If all goes well in the next few months, Chicago will be rewarded with a large, wrinkled, 120-pound bundle of joy next summer when Mauyak, a 16-year-old beluga whale, is expected to give birth at the Shedd Aquarium’s Oceanarium.
Eventually, when the baby is about a year old, keepers will take a blood sample to discover genetically which of the two male belugas at the Shedd is the father, Inuk or Naluark.
But if the keepers could extend the paternity test back through time to about 55 million years ago, they would find baby beluga’s ancient ancestors were most unwhale-like, four-legged, furry critters living not in water but on land.
The closest relative in the animal world to modern whales, in fact, is not another marine mammal. It is the hippopotamus. At least that is the conclusion of a controversial study in which Japanese scientists compared DNA material taken from whales and other modern, living mammal species, looking for close genetic connections.
The study’s findings have surprised many paleontologists, who traditionally have looked to fossils rather than DNA in their research. At the international meeting of the Society of Vertebrate Paleontology in Chicago this fall, some thought it must be wrong. Others embraced the results and the interest of genetic scientists in the quest to solve the riddle of how and why land animals millions of years ago waded into the water and transformed themselves into aquatic beasts of the deep.
Tracing the ancestry of whales has become one of the hottest areas of paleontology in the last 20 years, and the use of DNA comparisons is adding a new wrinkle. The flurry of interest by Shedd researchers over the pregnancy of the aquarium’s beluga is just one piece of an increasing scrutiny of the animal’s past and future.
Land-dwelling whale ancestors, paleontological research has shown, belonged to a group of hooved animals with an even number of toes on each foot, called artiodactyls. That means whales are related to modern artiodactyls, among them pigs, cows, deer, camels, llamas and hippos.
Placing whales as a closer relative to hippos than other artiodactyls, however, surprised the paleontologists.
“The molecular idea that hippos are closest to whales is shocking to paleontologists,” said Maureen O’Leary, a New York University paleontologist, “but I can’t explain away their evidence.”
Other animals also made the land-to-water transition, including seals, sea lions, sea cows, sea otters, manatees and dugongs. But whales did it first, and one of them–the blue whale–became the biggest animal ever to have lived on Earth.
“This is a much more dramatic evolutionary change than becoming a dog or a cow, making this jump from a completely land-based animal to a marine mammal,” said William Sanders, curator at the University of Michigan’s Museum of Paleontology. “A few other mammals made the transition, too, but whales did it first and the most elegantly.”
In the last few years, numerous primitive whale fossils have been identified, filling in the paleontological picture.
“Over the last three or four years, there has been an exciting (whale fossil) discovery every three or four months. It has become a very fast, dynamic field,” said Hans Thewissen, an anatomy professor at Northeastern Ohio Universities, who has made one of the field’s most important recent discoveries.
Doing genetic studies–comparing DNA strings from living animals to determine which ones are most closely related on an evolutionary scale–adds a new research tool to paleontology.
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Many paleontologists are skeptical, if not outright dismissive, of the DNA work. DNA and genetic analysis necessarily is limited to gathering data from tissue samples of living species and making comparisons.
Paleontologists work with fossils from which no DNA can be extracted. Still, the fossils can offer physical evidence of a vast profusion of long extinct animal and plant life that DNA analysis doesn’t detect.
The search for whale ancestry is possible, in part, because the bones of ancestral whales are relatively plentiful, found in widely scattered parts of the world.
The bones are in rock formed from the bottoms of shallow seas between 57 and 36 million years ago, later heaved above sea level in the ongoing clash and crash of continents and plate tectonics. The foothills of the Himalayas in Pakistan and the Sahara in Egypt have rich lodes of old whale bones.
Using these bones, whale paleontologists are tracing one of the most vivid pictures science has of how an animal evolved into its current niche in nature.
“There are much richer deposits of whale fossils than most other (animal) groups,” Sanders said. “Ultimately, we think we will find most of the missing links of whale evolution. We never imagined that this kind of evolutionary pattern would be so rich and diverse. That’s almost more than you can wish for.”
The land mammal that whales currently are most commonly believed to have evolved from is a long-extinct, nasty-looking hooved mammal the size of a wolf with a massive, bear-size head, the mesonychid (pronounced mayzoNEEKid).
When dinosaurs went extinct 65 million years ago, it cleared the way for mammals to dominate the world. A vast profusion of mammal life evolved to fill in the niches in the food chain left vacant by dinosaurs, the hyena-like mesonychid arising as a carnivorous hunter and scavenger.
About 55 million years ago, mesonychid apparently was not faring well on land in its competition with other carnivore species.
Paleontologists believe that in the quest for new, less competitive sources of food, mesonychid hungrily began eying dead and dying fish and other abundant, catchable marine life in shallow, slow-moving streams.
The theory is that mesonychid waded in and feasted so well that it spent increasing amounts of time in the water. Over generations and thousands of years, its limbs and body shape began to change to adapt to life in the water, becoming sleeker, legs growing shorter and feet becoming flipper-like.
But the Japanese DNA study could force the rethinking of many theories, including paleontology’s long-held belief that mesonychid is in the whale family tree, said Thewissen, who believes the DNA work is on the right track.
O’Leary, who co-authored a paper at the recent Chicago paleontological meeting that weighed DNA evidence with fossil evidence, also finds the DNA study intriguing.
“(The hippo/whale DNA study) wouldn’t preclude mesonychians from being direct whale ancestors,” she said. “Mesonychians could have given rise to both hippos and whales.”
In 1994 in Pakistan, Thewissen dug up the bones of Ambulocetus natans (“walking whale that swam”), the most primitive whale found so far. About 7 feet long, 49 million years ago it lived and hunted in the water, using feet resembling those of a seal to paddle around. And, like seals or otters, it came to shore to breed and give birth.
“It looks a lot like a crocodile and lived a lot like a crocodile,” Thewissen said. “Crocodiles are ambush predators that sit and wait for prey to wander too close to them. That’s probably what early whales were doing.”
Many regard Amublocetus as one of the greatest paleontological discoveries ever, a “missing link,” almost akin to finding the human ancestral skeleton that shows the deciding physiological changes that took Homo sapiens across the threshold from ape to humanity.
“The discovery of Ambulocetus changed everything,” O’Leary said. “Seeing a fossil whale capable of walking around on land inspired a lot of people to work on whales.”