Hi Justin

If present be the key to the past, one can broadly assume that acoustic signals were definitely used by reptiles and their feathered counterparts during courtship. Although much information about the color, biomechanical attributes and texture etc. may be lost during fossilization, speculative skills could be used to roughly reconstruct actual scenario.

Hi Justin and Syed,

This can, of course, only be purely speculative. We can predict something about dinosaur hearing (Gleich, O., Dooling, R.J., Manley, G.A. (2005) Audiogram, body mass, and basilar papilla length: correlations in birds and predictions for extinct archosaurs. Natur-wissenschaften 92, 595-598.  and Walsh, S.A., Barrett, P.M., Milner, A.C., Manley, G.A., Witmer, L.M. (2009) Inner ear anatomy is a proxy for deducing auditory capability and behaviour in reptiles and birds. Proc. Roy. Soc. B. 276, 1355-1360.), but putting reliable limits on frequency ranges and, especially, sensitivity, is not possible. We recently showed that although it is known that male Caparcaillie produce very-low-frequency sounds with their wings (Lieser, M., Berthold, P., Manley, G.A. (2005) Infrasound in the capercaillie (Tetrao urogallus).. J. Ornithol. 146, 395-398), the females do not respond to such sounds (Lieser, M., Berthold, P., Manley, G.A. (2006) Infrasound in the flutter jumps of the capercaillie (Tetrao urogallus): apparently a physical by-product. J. Ornithol. 147, 507-509.). The frequencies produced by such fluttering wings would, of course, by of higher frequency if the feathered dinosaurs were smaller than Capercaillie.

Detection is a product of hearing sensitivity and distance, making it even harder to speculate whether feathered dinosaurs used such sounds to communicate, as we have no idea how sensitive or how loud they were. If we knew more about their environment, we might understand better the selection pressures on communication. For example: Did they live in dense vegetation and be - generally - unable to see each other?

I agree with Geoffrey Manley,

We can use the try to determine the accoustic hearing range through study of inner ear morphology. Another interesting paper containing estimates of the hearing capability of a fossil maniraptoran (of the neornithid varity) was done for the phoracosid Llallawavis scagliai in this paper: :

A new Mesembriornithinae (Aves,Phorusrhacidae) provides new insights into the Phylogeny and Sensory Capabilities of terror Birds. Degrange, F.J.,Tambussi,C.P.,Taglioretti, M.L.,Dondas,A. 2015, Journal of Vertebrate Paleontology e912656.

They also list the hearing capabilities sensu Walsh et al. (2009) and sensi Gleich et al. (2005) for other extant avial dinosaurs.There paleognath birds (Struthio, Dromaius, and Rhea) end up with a very low frequency mean hearing sesitivity.

Now we need to study much more inner ears of extinct dinosaurs to get an idea if these taxa also heard, and likely vocalised, deeper. Most wing flapping seems to produce relatively low freqeuncy sounds compared to vocalisation in extant taxa.

Oh, and one more thing: a Tyrannosaurus could hear very low frequency sound so probably a large winged theropod in courtship flapping its wings would be like a table bell signalling that food in the form of an exhausted male in the middle of the mating period is available. Buts just a fency idea of a single case, not a general suggestion about the paleoecology of thes theropods ... 

Thanks for getting this discussion going everyone.

Dr. Manley,  I appreciate your response. I helped look at basilar papilla and hair cell morphology/number across a number of galliform species in 2011, including other members of Tetraoninae.  Our lab often worked on the Ruffed Grouse, which appears to have a slight auditory 'specialization' for low frequencies based on inner ear morphology.  Interestingly, that corresponds with the predominant frequencies produced during their courtship display (I imagine you knew this already). I read your capercaillie paper during my Masters and found it very interesting.  It got me thinking about the relative importance of visual features of the male's display to female Ruffed Grouse and prompted me to look for sex differences in mesopallium volume (akin to the work done on Manakins) but I found nothing at that level.  It was a really cool paper, so thank you. Further, I'd love to see any of the Tetrao species in person, one day perhaps.   I also heard something about male peacock tails making infrasound but not whether it was attended to by females.

Anyway, I think you are right to consider the ecology of the species, which may also relate to their mating system and perhaps tell something about the sounds they may have used, if that information were available.  For example, maybe some smaller archosaurs utilized open areas for courtship, forming tight leks where they could be assessed even at low amplitude.  Perhaps smaller species within dense vegetation used low frequencies to enhance sound propagation, or had higher frequencies selected for to fall under the radar of larger predators (or the opposite to evade high frequency specialists).  Think of the arms races! Body size I think is also important, as larger reptiles and birds typically can hear lower frequencies, as Jens has mentioned.

Jens, I am also thankful for your response.  I am not sure that accurately predicting auditory range from fossils is possible. If you get a well preserved basilar papilla under an SEM, you can see the variability in hair cell length/number/distribution across the gradient of the papilla before measuring or counting and species differences abound, even relative to papillar length. Also, I remain sceptical that most dinosaurs could vocalize at all.  Modern reptiles and birds have evolved significantly different mechanisms for vocalization, the larynx and syrinx respectively.  We have no evidence that dinosaurs had a larynx and only few archosaurs discovered to date have had any indication of interclavicular air sacs, which would suggest the presence of a syrinx or something that proceeded it.  This tells us that vocalization likely evolved somewhat independently in these two groups and that their ancestors may not have vocalized at all.  I know a mute Tyrannosaurus is a sad thought, but I think the evidence suggests that is the case.

Thanks for your time guys,

Justin

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