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Alligator vocal abilities + lungfish hearing

Ben Creisler

Recent non-dino papers that may be of interest:

Tobias Riede, Zhiheng Li, Isao T. Tokuda and Colleen Farmer (2015)
Functional morphology of the Alligator mississippiensis larynx and
implications for vocal production.
Journal of Experimental Biology (advance online publication)
doi: 10.1242/jeb.117101

Sauropsid vocalization is mediated by the syrinx in birds, and the
larynx in extant reptiles; but while avian vocal production has
received much attention, the vocal mechanism of basal reptilians is
poorly understood. The American alligator (Alligator mississippiensis)
displays a large vocal repertoire during mating and in
parent-offspring interactions. Although vocal outputs of these
behaviors have received some attention, the underlying mechanism of
sound production remains speculative. Here, we investigated the
laryngeal anatomy of juvenile and adult animals by macroscopic and
histological methods. Observations of the cartilaginous framework and
associated muscles largely corroborate earlier findings, but one
muscle, the cricoarytenoideus, exhibits a heretofore unknown extrinsic
insertion that has important implications for effective regulation of
vocal fold length and tension. Histological investigation of the
larynx revealed a layered vocal fold morphology. The thick lamina
propria consists of non-homogenous extracellular matrix containing
collagen fibers that are tightly packed below the epithelium but
loosely organized deep inside the vocal fold. We found few elastic
fibers but comparatively high proportions of hyaluronan. Similar
organizational complexity is also seen in mammalian vocal folds and
the labia of the avian syrinx - convergent morphologies that suggest
analogous mechanisms for sound production. In tensile tests, alligator
vocal folds demonstrated a linear stress-strain behavior in the low
strain region and nonlinear stress responses at strains larger than
15%, which is similar to mammalian vocal fold tissue. We have
integrated morphological and physiological data in a two-mass vocal
fold model providing a systematic description of the possible acoustic
space that could be available to an alligator larynx. Mapping actual
call production onto possible acoustic space validates the model's


Lungfish hear air-borne sound


Christensen, C. B., Christensen-Dalsgaard, J. and Madsen, P. T. (2015)
Hearing of the African lungfish (Protopterus annectens) suggests
underwater pressure detection and rudimentary aerial hearing in early
Journal of Experimental Biology 218: 381-387
doi: 10.1242/jeb.116012

In the transition from an aquatic to a terrestrial lifestyle,
vertebrate auditory systems have undergone major changes while
adapting to aerial hearing. Lungfish are the closest living relatives
of tetrapods and their auditory system may therefore be a suitable
model of the auditory systems of early tetrapods such as Acanthostega.
Therefore, experimental studies on the hearing capabilities of
lungfish may shed light on the possible hearing capabilities of early
tetrapods and broaden our understanding of hearing across the
water-to-land transition. Here, we tested the hypotheses that (i)
lungfish are sensitive to underwater pressure using their lungs as
pressure-to-particle motion transducers and (ii) lungfish can detect
airborne sound. To do so, we used neurophysiological recordings to
estimate the vibration and pressure sensitivity of African lungfish
(Protopterus annectens) in both water and air. We show that lungfish
detect underwater sound pressure via pressure-to-particle motion
transduction by air volumes in their lungs. The morphology of lungfish
shows no specialized connection between these air volumes and the
inner ears, and so our results imply that air breathing may have
enabled rudimentary pressure detection as early as the Devonian era.
Additionally, we demonstrate that lungfish in spite of their atympanic
middle ear can detect airborne sound through detection of
sound-induced head vibrations. This strongly suggests that even
vertebrates with no middle ear adaptations for aerial hearing, such as
the first tetrapods, had rudimentary aerial hearing that may have led
to the evolution of tympanic middle ears in recent tetrapods.