Fossil Pegs Origin of Dolphin Echolocation
Modern dolphins fine-tuned their ability to use sound to map their world at least 26 million years ago.
Modern dolphins fine-tuned their ability to echolocate –- using high-frequency sounds and their echoes to communicate, navigate and hunt –- at least 26 million years ago, according to a new fossil analysis.
In a study out of Monash University and Australia's Museum Victoria, researchers examined the 26-million-year-old ear bone of a xenorophid whale, one of the earliest ancestors of modern toothed whales - a group that includes dolphins as well as sperm whales, beaked whales and porpoises.
Using CT scanning, the scientists were able to view the ear bone's structures in sharp detail.
The cochlea of the ancient animal, the team found, was specialized for the ability to sense high-frequency sound. And that looked familiar.
"When I first looked at the inner ear of the xenorophid, I was blown away by just how similar this incredibly old toothed whale was to a modern echolocating dolphin," said study lead Travis Park, of Monash University and Museum Victoria, in a statement.
Echolocation allows some animals, such as bats and dolphins, to emit sounds and use their return echoes to map things in their world - from prey to predator to inanimate object. It's a kind of "sight" that's considered an evolutionary advantage that helped animals in the toothed whale category spread and diversify across the Earth.
The similarity between the ancient toothed whale's inner ear and that of today's dolphin, the researchers say, solves a long-running mystery of just when dolphins first evolved their ability to echolocate.
The finding also confirmed that ancient toothed whales could echolocate at all.
Researchers had previously thought the creatures could make high-frequency sounds. "But no one had actually ever looked to see whether they could actually hear these high frequency sounds as well," as Park told ABC Online's Rachel Brown.
Still unanswered, say the scientists, is what came before these super-sonic marine mammals.
"Our paper shows even the earliest known fossil odontocetes [toothed whales] have all the tools for echolocation seen in living dolphins," said study co-author Erich Fitzgerald, of Museum Victoria. "But they must have evolved from something that didn't quite have all the tricks of the odontocete trade."
Just how those earlier creatures evolved their way toward their future sonic prowess, then, remains an open question.
Park, Fitzgerald, and co-author Alistair Evans have published their findings in the journal Biology Letters.
Hippos turn out to have one of the longest family lineages in Africa, according to a new study that finds hippos were among the first large mammals to invade Africa 33–35 million years ago. The study, published in the journal Nature Communications, also sheds light on the unexpected family tree of these hefty, large-toothed animals -- including their close lineage to whales. Hippos are part of an animal group known as bothriodontines. Bothriodines "first appeared in Southeast Asia 37 million years ago," lead author Fabrice Lihoreau of Montpellier II University's Institute of Evolutionary Sciences explained to Discovery News. Some of these animals later traveled from Asia to Africa, "probably thanks to their ability to swim," he added.
For the study, Lihoreau and his team analyzed remains of a newly discovered hippo ancestor,
. It lived about 30 million years ago. "We can say that it was an herbivorous mammal weighing 155-220 pounds with a size close to that of a large sheep," Lihoreau said. "However, it was 20 times smaller than the living common hippopotamus. It must have looked like a small and slender hippo."
Other DNA studies found that hippos are closely related to whales, but that seemed hard to believe. They are not exactly twins. The teeth of
clinched the whale connection, and also allowed the researchers to reconstruct the family tree of hippos. As for how two such different animals -- whales and hippos -- could be so closely related, Lihoreau explained that their more direct ancestors evolved in different environments. The pre-whale group existed near a continental sea between India and Asia and ate either fish or meat. The pre-hippo group (anthracotheres) "were found in swamp deposits on the continent, and might have been restricted to fresh water and only feeding on plants," he said. "These ecological differences might explain two divergent evolutions."
The "sister group" to hippos includes, not only whales, but also dolphins and porpoises. These marine mammals don't fare well out of water, but hippos spend time both in water and on land. "Hippos are nowadays the last representatives, with beavers and capybaras, of a semi-aquatic lifestyle," Lihoreau said. He added that this way of living "was frequent in the past." Over time, it seems that most other species evolved to become either land or water specialists.
The sister group of hippos and cetaceans (whales, dolphins and porpoises) are ruminants. These are mammals that feast on plants, which they then ferment in their specialized stomach prior to digestion. Cows are in this group.
Deer are ruminants too -- so they are also related to hippos.
Yet another ruminant is the giraffe. Goats, sheep and antelopes are ruminants as well, putting them on the crowded extended hippo family tree.
The most divergent family in the bunch includes wild boars. These scrappy animals are distantly related to hippos. They are native to much of Europe, Asia, the Greater Sunda Islands and North Africa.
Camels are distantly related to hippos too. They are one of the most surprising members of the extended hippo family tree. While camels have evolved to withstand desert habitats, semi-aquatic hippos would not last long under such conditions. In fact, the hippo's unique skin has to be kept wet for much of the day. Their bodies overall can also dehydrate without sufficient water.
Llamas also belong on the extended hippo family tree. They are considered to be the native South American version of the camel, but they do not live in desert environments. Llamas instead have evolved for a high altitude existence.
Way down on the extended hippo family tree are members of the genus Canis, which includes wolves, coyotes, jackals and the domestic dog. Experts continue to debate canine history, but that of hippos is becoming more clear, thanks to the new study and other research. A big mystery still surrounds the precise common ancestor of hippos and cetaceans. In order to help identify this animal, the researchers are hoping to study when marine mammals became water specialists. Pinpointing when this occurred, Lihoreau said, "could help us reconstruct" the still mysterious long-lost ancestor, which might then be added to the already crowded hippo family tree.