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Killing Claws



Season's Greetings,

        Sorry it's taken me so long to get back to the guns on this one, but
my mail server just went down. 
        Sorry about that typo (Emu vs. Rhea). I meant emu, although
cassowaries are real SOBs and have torn up lots of unfortunate papuans over
the years (they also have an Oviraptor philoceratops-style cranial crest).
Apparently, the family dog was harassing an emu that had marauded onto the
family ranch. The emu made quick work of the dog, and when the boy ran out
to save the dog... I won't repeat the morbid details. Let's get down to
business. Greg Paul retorted to my post with this:

>That didactyl trackways have not been found does not show that dromaeosaurs
>and troodonts were tridactyl, because if they were the latter then the second
>toes distinctive morphology should still be apparent in trackways. 

        Quite right, but I would really like to stress how terribly deceptive
tracks, especially fossil tracks, can be. Greg Paul himself could not have
been more on the mark when he stated (in PDW, p. 131): "Prints are not...
simple molds of the foot, but record the complex interaction between the
appendage and the ground." Unless the substrate was ideally suited to
reception and faithful replication of the shape of the foot, the track is
only anatomically useful in a very general way. Such features as a large
pedal claw in a hypothetical tridactyl "sickle-clawed" theropod would be
very unlikely to be apparent due to deformation in a less than ideal
substrate. "Underprints" or "ghost" impressions would be even less likely to
record such a feature. One ironic example are the multitude of Eocene bird
tracks from Washington (Chuckanut Fm.) and Utah (Green River Fm.) that I
have studied that appear to be didactyl, sometimes even over a space of
several strides, although I would be very hesitant to accept these as
evidence of didactyl ciconiiform wading birds! 
        Along this line of reasoning, Jim Farlow posted:

>          Several years ago I collected footprints of both species of 
>     seriema (Chunga burmeisteri and Cariama cristata), a couple of REALLY 
>     COOL South American gruiform ground birds; ecologically they are sort 
>     of South America's answer to the secretarybird.  I was amazed to see 
>     that both species have a big, rather dromaeosaur-like claw on digit 
>     II, and both species walk with this claw carried off the ground. 

      [I have seen photos of seriemas, but they didn't seem to indicate any
unusual gesticulation of the second digit, but I'm sure that if anyone has
a right to say that they do, it's Jim. -SG]  

>     Footprints of both birds (at least the ones I collected) do not have 
>     an impression of the claw, or if they do, the claw impresses only when 
>     the foot sinks deeply into the substrate.

        I rest my case.
        I also got a few replies to this passage of my post:
        "Third, the wear experienced by normal locomotion would have been
miniscule compared to repeated contact with bone while dispatching prey (if
the claw were even used in this role at all)."

        Tim Williams:

>Not if the sickle-clawed theropod struck at the soft underbelly.  A 
>nice, swift evisceration, and down goes the prey.
>
>[ Are we being a bit too mammalocentric here?  Would an animal with a
>  rib cage extending all the way to its pelvis have a "soft underbelly"?
>  -- MR ]

        Mickey took the words right out of my mouth. To quote innumerable
others, dinosaurs aren't mammals.

Russ Anderson stated of this passage:

>       This is a dubious assertion. The amount of time in contact
>with the ground would dwarf that of time contacting bone (presumably
>less frequently than once a day--every few days?). Depending on the
>target area, contact with bone might be unlikely. Even a small gravel
>loading in the soil would cause significant abrasion, whereas the
>claw's hardness could be expected to be comparable to that of the
>(smooth!) bone and not such a problem even when it is contacted.

        Well, a lot of living birds do get a lot of pedal claw
locomotory-related abrasion. Birds like chickens and pheasants that walk
around a lot looking for food get especially worn (I believe there is a
cut-away diagram of this in Bakker's Dinosaur Heresies). If Greg Paul is
right (and he more than likely is), dormaeosaurs spent most of their time
sleeping, and would only have been up and about when on the hunt. Also, look
at carnivore teeth: they get a lot of wear from contact with bone.
Obviously, the jaw muscles exert a lot more force a lot more often than a
hypothetical "sicle claw's" claw would. But the tooth enamel is much harder
than bone or keratin claw sheaths. Perhaps the two factors would cancel each
other out, if the claw was indeed an instument of the hunt.   

        Thomas Holtz commented on the "fighting specimen", GI 100/25:

>Having seen slides of the fully prepared specimen, this shows some really
>interesting aspects of interspecific combat.  In particular, one of the
>hindfeet (the left, if I remember correctly) is placed with the sickle-claw
>in the neck of the Protoceratops, not the belly as previously thought! 

        I think is likely that this posistion was arrived at after the death
of one or both animals. Why? If I was a Velociraptor, that would be the last
place I would put my foot (or any other portion of my anatomy, for that
matter!). The powerful beak of Protoceratops would have been its main
defence, and I don't think a living Velociraptor would put its foot so very
close to it. 
        I also wrote in my post:
        "First, several living birds have modified toe claws to suit various
tasks. herons have bizzare comb-like medial claws that they use for
preening. Cassowaries and rheas have toe claws that they often use for
combat, much in the same manner that is postulated for dromaeosaurs."

        Tim Williams responded:

>I believe one of the major reasons sickle clawed theropods are thought to 
>have carried their claws above the ground is because they have peculiar 
>articulations on the toe bones that seem to let the toe sit hyperextended.  
>Also, the claw toes have been shortened.  One quite telling feature is that 
>the other two walking toes have become nearly equal in length, presumably for 
>stability, and the foot bones have been reinforced.  As far as I know, 
>cassowaries and rheas have none of these additional modifications.

        Sure, cassowaries and emus and rheas don't, but that is because
their second digits are not as specialized as those of dromaeosaurs and
troodonts. It would seem illogical to have a big claw mounted at the end of
a long, thin, spindly digit, so this digit is shorter than the others in
dromaeosaurs for this reason, and the other two have lengthened to
compensate for the abbreviated second digit. The second toe claws on some of
the ratites are only marginally larger than on the other toes, so there is
not as great of a need for this abbreviation. It would be interesting to see
the oseology of Farlow's seriemas with regards to this point.

        I also wrote:
        "Second, and perhaps more importantly, I know of no distinct,
irrefutable didactyl theropod tracks. Period."

        Tim Williams responded:
 
>I believe I saw something on Paleoworld or some similar program of Zhi-Ming 
>Dong in Alberta with Currie finding something that resembled two toed 
>theropod tracks.  He interperated them as belonging to Troodon and had his 
>hands with two fingers extended walk around over the trackway.

        This was in a program entitled "The Great Dragon Hunt" or something
along those lines and does a very nice job of covering the Sino-Canadian
expedition of a few years back. And yes, Dong and Currie were shown
examining a small theropod trackway in Dinosaur Provincial Park. I taped
this show and I reviewed it just a few minutes ago. There were two trackways
on the mud-crack covered slab, one of a small (looked smaller than an
ornithomimid), tridactyl theropod, and a single, partial track that only
showed two toes, because the posterior half was not preserved. There is no
way to tell what the missing digit was doing. None of the tracks were well
preserved. 
        I also wrote:
        "There would have been no need to hold it aloft to reduce wear (the
claws may have even been self-sharpening, like those of a cat, for all I know)."

        Tim Williams:

>Self-sharpening cat claws?  I thought cats used couches to sharpen their 
>claws....

        I was, of course, referring to this behavior, not implying that the
claws magically sharpen themselves. My cat Gilbert uses screens.
        On the issue of claws, I recall there was some debate over Baryonyx
walkeri's famous claw, specifically concerning rather it was pedal or
manual. I know it was generally assumed it was manual, but has further
preparation of the type and only(?) specimen (BMNH R9951) refuted or
confirmed this assumption?

Humbly, 

Sam Girouard

sampaula@pacificrim.net