A Monument of Inefficiency: The Presumed Course of the Recurrent Laryngeal Nerve in Sauropod Dinosaurs

Human speech and bird vocalization are complex communicative behaviors with notable similarities in development and underlying mechanisms. However, there is an important difference between humans and birds in the way vocal complexity is generally produced. Human speech originates from independent modulatory actions of a sound source, e.g., the vibrating vocal folds, and an acoustic filter, formed by the resonances of the vocal tract (formants). Modulation in bird vocalization, in contrast, is thought to originate predominantly from the sound source, whereas the role of the resonance filter is only subsidiary in emphasizing the complex time-frequency patterns of the source (e.g., but see ). However, it has been suggested that, analogous to human speech production, tongue movements observed in parrot vocalizations modulate formant characteristics independently from the vocal source. As yet, direct evidence of such a causal relationship is lacking. In five Monk parakeets, Myiopsitta monachus, we replaced the vocal source, the syrinx, with a small speaker that generated a broad-band sound, and we measured the effects of tongue placement on the sound emitted from the beak. The results show that tongue movements cause significant frequency changes in two formants and cause amplitude changes in all four formants present between 0.5 and 10 kHz. We suggest that lingual articulation may thus in part explain the well-known ability of parrots to mimic human speech, and, even more intriguingly, may also underlie a speech-like formant system in natural parrot vocalizations.

Directed, purposeful movement is one of the qualities that we most closely associate with living organisms, and essentially all known forms of life on this planet exhibit some type of self-generated movement or motility. Even organisms that remain sessile most of the time, like flowering plants and trees, are quite busy at the cellular level, with large organelles, including chloroplasts, constantly racing around within cellular boundaries. Directed biological movement requires that the cell be able to convert its abundant stores of chemical energy into mechanical energy. Understanding how this mechanochemical energy transduction takes place and understanding how small biological forces generated at the molecular level are marshaled and organized for large-scale cellular or organismal movements are the focus of the field of cell motility. This tutorial, aimed at readers with a background in physical sciences, surveys the state of current knowledge and recent advances in modeling cell motility.

Seven cases of nonrecurrent inferior laryngeal nerves have been presented from a review of 1,000 consecutive thyroidectomies over a 20 year period. In two of these seven cases, both a nonrecurrent nerve and an additional recurrent branch were present on the right side. This double nerve presentation has not been described before. Unless one is aware of this possibility, one might inadvertently injure the major nonrecurrent trunk, having identified only a small recurrent branch. We emphasize the need for a complete nerve identification technique.