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GIANT CERATOPSIDS AND HADROSAURS
A post in Digest 40 by G.S. Paul called attention to the very large Ceratopsipes
footprints noted from the Laramie Formation of Colorado by Lockley and Hunt
(1995, JVP, v. 15, p. 592-614); the presence of some footprints up to 60 to 80
cm wide suggested the presence of "great whopper horned dinosaurs" in the latest
Cretaceous (est. 15-25 tons). The post also noted that trackways further
indicate the presence of 20-30 ton hadrosaurs in the Cretaceous. This prompted
Nick Longrich (Digest 43) to note: "it seems unusual that nobody would even have
found a [bone] scrap of a giant duckbill or ceratopian . . . or has somebody?"
The quick answer is `yes'. In addition to the track sites, a number of
intriguing bones are known that verify the presence of giant hadrosaurs and
ceratopsids in the Late Cretaceous. Most material, with one or two exceptions,
is not sufficient to warrant the naming of new taxa. However, these bones,
along with a number of gigantic footprints, provide clear evidence that
remarkably huge ornithischian dinosaurs were part of the Campanian-Maastrichtian
faunas of North America.
Barnum Brown probably looked at more ceratopsid material than any person that's
ever lived, and he was so impressed with some gigantic ceratopsian bones in the
Hell Creek of Montana that he named a new species, Triceratops maximus, based on
a string of vertebrae and some ribs (1933, Amer. Mus. Novitates, no 649). He
wrote: "During ten seasons of field work in these strata [Lance-Hell Creek] I
personally have examined not less than five hundred Ceratopsian skulls and
partial skeletons [most not collected] . . . , but none of them in size
approached this record specimen - hence in all probabiliity its size cannot be
attributed to sex" [i.e., sexual dimorphism]. The cervical vertebrae have
diameters fully 30 to 70% larger than any other described species of
Lull in his monograph on the Ceratopsia (1933, Mem. Peabody Mus. Nat. Hist., v.
3) noted the "extraordinary size" of the vertebrae of T. maximus, which he
observed were similar in size to the vertebrae seen in the undescribed type of
T. "ingens." This latter species was earlier noted in print by Lull from the
Lance of Wyoming (1915, Am. Jour. Science, v 40, p. 319-348), the name
apparently derived from unpublished notes of Marsh. The "ingens" type (YPM
1828), which includes cranial and post-cranial material, remains largely
unprepared and poorly known (restudy is encouraged). Lull (1933, p. 133)
suggested: "T. `ingens' is a gigantic representative of the horridus species. .
. Triceratops maximus may prove to be but another huge specimen of the same
Ostrom and Wellnhofer (1986, Zitteliana, v. 14, p. 111-158) were exceptionally
conservative in their assessment of Triceratops, and they synonymized virtually
all the many described species of the genus within T. horridus (for contrasting
view, see recent article by Forster, 1996, JVP v. 16, who split O & W's single
species into 3 species and 2 genera). Nevertheless, even they (O & W)
acknowledged that the large size of T. maximus may "be taxonomically
significant" and that the taxon "may be unique," although they relegated the
species to nomen dubium because it is based on "inadequate material." They
considered T. ingens a nomen nudum, as it was originally published without a
description or diagnosis.
As Brown originally noted, the exceptionally large size of the T. maximus/ingens
material, when contrasted with the plethora of Triceratops specimens, may
suggest that an additional ceratopsid taxon is present in the Lancian faunas.
The 60 to 80 cm wide ceratopsid footprints noted in the Laramie Formation would
be consistent with a ceratopsid of size similar to that of "T. maximus."
Following the taxonomic assessments of Forster (1996) and Lehman (1996, Jour.
Paleontology, v. 70, p. 494-508), there appears to be a noteworthy diversity of
ceratopsid taxa in the end-Cretaceous Lancian age (late Maastrichtian) faunas of
North America. These include: Triceratops horridus, Triceratops prorsus,
Diceratops hatcheri, Torosaurus latus, Torosaurus utahensis, and the "El Picacho
ceratopsian" (unnamed but unique taxon similar to Pentaceratops in the Lancian
Naashoibito Member of New Mexico). "Triceratops" eurycephalus (Lance, Wyoming)
may conceivably represent an additional taxon; "the relatively small occipital
condyle and narrow mandibles do not resemble those of Triceratops" (nomen dubium
of Forster, p. 266), and "occital crest proportionately wider relative to skull
length than in any other species of Triceratops" (O & W, p. 144). "T. maximus"
may be an additional and gigantic Lancian taxon, or, less likely, an
exceptionally huge version of T. horridus or T. latus. Further study is needed.
I'll post a summary of occurrences of giant hadrosaurs from North America in an
upcoming Dinosaur Digest. There's a lot of intriguing material of note.
Iowa DNR-Geological Survey; Univ. Iowa, Dept. Geology