English: Aglaocetus moreni (Lydekker, 1894) - fossil baleen whale skull attributed to the Oligocene of Argentina. (FMNH P12955, Field Museum of Natural History, Chicago, Illinois, USA)

This species is also known as Cetotherium moreni and Cetotheriopsis moreni.

From museum signage: "First there were meat eaters, then came plankton feeders. Around 40 million years ago, a new group of whales diverged from the earliest toothed whales: baleen whales. Instead of teeth, these whales have a comb-like screen of tissue called baleen that grows from their upper jaws. Baleen allows whales to filter tiny plankton from the seawater, taking advantage of an abundant food source. All whales today can be divided into two groups, baleen whales and toothed whales.

[referring to skull shown above] The skull belonged to an early baleen whale. "

Classification: Animalia, Chordata, Vertebrata, Mammalia, Artiodactyla, Cetacea, Mysticeti, Aglaocetidae

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See info. at: en.wikipedia.org/wiki/Aglaocetus and

en.wikipedia.org/wiki/Baleen_whale