"Toothed whales" refers to a group of whales that have teeth in their mouth, unlike baleen whales which have baleen plates to filter their food instead. Full definition
The skull, which is among the oldest fossils ever found from that group, called Platanistoidea, confirms that Platanista belongs to one of the oldest lineages of toothed whales still alive today. (sciencedaily.com)
They found that ships are radiating underwater noise at high frequencies, 10,000 to 40,000 hertz — the same range that orcas and other toothed whales use. (sciencemag.org)
But why do many species of porpoises and other small toothed whales emit echolocation sounds at about 130 kHz? (sciencedaily.com)