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Monospecific bone beds [was Re: "Dissed Triceratops"]



Truett Garner wrote
>Unfortunately , Triceratops is one of several ceratopsians that have not
>been found in monospecific bone beds . Achelousaurus , Eniosaurus ,
>Styracosaurus , Pachyrhinosaurus , Centrosaurus (centrosaurines ) have been
>found in monospecific bone beds ,which constitutes the best evidence for
>herding behavior. Chasmosaurus is the only chasmosaurine to be found in
>such a bone bed. Triceratops seems to have been a solitary animal , based
>on the fossil record , but very capable of handling a T.rex .
        1) Many "monospecific" bone beds are not truly monospecific. To
illustrate an example from Big Bend, the "WPA 1" Quarry of _Chasmosaurus
mariscalensis_ fame contains the remains of up to 20 ceratopsians of that
species, but also contains the remains of at least six hadrosaurs of one,
(possibly two?) species, and a number of other varied taxa (theropods,
ankylosaurs, etc). I have yet to explore the northern examples of bone
bed-style deposits, but it is my understanding that many record several
species, even if one predominates (exception, Sternberg's _Albertosaurus_
bone bed, Currie pers. com.). Presumeably for this reason, I have recently
noted the use of the term "paucispecific" for such assemblages (indicating
an assemblage of only a few species).
        2) Statements by authorities to the contrary, the presence of a
paucispecific bone bed may have little to do with herding behavior. To use
Lehman's example, if a troup of Galapogos tortoise [what's the plural of
tortoise?] were to be caught in a flood, they might produce a paucispecific
bone bed. Should we suggest that they herd? (In all fairness, Lehman has
pointed out that such animals may indeed have a complex social structure of
which we are not currently aware, possibly weakening his argument.)
        To extend the point with speculation (again inspired by the thoughts
of Lehman), it is possible that, in the great white north, ceratopsians
frequented the floodplains of large river systems, consuming the
(presumably) abundant foliage by the river's edge. A large flood even might
collect these animals and their carcasses, depositing a convenient sampling
of the river valley in one place or another. Did they then herd?
        This is not to say that there is no evidence of herding at all.
Lehman himself (in his last Dinofest presentation) provided an interesting
parallel between the sample present at the WPA 1 quarry and elephant social
groups. My point is that one should deal with any such theory critically.
        3) The phylogenetic distribution of paucispecific bone beds is
interesting, but it *must* be compared with the geographic and temporal
distribution of these deposits, as well as those distributions for the taxa
in question. I would need to know, for example, are chasmosaurines and
centrosaurines found in the same deposits of a formation in which only
centrosaurines are recovered from paucispecific bone beds?
        4) Environmental factors must be considered as well. While it is
true that there may have been fundamental differences in the social behavior
of chasmosaurines and centrosaurines, it is also possible that dietary or
habitat preferences may have brought one or the other group more often into
the circumstances which might result in bone bed-style deposition. In the
example given above, chasmosaurines (in the north, at least) may have
preferred more upland vegetation, thus keeping them out of the path of
floodplain death.
        5) The taphonomic character of the deposit must also be considered
if we are going to start trying to make paleobiological interpretations from
bone bed sites. Bone bed deposits may represent the simultaneous or
near-simulataneous "mass-kill" of a group of animals, or an attritional
deposit representing the "weak" (or simply unfortunate) culled from the
"herd". The nature of the depositional setting may also bear on the
interpretation of the assemblage. For example, I have heard that many
northern bone bed assemblages are thought to have been formed during
flooding events. This would contrast with the relatively low-energy
environments postulated for the WPA 1 quarry in Big Bend. In any case, one
cannot a priori assume that the association of some animals with bone bed
assemblages is reliable data until the nature of the assemblages is assessed.
        6) Assessment of the social habits of _Triceratops_ on the basis of
a *lack* of bone beds of that taxon is reliance upon negative evidence,
which, as we all know, is not good. Were it not for the few (somewhat
peculiar) bone bed assemblages in Big Bend, _Chasmosaurus mariscalensis_
would be known only from single individuals. Such single deposits likely
represent "attritional" deposits, where the very young, very old, ill, and
infirm have passed out of the population. "Attritional" deposits
representing the death of only one member of the population, should probably
(IMHO) constitute the rule in taphonomy, rather than the exception, and
therefore are not good grounds upon which to hypothesize social interaction.
As they say, "every man dies alone."

        Anyway, food for thought. :)
        Wagner
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    Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
"Only those whose life is short can... believe that love is forever"-Lorien