Deinonychus eggshell and theropod egg taxonomy

[GUNTER.VANACKER@ELECTRABEL.COM]

A webpage with abstracts of The North American Paleontological Convention
2001 (June 26 - July 1)

www.ucmp.berkeley.edu/napc

mentions the discovery of dromaeosaurid eggshell.

AN ASSOCIATION BETWEEN A SPECIMEN OF DEINONYCHUS ANTIRRHOPUS AND THEROPOD
EGGSHELLS : PHYLOGENETIC AND BEHAVIORAL IMPLICATIONS (GRELLET-TINNER, Gerald
& Peter J. MAKOVICKY)

summary of the abstract :

" Rediscovered blocks of matrix (AMNH 3015; originally excavated by Barnum
Brown, 1931, Cloverly Formation, quarry containing Tenontosaurus tillettorum
and Deinonychus antirrhopus) yielded abundant quantities of eggshell, some
with very closely associated gastralia of D. antirrhopus.
Since these remains are less than 5mmm apart, the describers consider this
to be evidence of brooding behaviour. They state that a random occurence
between an articulated specimen of D. antirrhopus and large quantities of
closely apposed theropod eggshell (displays 2 structural layers) seems
unlikely.
The largest block of matrix appears to contain a whole (but crushed) egg,
squeezed between the articulated gastral elements."

A few comments :

While it is not certain that this is conclusive evidence for brooding
behaviour in dromaeosaurids, the discovery may have important implications
for theropod egg taxonomy.
I have compared the (at the moment limited) oological information to other
already described oofamilies that can be attributed to theropods.

The describers explicitly state that the mammillae of layer 1 consist of
acicular rhombohedral calcite crystals, similar to those in oviraptorid
(elongatoolithid) eggs.

I see at least another 2 shared characters between the Deinonychus eggshell
and elongatoolithid eggs;

The eggshell thickness varies from 0.44mm to 0.60mm which compares closely
with elongatoolithid eggs (but not with dendroolithid, prismatoolithid and
even continuoolithid eggshell, all considered to be produced by theropods,
and all have much thicker eggshell).

Elongatoolithidae : eggshell thickness E. excellens 0.30 - 0.90mm; E.
frustrabilis 0.40 - 0.70mm; E. subtitectorius 0.50 - 0.90mm, the three
former oospecies are all from Mongolia (Djadochta and Nemegt Formations).
Chinese elongatoolithid eggs tend to have slightly thicker eggshell; E.
andrewsi 1.10 - 1.50mm; E. elongatus 0.70 - 1.10mm; E. magnus 0.60 - 0.90mm
Dendroolithidae : 1.70 - 2.10mm
Prismatoolithidae : 0.80 - 1.00mm
Continuoolithidae : 0.94 - 1.24mm


The surface ornamentation of the Deinonychus eggshell appears to be
linearituberculate, which is also typcial for elongatoolithid eggs.

Elongatoolithidae : ornamentation fine linearituberculate
Dendroolithidae : rough and irregular
Prismatoolithidae : smooth or finely ornamented
Continuoolithidae : dispersituberculate


Preparation of the supposedly whole egg specimen may reveal a similar shape
(and size) as elongatoolithid eggs. Elongatoolithid eggs have an average
length of 14 to 17cm (5 1/2" to 6 3/4").

The point I'm trying to make (and the whole idea behind this message) is the
following :
Is it not very likely that at least some of the abundant elongatoolithid
oospecies from central Asia, belong in fact to deinonychosaurs, and that the
elongatoolithid egg type is not only produced by oviraptorids but may be the
standard (basal) egg type for Maniraptora (or even Maniraptoriformes).
Other specialized egg families were possibly only produced by some derived
coelurosaurs; dendroolithid by therizinosaurs, prismatoolithid by
troodontids, continuoolithid by Maniraptora incertae sedis.

Comments are welcome (perhaps some listmembers attended NAPC 2001, where
more may have been revealed).


There is generally agreement on the assignment of following oofamilies to
theropod clades :

Dendroolithidae (Zhao & Li, 1988)(Dinosauroid-Spherulithic Basic Shell Type)
; Therizinosauria, based on excellent embryonic remains discovered by the
British Terry Manning; this assignment is disputed by Kenneth Carpenter
(presence of premaxillary teeth, which is a credible argument).

Prismatoolithidae (Hirsch, 1994)(Prismatic Basic Shell Type)  ;
Allosauroidea, Preprismatoolithus coloradensis has been referred to
Allosaurus fragilis, while Preprismatoolithus sp. definitely belongs to the
smaller Portuguese allosauroid Lourinhanosaurus antunesi (embryonic remains
are available). Prismatoolithus levis known to belong to Troodontidae
(Oldman Fmt, Alberta & Two Medicine Fmt, Montana). It may seem peculiar that
while allosauroids and troodontids are not considered to be closely related,
they do produce eggs that are placed in the same oofamily, however, the
shape of the eggs differs considerably, with Preprismatoolithid eggs being
almost sphere-like, while Prismatoolithus eggs are 2 times longer then they
are wide. Allosauroid and troodontid eggs may have evolved convergently.

Continuoolithidae (Zelenitsky, Hills & Currie, 1996)(Ornithoid Basic Shell
Type)  ; previously thought to belong to Troodontidae, but now Maniraptora
incertae sedis. (Campanian, Oldman Fmt Alberta & Two Medicine Fmt Montana)

Elongatoolithidae (Zhao, 1975)(Ornithoid Basic Shell Type) ; Oviraptorids
(based on the famous embryo from the 90's AMNH expeditions to Mongolia). Now
also (possibly) Deinonychosauria.
The very large oogenus Macroelongatoolithus is placed in the same family,
but remains a mistery, a few suggestions below;

Macroelongatoolithus eggs (length 39.3 - 53.6cm or 15 1/2" - 21"; from Sigou
and Zeumagang Fmt of Henan, China, dated as early Cretaceous) are possibly
produced by :

1. previously referred to therizinosaurs, but this is unlikely since
Dendroolithus is a much better candidate for a therizinosaur oofamily.
2. previously referred to tyrannosaurids (Tarbosaurus); this referral was
tempting (the largest known predators must have produced the largest known
eggs ...). If I'm not mistaken, Tracy Ford mentioned earlier on the DML that
tyrannosaurids did not produce these macroelongatoolithid eggs, any
developments ?
3. has been referred to a giant oviraptorosaur, this is quite possible since
the closely related (smaller) elongatoolithid eggs are definitely produced
by Oviraptorids; if 2 to 2.5m (6 1/2 to 8 ft) long oviraptorosaurs produced
15 cm (6") long eggs, it is possible that a 2.4 to 3 times larger
oviraptorosaur (about 6m or 20ft) may have produced eggs that were 2.4 to 3
times larger (about 45cm or 18"). Although scaling eggs based on the size of
skeletons is probably even more trickier than scaling homologous skeletal
elements of related species. However, we now know that giant oviraptorosaurs
did exist (the giant caenagnathid from the Sandy Site, revealed earlier this
year by Triebold Industries, possibly a large Chirostenotes specimen).
4. possibly a giant deinonychosaur, we can now assume that deinonychosaur
eggs are of the elongatoolithid type, and we definitely have large
deinonychosaurs; the up to 7m (23ft) long Utahraptor ostrommaysorum and the
5.5m (18ft) long Achillobator giganticus.
5. possibly a giant ornithomimosaur (? deinocheirid).

The "Baby Louie" specimen that was discovered associated with a block of
Macroelongatoolithus eggs apparently did not yield the information that was
hoped for; the skull is remarkably short (may simply be ontogenetic) and
while the postcranial skeleton is articulated, most of the bones appear to
be crushed.

A related subject; the AMNH exhibit on the Mongolian discoveries (earlier
this year) displayed a nest with eggs and a hatchling (or very young
juvenile) troodontid ... any developments ? Were the skeleton and eggs found
associated and/or do they belong to the same species ?

Lastly, it would be helpfull for egg taxonomy if we could refer a theropod
species to the elusive oospecies Continuoolithus canadensis.
We know that it was not produced by troodontids; Dr. Holtz suggested earlier
that both Chirostenotes and Ricardoestesia were possible candidates.
Ricardoestesia is certainly a possibility, this is apparently a higly
derived maniraptoran and it would not be surpising if it would have produced
eggs that are so different from any other ornithoid eggs, that a whole new
oofamily had to be created. Too bad we don't have decent skeletal remains of
Ricardoestesia (nor embryonic remains). The suggestion that continuoolithid
eggs were produced by Chirostenotes may be possible (both have the Ornithoid
Basic Shell Type) but would'nt it be likely that the eggs of caenagnathids
were much more similar to the very closely related oviraptorids (both are
united in the clade Oviraptorosauria) that produced elongatoolithid eggs ?


Since dinosaur egg taxonomy is quite new, this may be one of the reasons
that the subject hasn't been discussed often on the DML. I believe, however,
that dinosaur eggs may (and already) deliver invaluable information on
dinosaur behaviour and even relationships between the different dinosaurian
clades.

I don't want to spoil things, but it is safe to say that the release of
Jurassic Park 3 will be followed by many discussions on dromaeosaur eggs and
parental care.



Regards,

Gunter Van Acker
Belgium

quote of the day; (Ellie Sattler) "... unless they figure out how to open
doors"