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Time to break away from the theropods temporarily
and tackle a sauropod. Agustinia was requested by Mike Keesey, so here it
is.
Agustinia Bonaparte 1999
= Augustia Bonaparte 1998 (preoccupied Zariquiey
1927)
A. ligabuei Bonaparte 1999
= Augustia ligabuei Bonaparte 1998
Etymology- "Honoring Agustin and Ligabue", Agustin
Martinelli being discoverer of the specimen and Dr. Giancarlo Ligabue being an
active philanthropist who supported the 1997 Patagonian
expediation.
Aptian, Early Cretaceous
Upper Section of Luan Cura Formation,
Argentina
Holotype- (MCF-PVPH-110) (15-16 m) last three
dorsal neural spines, six sacral neural spines, eleven caudal neural
spines, incomplete tibia, fibula (895 mm), metatarsal I (155 mm), metatarsal II
(155 mm), metatarsal III (210 mm), metatarsal IV (205 mm), proximal metatarsal
V, nine dermal ossifications
note: a femur was found with the specimen
represented by hundreds of small weathered fragments and was not
collected.
Diagnosis- fibula wraps anteromedially around
cnemial crest of tibia; dermal ossifiations with thick proximal/ventral
processes, starting as rhomboid transversely oriented midline plates, proceeding
to rectangular transversely oriented midline plates with dorsolateral spikes,
then to dorsolaterally projecting flattened spines.
Description-
Scaling the fibula from Rebbachisaurus gives a
length of 16 meters while scaling from Saltasaurus gives a length of 15 meters,
so Agustinia was about 15-16 meters.
The last three dorsal neural spines are
preserved. They are transversely rectangular in dorsal view and possess
four laminae. The supradiapophyseal laminae are shortest, the prespinal
lamina is longer and the postspinal lamina is longest.
The six sacral neural spines are fused to one
another along their pre- and postspinal laminae and similar to the dorsal spines
in morphology, being transversely expanded and rectangular, with four laminae
each.
The first three caudal neural spines are
represented, along with what probably represents the neural spines of caudals
6-13. These start out transversely expanded in caudals 1-3, then changes to
longitudinally elongate. The lateral laminae are prominent until the
eighth caudal, then become rugosities. The prespinal laminae are much more
prominent than the postspinal laminae in the proximal caudals.
Both lower limb elements are crushed
lateromedially, while the metatarsals are deformed. The tibia has a
pronounced, thin crest on the proximoposterior corner and a poorly developed
cnemial crest. The fibula wraps anteromedially around the cnemial crest,
which is an autapomorphy, and is placed anterior to the tibia in it's distal
half.
The metatarsals are very robust and decrease in
thickness towards metatarsal V. The first two metatarsals are subequal in
length and shorter than III and IV, which are also subequal. There may be
an incipient laterodistal process on metatarsal I, but the deformation makes
this uncertain. Both II and III have distal condyles for a phalanx, while
I lacks them. Metatarsal III is transversely wider (78%) compared to
I and II than all sauropods except Vulcanodon and Shunosaurus (should have
<65%) according to Sereno and Wilson (1998, Omeisaurus + Neosauropoda,
character # 73).
The osteoderms are truly unique and come in four
types.
The first type is roughly rhomboid and probably had
a median position. It resembles a Stegosaurus plate that's been rotated so
that the faces of the plate face anterodorsally and posteroventrally. The
anterodorsal face is convex, while the posteroventral face is concave. At
the base of the posteroventral face is a thick process with a sagittal ridge and
concave posterolateral areas adjacent to the ridge. It was probably
positioned on the midline of the dorsal area and is 200 mm on it's sagittal
axis.
The second type also had a median position, but
is rather different otherwise. It is a large rectangular plate, with
the faces pointing roughly anteriorly and posteriorly. There are two large
spikes projecting dorsolaterally. The spikes are anteroposteriorly
flattened and conical. Between the spikes and plate body is a ridge, the
area between the ridges is concave. There are also two thick processes
ventrolaterally that probably contacted the dorsolateral edges of the dorsal or
sacral neural spines. This ossification is 640 mm wide, 260 mm between
ridges.
The third type is a split version of type 2, so it
was paired. It has a dorsoventrally broad and bifurcated medial section,
with a thick ventral process. There are several ridges on the proximal
section, between which muscles probably attached. Again, there are two
spikes (one on each type 3). The spikes are dorsolaterally projected and
most are blunt, with subparellel edges, while one is conical and pointed.
These are 460 m long.
The fourth type is very similar to the third type,
but with less expanded proximal ends and smaller proximoventral processes.
They are also longer than type three, being 760 mm.
Relationships-
Agustinia is a sauropod based on- more than three
sacral vertebrae; metatarsals I and V with proximal ends subequal in area to
metatarsals II and IV. It is eusauropod based on- dorsal neural spines
broader transversely than anteroposteriorly; metatarsal III 25% or less of
tibial length; minimum shaft width of metatarsal I greater than II-IV.
Sauropod systematics are currently unresolved regarding basal forms such as
cetiosaurs and euhelopodids, but Agustinia shares several characters with
diplodocoids and titanosaurids, which would place it in the
Neosauropoda.
Titanosaurids and diplodocoids both have prespinal
and postspinal laminae in the posterior dorsal vertebrae and dorsalized proximal
caudal vertebrae (with laminae), but only diplodocoids have posterior dorsal
vertebrae with craniocaudally compressed neural spines and only Euhelopus and
titanosaurids have six sacral vertebrae. Diplodocoids and some
titanosaurids (Saltasaurus and Opisthocoelicaudia, not Alamosaurus, Malawisaurus
or Titanosaurus) have craniocaudally compressed proximal caudal neural
spines. Only titanosaurids have been discovered with dermal
ossifications. Bonaparte states the four perpendicular laminae with
postspinal laminae longest are more similar to rebbachisaurids than
titanosaurids. This makes it apparent that Agustinia is either a
diplodocoid or advanced titanosaurid, with the evidence about equal for
either. Both groups were common in Early Cretaceous South America. A
titanosaurid affinity is suggested by six sacral vertebrae and dermal
ossifications, while diplodocoid affinity is suggested by craniocaudally
compressed posterior dorsal neural spines and the orientation of the
laminae. Thus, I recommend placing Agustinia as Neosauropoda incertae
sedis, as either a diplodocoid or advanced titanosaurid.
references-
Bonaparte, J., 1998. An armoured sauropod from the
Aptian of northern Patagonia, Argentina, in Tomida, Y., Rich, T. H. &
Vickers-Rich, P., eds., 1998. Second Symposium Gondwana Dinosaurs, 12-13 July
1998, Abstracts with Program, National Science Museum, Tokyo: 10.
Bonaparte, J. F., 1999. An armoured sauropod
from the Aptian of northern Patagonia, Argentina, in Tomida, Y., Rich, T. H.
& Vickers-Rich, P., eds., 1999. Proceedings of the Second Gondwanan Dinosaur
Symposium, National Science Museum Monographs #15, Tokyo:
1-12.
The figures of the neural spines, dermal
ossifications, tibia, fibula and metatarsals are available as usual. As
for next time, Dan Bensen wants some dromaeosaurids, as did Mike Keesey, so I
guess I'll be writing about some of them. And for those of you who wrote
to me previously about species you wanted "Details on..." segments about, your
e-mails were destroyed with my old hard drive, so you might want to send me
those messages again.
Mickey Mortimer
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