page_title: Castoroides
section_title: Extinction
hierarchical_section_title: Castoroides / Extinction
caption_attribution_description: 日本語: カストロイデス（Castoroides ohioensis）の骨格標本。国立科学博物館の展示。 English: Skeleton of Giant beaver (Castoroides ohioensis). Exhibit in the National Museum of Nature and Science, Tokyo, Japan.
context_page_description: Castoroides, or giant beaver, is an extinct genus of enormous, bear-sized beavers that lived in North America during the Pleistocene. Two species are currently recognized, C. dilophidus in the Southeastern US and C. ohioensis in the rest of its range. C. leiseyorum was previously described from the Irvingtonian of Florida, but is now regarded as an invalid name. All species previously described as C. leiseyorum are considered to belong to C. dilophidus.
context_section_description: Fossils of the southeastern species, C. dilophidus, and of C. ohioensis have been dated from 11,000 years to about 1.4 Mya. Specimens from Toronto, Ontario, and the Old Crow Basin, Yukon Territory, are 130,000 years old (with an occurrence of 60,000 years ago,) but Castoroides died out about 10,000 years ago, along with several other American species, such as mammoths, mastodons, and ice-age horses. No Alaska and Yukon Territory (AK–YT) fossils of the Castoroides have been recorded after the Last Glacial Maximum (LGM) about 18,000 years BP.
  The extinction of the giant beaver may have been caused by ecological restructuring at the end of the Pleistocene. The arrival of humans in the Americas could have been a factor, but there is no evidence that humans hunted the giant beaver. It was one of the abundant Pleistocene megafauna—a wide variety of very large mammals that lived during the Pleistocene.
  Evidence from the lower Hudson Valley of New York shows that megafaunal populations collapsed many centuries in advance of the extinction event. At four localities (Otisville, Hyde Park, Binnewater Pond, and Pawelski Farm), the onset of the megafaunal population decline predates the Younger Dryas (at 12.9 cal ka BP). However, extinct megafauna (e.g., Castoroides) are securely dated to the very latest Pleistocene in nearby localities, indicating that population collapse preceded the actual extinction event. The timing of the population decline is of particular interest in that it predates a number of possible extinction mechanisms, including Younger Dryas climate change, the Clovis people and preexisting populations of indigenous peoples in North America, and the proposed extraterrestrial impact event. Sporormiella records from a sediment core recovered from Appleman Lake, Indiana show a pronounced decline in megafaunal populations during the Bølling–Allerød interstadial from 14.8 to 13.7 cal ka BP. Once again, this decline precedes the extinction for many taxa, indicating a population collapse well before the extinction event. A nutrient decelerating model suggests that as forage quality declines, herbivores must preferentially rely on those species with the highest nitrogen concentrations. Preferential feeding on plants with higher nitrogen concentrations tends to reduce plant litter quality, further limiting nitrogen availability in the soil. Over time, these feedback mechanisms decrease nitrogen availability, resulting in reduced forage production, decreased nitrogen concentrations, and reduced mammalian herbivore biomass.
caption: Mounted skeleton
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