Humpback whale. Picture THINKSTOCK
Humpback whale. Picture THINKSTOCK

The Evolutionary Studies Institute at the University of the Witwatersrand (Wits) has cracked open yet another secret from the ancient past.

It has discovered that some marine reptiles from millions of years ago had similar inner ears to modern-day aquatic creatures such as whales‚ sea turtles and crocodiles.

The inner ear may be a relatively tiny part of the body of any animal‚ but it is a powerful "map" of the lives lived by creatures, which have long since disappeared from our world.

This is because the inner ear contains a tiny sense organ responsible for balance and orientation. It gives clues to the locomotion of an animal — especially those in a three-dimensional environment like the sea.

The university said in a statement that an international team of researchers led by Dr James Neenan at Wits were surprised "that a completely extinct group of marine reptiles called sauropterygians (swimming reptiles from the age of dinosaurs) evolved similar inner ear proportions to those of some modern day aquatic reptiles and mammals", even though their lifestyle was so different.

Said Neenan: "Sauropterygians are completely extinct and have no living descendants‚ so I was amazed to see that nearshore species with limbs that resemble those of terrestrial animals had ears similar to crocodylians and that the fully-aquatic‚ flippered plesiosaurs had ears similar to sea turtles."

Unlike our gentle and placid sea turtles which have swum their way into many a story book or movie‚ plesiosaurs are described as "ferocious sea monsters similar to depictions of the mythical Loch Ness Monster"‚ and they hunted "anything from small fish and squid to large marine reptiles".

Then there are the pliosauromorphs‚ whose enormous heads‚ short necks and body shape are shared by modern whales.

"Whales have the unusual feature of having highly miniaturised inner ears [blue whales have a similar-sized inner ear to humans]‚ possibly the result of having such a short neck. Neenan and colleagues have now shown that ‘pliosauromorph’ plesiosaurs also have a reduced inner ear size‚ supporting this idea‚" said the statement.

These results are the product of convergent evolution‚ "the process in which completely unrelated organisms evolve similar solutions to the same evolutionary hurdles".

Said Neenan: "Nearshore sauropterygians swam in a similar way and had comparable lifestyles to modern-day crocodiles‚ so had similar inputs on the inner ear organ.

"Plesiosaurs also ‘flew’ under water with similar flippers to those of sea turtles‚ so it’s not surprising that the organ of balance and orientation evolved to be a similar shape between these unrelated groups."