The origin of marine mammals

In the past, the ancestors of today's mammalian marine animals - including whales, dolphins and dolphin dolphins - first brought their feet into the water, which led to a series of evolutionary changes to become a group of animals with larger nails. But the question is, what took place first - the process of losing the ability to walk or the transition from plant to meat?

New research published in PLoS ONE this week solved the question by analyzing a series of data on morphology, behavior and genome of mammals today and their ancestors. them. The ancestors probably moved from the ground to the water before changing their diets (and teeth). After the evolutionary relationships of the larger, re-arranged group of animals, Indohyus, half-water half-eaten herbivores that lived 48 million years ago, and hippos become the closest relatives of marine animals breast.

Michelle Spaulding, the study's lead author, said: 'If you rely solely on the data of today's living species to find a relationship in this group of animals, you will certainly miss the capital diversity. yes as well as a picture of the reality that took place. Indohyus is an interesting animal because it retains the herbivores 'teeth, but has new adaptive features such as ear bones that are suitable for underwater listening.'

The origins of whales, dolphins and dolphin dolphins - profound and hairless altered species - have long been confusing for mammalian researchers.Sixty years ago, researchers first showed that mammals have relatives of grass-eating hooves, especially those with equal toes like sheep, pigs and antelopes. In other words, whales and predatory dolphins are thought to be very close to grass-eating clawed groups. Newer genetic analyzes show that among hooves and hippopotamus are the closest living relatives of marine mammals.

Eocene 'walking' whales (Ambulocetus natans) are a close relative of mammal marine animals today.(Photo: Carl Buell)

No one has tried to connect hippos and whales together based on their appearance, so fossil evidence is an important way to determine the exact evolutionary steps that the ancestors of marine mammals have experience. In the past, the origin of whales was thought to be related to mesonychid, a group of single-hoof carnivores. The recent discovery of Indohyus, herbivores have clear characteristics adapted to the water environment, making it more difficult for researchers to understand, because they have the same ear bones as marine mammals - a characteristic Good listening point in water environment.

To separate the different steps in evolutionary history (predatory characteristics or pre-existing water adaptive characteristics), Spaulding and colleagues have mapped evolutionary relationships between more than 80 species and / or breeds. Fossil animals as well as animals today. These species are graded based on 661 morphological and behavioral characteristics (eg, with or without hair, how the ankle bone shape is). 49 DNA sequences taken from 5 nuclear genes were also considered; Genetic data and morphological data were all developed on the analyzes conducted by Maureen O'Leary (Stony Brook University) and John Gatesy (University of California at Riverside). In addition, Indohyus, today's predator (dog, cat) and a group of ancient mammals (creodont) are also included.

The team found that on the least complex evolutionary tree, Indohyus and similar fossils are closely related to whales, while mesonychid is much further away. The hippopotamus is still the closest living relative. These results suggest that the ancestors of mammals have moved into the water before becoming carnivores, but the carnivorous trait has begun to develop since they are still walking on land.

O'Leary said: 'The oldest direct whale probably started eating domestic prey while still able to walk on land. Indohyus has a number of adaptive traits for listening to water but still eating plants, while Ambulocetus (a walking whale that lives 50 million years ago) is a carnivore. '

'On the evolutionary tree there clearly appear deep contradictions,' Spaulding said. 'This evolutionary backbone is very solid, but there are relatively large unstable branches moving around this spine (Indohyus and mesonychids). We need to really recheck the traits thoroughly and consider which traits actually originate from different species to completely shed light on this evolutionary tree. '

Funding for research is supported by the National Science Foundation.