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pseudothumb (plural pseudothumbs)

1. A digit on a vertebrate that resembles but is not a thumb.
   • 2008, Heather Angel, Panda:

     But a panda's forepaws are specially adapted for manipulating bamboo stems, with a modified elongated wrist bone forming the pseudothmb covered by a fleshy pad.

   • 2016, Tim Halliday, The Book of Frogs, page 542:

     The extra digit is a "pseudothumb” containing a sheathed spine that can be pushed out.

   • 2021, Jonathan Bard, Evolution: The Origins and Mechanisms of Diversity, page 257:

     There are also at least two examples of more complex ectopic digits. The first is in the aye-aye, a Madagascan lemur, which has a distinct pseudothumb on its forelimb consisting of a bony part that is an expanded radial sesamoid and a dense cartilaginous extension (Hartstone-Rose et al., 2019). This pseudothumb receives attachments from muscles that facilitate abduction, adduction, and opposition, which together facilitate dexterity.