National Geographic

Claw Cuts and Postmortem Paleo Clues

“A tiger enrichment program was used to document actual bone damage unequivocally caused by claws.” As soon as I read that line in the abstract of this new study, I was hooked. An image hovering over the abstract pulled me in further. Embedded inside a piece of wood is a piece of bone. Reads the caption, “Figure 1. Bovid femur bolted in log, accessible to paws, but not jaws.” All this in the name of paleontology.

Fossil bones are rarely found pristine and intact. In the early days of their afterlives, bones can be burrowed into by insects, tumbled along stream beds, trampled, and otherwise come to bear the marks of postmortem history under the banner of what researchers call “bone modifications.” Sifting through these clues is part of the science of taphonomy – reconstructing how an organism died and what happened afterwards – and among the common clues that paleontologists regularly puzzle over are gouges, scrapes, and pits that seem to record bite marks. But when is such damage a clue of a prehistoric bite and when is it an indicator of scraping claws? This question is what led paleopathologist Bruce Rothschild and coauthors to devise bony toys for tigers.

Cow bone bolted into a log for the claw damage experiment. Image from  Rothschild et al., 2013.

Cow bone bolted into a log for the claw damage experiment. Image from Rothschild et al., 2013.

After carefully removing flesh from cow femora – thigh bones – so as not to damage the thin, surrounding membrane called the periosteum, researchers bolted one bone at a time inside a piece of wood. This allowed the tiger at Wichita, Kansas’ Sedgwick County Zoo to reach inside and paw the bone, but not mouth the scientific plaything. True to feline nature, the big cat was quite curious about the object. “The tiger expressed major interest in the object, pawing at the bone in the log,” Rothschild and colleagues write, “but was unable remove it from its bolted location.”

The tiger’s claws scratched the bone in at least four places. Each shallow rut created by the tiger “appeared marred and lacked periosteal covering compared to unscratched (control) regions” of the bone, the researchers report. Microscopic examination confirmed that the tiger’s claws punched through the outer periosteum to leave shallow scratches on the actual bone beneath.

Despite being composed of a material softer than bone, the tiger’s claws were able to slightly damage the cow femur. That’s a simple finding, but one that suggests that paleontologists should be on the lookout for claw scratches as they pore over fossil bones.

Frustratingly, however, the PLoS One study doesn’t go beyond a simple experiment to demonstrate that claws can damage bone tissue. The authors provide no details about the tiger’s behavior during the time the scratches were created, nor do they attempt to categorize what might separate a prehistoric claw mark from a bite wound or other damage. Likewise, I’m quite curious to know how claw scrapes created by tigers differ from those left by other cats, birds of prey, and other clawed vertebrates, as well as how scratches created by pawing differ from claw damage on bones that big cats grasp and gnaw. Documenting that claws can scratch skeletons is only a bare bones beginning to a thread of interrogation that may help us better understand the postmortem fates of creatures that perished so very long ago.

Reference:

Rothschild, B. Bryant, B., Hubbard, C., Tuxhorn, K., Kilgore, G., et al. 2013. The power of the claw. PLoS ONE 8, 9: e73811. doi:10.1371/journal.pone.0073811

There are 8 Comments. Add Yours.

  1. Bruce Rothschild
    September 10, 2013

    We agree that there are many areas for future research, but the sentinel point of this paper was a “proof of concept.” Will Rogers and Claude Bernard each communicated the observation that it is not so much what we don’t know that gets us into trouble, as what we know that ain’t so. Prior to the refuting evidence of this paper, most believed and vehemently expressed the opinion that claws could not damage bone. This study actually came about because of our perception that all facial damage in Tyrannosaurus rex could not be explained as the result of bites. We suggested that the alignment of such damage matched conspecific claws. This idea was resisted and evidence was required to allow further pursuit of that speculation. This paper proves that claws can damage bone and expands the differential considerations necessary in evaluation of marks on bone.
    This was neither a study of animal behavior, nor of how to distinguish among the various etiologies of bone damage. There is a vast literature addressing the challenges of distinguishing bite marks across family lines (e.g., hyaena and bears versus wolves). The blogger asks about claw damage from birds of prey, yet this had not been reported by previous investigators – because they were unaware that claws could. Now that we know that claws alter bone, it is time for behaviorists and forensic scientists and perhaps the blogger (who expresses interest in those attributes) to examine specificity.

  2. Laura
    September 10, 2013

    This sounds like a neat study but it shows the authors’ lack of knowledge on the extensive literature available on bone modifications caused by geological movement, weather, claws, worms, insects, digestion, stone tools, organic tools, and teeth of all kinds of creatures: carnivores, rodents, ungulates, alligators, and even humans.

  3. Old Geezer
    September 14, 2013

    “Fossil bones are rarely found pristine and intact.” I’m willing to bet that they rarely found after having been bolted inside a piece of wood. That a bone might very likely be found by a scavenger long before the muscle has been stripped or deteriorated away would suggest to me that it would more likely be subject to teeth marks instead of claw marks. Is the purpose of this study simply to have an exemplar for claw marks?

  4. Herman Diaz
    September 15, 2013

    “As soon as I read that line in the abstract of this new study, I was hooked.”

    Pun intended?

  5. Boesse
    September 15, 2013

    Geezer – the short answer is yes. The article is short, and all your questions about it can be answered (or left unanswered) after about 5 minutes of reading, as the article is freely online in the above link.

  6. Mon Acosta
    September 18, 2013

    “Frustratingly, however, the PLoS One study doesn’t go beyond a simple experiment to demonstrate that claws can damage bone tissue.”

    I have the same issues sometimes when reading health research articles that don’t provide information on their discussions nd don’t leave recommendation.

  7. Bruce Rothschild
    September 24, 2013

    I am pleased to see that blogger have acknowledged a whole spectrum of future study that this proof (that claws will actually mark bones) engenders.
    There does, however, seems to be a great deal of confusion about “proof of concept.” While there are a number of mechanisms by which bone can be marked, prior to this work, claws had been widely rejected as a possible cause. The issue was not to delineate possible causes, but to document this one. Work on attributing predator to tooth marks is in its infancy. There has been some fine, but limited work. With respect to tooth marks, it should be noted that tooth marks may vary with how the teeth were applied. There has been much speculation but how many have been actually subject to examination. Matching grooves on a tooth with the bone damage is a good start, but but actually cutting the bone with the tooth would provide more insights. The purpose of the current article was to test whether scratches on dinosaur bones were attributable to teeth impacts or if the situation was actually more complicated and required additional considerations. This publication clearly documents that it would be worthwhile to re-evaluate previous literature on tooth-mark attributions.
    Now that claws have been added to the mechanisms for bone marking, it will be up to the “behavioralists” to collaborate with students of bone to determine specificity of marks to specific behaviors and the perpetrators of that behavior.

  8. Austin
    October 3, 2013

    As far back as 1995, the Taung child was discovered to have most likely been killed by an eagle, which left claw marks on the skull. Granted, these were puncture marks, rather than scratches.

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