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What ever happened to Deinodon? (long)



Herewith a couple of excerpts from my 1995 article on tyrannosaurians for
Gakken:

(1) The first scientifically described tyrannosaurid specimens were
isolated teeth collected by Ferdinand Vandiveer Hayden in late 1854 or
early 1855 from the Judith River badlands in Nebraska Territory (now
in the state of Montana). A fanatic freelance fossil-hunter and
physician-turned-geologist, Hayden was named "man who picks up stones
running" by the Sioux Indians, through whose territory he frequently
passed. From time to time, he shipped his fossil collections to the
eminent paleontologist and physician Joseph Leidy at the Academy of
Natural Sciences of Philadelphia. (It was Leidy who discovered that
trichinosis is caused by parasites in undercooked meat.)  Leidy
discerned four different dinosaur genera among Hayden's tooth
specimens, and in 1856, he erected a new genus and species, Deinodon
horridus ("rough terrifying teeth"), for about a dozen medium-size to
large theropod teeth from the collection. He described them more fully
later, with illustrations, in a paper published in 1860. The teeth
Leidy illustrated appear (redrawn) in Figures 2 and 8; a list of the
Deinodon horridus teeth in the Academy of Natural Sciences of
Philadelphia collection is given in Table 2, the first such tabulation
ever published.

[I can't transmit Figures 2, 8 and Table 2, unfortunately; but if you have
the Gakken mag, they're there. Or you can wait until _Historical
Dinosaurology_ #6. :-)]

        Leidy knew that since the teeth were isolated specimens, there
was no guarantee that they belonged to the same species, let alone to
a single individual. In fact, he recognized two distinct kinds: thick,
large teeth usually serrated along the leading and rear edges (for
example, Figure 2A, C-G), and smaller teeth with keels along the sides
but none on the leading surface (Figure 2B, H, I; Figure 8). The first
kind was practically indistinguishable from teeth of the British
dinosaur Megalosaurus bucklandii (so, in 1857, Leidy briefly referred
his species to the British genus as Megalosaurus horridus). But the
second kind had a distinctive D-shaped horizontal cross-section
previously unknown among carnivorous dinosaurs: The sectioned keels
formed the corners of the D, the sectioned bulging front surface
formed the arc of the D, and the sectioned flat rear surface formed
the straight bar of the D. In some specimens (Figure 2I, 8), a low
ridge ran vertically up the flat rear surface. Leidy decided that the
differently shaped teeth corresponded merely to different tooth
positions in a single species and did not represent different species
of dinosaurs.
        In this, it turned out, Leidy was pretty much
correct. Bladelike teeth grew in the maxillae and dentaries, the
tooth-bearing upper and lower jawbones, of most large carnivorous
dinosaurs. D-sectioned teeth, however, occurred only at the front of
the snout in the premaxillae of tyrannosaurids and a scattered few
other kinds of theropods. They are a diagnostic feature that helps to
define the family Tyrannosauridae.

(2) In distinguishing Laelaps aquilunguis from Deinodon horridus, Cope
noted that Laelaps did not have the distinctive D-sectioned teeth of
Deinodon; all its teeth were the bladelike, serrated-front-and-back
variety. No doubt prompted by Cope's paper, Leidy reconsidered his
original position that the Deinodon teeth all belonged to a single
species. In 1868, he removed three of the four D-sectioned teeth
(Figure 2B, I and Figure 8: the ones indicated by daggers in Table 2)
from the syntype series of Deinodon horridus and made them syntype
specimens of the new genus and species Aublysodon mirandus.
        Cope, however, objected. He asserted that in his Laelaps
description he had already singled out precisely those three teeth as
"typical" of Deinodon, because they were the distinctive teeth that
permitted Deinodon to be distinguished from Megalosaurus and
Laelaps. In singling out those teeth, Cope declared, he had become
first revisor of the species and had restricted the type specimen of
Deinodon horridus to just the three "typical" teeth.  Thus the type
specimen of Deinodon horridus was no longer the entire series of teeth
Leidy used in 1856 and 1860. Leidy's Aublysodon mirandus, Cope
asserted, was a junior objective synonym of the revised Deinodon
horridus the instant Leidy published its description, because it was
based on exactly the same three teeth.
        Cope was, of course, primarily interested in protecting the
integrity of his genus Laelaps: Complete dentitions of Megalosaurus
and Laelaps were then unknown (as they still are even today), so there
was no way to be certain that those dinosaurs lacked D-sectioned teeth
(though they probably did). By making just the D-sectioned teeth the
new syntype specimens of Deinodon horridus, Cope tried to ensure that
Laelaps would not be sunk in the future as a junior synonym of the
older name Deinodon. But Cope further asserted that Deinodon happened
to be preoccupied by an earlier-named snake genus. So the second
generic name applied to the three "typical" teeth, Aublysodon, would,
according to the rules, become the correct name of the genus after
all!
        Thenceforward Cope always referred to Leidy's species by the
name Aublysodon horridus (the trivial name mirandus being junior to
horridus by twelve years). And as Cope himself explained in 1877, it
had not escaped his notice that Aublysodon was junior to Laelaps by
two years, so in the unlikely event a synonymy between his and Leidy's
taxon were later established, Laelaps still had priority over
Aublysodon.
        But Cope's hopes for the name Laelaps were dashed by his
diehard paleontological rival Othniel Charles Marsh. Marsh, or someone
working for him, discovered that the name had previously been given to
a genus of spiders in 1835. So in an 1877 paper Marsh quite
offhandedly in a footnote, as if it were a trivial matter (but no
doubt with a certain amount of glee), proposed Dryptosaurus to replace
the preoccupied Laelaps. Cope was infuriated; he retorted that Marsh's
action was incorrect because the earlier Laelaps was merely a junior
synonym. Unfortunately for Cope, this does not matter, and Marsh's
name has become the accepted name for the genus. Thus, Laelaps
aquilunguis became Dryptosaurus aquilunguis, and Laelaps macropus
became Dryptosaurus macropus. Naturally, Cope himself never accepted
Marsh's generic name or reasoning and continued to employ Laelaps the
rest of his life.

(3) Marsh seems to have been the first to pay taxonomic attention to
the presence or absence of serrations on the edges of tyrannosaurid
teeth. In 1892, he selected the one small, unserrated premaxillary
tooth (ANSP 9535; Figure 8) of Leidy's three D-sectioned type teeth of
Aublysodon mirandus as "typical" of that genus and species. The other
two serrated D-sectioned teeth he left in Deinodon horridus. This is
exactly similar to what Cope did with Deinodon horridus in 1866: Marsh
restricted the definition of the taxon to a subset of its previous
syntype series. (This aspect of his 1892 paper, incidentally, seems to
have been overlooked by most subsequent workers.) Then he erected
Aublysodon amplus (Figure 9) and Aublysodon cristatus (Figure 10) for
other unserrated D-sectioned teeth from the Lance Formation that had
accumulated in the Yale Peabody Museum collections. (Recall that the
Aublysodon mirandus tooth is from the older Judith River Formation.)
Aublysodon amplus (meaning "large") tooth crowns were about twice the
size (almost 3 cm) of ANSP 9535, Aublysodon cristatus crowns were
somewhat smaller (about 1 cm). The latter had ridges running down the
flat rear face.
        Marsh did not consider Aublysodon a dinosaur. In his paper, he
commented on the differences between Aublysodon teeth and other
theropod teeth and concluded they were the incisors of some unknown
kind of mammal, even though it would have been a very large mammal for
the Late Cretaceous. This is probably why Aublysodon is not noted in
Marsh's summary work of 1896, Dinosaurs of North
America. Paleontologists did not accept Marsh's opinion, and later
discoveries have confirmed Marsh's speculation as incorrect. This is
the only instance I know of that tyrannosaurid fossils were ever
seriously referred to the class Mammalia.
        We have seen how the syntype series of teeth on which Leidy
based the species Deinodon horridus was whittled down. Of the original
fifteen specimens (Table 2), Cope nominated three as "typical," the
same three that Leidy used to establish the species Aublysodon
mirandus. Then Marsh, of course ignoring Cope's work, nominated one of
those as "typical" of Aublysodon mirandus, implicitly leaving the
other two as syntypes of Deinodon horridus. The situation, confusing
to those unused to problems of zoological nomenclature, was reviewed
in 1899 by Oliver Perry Hay, who decided that Cope was after all not
justified in declaring the genus Deinodon preoccupied: The supposed
senior-homonym snake genus was not spelled the same way and had a
different derivation. But Hay did agree that Deinodon was based on the
three "typical" teeth, and that Laelaps (that is, Dryptosaurus) was
therefore distinct from Deinodon. And like Cope, Hay sank Aublysodon
mirandus as a junior objective synonym of Deinodon
horridus. (Unfortunately, Hay overlooked Marsh's Aublysodon paper.)
Finally, Hay noted that Cope had left nameless all the other teeth
originally in the Deinodon horridus syntype series. Since they were
supposedly generically indistinguishable from Laelaps teeth, Hay made
them a new species of the genus Dryptosaurus: He called them
Dryptosaurus kenabekides, the trivial name meaning "descended from the
Kenabeek," a large reptilian monster of native American folklore. We
now know, thanks to Baird and Horner (in papers of 1977 and 1979),
that the genus Dryptosaurus is not a tyrannosaurid, whereas the
Deinodon teeth almost certainly are; therefore the best name for Hay's
species is ?Deinodon kenabekides.