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April 28, 2009

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Fossil snake said to break length record

Feb. 4, 2009
Courtesy Indiana University
and World Science staff

Sci­en­tists have re­cov­ered fos­sils from a 60-mil­lion-year-old South Amer­i­can snake whose length and weight might make to­day’s ana­con­das and re­tic­u­lat­e pythons seem a bit cut­er and more cud­dly.

Named Ti­tanoboa cer­re­jo­nen­sis by its dis­cov­er­ers, the size of the snake’s ver­te­brae sug­gest it weighed 1,140 kilo­grams (2,500 pounds) and spanned 13 me­ters (42.7 feet)—at least, U.S. re­search­ers say. The long­est snake spe­cies to­day is the reticu­lated py­thon of South­east Asia, which grows to 10 me­ters.

A re­port on the new find ap­pears in this week’s is­sue of the re­search jour­nal Na­ture.

“At its great­est width, the snake would have come up to about your hips,” said In­di­ana Uni­ver­s­ity Bloom­ing­ton ge­olo­g­ist Da­vid Polly, who iden­ti­fied the po­si­tion of the fos­sil ver­te­brae that made a size es­ti­mate pos­si­ble. 

“The size is pret­ty amaz­ing. But our team went a step fur­ther and asked, how warm would the Earth have to be to sup­port a body of this size?”

Crews led by Smith­so­nian Trop­i­cal Re­search In­sti­tute ge­olo­g­ist Car­los Jaramillo and Uni­ver­s­ity of Flor­i­da, Flor­i­da Mu­se­um of Nat­u­ral His­to­ry ver­te­brate pa­le­on­tolo­g­ist Jon­a­than Bloch dis­cov­ered the fos­sils in the Cer­re­jon Coal Mine in north­ern Co­lom­bia and in­ves­t­i­gated what the snake’s en­vi­ron­ment might have been like. Pa­le­on­tolo­g­ist Ja­son Head of the Uni­ver­s­ity of Toronto-Mississauga, the re­port’s lead au­thor, used in­forma­t­ion gleaned by his col­la­bo­ra­tors to make an es­ti­mate of Earth’s tem­per­a­ture 58 to 60 mil­lion years ago in an ar­ea en­com­passed by mod­ern-day Co­lom­bia.

Pa­le­on­tologists have long known of a rough cor­rela­t­ion be­tween a time per­i­od’s tem­per­a­ture and the size of its cold-blood­ed crea­tures. As the Earth’s tem­per­a­ture in­creases, so does the up­per size lim­it on poik­ilo­therms.

“There are many ways the anat­o­my of a spe­cies is cor­related with its en­vi­ron­ment on broad scales,” Polly said. “If we un­der­stand these cor­rela­t­ions bet­ter, we will know more about how cli­mate and cli­mate change af­fect spe­cies, as well as how we can in­fer things about past cli­mates from the mor­phol­o­gy of the spe­cies that lived back then.”

As­sum­ing the Earth to­day is not par­tic­u­larly un­usu­al, Head es­ti­mated a snake of Ti­tanoboa’s size would have re­quired an av­er­age an­nu­al tem­per­a­ture of 30 to 34 de­grees C (86 to 93 F) to sur­vive. By com­par­i­son, the av­er­age yearly tem­per­a­ture of to­day’s Car­ta­ge­na, a Co­lom­bi­an coast­al city, is about 83 F.

“Trop­i­cal ecosys­tems of South Amer­i­ca were sur­pris­ingly dif­fer­ent 60 mil­lion years ago,” said Bloch. “It was a rain­for­est, like to­day, but it was even hot­ter and the cold-blood­ed rep­tiles were all sub­stanti­ally larg­er. The re­sult was, among oth­er things, the larg­est snakes the world has ev­er seen... and hope­fully ev­er will.”

The trop­i­cal rain­for­est at Cer­re­jon ap­pears to have thrived at a tem­per­a­ture of 32 C (90 F), five de­grees warm­er than the up­per tem­per­a­ture lim­it for trop­i­cal rain­for­ests in mod­ern times, re­search­ers said. 

“These da­ta chal­lenge the view that trop­i­cal vegeta­t­ion lives near its cli­mat­ic op­ti­mum, and it has pro­found im­plica­t­ions in un­der­standing the ef­fect of cur­rent glob­al warm­ing on trop­i­cal plants,” said Car­ols Jaramillo, a palaeob­otanist at the Smith­so­nian Top­i­cal Re­search In­sti­tute.

Ev­o­lu­tion has pro­duced a wide va­ri­e­ty of gi­gantic an­i­mals over the last sev­eral hun­dred mil­lion years—di­no­saurs, an­cient dra­gonflies and to­day’s blue whale, to name a few. Why some spe­cies’ lin­eages pro­duce mon­sters re­mains a mat­ter of de­bate among ev­o­lu­tion­ary bi­ol­o­gists and ecol­o­gists.

The sci­en­tists clas­si­fy Ti­tanoboa as a boine snake, a type of non-venomous con­stric­tor that in­cludes ana­con­das and bo­as.

Polly ex­trap­o­lat­ed the place­ment of Ti­tanoboa fos­sil ver­te­brae by com­par­ing the fos­sils’ struc­ture to the ver­te­brae of to­day’s boine snakes. Snake ver­te­brae get big­ger near a snake’s mid­sec­tion, but they are al­so struc­tured dif­fer­ently than ver­te­brae clos­er to a snake’s head or tail. Us­ing a com­put­er mod­el he wrote, Polly es­ti­mated the fos­sil ver­te­brae orig­i­nate near Ti­tanoboa’s mid­dle. That means that if Pol­ly’s mod­el is in­cor­rect about the bone’s place­ment, the snake could have been even big­ger.

* * *

Scientists have recovered fossils from a 60-million-year-old South American snake whose length and weight might make today’s anacondas and reticulated pythons seem a bit cuter and more cuddly. Named Titanoboa cerrejonensis by its discoverers, the size of the snake’s vertebrae suggest it weighed 1,140 kilograms (2,500 pounds) and measured 13 meters (42.7 feet) nose to tail tip—and that’s a conservative estimate, researchers say. A report on the find appears in this week’s issue of the research journal Nature. “At its greatest width, the snake would have come up to about your hips,” said Indiana University Bloomington geologist David Polly, who identified the position of the fossil vertebrae, which made a size estimate possible. “The size is pretty amazing. But our team went a step further and asked, how warm would the Earth have to be to support a body of this size?” Crews led by Smithsonian Tropical Research Institute geologist Carlos Jaramillo and University of Florida, Florida Museum of Natural History vertebrate paleontologist Jonathan Bloch discovered the fossils in the Cerrejon Coal Mine in northern Colombia and investigated what the snake’s environment might have been like. Paleontologist Jason Head of the University of Toronto-Mississauga, the Nature report’s lead author, used information gleaned by his collaborators to make an estimate of Earth’s temperature 58 to 60 million years ago in an area encompassed by modern-day Colombia. Paleontologists have long known of a rough correlation between a period or epoch’s temperature and the size of its poikilotherms (cold-blooded creatures). As the Earth’s temperature increases, so does the upper size limit on poikilotherms. “There are many ways the anatomy of a species is correlated with its environment on broad scales,” Polly said. “If we understand these correlations better, we will know more about how climate and climate change affect species, as well as how we can infer things about past climates from the morphology of the species that lived back then.” Assuming the Earth today is not particularly unusual, Head estimated a snake of Titanoboa’s size would have required an average annual temperature of 30 to 34 C (86 to 93 F) to survive. By comparison, the average yearly temperature of today’s Cartagena, a Colombian coastal city, is about 83 F. “Tropical ecosystems of South America were surprisingly different 60 million years ago,” said Bloch. “It was a rainforest, like today, but it was even hotter and the cold-blooded reptiles were all substantially larger. The result was, among other things, the largest snakes the world has ever seen... and hopefully ever will.” The tropical rainforest at Cerrejon appears to have thrived at a temperature of 32 degrees Celsius (90 Fahrenheit), five degrees warmer than the upper temperature limit for tropical rainforests in modern times. “These data challenge the view that tropical vegetation lives near its climatic optimum, and it has profound implications in understanding the effect of current global warming on tropical plants,” said Carols Jaramillo, a palaeobotanist at the Smithsonian Topical Research Institute. Evolution has produced a wide variety of gigantic animals over the last several hundred million years—dinosaurs, ancient dragonflies and today’s blue whale, to name a few. Why some species’ lineages produce monsters remains a matter of debate among evolutionary biologists and ecologists. The scientists classify Titanoboa as a boine snake, a type of non-venomous constrictor that includes anacondas and boas. Polly extrapolated the placement of Titanoboa fossil vertebrae by comparing the fossils’ structure to the vertebrae of today’s boine snakes. Snake vertebrae get bigger near a snake’s midsection, but they are also structured differently than vertebrae closer to a snake’s head or tail. Using a computer model he wrote, Polly estimated the fossil vertebrae originate near Titanoboa’s middle. That means that if Polly’s model is incorrect about the bone’s placement, the snake could have been even bigger.