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February 24, 2015

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A land where strange crocs proliferated

Feb. 24, 2015
Courtesy of the American Museum of Natural History
and World Science staff

Thir­teen mil­lion years ago, as many as sev­en dif­fer­ent spe­cies of croc­o­diles hunt­ed in the swampy wa­ters of what is now north­east­ern Pe­ru, new re­search finds.

But these rep­tiles, in­clud­ing a sur­pris­ingly cute-looking one with round teeth, weren’t quite like the preda­tors fa­mil­iar to us to­day—they tended to fo­cus on eat­ing mol­lusks, like clams and snails, ac­cord­ing to sci­en­tists.

A reconstruction of Gna­tusuchus pe­basen­sis, a short-faced cai­man with glob­u­lar teeth that is thought to have used its snout to shov­el mud bot­toms. (© Al­do Beni­tes-Palo­mino)


With mol­lusks plen­ti­ful, this was the larg­est num­ber of croc­o­dile spe­cies co-existing in one place at any time in Earth’s his­to­ry, sci­en­tists say. The work is pub­lished Feb. 24 in the jour­nal Pro­ceed­ings of the Roy­al So­ci­e­ty B.

While the mod­ern Am­a­zon Riv­er ba­sin is one of the world’s most bi­o­log­ic­ally di­verse places, “the ori­gins of this ex­tra­or­di­nary di­vers­ity are really poorly un­der­stood,” said John Flynn, cu­ra­tor of fos­sil mam­mals at the Amer­i­can Mu­se­um of Nat­u­ral His­to­ry in New York and an au­thor of the pa­per.

“Be­cause it’s a vast rain for­est to­day, our ex­po­sure to rocks—and there­fore, al­so to the fos­sils those rocks may preserve—is ex­tremely lim­it­ed.”

How­ev­er, sci­en­tists have been able to iden­ti­fy an ar­ea of fos­sil beds, he said, with “many new and pe­cu­liar spe­cies… And what we’ve found is­n’t nec­es­sarily what you would ex­pec­t.”

Be­fore the Am­a­zon River formed, about 10.5 mil­lion years ago, the region had a mas­sive wet­land sys­tem, bi­ol­o­gists say, filled with lakes, swamps, and riv­ers draining north­ward to­ward the Car­ib­be­an. To­day the pat­tern is east­ward riv­er flow to the At­lantic Ocean in­stead, and the peak in mol­lusk pop­u­la­tions has long since passed, ac­cord­ing to Flynn and col­leagues.

Since 2002, Flynn has been co-leading ex­pe­di­tions at fos­sil out­crops of an ar­ea called the Pe­bas Forma­t­ion in north­east­ern Pe­ru. These out­crops have pre­served life from the an­cient Mi­o­cene Epoch. Three of the croc­o­dile spe­cies un­earthed in this ar­ea are new to sci­ence, the strang­est of which is Gna­tusuchus pe­basen­sis, a short-faced cai­man with glob­u­lar teeth that is thought to have used its snout to shov­el mud bot­toms, dig­ging for clams and oth­er mol­lusks. 

The re­search­ers al­so re­cov­ered what they called the first un­am­big­u­ous fos­sil specimen of the liv­ing smooth-fronted cai­man Pa­le­o­suchus, which has a long­er and high­er snout shape for catch­ing a va­ri­e­ty of prey, like fish and oth­er ac­tive swim­mers.

“We un­cov­ered this spe­cial mo­ment in time when the an­cient mega-wet­land ecosys­tem reached its peak in size and com­plex­ity, just be­fore its de­mise and the start of the mod­ern Am­a­zon Riv­er sys­tem,” said Rodolfo Salas-Gismondi, lead au­thor of the pa­per and a grad­u­ate stu­dent at the Uni­vers­ity of Mont­pel­lier, in France. 

“At this mo­ment, most known cai­man groups co-existed: an­cient lin­eages bear­ing un­usu­al blunt snouts and glob­u­lar teeth along with those more gene­ralized feed­ers rep­re­sent­ing the be­gin­ning of what was to come.”

The new re­search sug­gests that with the in­cep­tion of the Am­a­zon Riv­er Sys­tem, mol­lusk popula­t­ions de­clined and duropha­gous croc­o­diles died out as cai­mans with a broader pal­ate di­versified. To­day, the investi­gators said, six spe­cies of cai­mans live in the whole Am­a­zon ba­sin, al­though unlike before, no more than three ev­er co-exist in the same ar­ea. 


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Thirteen million years ago, as many as seven different species of crocodiles hunted in the swampy waters of what is now northeastern Peru, new research shows. But these reptiles, including a cute-looking one with round teeth, weren’t quite like the predators familiar to us today—they tended to focus on eating mollusks, like clams and snails, according to scientists. With mollusks plentiful, this was the largest number of crocodile species co-existing in one place at any time in Earth’s history, scientists say. The work is published today in the journal Proceedings of the Royal Society B. While the modern Amazon River basin is one of the world’s most biologically diverse places, “the origins of this extraordinary diversity are really poorly understood,” said John Flynn, Frick Curator of Fossil Mammals at the American Museum of Natural History and an author on the paper. “Because it’s a vast rain forest today, our exposure to rocks--and therefore, also to the fossils those rocks may preserve--is extremely limited.” However, scientists have been able to identify an area of fossil beds, he said, with “many new and peculiar species… And what we’ve found isn’t necessarily what you would expect.” Before the Amazon basin had its river, which formed about 10.5 million years ago, it contained a massive wetland system, biologists said, filled with lakes, swamps, and rivers that drained northward toward the Caribbean. Today the pattern is eastward river flow to the Atlantic Ocean instead, and the peak in mollusk availability has long since passed, according to Flynn and colleagues. Since 2002, Flynn has been co-leading expeditions at fossil outcrops of an area called the Pebas Formation in northeastern Peru. These outcrops have preserved life from the ancient Miocene era. Three of the crocodile species unearthed in this area are new to science, the strangest of which is Gnatusuchus pebasensis, a short-faced caiman with globular teeth that is thought to have used its snout to “shovel” mud bottoms, digging for clams and other mollusks. The researchers also recovered what they called the first unambiguous fossil representative of the living smooth-fronted caiman Paleosuchus, which has a longer and higher snout shape for catching a variety of prey, like fish and other active swimmers. “We uncovered this special moment in time when the ancient mega-wetland ecosystem reached its peak in size and complexity, just before its demise and the start of the modern Amazon River system,” said Rodolfo Salas-Gismondi, lead author of the paper and a graduate student at the University of Montpellier, in France. “At this moment, most known caiman groups co-existed: ancient lineages bearing unusual blunt snouts and globular teeth along with those more generalized feeders representing the beginning of what was to come.” The new research suggests that with the inception of the Amazon River System, mollusk populations declined and durophagous crocodile species went extinct as caimans with a broader palate diversified into the generalist feeders that dominate modern Amazonian ecosystems. Today, he said, six species of caimans live in the whole Amazon basin, although only three ever co-exist in the same area and they rarely share the same habitats. This is in large contrast to their ancient relatives, the seven diverse species that lived together in the same place and time.