Mammals include any animal of the Mammalia, a large class of warm-blooded vertebrates having mammary glands in the female, a thoracic diaphragm, and a four-chambered heart. The class includes the whales, carnivores, dolphins, porpoises, rodents, bats, primates, etc. Mammals have the body more or less covered with hair, nourish the young with milk from the mammary glands, and, with the exception of the egg-laying monotremes, give birth to live young.

The exact causes behind the Permian-Triassic mass extinction have been much debated. Two separate pulses of CO2 into the atmosphere - a "one-two punch" - may have helped fuel the die-off, new research suggests. Changes to ocean acidity would have been one of the consequences, according to the study in Science journal. Computer models suggested that this CO2 may have been released by massive bouts of volcanism from the Siberian Traps, now represented as a large region of volcanic rock in northern Eurasia. The Permian-Triassic mass extinction, which took place 252 million years ago, wiped out more than 90% of marine species and more than two-thirds of the animals living on land. The event is thought to have played out over a 60,000-year period and acidification of the oceans lasted for about 10,000 years. The team led by Dr Matthew Clarkson from the University of Edinburgh analysed rocks unearthed in the United Arab Emirates - which were on the ocean floor at the time. The rocks preserve a detailed record of changing oceanic conditions at the time. They then developed a climate model to work out what drove the extinction. The researchers think the rapid rate of release of carbon was a crucial factor in driving the ocean acidification. The carbon was released at a similar rate to modern emissions. Dr Clarkson commented: "Scientists have long suspected that an ocean acidification event occurred during the greatest mass extinction of all time, but direct evidence has been lacking until now.

New species of dolphin identified. A team of researchers says it has identified a new species of humpback dolphin. Physical and genetic evidence suggests that cetaceans found in waters off northern Australia are distinct within the humpback family. This general group grows up to 2.4m in length and inhabits coastal waters from the Atlantic to the Pacific. The evidence for the distinct species in northern Australia is outlined in the academic journal Molecular Ecology. "Based on the findings of our combined morphological and genetic analyses, we can suggest that the humpback dolphin genus includes at least four member species," said co-author Martin Mendez, from the Wildlife Conservation Society's Latin America and the Caribbean programme. Dr Mendez added: "This discovery helps our understanding of the evolutionary history of this group and informs conservation policies to help safeguard each of the species." New species scheme for humpback dolphins: Atlantic humpback dolphin (Sousa teuszii), which occurs in the eastern Atlantic off West Africa An Indo-Pacific humpback dolphin (Sousa plumbea), which ranges from the central to the western Indian Ocean Another species of Indo-Pacific humpback dolphin (Sousa chinensis), inhabiting the eastern Indian and western Pacific Oceans Fourth Sousa species found off northern Australia yet to be named The authors analysed physical data gathered mostly from beached dolphins and museum specimens.