Torosaurus

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Torosaurus
Skeletal reconstruction of Torosaurus

Skeletal reconstruction of Torosaurus

Temporal occurrence
Upper Cretaceous (late Maastrichtian )
69.9 to 66 million years
Locations
Systematics
Marginocephalia
Ceratopsia
Neoceratopsia
Ceratopsidae
Chasmosaurinae
Torosaurus
Scientific name
Torosaurus
Marsh , 1891
Art
  • Torosaurus latus Marsh, 1891

Torosaurus is a genus of pelvic dinosaurs from the group of Ceratopsidae within the Ceratopsia . He lived in the late Cretaceous in North America . According to research carried out in 2010, Torosaurus could be the full-blown form of Triceratops , after which Torosaurus wouldonly be a younger synonym of that genus.

features

With an estimated length of 7.65 meters and a maximum weight of over 6 tons , Torosaurus was one of the largest Ceratopsidae, but slightly smaller than its relative Triceratops . Its skull , including the neck shield, reached a length of over 2 meters, making it one of the longest skulls of all land-dwelling animals. The muzzle was pointed and parrot-beak-like, but the cheek region was broad and expansive.

The nasal horn was small, but the two over-eye horns were very long. The neck shield was like all Ceratopsidae from the parietal and the shed leg , he was provided with very long and large, paired openings.

Nothing is known of the rest of the Torosaurus physique , presumably it resembled that of the other Ceratopsidae. As a result, it was a stocky dinosaur with strong limbs that moved on all fours. Like all Ceratopsidae it ate plants, for which it was well equipped with its tooth batteries (teeth arranged in rows, which were replaced by the following tooth when they were worn out).

Locations and dating

Torosaurus fossil remains have been found in Canada ( Saskatchewan ) and several locations in the United States ( Wyoming , Montana , North Dakota , South Dakota , Utah , New Mexico, and Texas ). The finds are dated in the Upper Cretaceous (late Maastrichtian ) to an age of 69 to 66 million years . Torosaurus , like its contemporary Triceratops, was one of the last dinosaurs to live before the mass extinction at the end of the Cretaceous period .

Skull of Torosaurus (B) compared to Triceratops (A)

Naming and types

The name given by Othniel Charles Marsh in 1891 is derived from the Greek words toreo (= "pierced", "perforated") and sauros ("lizard") and alludes to the anatomy of the neck shield. This is not massive, as in the case of the Sterrholophus (today a synonym for Triceratops ) that he described a few months earlier , but has a pair of large openings ( "the posterior crest," which "is perforated by a pair of large openings." explains: "The open perforations in the parietal, which have suggested the name Torosaurus, readily separate this genus from all the gigantic species hitherto known in the Ceratopsidae." “). Thus, an etymological derivation of the name from the Spanish word " toro " for "bull" has no basis.

The type and only recognized species today is Torosaurus latus . The species T. gladius and T. utahensis described later are synonymous with T. latus .

Systematics

Torosaurus is classified within the Ceratopsidae in the Chasmosaurinae , which were characterized by large over-eye horns and a long neck shield. It belongs to the Triceratops - Torosaurus clade and, according to cladistic studies, is most closely related to Nedoceratops .

Eventual match with Triceratops

Due to the fact that with Torosaurus and Triceratops two closely related Ceratopsidae occurred at the same time in the same region, it is currently being discussed whether both species are not identical. The only significant difference between them is the shape of the neck shield. At the same time there are a number of fossil finds of juvenile Triceratops , while those of Torosaurus are absent. In addition, Triceratops differs from other Ceratopsidae by a temporal bone scale that remains short despite general growth processes. To explain these circumstances, in the course of his investigations into the ontogeny of the dinosaurs found in the Hell Creek Formation in 2009 , John Scanella developed the theory that Torosaurus is only the fully grown form of Triceratops, that is, both are only different stages of development of the same genus .

In a study published in 2010, Scanella and his mentor Jack Horner, who teaches at Montana State University , presented further evidence that supports his theory. The investigation of the growth lines of 29 Triceratops and 9 Torosaurus skulls showed, according to the authors, that all Torosaurus skulls actually came from adult individuals, while the Triceratops skulls can be assigned to juvenile or young adult specimens. In addition, about half of the subadult Triceratops skulls examined had two areas with depressions and thinner bone structure, which are congruent with the places where the neck shield of the Torosaurus has holes. As a result - according to the authors - a metamorphosis of the skull and neck shield would have set in when the animals grew up. The neck shield would have continued to grow, become thinner and ultimately broken in some places, while at the same time the angle of the horns to one another changed. This process was made possible by the well-perfused metaplastic bone tissue of the neck shield and horns.

However, Scanella's and Horner's explanations revealed weaknesses. If the so-called "toromorphosis" by the authors really represented the last development stage in the life of a Triceratops , significantly more fossil remains of Torosaurus than of Triceratops - "young animals" should have been found. However, exactly the opposite is true. Therefore, Scannella and Horner concluded that there must have been a high mortality among subadults needs or fully grown animals hills preferred habitat where erosion the fossilization prevented. In addition, there are no finds that could document the transition from Triceratops to Torosaurus . For example, the holes in the openwork neck shields of the Torosaurus are always perfectly shaped. However, there are no indications of an incipient perforation in the fossils. The authors therefore refer to Nedoceratops , where the independence as a genus is disputed. Therefore it could represent just such a link. The number of osteoderms on the edge of the neck shield also differs in the two genera (five in Triceratops compared to ten or twelve in Torosaurus ) and they are also partially positioned differently. Scanella and Horner also pointed out, however, that these features are generally very variable in the fossils found and assumed that the number and position of the osteoderms may have changed during growth.

In 2011, Andrew Farke argued primarily against the view that Nedoceratops hatcheri was a transitional form between Triceratops and Torosaurus . In addition to the fact that an increase in the number of osteoderms on the neck shield would be a unique process in the Ceratopsia group , he pointed out that the formation of holes in the neck shields does not necessarily have to be related to the age of an animal and so do the thin bone structures in the neck shield may have been used to support muscles.

Nicholas Longrich and Daniel Field also pleaded for a rejection of the theory in 2012, Torosaurus and Triceratops being synonymous with each other. For example, the fossil sites of the two dinosaurs did not exactly match. So far, only remains of Triceratops have been found in the far north of the United States , while in the far south the same applies to Torosaurus . However, this could also be a sampling error. The authors also criticized the fact that the age of dinosaurs at the time of their death can also be determined differently than Scanella and Horner did in their study. They carried out their own investigation on the basis of 24 features of skulls, which indicate the age of the animals, and came to the conclusion that in the Torosaurus specimen YPM 1831 some skull elements are not connected, which indicates that it this could be a relatively young animal. The specimen ANSP 15192, which showed missing connections to the bones of the snout, was probably grown up but still relatively young. At the same ten would Triceratops -Exemplare the same stage of development as adult Toro dinosaurs reached. The investigations also showed that the depressions in the neck shields of some Triceratops did not always appear at the point where the characteristic holes of the Torosaurus were to be found. Instead, some of them were also on the temporal bones and were therefore not completely surrounded by the neck shield. There are also structural differences: The depressions in the Triceratops are surrounded by thicker bones, whereas the holes in the Torosaurus are bounded by thinner bones. Longrich and Field also drew attention to another difference between the two genera. The temporal bone scale in Torosaurus is elongated, thicker on the inside and concave on the outside, while in Triceratops it is concave on the inside and becomes flat at the tip. In addition, it was noted that an alternative explanation for Horner's observation, presented in a histological work, that all Triceratops specimens found have a subadult bone structure, could be that Triceratops , unlike its relatives, simply retained this into old age.

literature

Individual evidence

  1. ^ Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ et al. 2010, ISBN 978-0-691-13720-9 , pp. 265-266, online .
  2. John B. Scannella, John R. Horner : Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny. In: Journal of Vertebrate Paleontology, Vol. 30, No. 4, 2010, ISSN  0272-4634 , pp. 1157-1168, doi : 10.1080 / 02724634.2010.483632 .
  3. ^ Montana State University, " Triceratops and Torsaurus Were Same Dinosaur at Different Stages" . ScienceDaily , July 14, 2010.
  4. ^ The Paleobiology Database
  5. Ben Creisler: Dinosauria Translation and Pronunciation Guide ( Memento of October 13, 2011 in the Internet Archive )
  6. ^ Scannella J., 2009, "And then there was one: synonymy consequences of Triceratops cranial ontogeny," Journal of Vertebrate Paleontology 29 : 177A
  7. a b Scannella, J. and Horner, JR (2010). " Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny." Journal of Vertebrate Paleontology , 30 (4): 1157-1168. doi : 10.1080 / 02724634.2010.483632
  8. ^ Farke, AA (2011) " Anatomy and taxonomic status of the chasmosaurine ceratopsid Nedoceratops hatcheri from the Upper Cretaceous Lance Formation of Wyoming, USA. " PLoS ONE 6 (1): e16196. doi : 10.1371 / journal.pone.0016196
  9. a b Longrich, NR, Field, DJ: Torosaurus is not Triceratops : Ontogeny in chasmosaurine ceratopsids as a case study in dinosaur taxonomy . In: PLoS ONE . 7, No. 2, 2012. bibcode : 2012PLoSO ... 7E2623L . doi : 10.1371 / journal.pone.0032623 . PMID 22393425 . PMC 3290593 (free full text).
  10. Horner, JR, Lamm, ET., 2011, "Ontogeny of the parietal frill of Triceratops : a preliminary histological analysis", Comptes Rendus de l'Academie des Sciences Paris série D 10 : 439-452

Web links

Commons : Torosaurus  - collection of images, videos and audio files