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Re: Argentinosaurus



In a message dated 96-08-06 16:49:03 EDT, Thomas_R_HOLTZ@umail.umd.edu (th81)
writes:

> Estimates for the length of Argentinosaurus are pretty vague, given
> out lack of knowledge of exactly how long a typical titanosaur's
> neck and tail were, but values near 30 m (100') sound good to me.

Here is the as-yet-unedited, raw text from a future DINOSAUR FOLIOS
installment on _Argentinosaurus_. There's more to be added since I first
wrote this in 1993, but it does carry an estimate of the animal's length and
weight, based on the sizes of the dorsal vertebrae. It seems to be comparable
in size to _Nurosaurus_, an undescribed large sauropod from Inner Mongolia.

        ARGENTINOSAURUS

Order: Brontosauria
        Suborder: Sauropoda
                Family: Andesauridae

Describers: Jose Fernando Bonaparte and Rodolfo A. Coria
Year described: 1993
Etymology: Argentino-, Latinized combining form of Argentina, the country in
which the type specimen was discovered; and -saurus, Latinized combining form
of sauros, a masculine Greek noun for "lizard"; thus, "Argentina lizard"
Type species: Argentinosaurus huinculensis
Current status: Valid genus

        ARGENTINOSAURUS HUINCULENSIS

Describers: Jose Fernando Bonaparte and Rodolfo A. Coria
Year described: 1993
Etymology: huinculensis, a Latin word meaning "from Huincul," referring to
Plaza Huicul, the municipality in Neuquen Province, Argentina, where the type
specimen was discovered and where it is now kept
Average adult size: Approximately 90 feet (27.5 meters) long
Average adult weight: Approximately 50 tons (50,000 kg)
Range: Central South America (west central Argentina)
Period: Late Early to early Late Cretaceous (Albian-Cenomanian stages, about
90-112 million years ago)
Diet: Plants
Current status: Valid species; type species of the genus Argentinosaurus
General description and taxonomic history:
        Gigantic--not just very large--sauropod dinosaurs have been known from
Argentina since 1929, when Friedrich von Huene described the 7.5-foot-long
(231 cm) thigh bones of the Late Cretaceous Antarctosaurus giganteus. The
latest such discovery, from the same general area where Antarctosaurus
giganteus was found, establishes the existence of an equally enormous
sauropod in earlier rocks of Neuquen Province. As usual, no skull material
was unearthed, but the six enormous dorsal vertebrae and partial sacrum are
very distinctive. There is little question that the material belongs to no
previously known Argentine sauropod genus, so its describers have given it
the new name Argentinosaurus huinculensis.
        Despite their size--almost 5.5 feet tall (165 cm) when complete--the 
dorsal
vertebrae of Argentinosaurus were lightly built, with deep, weight-saving
excavations (pleurocoels) in the vertebral bodies (centra) and thin, bony
buttresses extending upward from the centra onto the neural spines and
rib-bearing transverse processes. Powerfully developed "extra joints"
(hyposphenes and hypantra) between adjacent vertebrae helped to stiffen and
strengthen the spinal column, to support the creature's tremendous weight.
The uniquely shaped hyposphenes and hypantra are among the characters
distinguishing Argentinosaurus as a new genus.
        Most Cretaceous sauropods of South America fall into the family
Titanosauridae, whose members had undivided neural spines on the neck and
back vertebrae. Having single neural spines is a primitive character retained
from prosauropods and basal sauropods such as Cetiosaurus. (The well-known
"advanced" Late Jurassic sauropods of North America and Asia--Apatosaurus,
Diplodocus, Camarasaurus, Euhelopus, and Mamenchisaurus--had neural spines
cleft in two on long stretches of their neck and back vertebrae.) The huge
vertebrae of Argentinosaurus were all single-spined; but whereas primitive
sauropods had neural spines that were transversely narrow, like knife blades
lined up in a row, the neural spines of Argentinosaurus were transversely
broad: slenderer in side view than in front view. This is different from the
condition in "true" titanosaurids, whose single neural spines were not
flattened front-to-back. Furthermore, in titanosaurids the
hyposphene-hypantrum joints between the vertebrae were poorly developed. So
although Argentinosaurus is clearly related to the titanosaurids, it is not
actually one of them.
        Jose F. Bonaparte and Rodolfo A. Coria, the describers, noted that two
previously described Argentine "titanosaurids," Andesaurus delgadoi and
Epachthosaurus sciuttoi, seem more closely related to Argentinosaurus than to
any "true" titanosaurids. Previously classified in the subfamily Andesaurinae
of the family Titanosauridae, these genera were removed from Titanosauridae
and placed, along with Argentinosaurus, into the family Andesauridae, which
the describers elevated in rank from subfamily. The describers considered
Andesauridae and Titanosauridae to be sister groups within the larger clade
Titanosauria, which they also defined.
        Both Andesaurus and Epachthosaurus were considerably smaller than
Argentinosaurus. If we assume that Argentinosaurus was built to roughly the
same proportions as its smaller relatives, we may estimate its overall size
by scaling up their dimensions. In particular, given a tibia 155 cm long, the
hindlimb would have had a total length, from hip socket to the sole of the
foot, of about 4.5 meters (about 14.5 feet). Much of this length, about 2.4
meters, would have been its thigh bone (femur)--a bit longer than in the
previous record-holder, Antarctosaurus giganteus. The forelimb would have
been about equally long: the humerus would have been shorter than the femur,
but the ulna plus metacarpals would have been longer than the tibia plus
metatarsals. The ridge of the back would have been at least another meter
above the ground, particularly in the shoulder region, where it was probably
higher than at the hips, Brachiosaurus-style. Thirteen or so dorsal
vertebrae, each more than 50 cm long, add up to a back 6-7 meters long, to
which we may add another 1.5 meters of sacral vertebrae, 6-7 meters of neck
(titanosaurian necks seem to have been short and thick), and perhaps 12 more
meters of tail. (Titanosaurians probably had short, chunky tails, without the
long whiplashes of the diplodocids--although we do not know this for certain,
because no complete titanosaurian tail has ever been discovered.) This adds
up to an animal 25.5 to 27.5 meters (83.5-90 feet) long and about 6 meters
(20 feet) high at the shoulder.
        This is about as long as the famous Diplodocus carnegii skeleton. But 
the
length of Diplodocus comprised mainly neck and tail; its body, independent of
neck and tail, was not much larger than that of a good-sized African
elephant. So whereas Diplodocus may have weighed in the neighborhood of 12-15
tons (12-15,000 kg), Argentinosaurus, with a torso 50% longer, taller, and
wider, probably weighed almost 3.5 times as much: 40-50 tons. These
dimensions make it South America's largest known dinosaur.
Type specimen: PVPH-1, a very incomplete skeleton including only 3 partial
anterior dorsal vertebrae (specificially, the partial neural arch of dorsal
?1, and dorsals ?2-3 lacking upper parts of the neural spines), 3 partial
posterior dorsal vertebrae (nearly complete: 2 in articulation, the third
isolated; all 6 vertebrae with centra about 49 cm in diameter and restored
total heights of about 120-165 cm), much of the sacrum (incomplete sacrals
1-5 of a total of 6, plus right sacral ribs), a partial hollow thoracic rib,
and a nearly complete right tibia 155 cm long, all found in the same place
and apparently belonging to the same individual; presently in the collection
of the Museo Municipal "Carmen Funes" at Plaza Huincul, Neuquen Province,
Argentina
Discoverer: Personnel from the Museo Municipal "Carmen Funes"
When discovered: January-February 1989
Where discovered: In the Huincul Member of the Rio Limay Formation, about 8
km (5 miles) east of the intersection of provincial highway 17 and national
highway 22, near the hotel "Las Overas" at Plaza Huincul, Neuquen Province,
Argentina
Other important specimens: None known
Diagnosis: Very large andesaurid sauropod
Cranium and mandible: Unknown
Vertebral column:
Pectoral girdle: Unknown
Forelimb: Unknown
Pelvic girdle:
Hind limb:
References: Bonaparte 1989; Bonaparte & Coria 1993