Bonapartenykus

Bonapartenykus was an alvarezsauroid theropod that roamed modern-day Patagonia during the latest Cretaceous period. Named in honour of renowned Argentine palaeontologist Jose Bonaparte, it represents one of the largest known members of the alvarezsaurian family, spanning over two metres in length. Most late Cretaceous alvarezsaurs from the Northern Hemisphere were tiny and insectivorous, but South American forms like Bonapartenykus retained a noticeably bulkier, heavier physique. Strikingly, the type specimen was discovered directly associated with two partially crushed fossilised eggs and numerous eggshell fragments, providing invaluable evidence regarding alvarezsaurian reproductive biology and egg micro-structure. Its robust hindlimbs and specialized pelvic bones suggest it was a capable runner that likely used strong forelimbs to tear into insect nests or forage on the Late Cretaceous forest floor.

The holotype specimen was found associated with fossil eggs and eggshells.

Where and when

Bonapartenykus lived in the Late Cretaceous, from 72 to 66 million years ago (Maastrichtian age). Its remains come from Argentina, in the Allen Formation.

The numbers

Length 2.4 m (estimates run from 2.2 to 2.6 m). Mass about 42 kg. Hip height about 0.8 m. That is 1.4 human-lengths, or 0.21 of a double-decker bus. These are estimates from partial skeleton; fields marked estimated by the site are length, mass, first ma, last ma, hip height.

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