Nuthetes and other Purbeck theropods

["Mickey Mortimer" <Mickey_Mortimer111@msn.com>]

Thanks to Darren Naish, I now have copies of the the two dinosaur papers
from the Purbeck volume. As ornithischians are boring :-) , I'll discuss the
theropods.

Nuthetes Owen 1854
N. destructor Owen 1854
= Megalosaurus destructor Steel 1970
Early-Middle Berriasian, Early Cretaceous
Cherty Freshwater and Marly Freshwater Members of Lulworth Formation of
Purbeck Limestone Group, England
Holotype- (DORCM G 913) (~2.3 m) (skull ~250 mm) partial dentary, teeth
Referred- (BMNH 48207) dentary fragments, teeth
(BMNH 48208) several teeth
(BMNH R 15870-15878) nine teeth (1.5-16.0 mm)
(CAMSM J13951) tooth
Description-
Initial comparisons are to dromaeosaurs, as Milner proposed Nuthetes was a
member of this clade at the 1999 Purbeck Limestone meeting. The holotype
anterior dentary fragment suggests a cranial length of ~250 mm, and a total
length of 2.3 meters, scaling from Deinonychus.
There's an upper row of foramina, like dromaeosaurs and most other
theropods, which are circular anteriorly unlike Sinornithosaurus'. A lower
row seems to be absent, replaced by a groove that runs posterodorsally until
fading around the seventh tooth. This seems unique within dromaeosaurs.
Separate interdental plates are present, like Sinornithosaurus (in the
anterior dentary at least) and Bambiraptor. The symphysis is represented by
horizontal striations. The Mackelian groove is reduced to a poorly defined
shallow depression terminating at the fifth tooth, with a foramen directly
anterior. In Deinonychus and Saurornitholestes, the groove is shallow but
well defined and the foramen located at the third or fourth tooth.
Velociraptor's looks similar, but may end a bit more posteriorly, while
Dromaeosaurus' ends more anteriorly, at the second tooth or so.
Sinornithosaurus' extends to the third tooth, but is deep and narrow.
Teeth (numbering >9) are typically theropod in several respects; they are
laterally compressed, recurved and serrated. The tip of some (all?) recurved
teeth is located posterior to the alveolar edge, which is seen in
dromaeosaurs. Milner reports the extent of serration on mesial carinae
varies from the apical third to the whole crown, while the distal serrations
are restricted to the apical half when present at all. I'm unaware of this
occurring in any other theropod, as most lose their mesial serrations before
their distal ones. And indeed one can see in plate 1 (6, 10) that distal
serrations extend to the base of the crown in at least some teeth. Thus, I
think Milner confused mesial and distal a few times in the text. What I
suspect is really the case is that the mesial carinae are serrated for up to
half their length (sometimes unserrated) while the distal carinae are
completely serrated. This is similar to "velociraptorines" and
Sinornithosaurus, but distinct from Dromaeosaurus (whch seemingly always has
serrated mesial carinae) and Microraptor and Cryptovolans (which lack mesial
serrations). Heterodonty is observed, as 40% of the teeth are longer and
more slender than the rest. This seems more developed than in
Saurornitholestes. Constriction between the crown and root is comparable to
Saurornitholestes, so is much less than in Microraptor. The DSDI varies from
1.14 to 1.55, which is almost identical to Sinornithosaurus (1.13-1.43),
larger than dromaeosaurines (.81-1.18) and comparable to the low end of
"velociraptorines" (1.19-2.33). Serrations are smaller than in most
dromaeosaurs (4.5-8/mm compared to 2.5-2.8/mm in Dromaeosaurus, 2.4-2.6/mm
in Utahraptor, 4-5/mm in Saurornitholestes, 3.2-3.6/mm in Deinonychus, 5/mm
in Bambiraptor and Velociraptor; 3-3.6/mm in Achillobator) except for
Sinornithosaurus and Microraptor, which have 7-14/mm and 8/mm respectively.
Serrations have blunt rounded tips, unlike in "velociraptorine" and some
anterior Sinornithosaurus teeth. Dromaeosaurines, Microraptor and most
Sinornithosaurus teeth share this plesiomorphy with Nuthetes. Some
serrations are asymmetrical, being almost hooked apically. Sinornithosaurus
has only perpendicular serrations, while "velociraptorines'" and
Microraptor's are hooked. Dromaeosaurus shows similar variation to Nuthetes.
A premaxillary tooth is said to be serrated only mesially, which is also
seen in the first premaxillary tooth of Sinornithosaurus' holotype. However,
Milner could have reversed the terms again and the distal carina may be the
serrated one. In any case, Deinonychus, Dromaeosaurus and probably
Utahraptor and Saurornitholestes differ in having both carinae serrated on
premaxillary teeth. Most of Sinornithosaurus' anterior teeth are unserrated
(as is reported for Microraptor), except for a few serrations on the first
one, as mentioned above. The tooth is said to be D-shaped, but
dromaeosaurines are often said to exhibit this condition as well, though it
is quite different from the tyrannosauroid morphology. This tooth has a few
strange characters as well- the enamel is striated, some serrations have a
lingual midline ridge, and others have been combined in labial view.
Comments- The 'granicones' associated with Nuthetes are solemydid turtle
limb and tail(?) scutes (Barrett et al., 2002).
Milner assigns Nuthetes to the Dromaeosauridae based solely on the high
DSDI, though she also compares the Mackelian groove and posterior extent of
tooth tips to Deinonychus. She distinguishes it from "velociraptorines" by
the absence of apically inclined serrations, despite the fact she earlier
describes and illustrates these in the taxon. Although Milner says
dromaeosaurines are distinguished from Nuthetes by their low DSDI and that
Nuthetes compares most closely to "velociraptorines", she never actually
assigns it to the Velociraptorinae. No comparison or mention is made to
non-dromaeosaurid dromaeosaurs.
Other taxa besides "velociraptorines" have high DSDI's however. Within
coelurosaurs, these include basal tyrannosauroids (Eotyrannus, Dryptosaurus)
and Richardoestesia. Eotyrannus differs in having fused interdental plates,
Dryptosaurus' maxillary teeth differ in their wide interdenticle spaces, and
both differ in having much larger serrations (1.6-2.6/mm). That
Richardoestesia is not discussed by Milner is confusing, as she lists it in
her table of DSDI values as having a range almost identical to Nuthetes
(1.06-1.53). Richardoestesia has a Mackelian groove that is shallow like
dromaeosaurids and an upper row of circular foramina. Further details are
difficult to make out, though an anterior foramen may be present. It also
has unfused interdental plates like Nuthetes. Notably, Richardoestesia
exhibits similar heterodonty, with some teeth being quite elongate and
others being shorter. And like dromaeosaurs, at least some teeth have tips
extending posterior to their distal base. Serration morphology is similar,
with blunt rounded tips slightly hooked apically. Richardoestesia also has
mesial serrations that vary in extent down the carina, from extending the
complete crown edge to being absent. One of the characteristics of the genus
is the minute distal serration size (5-6/mm in Judithian material; 5-12/mm
in Aguja material), and this agrees with Nuthetes (4.5-8/mm). The
tentatively identified premaxillary tooth of Richardoestesia is only
serrated on one carina, with a cross section similar to Dromaeosaurus. There
are some differences between known teeth of Nuthetes and some varieties seen
in Richardoestesia however. Nuthetes shows none of the elongate straight
teeth with convex distoapical margins known to exist in the anterior dentary
of Richardoestesia, nor the elongate "stacked banana" serrations seen
mesially in some teeth of that genus. Also, none of the straight R.
isosceles morphotypes are present. Due to the great variety in the genus,
its wide spatiotemporal range, and possible overlap with Paronychodon and/or
bird teeth, much work needs to be done sorting out the source of this
variation, the number of species involved and their relationships. In any
case, Nuthetes does seem to resemble this taxon more than any other. Whether
its teeth would be assigned to Richardoestesia if found today is unknown,
though I can't find any differences between it and some morphotypes of the
latter. Interestingly, Nuthetes would actually have priority over
Richardoestesia if they were found to be synonymous. But since the current
concept of Richardoestesia is a morphotype found from the
Kimmeridgian-Maastrichtian on four continents, it's unlikely all specimens
are congeneric. Notably, some of the supposedly eumaniraptoran-like teeth
from the Middle Jurassic of England resemble Nuthetes and may be related as
well. The tooth in figure 18.7.C of Metcalf and Walker (1994) in particular
resembles the premaxillary tooth of N. destructor. Further work may show
Richardoestesia to be related to deinonychosaurs, perhaps near the base of
the clade, which could involve the proposed connection to Paronychodon and
birds (Sankey et al., 2002; Rauhut, 2002).
References-
Milner, 2002. Theropod dinosaurs of the Purbeck Limestone Group, southern
England, pp. 191-201. in Milner and Batten (eds), 2002. Life and Environment
in Purbeck Times. Special Paper in Palaeontology 68, 268.
Barrett, Clarke, Brinkman, Chapman and Ensom, 2002. Morphology, histology
and identification of the 'granicones' from the Purbeck Limestone Formation
(Lower Cretaceous: Berriasian) of Dorset, southern England. Cretaceous
Research 23, 279-295.

Neotheropoda indet.
Berriasian, Early Cretaceous
Purbeck Limestone Group, England
Material- (BMNH 44806) tooth (64 mm)
(BMNH R 2566a) tooth (28.5 mm)
(BMNH R 2566b) tooth (31.5 mm)
(BMNH R 2566c) tooth (26.5 mm)
(BMNH R 2567a) tooth
(BMNH R 2567b) tooth
(BMNH R 2821) tooth (56.8 mm)
(BMNH R 6908) partial metatarsal III (~280 mm)
(CAMSM J 13956) pedal phalanx III-1 (24 mm)
Comments-
A number of large teeth are present, previously referred to Altispinax
and/or Megalosaurus, which show the typical "carnosaur/megalosauroid"
morphology- laterally compressed, serrated carinae, low DSDI (1.00-1.20).
Neither these nor the pedal phalanx are illustrated.
Milner tentatively assigned a distal metatarsal III to the Eumaniraptora
based on slenderness, non-arctometatarsal condition and spatiotemporal
occurance (earlier than known oviraptorosaurs, which are said to be only
known from Mongolia and Canada). However, dromaeosaurid third metatarsi (and
Microraptor's and Bambiraptor's) are distinguished by their ginglymoid
distal articulation, which this specimen lacks. Sinornithosaurus also lacks
such an articulation, but has an (sub?)arctometatarsal condition and
posteroproximal extension on the articular surface, unlike the Purbeck
material. Troodontids also differ in having the latter extension and
ginglymoid articulation. Basal birds have ginglymoid third metatarsals too
(eg. Rahonavis, Sapeornis, Confuciusornis). So contra Milner, I find this
metatarsal to most likely not be eumaniraptoran. Most other
maniraptoriformes have their third metatarsal reduced proximally to varying
degrees, unlike the present specimen. These include ornithomimosaurs,
Caudipteryx, caenagnathids, avimimids and mononykines. Those of segnosaurs
are more expanded distally and stouter. A number of basal taxa can be
excluded from consideration due to their ginglymoid metatarsals-
Compsognathus, allosaurids, Acrocanthosaurus, Sinraptor, Torvosaurus.
However, there are still several equally plausible alternatives left for the
Purbeck metatarsal, which resembles not only oviraptorids, but also such
taxa as Fukuiraptor, Nqwebasaurus, Elaphrosaurus and Masiakasaurus. I
recommend classifying it as Neotheropoda indet..

Mickey Mortimer