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Argyrosaurus superbus

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Forgotten Giants species #4: Argyrosaurus superbus

Location of holotype site: Left bank of the Río Chico, near the Pampa Pelada, to the northeast of Lake Colhué-Huapi, Chubut, Argentina.
Length: ~90+ ft.
Mass: ~50 tons
Time: Late Cretaceous, but beyond that, estimates vary. Its formation, the Bajo Barreal, has been dated using some methods to the Santonian and Campanian epochs, but by others to the earlier Cenomanian. Its contemporaries include dinosaur species which sometimes overlap into the Allen formation and other faunas considered to be Campanian in age, so the former estimate is what I find more likely.

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After a LONG time of studying and cross-scaling, here is the FIRST EVER scientific restoration of the mysterious "silver lizard" of Argentina, Argyrosaurus superbus. Named for its proximity to silver mining towns, this is one of the largest and strangest giant dinosaurs ever found - and ironically it was also one of the first to be named.

The obscure discovery of this massive plant-eater over a century ago was barely reported in the papers, but for a while Argyrosaurus was actually the largest dinosaur known to science. Described a full 10 years before Brachiosaurus, and over three decades before its record was beaten by Antarctosaurus giganteus, this monster is still known from only a handful of remains, yet they indicate a creature unusually massive and large even by the standards of other South American titanosaurs.

Argyrosaurus is characterized by very long, wide humeri proportionally similar to a giant snowboard, and massive femora wider than those of almost any other known sauropod, which rival those of Antarctosaurus giganteus for sheer size. The lower arm is relatively short, the shoulder blade large and deep, and the vertebrae massive and roughly similar in shape to those of Epachthosaurus.

Several likely specimens of Argyrosaurus are known, mostly just isolated limb bones from individuals of spanning a wide range of sizes and ages. The most complete specimen is the referred teenager PVL 4628, which includes both limb elements and vertebrae, and is the only specimen complete enough to give an idea of the overall proportions of Argyrosaurus. Thus it is the critical "keystone" specimen for unlocking the secrets of this mysterious dinosaur and its relatives. The isolated scapula indicates that PVL 4628 was not a mature animal, as its coracoid and scapula were not yet fused. It would have been roughly 65-70 ft. in length at the time of its death, while the largest individuals, known only from colossal limb bones, could have topped 90 ft. And given the extremely robust proportions of this dinosaur, it would have been several times as massive as most dinosaurs of similar length.

Argyrosaurus is the founding member of a family which currently contains only one other genus, the even more incompletely known Paralititan, which was similarly robust and heavy-bodied for its length even by titanosaur standards. Their closest relative outside the family appears to be the far smaller Epachthosaurus, which puts the Argyrosauridae in a relatively derived position - more primitive than Antarctosaurids and Saltasauroids, but more advanced than Lognkosaurians.

This animal is also remarkable in having a highly weird and RECURRING tendency to leave behind its right femur as fossil evidence, and not much else.* :XD:

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References:

Lydekker, R., 1893. "Contributions to the study of the fossil vertebrates of Argentina. I. The dinosaurs of Patagonia", Anales del Museo de la Plata, Seccion de Paleontologia 2: 1-14

Powell, J.E., 2003, "Revision of South American titanosaurid dinosaurs: palaeobiological, palaeobiogeographical and phylogenetic aspects", Records of the Queen Victoria Museum 111: 1-173

von Huene, F., 1929. Los saurisquios y ornitisquios del Cretacéo Argentino. Anales del Museo de La Plata (series 3) 3: 1–196. [In Spanish]

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Some referred remains:

The assigned material comes from 8 localities, some of which do not correspond to the provinces of Chubut and Neuquén. For this reason, they are listed with geographic, stratigraphic, and chronologic provenance. The old geo-terminology "pre-Maastrichtian Senonian" refers to two consecutive Late Cretaceous epochs, the Santonian and Campanian, which were respectively the third-last and second-last epochs of the entire Mesozoic.

1. An anterior caudal vertebra (Huene, 1929:79). West bank of Lake Colhué-Huapi, Chubut Province. Chubut Group, Castillo Formation or Bajo Barreal Formation. Pre- Maastrichtian Senonian.
2. Two caudal vertebrae “…of the region of Neuquén” (Huene op. cit.:7). Geographic and stratigraphic provenance unknown.
3. An incomplete femur (Lydekker, 1893, pl. 5, 2; Huene, 1929:80, pl. 38, 1). To the south of the bend of the Río Sengerr, Chubut Province, probably Bajo Barreal Formation. Pre-Maastrichtian Senonian.
4. An incomplete right femur (Huene, op. cit.:80, pl. 38, 2). Near the railroad bridge over the Río Neuquén, Neuquén Province. Neuquén Group, Río Colorado Formation, perhaps Bajo de la Carpa Member. Pre-Maastrichtian Senonian.
5. A complete right femur (Huene, op. cit.:80-81, pl. 38, 3). Sierra San Bernardino, 45 km west of Colonia Sarmiento, Chubut Province. Chubut Group. Bajo Barreal Formation. Pre-Maastrichtian Senonian.
6. A humerus of a juvenile individual, referred with doubts to Argyrosaurus (Huene, op. cit.:81, pl. 37, 6). Probably from Neuquén. Uncertain geographic and stratigraphic provenance.
7. A left humerus, referred with doubts to Argyrosaurus superbus Huene, op. cit.:81, pl. 37, 4). Left margin of the Río Uruguay, near Colón, Entre Ríos Province. ?Asencio Formation. Upper Cretaceous.
8. Caudal vertebrae (Huene, op. cit.:79). To the east of the Río Leona, between lakes Viedma and Argentino, Santa Cruz Province, Upper Cretaceous (Dibenedetto, pers. comm.).

Source: Dinodata


*NOTE: the unnamed and uncatalogued "Argyrosauridae" femur from Powell (2003) is most likely a lognkosaur judging from its proportions, not an Argyrosaur.
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