate is warming so rapidly that `` we 'll basically block off their ability to respond to the temperature increase , '' Head said . Instead of evolution , he said , we 'll see extinction . Or , as Morrison sang , `` This is the end , my only friend . '' More space and science news from CNN Light Years . Follow @ CNNLightYears on Twitter .
Lizard 's size confirms elevated global temperature during Paleocene greenhouse period . The cold-blooded animals depend on warmth from their surroundings to heat their bodies . Man-made global warming in the 21st century pushing temperatures back up in that direction .