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Re: Nanosaurus rex



In a message dated 95-08-17 09:09:39 EDT, us009472@interramp.com (Michael
Edward Purvis) writes:

> Saw this little beast mentioned in literature I've 
>been looking at. Listed as a hypsilophodont. Anyone have any 
>detailed data on it,or references I could look up?
>
> Nanosaurus rex... talk about a name to generate confusion 
>among the general public....

It so happens I just finished another article for Gakken in which I cover
_Nanosaurus_ and similar small ornithopods. Herewith an excerpt from the
English-language version sent to Japan (sorry for the rather long, not
particularly well edited posting):

        North American ornithopods are known from Upper Jurassic and Lower
Cretaceous dinosaur-bearing formations, and by a considerable margin they are
the commonest dinosaurs in Upper Cretaceous rocks. The few North American
ornithischians known from rocks earlier than Upper Jurassic are not
ornithopods but belong instead to more primitive ornithischian orders, such
as Lesothosauria, Heterodontosauria, and Ankylosauria. The geologically
earliest-known North American ornithopods occur in the famous Morrison
Formation, which also yields such interesting dinosaurs as _Apatosaurus_,
_Allosaurus_, _Stegosaurus_ and _?Diracodon_, _Diplodocus_, and
_Brachiosaurus_. Spencer Lucas has recently (1993) named the Morrison
land-vertebrate faunal age the Comobluffian, after Como Bluff, Wyoming, where
many dinosaurs typical of this age were discovered. Ornithopods were a
relatively minor part of the known Comobluffian fauna and, with the exception
of _Camptosaurus_, are largely ignored in popular dinosaur books, which tend
to concentrate on the larger, more dramatic Comobluffian dinosaurs.
        Comobluffian ornithischians were first discovered in 1877, the year the
great western "dinosaur rush" began, and O. C. Marsh lost little time
capitalizing on them. Although most of his interest lay with the Morrison
giants, he was also fascinated with the then novel idea of small dinosaurs,
perhaps all the more so because E. D. Cope's workers seemed to have such
little luck finding them. The first Comobluffian ornithischian Marsh
described, and the first small ornithischian known from North America, was
_Nanosaurus agilis_ ("agile minute lizard"), in 1877. His description was
almost outrageously brief, providing neither illustrations nor locality
information beyond "Mesozoic deposits of the Rocky Mountains," but he
referred to it triumphantly as "the most diminutive dinosaur yet discovered"
and "not larger than a cat." In the same paper, he erected the second species
_Nanosaurus victor_ ("small lizard, conqueror") for a larger specimen "the
size of a fox." Subsequent work showed that the latter species was not an
ornithischian at all. In 1881, Marsh renamed it _Hallopus victor_ and
classified it as a new kind of dinosaur in the group Hallopoda. Almost 90
years later, in 1970, British paleontologist Alick D. Walker showed it was
not a dinosaur after all (it had previously been reclassified as a theropod)
but an odd kind of agile, long-legged, cursorial crocodilian.
        Later in 1877, another small ornithischian, a somewhat larger animal 
than
the type specimen of _Nanosaurus agilis_, found its way into Marsh's
collection, and he named it _Nanosaurus rex_ ("small lizard, king").
Collected by Benjamin Franklin Mudge from Garden Park, Colorado, the specimen
is a small ornithopod femur 10.1 cm long. It was becoming clear to Marsh that
a whole new family of small dinosaurs had been uncovered in the Morrison; he
named the family Nanosauridae in his 1878 _Nanosaurus rex_ paper. Marsh kept
Nanosauridae distinct from Hypsilophodontidae throughout his life, but during
the 20th century, _Nanosaurus_ came to be regarded as a hypsilophodontid by
virtue of its small size and close but superficial resemblance to the Wealden
genus _Hypsilophodon_.
        Some _Nanosaurus agilis_ remains were eventually illustrated by Marsh in
1894, and a more detailed look at the specimen was provided by Friedrich von
Huene and Richard Swann Lull in 1908. But it was not until Peter Galton's
creation of the primitive ornithischian family Fabrosauridae in 1978 that an
accurate assessment of the status of _Nanosaurus_ became possible. Galton
showed that the sandstone slab containing the type specimen of _Nanosaurus
agilis_ held two right femora, indicating that the remains of two animals
were jumbled together on it. He determined (oddly enough) that the smaller
femur belonged to a _Nanosaurus rex_, the larger to the type specimen of
_Nanosaurus agilis_. Having previously (1973) described a headless but
otherwise splendid _Nanosaurus rex_ specimen with coauthor James A. "Dinosaur
Jim" Jensen, Galton was in an excellent position to show that Marsh's two
_Nanosaurus_ species belonged to different ornithischian families, not just
different genera. He made _Nanosaurus rex_ the type species of the
hypsilophodontid genus _Othnielia_ (honoring Othniel Charles Marsh).
_Nanosaurus agilis_ (the type species of the genus) he referred to
Fabrosauridae.
        The locality where the _Nanosaurus agilis_ sandstone slab was found is 
not
known with certainty; it may or may not have been in the horizon near Garden
Park, Colorado from which the _Hallopus victor_ type specimen came. But most
workers agree it was probably from somewhere in the Morrison Formation,
because the type femur of _Othnielia rex_ comes from the Morrison at Garden
Park, and the remains of an _Othnielia_ were on the slab with those of the
_Nanosaurus agilis_.
        Somewhat better locality information is available for a different suite 
of
small ornithopod specimens, collected in 1878 by Samuel Wendell Williston for
Marsh at Como Bluff, Wyoming. The first to be described was a nondescript
series of 11 incomplete small caudal vertebrae, for which Marsh erected the
new genus and species _Laosaurus celer_ ("swift petrified lizard," from the
Greek _laos_, meaning "stone" or "crag"). The vertebrae belonged to a
hypsilophodontid somewhat more than 2 meters long, evidently too large to be
a _Nanosaurus_. Authorities agree that the specimen probably came from
William Harlow Reed's Quarry 9, even though no available records positively
substantiate this. The vertebrae, unfortunately, are so incomplete that they
cannot be identified even to the generic level--and even if they were
complete, it would not be enough, because such vertebrae are very similar
among different small ornithopod genera. So, despite a substantial literature
that has accumulated concerning _Laosaurus_, Galton had to abandon it as a
doubtful genus.
        Marsh created a second species of _Laosaurus_ in the same paper: 
_Laosaurus
gracilis_ ("slender"), for an incomplete skeleton including 13 dorsal
vertebrae, 8 caudal vertebrae, the lower part of a left hind leg, and a
partial right hind foot, also probably but not certainly from Reed's Quarry
9. The vertebrae are significantly smaller than those of _Laosaurus celer_,
and the skeleton when complete would have been only about 1.35 meters long
(merely twice the size of the Solnhofen _Compsognathus_). Galton noted its
detailed similarities with the type and referred material of _Othnielia rex_
and concluded that _Laosaurus gracilis_ was based on an _Othnielia rex_
individual. Had Marsh had a better type specimen of _Nanosaurus rex_ for
comparison, he might have been able to classify the _Laosaurus gracilis_
material correctly in that species.
        Marsh added a third, substantially larger species to his genus 
_Laosaurus_
later in 1878 when he described _Laosaurus altus_ ("tall") from a partial
skeleton including fragmentary skull material from Reed's Quarry 5 in the
Brushy Basin Member of the Morrison Formation at Como Bluff. When complete,
the skeleton would have been more than 3 meters long. Preoccupied with other
dinosaur discoveries, Marsh did little more with _Laosaurus altus_ until
1894, when he realized it was different from _Laosaurus_ and redescribed it
as the type species of the new genus _Dryosaurus_ ("oak-tree lizard," so
called because he envisioned it as living in a forested environment).
Although C. W. Gilmore described two excellent specimens of _Dryosaurus
altus_ from Dinosaur National Monument in 1925, very little descriptive work
was done with the species until Galton's series of papers from 1977-1983.
Galton classified _Dryosaurus_ as a hypsilophodontid, but even more recent
work by Andrew R. Milner, David Norman, and Paul C. Sereno showed that
_Dryosaurus_ occupies an intermediate position between Hypsilophodontidae and
Iguanodontidae in Ornithopoda, and that it is best classified in its own
family Dryosauridae (created by Milner and Norman in 1984).
        In 1879, Marsh himself discovered the remains of two small ornithopods 
at
Reed's Quarry 7, known as Three Trees Quarry, at Como Bluff. The better
specimen is a nearly headless but otherwise very complete, articulated
skeleton of an individual 1.86 meters long now mounted in a slab; the other
comprises various skeletal parts, some duplicating those on the slab. Teeth
and jaw material are present. Both specimens were found together and are
presently catalogued as YPM 1882 in the collection of the Peabody Museum at
Yale University, New Haven, Connecticut. Marsh made them syntypes of a new
species, _Laosaurus consors_ ("companion"), in 1894 when he created the genus
_Dryosaurus_. He also used them, together with generous amounts of plaster
and imagination, to reconstruct the skeleton of _Laosaurus_ for his 1896
monograph on North American dinosaurs. As before, little was done with the
material once Marsh finished with it until Galton's redescriptions of the
small ornithischians of North America. Galton tentatively referred the
material to the species _Othnielia rex_, but later, in a co-authored 1990
paper with Robert T. Bakker, James Siegwarth, and James Filla (on the
distinctive new genus and species of small North American ornithopod _Drinker
nisti_), he decided it should remain a separate species within the genus, as
_Othnielia consors_.
        In the same 1881 paper in which Marsh renamed _Nanosaurus victor_ (and
described a number of other new dinosaurs), he also introduced a new
classification of Owen's Dinosauria, including both the small and the large
forms, and incorporating the new discoveries emerging from the Morrison
Formation. The basis of his classification was dinosaurian foot anatomy, as
can be seen from his choices for the names of several of the suborders:
Sauropoda, Theropoda, Hallopoda, and of course Ornithopoda, the group with
which this review is concerned. There is indeed a close resemblance between
the feet of birds and advanced ornithopods such as _Iguanodon_, just as there
is a close resemblance between the feet of birds and theropods. It is small
wonder that some dinosaurologists of the late 19th century, taking into
account the ornithopod foot, the ornithischian pelvis, and the bipedal
stance, saw ornithopods, particularly the smaller ones, as probable bird
ancestors. We now know this was an error, and that these characters arose
separately and convergently in ornithopods and in theropods plus birds.
                                     ^^^^^^^^^^^^^^^^^^^^^^^
                      
Of course, this isn't the whole story, but it should guide you to the
relevant literature. Incidentally, I will welcome with open arms additions,
corrections, and comments on the narrative above!

G.O.