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Re: did mosasaurs echolocate?



REPLY: A most useful, scholarly reply to my own
tentative speculations, and very much appreciated (in
my book, I shall be referring to this posting). Over
20 years ago, preliminary research was done to
indicate that a certain small hawk uses a type of
echolocation to find hidden prey; when I relocate the
reference in my files, I'll post it. As you note, the
hearing morphology of avian dinosaurs is dissimilar to
bats, and your data on mosasaurs is concise.
*******************************************************
--- "Jaime A. Headden" <qilongia@yahoo.com> wrote:
>   Stephan Pickering brings up an interesting
> perspective on mosasaurs
> using cetaceans as a jump-off point (or comparison),
> and brings to voice
> some other taxa which can be used, in conversation
> with Davic Marjanovic.
> Thus, I would like add some certain mechanical
> constraints to
> mammalian-style echolocation, if inferred for
> reptiles, and perhaps answer
> the question with some gross, soft anatomy.
> 
>   Known warm-blooded echolocators include oilbirds
> (*Steatornis* sp.),
> most microchiropteran bats, and cetaceans. All taxa
> use a fluid medium in
> which to transmit a pulse of energy which, when
> recieved in the ear,
> translates as sound after bouncing of an object of
> high density (close to
> meeting solid state). Oilbirds, as in some bats (and
> the cave swiftlet),
> echolocate in caves and darkness, and use a simple
> set of vocally induced
> frequencies (sounding as clicks) to navigate; as in
> bats, the ear receives
> the signals via minute vibrations of the vibrissae
> in the cochlea (a bat
> can deafen itself if it hears its own clicks,
> resulting in a specialized
> stapedial muscle that detaches the bone from the
> cochlear wall when it
> transmits, but reasserts the bone in time to receive
> the muted return
> signal), and the ear bone(s) are/is slender, not
> thick. This is the first
> constraint on echolocation: tests show that a thick
> stapes is incapable of
> vibrating at the rates needed for high-frequency
> reception, meaning
> echolocation is impossible, and such stapes are
> known in all mosasauroids
> as well as lizards and most dinosaurs where the
> stapes is known. Oilbird
> and swiftlets use low frequency sounds, however, and
> it is quite effective
> for the limited use they put it through. Typically,
> however, both birds
> hunt by vision rather than hearing.
> 
>   Cetaceans are more specialized in that odontocetes
> (not mysticetes) use
> either the spermaceti organ (*Kogia* and *Physeter*)
> or the melon
> (Delphinioidea, possibly paraphyletic, including
> monodontids, extinct
> odobenocetopsids, extinct and living porpoises and
> dolphins, and orca and
> blackfish), which is connected to the pharynx and
> transmits sound at a
> frequency audible to the human ear, unlike most bat
> sounds (both are
> high-frequency, though, but dolphins have been known
> to use low, medium,
> and high frequency sounds in combination -- call it
> "language", some say);
> this structure is unique to cetaceans and involves
> an osteological marker,
> including a distinct depressed rostrum and an
> assymetrical premaxillary /
> frontal system which is concave on its dorsal
> surface and "cups" the organ
> of transmission, as Dave Marjanovic detailed.
> 
>   However, cetacean hearing involves the lower jaw
> and a unique,
> mechanical array of teeth that are utilized much as
> an antenna array such
> as the Big Ear. The ear bones of cetaceans are
> similarly delicate, and
> study of fossil cetacean ear ossicles has resulted
> in the finding of
> stapes that could and could not receive
> echolocation. This gives us our
> second constraint: transmitting organ. In cetaceans,
> bats, and birds, the
> pharynx is a highly adapted structure which is
> capable at first of
> producing high-frequency sounds, and cetaceans and
> bats can modulate them;
> birds cannot, having shifted this ability to the
> syrinx. Reptiles have
> nowhere near the known pharyngeal adaptation to
> either produce
> high-frequency sounds, or hear them, with some
> exceptions, the best being
> gekkonids. For a more detailed discussion on reptile
> hearing, Melissa
> Kaplan* has done work on this subject, and a short
> synthesis can be found
> at:
> 
>   http://www.anapsid.org/reptilehearing.html
> 
>   In short, the cranial anatomy of squamates is
> specialized to
> low-frequency sound, and the likelihood of mosasaurs
> having echolocation
> is very, very slim given their large stapes, loose
> skulls, and
> craniofacial anatomy. More like, as in extant sea
> snakes and marine
> iguanas, who regularly use their tongues when
> underwater when they
> navigate, their sense of taste was of some utility,
> and in monitors and
> monitor-like mosasauroids the cranial arrangement is
> almost identical,
> resulting in a very simple simile to be drawn. This
> is not exact; it is
> possible, but not likely given comparisons of
> echolocating animals and
> their gross anatomy with comparison to extant
> reptile hearing, that
> mosasauroids have acheived another form of
> underwater sensing, aside from
> (but including) vision; the presence of overlapping
> concurrent fields of
> vision is high in the taxa, but not as in
> binocularly-capable animals,
> this leaving the two chemosenses, which
> lepidosaurian reptiles have
> prefected on the tongue, nasal organs, and the
> Jacobsen's organs; crocs,
> similarly, have developed organs similar to the
> selachian ampullae of
> Lorenzini in their skin, but this is akin to the
> sense of touch, and does
> not help the croc hunt prey (but does to help
> navigate in some cases).
> Cetaceans, despite their mean body size, have very
> large eyes with acute
> vision, and it is a problem [for me, anyway] to
> refer to their eyesight
> being poor because of the ratio of the size of the
> eye to its gross
> weight.
> 
> * Melissa Kaplan, who wrote _Iguanas for Dummies_
> (HungryMinds, Inc.,
> 2000), is a veterinarian who specializes in
> herpetiles, mostly iguanas,
> and whose work has come through some extraordinary
> means. Her website,
> http://www.anapsid.org, goes into some detail on the
> subject of her work,
> including many things reptilian.
> 
>   Cheers,
> 
> =====
> Jaime A. Headden
> 
>   Little steps are often the hardest to take.  We
> are too used to making leaps in the face of
> adversity, that a simple skip is so hard to do.  We
> should all learn to walk soft, walk small, see the
> world around us rather than zoom by it.
> 
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