Naturwissenschaften (2005) 92: 595–598 DOI 10.1007/s00114-005-0050-5 SHORT COMMUNICATION Otto Gleich . Robert J. Dooling . Geoffrey A. Manley Audiogram, body mass, and basilar papilla length: correlations in birds and predictions for extinct archosaurs Received: 6 May 2005 / Accepted: 2 September 2005 / Published online: 18 October 2005 # Springer-Verlag 2005 Abstract The inner ear in the group of archosaurs (birds, crocodilians, and extinct dinosaurs) shows a high degree of structural similarity, enabling predictions of their function in extinct species based on relationships among similar variables in living birds. Behavioral audiograms and mor- phological data on the length of the auditory sensory epi- thelium (the basilar papilla) are available for many avian species. By bringing different data sets together, we show that body mass and the size of the basilar papilla are sig- nificantly correlated, and the most sensitive frequency in a given species is inversely related to the body mass and the length of the basilar papilla. We also demonstrate that the frequency of best hearing is correlated with the high-fre- quency limit of hearing. Small species with a short basilar papilla hear higher frequencies compared with larger spe- cies with a longer basilar papilla. Based on the regression analysis of two significant correlations in living archosaurs (best audiogram frequency vs body mass and best audio- gram frequency vs papillar length), we suggest that hearing in large dinosaurs was restricted to low frequencies with a high-frequency limit below 3 kHz. Introduction The dimensions of the auditory sensory epithelium are re- lated to the hearing range in vertebrates [16]. The present study provides an analysis within the group of archosaurs comparing new data on cochlear dimensions in fossil Archaeopteryx [3] and in two dinosaur species [9, 19] with data from Caiman and from extant avian species. Birds are highly vocal animals, and consequently, there are consider- able data sets available on avian hearing from behavioral as well as anatomical and physiological techniques [8]. Here, we compare the frequency of best hearing and a measure of the high-frequency limit of hearing derived from behavior- ally determined audiograms of many avian species with morphological parameters (body mass and the length of the basilar papilla) and use the resulting correlations to predict the functional characteristics of the hearing organs of some extinct relatives. Methods Behavioral audiograms for a number of bird species were taken from publications that are listed in Fay [4] and Dooling ([2]; for detailed references of audiogram data, see S1). These data form the basis for our comparison of hearing in a total of 37 species. For each species, the raw audiogram data points [threshold in decibel sound pressure level (dB SPL) and frequency in kilohertz] were used to calculate a best-fit third-order polynomial in 100-Hz fre- quency steps for the range of frequencies for which thresh- olds had been measured. From these functions, we determined the frequency of best hearing (i.e., the frequen- cy with the lowest threshold) and the high-frequency limit of hearing (defined as the point on the high-frequency side of the audiogram where threshold rises to ≥30 dB above the lowest threshold, corresponding to the highest frequency represented on the basilar papilla; [9]). Direct measurements of the length of the basilar papilla were obtained for 19 bird species and for Caiman crocodilus from a number of publications (see S1 for a complete list of Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00114-005-0050-5 and accessible for authorised users. O. Gleich (*) ENT Department, University of Regensburg, Franz-Josef-Strauß-Allee 11, 93042 Regensburg, Germany e-mail: otto.gleich@klinik.uni-regensburg.de Tel.: +49-941-9449426 Fax: +49-941-9449424 R. J. Dooling Department of Psychology, University of Maryland, College Park, MD 20742, USA G. A. Manley Lehrstuhl für Zoologie, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany