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Snakes preyed on dino hatchlings, study concludes

March 2, 2010
Courtesy of the University of Toronto
and World Science staff

Sixty-se­ven mil­lion years ago, when di­no­saur hatch­lings first scram­bled out of their eggs, their first—and last—glimpse of the world might have been the open jaws of a huge snake named Sana­jeh in­di­cus, re­search­ers say.

The con­clu­sion is based on the dis­cov­ery in In­dia of a nearly com­plete fos­sil­ized ske­l­e­ton of a prim­i­tive, 3.5-meter (11 foot) long snake coiled in­side a di­no­saur nest.

A life-sized re­con­struc­tion of the mo­ment just be­fore pres­er­va­tion. The scales and pat­tern­ing of Sana­je­h’s skin is based on mod­ern rel­a­tives of the fos­sil snake. The hatch­ling di­no­saur is re­con­struct­ed from known skele­tal ma­te­ri­als, but its col­or is con­jec­tur­al. The eggs are based di­rect­ly on the fos­sils. (Cred­it: Sculp­ture by Tyl­er Keil­lor and orig­i­nal pho­tog­ra­phy by Xi­mena Er­ick­son; im­age mod­i­fied by Bon­nie Miljour</font> )

The snake lacked the wide-jawed gape seen in mod­ern snakes such as pythons and bo­as, which would have pre­vented it from eat­ing hard di­no­saur eggs, sci­en­tists say. But ba­by di­no­saurs would have been just the right prey size for a large snake, said Ja­son Head, a pa­le­on­tol­ogist at the Uni­vers­ity of To­ron­to Mis­sis­sau­ga.

“Liv­ing prim­i­tive snakes are small an­i­mals whose di­et is lim­it­ed by their jaw size, but the ev­o­lu­tion of a large body size in Sana­jeh would have al­lowed it to eat a wide range of prey, in­clud­ing di­no­saur hatch­lings,” said Head. “This is the first di­rect ev­i­dence of feed­ing be­hav­ior in a fos­sil prim­i­tive snake, and shows us that the ecol­o­gy and early ev­o­lu­tion­ary his­to­ry of snakes were much more com­plex than we would think just by look­ing at mod­ern snakes to­day.”

The fos­sils were first found in 1987 by di­no­saur egg ex­pert Dhanan­jay Mo­habey from the Ge­o­log­i­cal Sur­vey of In­dia, in rocks of the Lameta Forma­t­ion in Gu­ja­rat, a state in west­ern In­dia known for its rich fos­sil rec­ord of di­no­saurs and their eggs. Orig­i­nally iden­ti­fied as a hatch­ling di­no­saur, the fos­sils were rec­og­nized to in­clude a snake by di­no­saur pa­le­on­tol­ogist Jeff Wil­son from the Uni­vers­ity of Mich­i­gan and Mo­habey in 2001.

“I saw the char­ac­ter­is­tic ver­te­brae of a snake be­side the di­no­saur egg­shell and larg­er bones, and I knew it was an ex­tra­or­di­nary spec­i­men ... even if I could­n't put the whole sto­ry to­geth­er at that point. I just knew we needed to ex­am­ine it fur­ther,” said Wil­son. They in­vit­ed snake spe­cial­ist Head and ge­ol­o­gist Shanan Pe­ters from the Uni­vers­ity of Wisconsin-Madison, to col­la­bo­rate on the study of the fos­sils, in­clud­ing field and lab work in In­dia, the Un­ited States and Can­a­da.

Sana­jeh in­di­cus, which means “an­cient gape from In­di­a,” is rep­re­sented by a nearly com­plete skull and low­er jaws along with ver­te­brae and ribs coiled around a crushed ti­tan­o­saur egg, next to the re­mains of a 0.5-meter-long ti­tan­o­saur hatch­ling. These di­no­saurs, part of a larg­er group called sauropods, were long-necked, four-leg­ged plant-eaters that grew to weigh up to 100 tons, and Wil­son said they likely grew quickly in their first year, be­yond the reach of preda­tors like Sana­jeh.

The findings—a­long with two oth­er si­m­i­lar snake-egg pair­ings, sug­gest that snakes fed on ti­tan­o­saur hatch­lings when they emerged from their eggs. “The eggs were laid in loose sands and cov­ered by a thin lay­er of sed­i­ment. We think that the hatch­ling had just ex­ited its egg, and its move­ment at­tracted the snake,” ex­plained Mo­habey. “It would have been a smor­gas­bord,” said Head. “Hun­dreds or thou­sands of de­fense­less ba­by sauropods could have sup­ported an ec­o­sys­tem of preda­tors dur­ing the hatch­ing sea­son.”

The re­mains cap­ture a mo­ment in Cre­ta­ceous time. “Burial was rap­id and deep,” said Pe­ters. “Probably a pulse of slushy sand and mud re­leased dur­ing a storm caught them in the ac­t.”

The study ap­pears in the March 2 is­sue of the re­search jour­nal Pub­lic Li­brary of Sci­ence Bi­ol­o­gy.

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Sixty-seven million years ago, when dinosaur hatchlings first scrambled out of their eggs, their first—and last—glimpse of the world might have been the open jaws of a huge snake named Sanajeh indicus, researchers say. The conclusion is based on the discovery in India of a nearly complete fossilized skeleton of a primitive, 3.5-metre (11 foot) long snake coiled inside a dinosaur nest. The snake lacked the wide-jawed gape seen in modern snakes such as pythons and boas, which would have prevented it from eating hard dinosaur eggs, scientists say. But baby dinosaurs would have been just the right prey size for a large snake, said Jason Head, a paleontologist and assistant professor in the Department of Biology at the University of Toronto Mississauga. “Living primitive snakes are small animals whose diet is limited by their jaw size, but the evolution of a large body size in Sanajeh would have allowed it to eat a wide range of prey, including dinosaur hatchlings,“ said Head. “This is the first direct evidence of feeding behavior in a fossil primitive snake, and shows us that the ecology and early evolutionary history of snakes were much more complex than we would think just by looking at modern snakes today.“ The fossils were first found in 1987 by dinosaur egg expert Dhananjay Mohabey from the Geological Survey of India, in rocks of the Lameta Formation in Gujarat, a state in western India known for its rich fossil record of dinosaurs and their eggs. Originally identified as a hatchling dinosaur, the fossils were recognized to include a snake by dinosaur paleontologist Jeff Wilson from the University of Michigan and Mohabey in 2001. “I saw the characteristic vertebrae of a snake beside the dinosaur eggshell and larger bones, and I knew it was an extraordinary specimen ... even if I couldn't put the whole story together at that point. I just knew we needed to examine it further,“ said Wilson. They invited snake specialist Head and geologist Shanan Peters from the University of Wisconsin-Madison, to collaborate on the study of the fossils, including field and lab work in India, the United States and Canada. Sanajeh indicus, which means “ancient gape from India“, is represented by a nearly complete skull and lower jaws along with vertebrae and ribs coiled around a crushed titanosaur egg, next to the remains of a 0.5-metre-long titanosaur hatchling. These dinosaurs, part of a larger group called sauropods, were long-necked, four-legged plant-eaters that grew to weigh up to 100 tonnes, and Wilson said they likely grew quickly in their first year, beyond the reach of predators like Sanajeh. The findings—along with two other similar snake-egg pairings, suggest that snakes fed on titanosaur hatchlings when they emerged from their eggs. “The eggs were laid in loose sands and covered by a thin layer of sediment. We think that the hatchling had just exited its egg, and its movement attracted the snake,“ explains Mohabey. “It would have been a smorgasbord,“ said Head. “Hundreds or thousands of defenseless baby sauropods could have supported an ecosystem of predators during the hatching season.“ The remains capture a moment in Cretaceous time. “Burial was rapid and deep,“ said Peters. “Probably a pulse of slushy sand and mud released during a storm caught them in the act.“ The study appears in the March 2 issue of the research journal Public Library of Science Biology.