The dance of splitting and lumping will go on
as long as there are two people and something to classify. On the one hand are
the creators of new names. Are they revealing the hidden biological diversity
of the past and present, or are they necessary evils at best, scurrilous egotistical rogues who turn taxonomy into tacky monuments to
their own questionable genius at worst? On the other hand are the lumpers. Are
they providing clarity against confusing multiplicity, or are they cranky
reactionary gatekeepers who secretly (or not-so-secretly) flatter themselves
as lonely upright crusaders against disorder and incompetence? Well, fellas, you can make questionable decisions splitting or lumping!
Consider, for a moment, the case of Hypsibema:
Late in 1869, Edward Drinker Cope presented a group of bones from North
Carolina to the Academy of Natural Sciences of Philadelphia. He proposed to
name the assortment Hypsibema crassicauda. The description takes up a
grand total of 112 words (no illustrations, of course) and is reprinted below
in its entirety:
"He [Cope] exhibited a number of remains of fossil reptiles, from Sampson
Co., North Carolina, of cretaceous age, which were intrusive in miocene
beds. Among these were humerus, tibia, fibula, metatarsus, caudal vertebra,
and perhaps cervical vertebrae and ungueal phalange of a Dinosaur, discovered together by Prof. W. C. Kerr, Director of the Geological
Survey of North Carolina. The remains indicated a species having the same
general form and size as the Hadrosaurus foulkei. The caudal vertebra was of very different form, and resembled more that
of Hylaeosaurus, minus the diapophyses. This vertebra was elongate, depressed and
angulate. The animal presented various other points distinguishing it from Hadrosaurus, and was named Hypsibema crassicauda."
Note that Cope had received them second-hand, with no other information about
their association other than they were "together". He was young at this time,
not yet 30 and just getting started in this dinosaur business, but this was
just one example of a worrying tendency that would show up again in his
career: despite all of his undoubted paleontological acumen, he never seemed
to twig to the idea that perhaps collections of bones found in the same
general area did not necessarily belong to the same species or even genus. (See also Monoclonius.)
Because H. crassicauda was thought to have hadrosaurian affinities,
Lull and Wright (1942) naturally included it in "Hadrosaurian Dinosaurs of North America". By that point Cope's bounty had been reduced to a caudal
vertebra, the distal end of a humerus, a tibial shaft, and a partial
metatarsal II, catalogued as USNM 7189 (National Museum of Natural History,
Washington, D.C.). Lull and Wright passed the following judgment: "The
material is too meager and uncharacteristic to permit a real definition of the
genus and species, and the form must therefore be considered a
nomen nudum [as mentioned
here, basically a nomen dubium as understood today]. It indicates,
however, the presence in North Carolina of Cretaceous hadrosaurs of uncertain
affinities." Well, hallelujah, and so forth; insert your own uproar as the
mood strikes. (One slightly disconcerting note: Lull and Wright thought the
caudal resembled the caudal of fellow North Carolina form
Hadrosaurus tripos. Hadrosaurus tripos is now regarded as a
Pliocene whale.)
In hindsight it is very easy to say that Cope shouldn't have bothered naming
Hypsibema crassicauda. The material isn't great and there is no real
evidence that any of the bones belong to the same thing. It can be counter-argued
that he didn't know any better and was acting within the bounds of mid-19th
century vertebrate paleontology, but it still is not his finest hour. (None of the surviving bones can even articulate, for crying out loud. Even if they'd been found in an area the size of a square foot they could still easily be a hydraulic concentration of random fauna, and here he is thinking they're the same thing after getting them second-hand at best?)
So much for the 19th century.
Elsewhere and elsewhen, in 1942 geologists of the Missouri Geological Survey were studying
clay units in southeastern Missouri. One of them, Dan Stewart, came into
contact with Lulu Chronister, who told him about bones found on the Chronister
farm during the digging of a well. One thing led to another, and in early 1945
Stewart and Charles Gilmore (of Thescelosaurus and
Alamosaurus fame around here) published a description of 13 caudal
centra (neural arches apparently lost around the time of discovery) and two
fragments, catalogued as USNM 16735. They used the bones as the basis of new
sauropod Neosaurus missouriensis (Gilmore in Gilmore and Stewart 1945).
If you've never heard of Neosaurus missouriensis, it's because
Neosaurus turned out to be preoccupied, and Gilmore quickly substituted
Parrosaurus (Gilmore 1945). Gilmore (in Gilmore and Stewart 1945:25)
commented that "[t]he specimen on which the present paper is based consists
only of caudal centra that in the ordinary course of events would be
considered too meager for generic designation, but in view of the uniqueness
of both its geographical and geological occurrence the name
Neosaurus missouriensis is proposed for its reception."
Neither Hypsibema crassicauda nor
Parrosaurus missouriensis garnered much attention over the next few
decades. Then, in 1979 Donald Baird and Jack Horner published a review of
Cretaceous North Carolina dinosaurs. Things did not go well for
Hypsibema crassicauda at first; Baird and Horner determined that the
type material was chimeric. They restricted the type to just the caudal
vertebra, because Cope had based the species name ("thick-tailed") on it, and
identified it as belonging to a sauropod. They then pulled the tibial and
metatarsal fragments as hadrosaurian, and identified the "humerus" as the
distal end of a tyrannosaurid femur. So far, this is just another case of the
clinical dissection of an obscure questionable name.
Then, though, the authors brought out
Parrosaurus missouriensis. Technically speaking, with a publication
title of "Cretaceous dinosaurs of North Carolina" they could have ignored
P. missouriensis and nobody would have felt shortchanged, but they
opted to go the extra mile. In fact, they went farther than the extra mile,
sinking Gilmore's species into Cope's species: "Now that
Hypsibema has been freed of hadrosaurian encumbrances its genetic
identity with Parrosaurus becomes obvious. Every morphological feature
cited for the Missouri vertebrae can be matched in those from North Carolina.
Indeed, the possibility of specific identity cannot be dismissed..."
The bit about sauropod (mis)identification is a topic for another time and
place. For the moment, the critical piece is sinking one poorly known species
into a different poorly known genus on the basis of exactly one piece of
overlapping material: the caudal of H. crassicauda, with remnants of
the neural arch (which you don't even get with P. missouriensis). Even
if they are very similar, that's asking a lot out of dinosaurian caudal centra, which are not generally noted for having unusually high concentrations of apomorphies.
Implicitly this classification is saying that the rest of the body of the two
forms will not differ significantly, a bold statement all around. Whether or not you agree with the synonymization, I suspect you'd probably agree that it's not an ideal situation.
Because for many years there was little interest in the disposition of H. crassicauda and P. missouriensis (although missouriensis became the state dinosaur of Missouri during that time frame), the generic synonymization has persisted. Recent developments in Missouri bode fair to spur a reassessment, though.
[Note: despite the url for this entry, I did not write it in August 2018, I only started working on a post with a couple of the ideas and gave it a custom url because I didn't like the automatic version. (For that matter, the present entry owes much more to another and even older post idea.) Of course, I had long forgotten about the custom link when I dusted it off. Seeing as there's no critical reason to change it, I'll let it stay.]
References
Baird, D., and J. R. Horner. 1979. Cretaceous dinosaurs of North Carolina.
Brimleyana: The Journal of the North Carolina State Museum of Natural History
2:1–28.
Cope, E. D. 1869. [Remarks on Hypsibema crassicauda and Hadrosaurus tripos.] Proceedings of the Academy of Natural Sciences of Philadelphia 21:192.
Gilmore, C. W. 1945. Parrosaurus, n. name, replacing
Neosaurus Gilmore 1945. Journal of Paleontology 19(5):540.
Gilmore, C. W., and D. R. Stewart. 1945. A new sauropod from the Upper
Cretaceous of Missouri. Journal of Paleontology 19(1):23–29.
Lull, R. S., and N. E. Wright. 1942. Hadrosaurian dinosaurs of North America.
Geological Society of America Special Paper 40.
