Here are a couple of stories:
First from National Geographic, China's Rare River Dolphin Now Extinct, Experts Announce. The baiji's demise is attributed to overfishing, dam-building, environmental degradation, and ship collisions.
Rare Yangtze dolphin may be extinct: After a month, scientists fail to locate species; pollution named as main culprit
Chinese River Dolphin (Baiji) Feared Extinct, Hope Remains for Finless Porpoise
Fossils indicate that the ancestors of Lipotes vexillifer entered the Yangtze during the Miocene Epoch (some 20 million years ago) from the Pacific, adapting to life in freshwater. Not only is this the loss of an ancient lineage, it's the loss of an intelligent and likely sentient one. You can read more about the Yangtze River Dolphin and extinction at Wikipedia.
Reading these reports this evening, I started thinking about an sf novel, stealing a bit from The Day the Earth Stood Still and a few other sources, in which a nomadic alien species obsessed with cataloging the galaxy's biodiversity arrives at Earth. After conducting their own survey of life on this planet and discovering that man has pushed the biosphere to the edge of collapse, the aliens deliver an ultimatum to the people of Earth: Each time a species — any species — goes extinct and the cause can be traced to direct or indirect human activity, precisely 1,000,000 human beings will be executed. The aliens have technology far beyond that of early 21st Century man (this is a space opera, after all), and to prove this is no idle threat, they depopulate a couple of major cities as a demonstration. But all hope is not lost! After all, there are currently 6.5 billion humans. At only 1,000,000 per extinction, let's see...Homo sapiens sapiens might survive a a year or so before The End. Afterwards, once humanity is culled to a population of only a few hundred thousand "wild" individuals, they will be maintained by the aliens on a preserve in East Africa, near where the human species might have originally evolved. After all, this is a civilized and "humane" alien race. They will not be the cause of human extinction. Before departing to continue their galactic survey, they leave a base ship whose purpose is to restore Earth and keep humans from ever again developing the technology needed to cause ecological havoc.
Maybe once I'm done with The Dinosaurs of Mars...