Amargasaurus

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Amargasaurus
Skeleton cast in the foyer of the Melbourne Museum

Skeleton cast in the foyer of the Melbourne Museum

Temporal occurrence
Lower Cretaceous ( Barremium to Lower Aptian )
130.7 to 123 million years
Locations
Systematics
Lizard dinosaur (Saurischia)
Sauropodomorpha
Sauropods (Sauropoda)
Diplodocoidea
Dicraeosauridae
Amargasaurus
Scientific name
Amargasaurus
Salgado & Bonaparte , 1991
Art
  • Amargasaurus cazaui
Front view of the Amargasaurus skeleton cast in the Melbourne Museum
Live artistic representation of Amargasaurus

Amargasaurus is a genus of sauropod dinosaur thatlived in South Americaduring the Lower Cretaceous .

So far, a single, almost complete skeleton including a fragmentary skull is known that comes from the La Amarga Formation in the Argentine province of Neuquén . Making it one Amargasaurus to the known best sauropods of the Cretaceous. The most striking feature was a double row of long vertebral spines (forked spinous processes ), which ran over the neck and trunk. However, their function is unclear.

Amargasaurus is a representative of the Dicraeosauridae and was closely related to the genera of the Upper Jurassic Dicraeosaurus and Brachytrachelopan . The only species is Amargasaurus cazaui .

features

Build and size

As with all sauropods, it was a herbivore with a barrel-shaped body and a long neck and tail. Amargasaurus was a relatively small sauropod - length estimates of the only known specimen are 9 or 10 meters. The weight is estimated by Gerardo Mazzetta and colleagues (2004) at 2.6 tons. As with other representatives of the Dicraeosauridae, the neck with almost 2.4 meters in length was relatively shorter than that of all other sauropods. According to Leonardo Salgado and José Bonaparte (1991), Amargasaurus , unlike some representatives of the Titanosauria , showed no adaptation to a possible straightening on the hind legs and was therefore probably four-legged .

skull

Only the posterior area of ​​the skull, especially the skull and the temples , has survived, while the muzzle and jaw are missing. However, the skull probably followed the construction plan typical of related genera with a horse-like, elongated snout that was almost rectangular in plan view and narrow, pin-like tooth crowns . As in related genera, the nostrils were shifted far back. In the first skeletal reconstructions, Amargasaurus is shown with a skull that is only slightly tilted downwards. Leonardo Salgado (1999) notes, however, that the long spinous processes of the cervical vertebrae make such a position of the skull anatomically impossible - instead, unlike in related species, the skull has always been kept approximately vertical.

The skull can only be compared with the closely related genera to a limited extent , since the species Dicraeosaurus hansemanni is the only other representative of the Dicraeosauridae so far from which skull material is also available. Both representatives, however, show common skull features that are missing from all other known sauropods: The paired frontal bone was fused together. The basipterygoid processes, which connect the skull with the top of the oral cavity, were extremely elongated. This feature was even more pronounced in Amargasaurus than in Dicraeosaurus . Furthermore, the supratemporal window , a skull window of the temple region, was greatly reduced in size and oriented to the side - in contrast to other diapsid reptiles , in which it is always oriented upwards. In contrast to Dicraeosaurus and other sauropods, the basal tubera - bulbous outgrowths that are located on the underside of the skull - were fused together.

Trunk skeleton and limbs

The spine was composed of 13 cervical, 9 back and probably 5 cross vertebrae, the number of tail vertebrae is unknown. The vertebral bodies of the cervical and anterior vertebrae were opisthocoel, that is, they were convex on the anterior side and concave on the posterior side . The other vertebrae, on the other hand, were amphipathic (flat on both sides). As with other dicraeosaurids, lateral cavities (pleurocoels) of the vertebrae were missing. A unique feature were the strongly developed transverse processes ( diapophyses ) of the anterior dorsal vertebrae, which indicate strongly pronounced ribs.

The most striking feature were the extremely long spinous processes of the cervical and dorsal vertebrae, which, like other representatives of the Dicraeosauridae, forked into two branches up to the roof of the vertebral hole. In their considerable length and their spiky shape, however, they differ significantly from those of all other sauropods. The spinous processes had a rounded cross-section and tapered upwards. They reached their greatest height in the middle of the neck, where they measured 60 cm in length at the eighth cervical vertebra. In the area of ​​the neck, they were bent backwards by about 50 ° so that their tips towered over the respective subsequent vertebra. The spinous processes of the last two vertebrae, the sacral vertebrae and the anterior caudal vertebrae were also greatly elongated, but differed significantly from those of the previous vertebrae: These spinous processes were not bifurcated and laterally widened upwards, which gave them a paddle-like shape.

The shoulder and pelvic girdles as well as the fore and hind limbs were similar to those of the related Dicraeosaurus and do not have any unique characteristics. The pelvis was relatively wide because the distance between the ilia on either side of the sacrum was increased. Hands and feet are not known to be fossilized, but they were probably five-pointed, like all sauropods, whereby the fingers of the hand were strongly receded, but the toes of the foot were fully developed.

Systematics

Relationships and temporal distribution of the Diplodocoidea . From Sereno et al. 2007

Amargasaurus is a member of the Dicraeosauridae, one of three groups within the Diplodocoidea . The Dicraeosauridae are currently assigned three genera with a total of four species - in addition to Amargasaurus cazaui , these are Dicraeosaurus hansemanni and Dicraeosaurus sattleri from the Upper Jurassic of Tanzania and the recently described Brachytrachelopan mesai from the Upper Jurassic Argentina. Amargasaurus is the only named representative from the Lower Cretaceous, although an unnamed find from Brazil shows that representatives of this group still existed at the end of the Lower Cretaceous.

The relationships within the Dicraeosauridae are relatively undisputed. Three more recent analyzes from 2005, 2007 and 2011 came to the conclusion that Dicraeosaurus and Brachytrachelopan are more closely related than to Amargasaurus - Amargasaurus is the sister taxon of a clade formed by Brachytrachelopan and Dicraeosaurus . A study from 1999 came to a different conclusion, which suggested that Dicraeosaurus is paraphyletic and that Dicraeosaurus sattleri actually represents a second species of Amargasaurus .

Find, research history and naming

The only skeleton was recovered by Guillermo Rougier in February 1984 during an expedition led by José Bonaparte . This expedition was the eighth paleontological expedition carried out in Patagonia of a project on the Jurassic and Cretaceous terrestrial vertebrate fauna of South America, which began in 1976. The same expedition also discovered the skeleton of the theropod Carnotaurus .

The site is located in Wadi La Amarga in the Picún Leufú department in the Argentine province of Neuquén . The skeleton ( holotype , copy number MACN-N 15) has largely been preserved in the original anatomical combination: The trunk and cervical spine, consisting of 22 vertebrae, articulated with the skull and the sacrum. Only the temporal region and the cerebral skull have survived from the skull , while the sacrum is completely but partially eroded before the carcass was filled with sediments . Of the caudal vertebrae, only three anterior, three middle, one posterior and fragments of other vertebral bodies have been preserved. From the shoulder girdle is the shoulder blade (scapula) with coracoid (coracoid) available from the pool only the ilium (ilium). The limbs are also not fully known; the hand and - apart from two metatarsals - the foot are missing. The skeleton is kept in the collection of the Museo Argentino de Ciencias Naturales Bernardino Rivadavia in Buenos Aires .

The first, but unofficial mention of the new dinosaur was published by Bonaparte in 1984 in the Italian book Sulle Orme dei Dinosauria . Here Bonaparte referred to the species as Amargasaurus groeberi , although the species name was changed to Amargasaurus cazaui in the 1991 official first description . The first description was made by Leonardo Salgado and José Bonaparte in Spanish in the journal Ameghiniana . Another description focused on the skull followed a year later.

The name Amargasaurus ( Amarga ; Greek sauros - "lizard") points to the Wadi La Amarga, in which the skeleton was found. The second part of the species name, cazaui , honors the scientist Luis B. Cazau, employed by the Argentine oil company YPF Sociedad Anónima , who drew attention to the paleontological importance of the La Amarga formation .

Paleohabitat

Amargasaurus comes from the La Amarga Formation , a sequence of rocks belonging to the Neuquén Basin , which is dated from the Barremium to the Lower Aptian . The fossils, like most of the other vertebrate finds of the La Amarga Formation, were discovered in the lowest of the three strata ( sub -formations ), the Puesto Antigual member . This stratum is about 29 meters thick and consists of sandstones that were deposited in a pigtail system under high-energy flow conditions. The Amargasaurus fossils themselves were recovered from a sandy conglomerate site. Other dinosaur finds in the formation include herbivores such as the original Diplodocoidea Zapalasaurus , the titanosaur Amargatitanis , remains of original representatives of the titanosaurs and rebbachisaurs and the only stegosaur found in South America to date . Carnivorous dinosaurs were represented by the small ceratosaur Ligabueino , and dental finds indicate the presence of a large representative of the Tetanurae . In addition to dinosaurs, a crocodile relative has been identified with Amargasuchus - the upper jaw of this animal was found together with the bones of the Amargasaurus skeleton. Vincelestes neuquenianus from the group of Cladotheria , the only mammal described so far from the Lower Cretaceous South America, is particularly scientifically significant .

Paleobiology

Function of the elongated spinous processes

Artistic live representation of Amargasaurus with skin sail

Both the appearance of the spinous processes of the cervical and dorsal vertebrae and their function are unclear. Presumably these prickly protrusions protruded from the neck and were thus visible from the outside. Their rough surface in the upper section suggests that the spinous processes in the living animal were possibly covered with horn . It is not known whether they stood apart from one another or were connected by a sail made of skin.

Leonardo Salgado and José Bonaparte (1991) suspect that they were adaptations to defend against predators , which is indicated by the pointed shape of the spines. According to these researchers, other possible functions could be the display to conspecifics, for example for courtship or to intimidate rivals. Jack Bailey (1997) points out that the spine-like spinous processes show similarities with those of the sail-bearing pelycosaurs such as Dimetrodon , and sees this as an indication that Amargasaurus also had such a sail. According to Bailey, this sail could have been used for display. In contrast to the pelycosaurs, the spinous processes of Amargasaurus were forked and thus formed a double row. Since the distance between the two rows was only 3 to 7 cm, Bailey believes it is unlikely that two separate sails existed - instead, the rows would have formed a framework that was completely spanned by a single skin. In addition, Bailey points out that the spinous processes from the penultimate vertebra were structured significantly differently than those of the previous vertebrae. According to the researcher, these paddle-shaped appendages resemble those of today's hump-bearing ungulates like the bison , which would indicate that the sail merged into a fleshy hump in the rear part of the trunk.

Running speed

Leonardo Salgado and José Bonaparte (1991) suspect that the Amargasaurus moved slowly because the forearms and lower legs were proportionally short, similar to other animals that were not designed to run fast. Gerardo Mazzetta and Richard Fariña (1999), on the other hand, come to the conclusion that Amargasaurus was able to run fast: These researchers argue that the leg bones are particularly stressed by bending moments when running and that their resistance to bending moments is a limiting factor for the maximum speed of a person Animal. The researchers explain that the leg bones of Amargasaurus are even stronger than those of today's white rhinoceros , a species adapted to galloping.

supporting documents

Main literature

  • Jack Bowman Bailey: Neural spine elongation in dinosaurs; sailbacks or buffalo-backs? In: Journal of Paleontology. Vol. 71, No. 71, 1997, ISSN  0022-3360 , pp. 1124-1146, JSTOR 1306608 .
  • Fernando E. Novas : The age of dinosaurs in South America. Indiana University Press, Bloomington IN 2009, ISBN 978-0-253-35289-7 .
  • Leonardo Salgado , José F. Bonaparte : Un nuevo sauropodo Dicraeosauridae, Amargasaurus cazaui gen. Et sp. nov., de la Formacion La Amarga, Neocomiano de la Provincia del Neuquén, Argentina. In: Ameghiniana . Vol. 28, No. 3/4, 1991, pp. 333-346.
  • Leonardo Salgado, Jorge O. Calvo : Cranial osteology of Amargasaurus cazaui Salgado and Bonaparte (Sauropoda, Dicraeosauridae) from the Neocomian of Patagonia. In: Ameghiniana. Vol. 29, No. 4, 1992, pp. 337-346.

Supplementary literature

  • Sebastián Apesteguía: The sauropod diversity of the La Amarga Formation (Barremian), Neuquén (Argentina). In: Gondwana Research . Vol. 12, No. 4, 2007, ISSN  1342-937X , pp. 533-546, doi : 10.1016 / j.gr.2007.04.007 .
  • José F. Bonaparte, Fernando E. Novas, Rodolfo A. Coria : Carnotaurus sastrei Bonaparte, the horned, lightly built carnosaur from the Middle Cretaceous of Patagonia (= Contributions in Science. No. 416, ISSN  0459-8113 ). Natural History Museum of Los Angeles County, Los Angeles CA 1990, digitized version (PDF; 4.99 MB) .
  • Luis M. Chiappe : A new trematochampsid crocodile from the Early Cretaceous of north-western Patagonia, Argentina and its palaeobiogeographical and phylogenetic implications. In: Cretaceous Research. Vol. 9, No. 4, 1988, ISSN  0195-6671 , pp. 379-389, doi : 10.1016 / 0195-6671 (88) 90009-2 .
  • Donald F. Glut : Dinosaurs. The Encyclopedia. McFarland & Company, Jefferson NC et al. 1997, ISBN 0-89950-917-7 .
  • Héctor A. Leanza, Sebastián Apesteguía, Fernando E. Novas, Marcelo S. de la Fuente: Cretaceous terrestrial beds from the Neuquén Basin (Argentina) and their tetrapod assemblages. In: Cretaceous Research. Vol. 25, No. 1, 2004, pp. 61-87, doi : 10.1016 / j.cretres.2003.10.005 .
  • Gerardo V. Mazzetta, Richard A. Fariña: XIV jornadas Argentinas de paleontologia de vertebrados. Estimacion de la capacidad atlética de Amargasaurus cazaui Salgado y Bonaparte, 1991, y Carnotaurus sastrei Bonaparte, 1985 (Saurischia, Sauropoda-Theropoda). In: Ameghiniana. Vol. 36, No. 1, 1999, pp. 105-106.
  • Gerardo V. Mazzetta, Per Christiansen, Richard A. Fariña: Giants and Bizarres: Body Size of Some Southern South American Cretaceous Dinosaurs. In: Historical Biology. Vol. 16, No. 2/4, 2004, ISSN  0891-2963 , pp. 71-83, doi : 10.1080 / 08912960410001715132 , digitized version (PDF; 5747.66 kB) .
  • Oliver WM Rauhut , Kristian Remes, Regina Fechner, Gerardo Cladera, Pablo Puerta: Discovery of a short-necked sauropod dinosaur from the Late Jurassic period of Patagonia. In: Nature . Vol. 435, No. 7042, 2005, pp. 670-672, doi : 10.1038 / nature03623 .
  • Leonardo Salgado : The macroevolution of the Diplodocimorpha (Dinosauria; Sauropoda): a developmental model. In: Ameghiniana. Vol. 36, No. 2, 1999, pp. 203-216.
  • Daniela Schwarz, Eberhard Frey , Christian A. Meyer: Pneumaticity and soft-tissue reconstructions in the neck of diplodocid and dicraeosaurid sauropods. In: Acta Palaeontologica Polonica. Vol. 52, No. 1, 2007, ISSN  0567-7920 , pp. 167-188, online .
  • Philip Senter: Necks for sex: sexual selection as an explanation for sauropod dinosaur neck elongation. In: Journal of Zoology. Vol. 271, No. 1, 2007, ISSN  0952-8369 , pp. 45-53, doi : 10.1111 / j.1469-7998.2006.00197.x .
  • Paul C. Sereno , Jeffrey A. Wilson, Lawrence M. Witmer , John A. Whitlock, Abdoulaye Maga, Oumarou Ide, Timothy A. Rowe : Structural Extremes in a Cretaceous Dinosaur. In: PLoS ONE . Vol. 2, No. 11, 2007, e1230, doi : 10.1371 / journal.pone.0001230 .
  • Michael P. Taylor, Darren Naish: The phylogenetic taxonomy of Diplodocoidea (Dinosauria: Sauropoda). In: PaleoBios. Vol. 25, No. 2, 2005, ISSN  0031-0298 , pp. 1-7.
  • Paul Upchurch , Paul M. Barrett , Peter Dodson : Sauropoda. In: David B. Weishampel , Peter Dodson, Halszka Osmólska (eds.): The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 , pp. 259-324.
  • John A. Whitlock: A phylogenetic analysis of Diplodocoidea (Saurischia: Sauropoda). In: Zoological Journal of the Linnean Society. Vol. 161, No. 4, 2011, ISSN  0024-4082 , pp. 872-915, doi : 10.1111 / j.1096-3642.2010.00665.x .
  • Jeffrey A. Wilson: Overview of Sauropod Phylogeny and Evolution. In: Kristina Curry Rogers, Jeffrey A. Wilson (Eds.): The Sauropods. Evolution and Paleobiology. University of California Press, Berkeley CA et al. 2005, ISBN 0-520-24623-3 , pp. 15-49.

Individual evidence

  1. ↑ a b Novas 2009 , pp. 151–152
  2. ↑ a b c d e f g Novas 2009 , pp. 172–174
  3. ↑ a b Mazzetta et al. 2004 , p. 4
  4. ↑ a b c Upchurch et al. 2004 , p. 304
  5. ↑ Senter 2007 , pp. 5-6
  6. ↑ a b Salgado and Bonaparte 1991 , pp. 344-346
  7. ↑ a b c d e Salgado and Bonaparte 1991 , pp. 333–336
  8. ↑ Wilson 2005 , pp. 36-37
  9. ↑ a b Salgado and Calvo 1992 , pp. 341, 345-346
  10. ↑ a b Salgado 1999 , pp. 213-214
  11. ↑ Salgado and Bonaparte 1991 , p. 342
  12. ↑ a b Salgado and Bonaparte 1991 , pp. 338-340
  13. ↑ a b Bailey 1997 , pp. 1124, 1139
  14. ↑ Salgado and Bonaparte 1991 , p. 335
  15. ↑ a b Sereno 2007 , p. 5
  16. ↑ Rauhut et al. 2005
  17. ↑ a b Whitlock 2011 , p. 17
  18. ↑ Taylor and Naish 2005 , p. 3
  19. ↑ Bonaparte et al. 1990 , p. 2
  20. ↑ Glut 1997 , p. 123
  21. ^ Salgado and Bonaparte 1991
  22. ^ Salgado and Calvo 1992
  23. ↑ Leanza 2004 et al., Pp. 65-66
  24. ↑ Chiappe 1988 , p. 381
  25. ↑ Apesteguía 2007 , pp. 533-534, 540
  26. ↑ Schwarz 2007 , pp. 174, 180
  27. ↑ Salgado and Bonaparte 1991 , p. 344
  28. ^ Mazzetta and Fariña 1999

Web links

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