Study re­veals first di­rect ev­i­dence of Basilosaurus isis’ diet

15-me­tre-long an­cient whale, dis­cov­ered in Wadi Al-Hi­tan, was top ma­rine preda­tor

The Daily News Egypt - - Front Page - By Mo­hammed El-Said

Be­fore 37m years, the Fay­oum desert— where the 200 sqkm Wadi Al-Hi­tan is lo­cated—was cov­ered with water as part of the old Mediter­ranean Sea, “Tethys Sea,” which has ex­isted about 200m years ago. In this en­vi­ron­ment, Basilosaurus isis lived as one of the biggest ma­rine preda­tors in his­tory top­ping the eco­log­i­cal pyra­mid.

Ac­cord­ing to a study pub­lished on Wed­nes­day in the open-ac­cess jour­nal PLOS ONE, an in­ter­na­tional re­search team re­vealed for the first time the diet of Basilosaurus isis. The 15-me­tre-long and 1.5-met­ric-tonne an­cient whale was an apex preda­tor that lived in the late Eocene about 38-34m years ago.

In 2010,a team, led by Man­jaVoss from the Mu­seum of Nat­u­ral His­tory in Berlin, un­cov­ered the stom­ach con­tents of an adult Basilosaurus isis in the WadiAl-Hi­tan. The dis­cov­ery re­vealed the re­mains of sharks, large bony fish, and, most nu­mer­ously, bones from Dorudon atrox, a smaller species of an­cient whale.

The Wadi Al- Hi­tan, which is now a UNESCO world her­itage site, was once a shal­low sea dur­ing the late Eocene pe­riod and is re­mark­able for its wealth of ma­rine fos­sils.

The Basilosaurus skele­ton was dis­tinct from other skele­tons in the clus­ter, con­tain­ing Basilosaurus isis in­cisors and sharp cheek teeth, as well as bones. Most of the fish and Dorudon whale re­mains showed signs of break­age and bite marks, and tended to be clus­tered within the body cav­ity of the an­cient whale.

The dis­cov­ery de­rives its im­por­tance from be­ing the first di­rect ev­i­dence of Basilosaurus’s diet. The study con­firms a preda­tor- prey- re­la­tion­ship of the two most fre­quently found fos­sil whales in Wadi Al- Hi­tan, Basilosaurus isis, and Dorudon atrox. It also ex­tends our knowl­edge of an­cient whales, and com­pletes the big­ger pa­le­oe­co­log­i­cal pic­ture of the late Eocene’s oceans of Egypt, said Voss.

She in­formed Daily News Egypt that the field work of the study lasted for three weeks in De­cem­ber 2010, and again in sum­mer 2016, in­clud­ing the study of the stom­ach con­tent re­mains and com­par­isons with other Basilosaurus and Dorudon spec­i­mens.

Pro­fes­sor Olivier Lam­bert from the Royal Bel­gian In­sti­tute of Nat­u­ral Sciences in­formed Daily News Egypt that the study is a very fine, im­por­tant con­tri­bu­tion, as “we have a very lim­ited knowl­edge of the prey types for most ex­tinct whales, as stom­ach con­tents are ex­tremely rare. Any new, well an­a­lysed find is thus im­por­tant,” he said.

Lam­bert ex­plained that Basilosaurids rep­re­sent a key group in the evo­lu­tion­ary his­tory of cetaceans. “First they are the ear­li­est whales to be fully aquatic ( their hind limbs are so re­duced that they can­not bear their weight on land any more). Se­cond, they most likely gave rise to the two mod­ern lin­eages: the mys­tice­tus ( baleen whales and rel­a­tives) and the odon­to­cetes ( echolo­cat­ing whales and dol­phins),” he pointed out.

Ac­cord­ing to Lam­bert, find­ing clues on Basilosaurids’ trophic in­ter­ac­tions ( preda­tor- prey in­ter­ac­tions) is cru­cial to bet­ter un­der­stand­ing the ecol­ogy of the last com­mon an­ces­tor of all mod­ern whales and dol­phins.

Basilosaurus is a very strange whale, with body pro­por­tions de­part­ing from all other con­tem­po­ra­ne­ous cetaceans. Be­cause no mod­ern ana­logue could be found, the ecol­ogy of this an­i­mal is still poorly un­der­stood, even if this is one of the most com­mon late Eocene whales, Lam­bert con­cluded.

Skele­tons of Basilosaurus isis (A) and Dorudon atrox (B)

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