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RE: Nomina Dubia Part II: Rapator
No one ever suggested naming new taxa based on fragmentary remains is a good
rule to follow, we're talking about how to deal with them once they've already
been named. You're being pragmatic and following the status quo in treating
fragmentary specimens as nomina dubia once they've been called such by an
authority because that's easier than doing the detailed comparative work and
making the tough synonymization decisions.
Again, my issue with your methodology is its subjectivity. What's
"compelling"? What autapomorphies are "striking"? Does Struthiomimus have any
striking autapomorphies? Are you compelled by the manus being slightly longer
compared to the humerus than other ornithomimosaurs? Would you name
Struthiomimus today based on those characters I listed? If not it seems like a
problem since it's a universally recognized valid taxon, if so it seems you're
being inconsistant since you reject those kinds of characters for poorly known
taxa like Rapator. Things are only going to get more subtle in the future as
we find more and more new taxa that bridge the gap between what seem like
distinctive characters now, and more specimens of taxa that will show
characters that seem valid today are due to individual or ontogenetic variation.
> Date: Sun, 30 May 2010 18:10:24 -0700
> From: firstname.lastname@example.org
> To: email@example.com
> Subject: RE: Nomina Dubia Part II: Rapator
> Short answer: Fragmentary specimens should only be named when there is
> compelling reason to do so. In other words, only if the specimen shows
> striking new autapomorphies or combinations of characters (e.g.,
> _Xenoposeidon_, based on an incomplete dorsal vertebra).
> Naming a fragmentary specimen because it has a few characters that *might*
> turn out to be unique sounds like a ticking time-bomb. Somewhere down the
> line there's going to be an issue over whether this specimen is a nomen
> dubium, or whether a newer and better named specimen should be referred to
> it. So yes, I agree that avoiding potential nomina dubia is a pragmatic
> approach that follows the status quo. But to me this seems preferable than a
> proliferation of dodgy names that contribute very little (if anything) to
> dinosaur paleontology.
> --- On Fri, 28/5/10, Michael Mortimer wrote:
>> From: Michael Mortimer
>> Subject: RE: Nomina Dubia Part II: Rapator
>> To: firstname.lastname@example.org
>> Received: Friday, 28 May, 2010, 11:40 PM
>> Tim Williams wrote-
>>> Yes, and here we come to the crux of why we have
>> different opinions. For the vast majority of characters, I
>> would tend to treat them as potentially non-diagnostic.
>> These include shape or length of horn cores, length and
>> depth of sulci, size and orientation of metacarpal
>> processes, degree of fusion of metatarsals, and so on.
>>> So for our old friend _Ceratops_, I think we can
>> safely assume (and I concede that it is *just* an
>> assumption) that because of the huge variation in the length
>> and orientation of postorbital horn cores known within
>> *other* ceratopsian species, that _Ceratops_ cannot be
>> diagnosed based on the length and orientation of its
>> postorbital horn cores. I think we can say this even in the
>> absence of a specimen-level statistical analysis of
>> variation in ceratopsian horn cores.
>>> Yes, I agree. It's all very warm-and-fuzzy, and so
>> often in the eye of the beholder. But I think at a
> characters that we
>> suspect may be prone to intraspecific (including
>> ontogenetic) variation. I know there is no standard
>> operating procedure for this; your _Australovenator_ is a
>> perfect example of this.
>>> That's an excellent question. If push comes to shove:
>> you can't. Not for most characters anyway. I suspect that a
>> taxon based on a partial skeleton gets treated far more
>> leniently than a taxon based on just one or a few elements.
>> But given we have multiple elements for _Australovenator_,
>> the sum total of 'diagnostic' characters at least offers the
>> chance of a unique combination of characters.
>>> It's perhaps unfair that _Rapator_ is considered a
>> nomen dubium when we haven't actually tested the validity of
>> its metacarpal characters. Instead we've just *assumed* that
>> its characters are not reliable for diagnosing a genus.
>>> But let's say we did erect a new name for *every*
>> fragmentary specimen that has one or two characters that are
>> possibly diagnostic. The result would be a proliferation of
>> new genera and species. Such a policy would lead to an
>> explosion of highly suspect taxa, and spawn a thousand
>> arguments over whether this-or-that genus had priority. Your
>> question regarding whether _Australovenator_ should be
>> referred to _Rapator_ (based on shared characters mentioned
>> by Agnolin &c) would be repeated dozens of times over.
>> This sounds like a
>>> without us throwing more dodgy names into the mix.
>>> Your approach of giving any and all characters the
>> benefit of the doubt would justify naming taxa such as
>> _Serendipaceratops_, based on a single ulna that was said to
>> have unique proportions. I would say that
>> _Serendipaceratops_ should probably not have been named,
>> because the fact that the ulna is shaped a little
>> differently to all other known ornithischian ulnae does not
>> stack up as a 'good' diagnostic character.
>>> I think the current approach, whereby names like
>> _Rapator_ and _Ceratops_ and _Serendipaceratops_ are
>> regarded as
>> *tested* whether or not their characters are subject to
>> intraspecific variation, is an attempt at damage control.
>> While it might seem unfair, from a taxonomic perspective
>> these names tend to cause more trouble than what their
>> To me, your approach seems more like following the status
>> quo than actually doing science. You give characters
>> the benefit of the doubt too, but only when they're listed
>> as being diagnostic by their authors. If you've ever
>> gone through the diagnosis of any taxon, you'd understand
>> why I don't value characters listed in diagnoses more than
>> As an example I've studied more than Australovenator, take
>> Struthiomimus. You'd think it was obviously
>> diagnostic. Known from complete specimens and
>> such. However...
>> Osborn (1917) erected Struthiomimus for Ornithomimus altus
>> because it possessed metatarsal V, which he incorrectly
>> thought was absent from Ornithomimus velox. Later authors
>> often realized Osborn's error and synonymized the genera,
>> though Parks (1926, 1928, 1933) did name four additional
>> species in Struthiomimus because they possessed the
>> metatarsal (S. ingens, S. currelli, S. brevetertius and S.
>> samueli). Russell (1972) revised ornithomimid taxonomy and
>> was the first author to use real morphological differences
>> to validate the separation of Struthiomimus from
>> Ornithomimus edmontonicus (and his new genus
>> Dromiceiomimus), though several characters he cites are now
>> seen as invalid due to the recent synonymization of
>> Dromiceiomimus with Ornithomimus edmontonicus. Notably,
>> Dromiceiomimus samueli also has a humerus shorter than its
>> scapula, antebrachium length overlaps Dromiceiomimus', and
>> preacetabular, tibial, metatarsal and pedal digit length are
>> no longer distinct. Furthermore, all the characters proposed
>> by Russell to be apomorphies of Struthiomimus are
>> symplesiomorphies when viewed in a cladistic context. The
>> robust forelimb is plesiomorphic, being seen in all
>> ornithomimosaurs except Dr
>> and Sinornithomimus. The curved manual unguals are also
>> plesiomorphic, present in all ornithomimosaurs except
>> Dromiceiomimus, Anserimimus and "Gallimimus" "mongoliensis".
>> Dromiceiomimus is the only ornithomimosaur known with a
>> presacral column not longer than its hindlimb, as opposed to
>> Struthiomimus, Anserimimus, Gallimimus and Sinornithomimus.
>> The proximal caudal centra are also posteriorly wide (over
>> half their length) in Garudimimus, "Grusimimus", Gallimimus,
>> Ornithomimus sp. nov. and O? sedens. The transition point is
>> also posterior to the fourteenth caudal in Harpymimus,
>> Anserimimus and Gallimimus. Metacarpal I is shorter than
>> metacarpal II in all ornithomimosaurs except Anserimimus,
>> Dromiceiomimus and Ornithomimus. The elongate manual ungual
>> I (longer than ungual II) may be primitiv!
>> e for orn
>> homimids, also being present in "Grusimimus",
>> Sinornithomimus and Anserimimus. The elongate manual ungual
>> III (longer than phalanx III-3) is here found to be
>> synapomorphic of a larger clade also containing Gallimimus
>> bullatus, "G." "mongoliensis" and Ornithomimus? sedens.
>> Makovicky et al. (2004) proposed an elongate manus (>7%
>> longer than humerus) as an additional apomorphy of
>> Struthiomimus, and this seems to be true as it is otherwise
>> present only in the somewhat distantly related Ornithomimus?
>> sedens, Harpymimus and Pelecanimimus. Kobayashi et al.
>> (2006) and Longrich (2008) both proposed a small skull
>> (<50% of femoral length) is unique to Struthiomimus, but
>> this is also found here to be characteristic of the larger
>> clade also containing Gallimimus bullatus, "G."
>> "mongoliensis" and Ornithomimus? sedens. Longrich also
>> proposed many characters to distinguish Struthiomimus from
>> Dromiceiomimus (Ornithomimus in his use) and his new large
>> Dinosaur Park ornithomimid, but most were not examined in a
>> broader context. The convex ventral maxillary edge is also
>> seen in Gallimimus bullatus, Sinornithomimus and probably
>> "Gallimimus" "mongoliensis", for inst
> bital portion of the frontal
>> and dorsally flat distal caudal centra (in posterior view).
>> The latter may be plesiomorphic however, as it is also found
>> in Patagonykus and Aniksosaurus. Broad pedal unguals also
>> seem plesiomorphic, being present in Anserimimus, Gallimimus
>> bullatus and Garudimimus. Finally, the elongate
>> proximodorsal process on its pedal unguals is primitive,
>> found in Sinornithomimus, "Grusimimus", Garudimimus and
>> Harpymimus as well.
>> So of the characters listed by Osborn (1917) and Russell
>> (1972), none withstand scrutiny. Nor did over half of
>> Longrich's (2008). Which ones are we left with as
>> Diagnosis- (after Longrich, 2008) frontal with an orbital
>> rim that is completely convex in dorsal view; frontals
>> abruptly expanding posteriorly, with the anterolateral edge
>> angled 40 degrees to the midline; strongly flattened dorsal
>> edge of distal caudal vertebrae; ventrolateral edges of
>> pedal unguals rounded (unknown in most taxa).
>> (after Makovicky et al., 2004) manus 8% longer than humerus
>> (also found in Ornithomimus? sedens).
>> Gee, those seem like exactly the kinds of characters you
>> tend to dismiss. Minor proportions and angles,
>> convexities of surfaces that aren't known or examined in
>> most taxa. So unless I want to blindly follow
>> professional authority and say "Struthiomimus is valid
>> because everybody has thought so, it's complete and has had
>> long diagnoses; Rapator is a nomen dubium because the most
>> recent reviews say so, it's known from one bone and has no
>> explicit diagnosis published", I have to value these as much
>> as any other character until they've been shown to be
>> You admit that you have no objective reason to value
>> Australovenator's supposed diagnostic characters over
>> Rapator's, you just 'feel' some characters are better than
>> others and figure Australovenator has a better chance at
>> validity due to its relative completeness. Then you
>> defend your approach with a pragmatic reason rather than a
> out fragmentary
>> specimens would make my job easier, but I don't study these
>> issues because they're easy, I study them because I actually
>> care about the identity and relationships of the
>> animals. If it takes hard work to find out which name
>> to call them, then so be it. It makes it more
>> interesting and fun.
>> Mickey Mortimer
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