The remarkable, recently extinct “mole‐duck” Talpanas lippa (Aves: Anseriformes) from Kauai, Hawaii: behavioral implications of its neuroanatomy and skull morphology

Abstract

Divergent evolution of island birds is well documented, and Talpanas lippa, from ~5400‐year‐old lake deposits in Kauai, may be among the strangest cases. Talpanas has synapomorphies of Anatidae and potentially oxyurines. Postcranial bones indicate that Talpanas was probably flightless and terrestrial. We microCT scanned the preserved skull elements followed by 3D visualization of the brain endocast and inner ear. We also microCTed heads of other ducks (Anas, Mergus, Oxyura), as well as those of potential analogs (kiwi, platypus), and generated brain cast, inner ear, eyeball, and skull models. The neuroanatomy of Talpanas was like that of no other known bird. The visual system was extraordinarily reduced, as evidenced by the small optic nerves and the almost indiscernible optic lobes, which, consistent with the small eyeball size as judged by orbital osteology, suggest that Talpanas was not very reliant on sight. Kiwis (Apteryx) also have very reduced visual systems, but not to the extent seen in Talpanas. Kiwis, on the other hand, have dramatically expanded the olfactory apparatus, but, in Talpanas, the olfactory bulbs were unexpanded and comparable to those of other anatids. Without question, the major sensory modality used by Talpanas was the somatosensory (touch) system, as shown by the unparalleled expansion of the trigeminal system. Kiwis and, to a lesser extent, oxyurines have enlarged trigeminal ganglia, but in Talpanas they were enormous, dominating the ventral aspect of the brain cast and excavating the skull internally and externally. Perhaps a better extant analog for Talpanas is the platypus, which likewise has reduced vision, moderate olfaction, and is a somatosensory specialist with an expanded trigeminal system. The palate and braincase indicate that Talpanas had a broad low bill that was richly supplied with tactile nerve endings. Muscle scars and mandibular differences may signal a feeding apparatus that also diverged from its dabbling duck heritage. The picture of Talpanas that emerges is of a very different duck: a flightless, weakly‐sighted, potentially nocturnal animal foraging with its broad sensate bill in the moist underbrush of Kauai.Support or Funding InformationUS National Science Foundation (IOB‐0517257, IOS‐1050154, IOS‐1456503 to LMW), and the Ohio University Heritage College of Osteopathic Medicine