Titanosaur

Taxobox
name = Titanosaurs
fossil_range = Late Jurassic-Late Cretaceous

---

image_width = 250px
image_caption = Life restoration of "Alamosaurus".
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo =Saurischia
subordo = Sauropodomorpha
infraordo = Sauropoda
unranked_familia = Titanosauria
unranked_familia_authority = Bonaparte & Coria, 1993
superfamilia = Titanosauroidea
superfamilia_authority = Lydekker, 1895
subdivision_ranks = Families
subdivision =
* Andesauridae
* Antarctosauridae
* Euhelopodidae
* Nemegtosauridae
* Saltasauridae

Titanosaurs (members of the groups Titanosauria and/or Titanosauroidea) were a diverse group of sauropod dinosaurs, which included "Saltasaurus" and "Isisaurus". It includes some of the heaviest creatures ever to walk the earth, such as "Argentinosaurus" and "Paralititan" — which might have weighed up to 100 tonnes (110 short tons) or, perhaps, even double that, if some poorly-described data are to be believed (see "Bruhathkayosaurus"). They were named after the mythological Titans, the early deities of Ancient Greece, who preceded the Twelve Olympians.

Description

Titanosaurs had small heads, even when compared with other sauropods. The head was also wide, similar to the heads of "Camarasaurus" and "Brachiosaurus" but more elongated. Their nostrils were large ('macronarian') and they all had crests formed by these nasal bones. Their teeth were either somewhat spatulate (spoon-like) or like pegs or pencils, but were always very small.

Their necks were relatively short, for sauropods, and their tails were whip-like, but not as long as a diplodocid. While the pelvis (hip area) was slimmer than some sauropods, the pectoral (chest area) was much wider, giving them a uniquely 'wide-gauged' stance. As a result, the fossilised trackways of titanosaurs are distinctly broader than other sauropods. Their forelimbs were also stocky but their rear limbs were longer. Their vertebrae (back bones) were solid (not hollowed-out), which may be a throwback to more primitive saurischians. Their spinal column was more flexible, so they were probably more agile than their cousins and better at rearing up.

From skin impressions found with the fossils, it has been determined that their skin was armored with a small mosaic of small, bead-like scales around a larger scale. One species has even been discovered with bony plates, like the "Ankylosaurus".

While they were all huge, many were fairly average in size compared with the other giant dinosaurs. There were even some island-dwelling dwarf species, probably the result of allopatric speciation and insular dwarfism.

Range

The titanosaurs were the last great group of sauropods before the Cretaceous-Tertiary extinction event, about 90–65 million years ago and were the dominant herbivores of their time. The fossil evidence suggests they replaced the other sauropods, like the diplodocids and the brachiosaurids, which died out between the late Jurassic and the mid-Cretaceous Periods.

They were widespread, especially in the southern continents (then part of the supercontinent of Gondwana) and even in Australia, where sauropod remains in Queensland have been determined to be titanosaurid.cite book|author=Molnar R.E. and Salisbury S.W.|year=2005|chapter=Observations on Cretaceous Sauropods from Australia|editor=Carpenter, Kenneth and Tidswell, Virginia (ed.)|title=Thunder Lizards: The Sauropodomorph Dinosaurs|pages=454–465|publisher= Indiana University Press|id=ISBN 0-253-34542-1] New remains from an outback town in Queensland, from rocks around 96 million years old, show that Australia too had large titanosaurs, around 25 meters long (82 feet).cite web |url=http://www.theaustralian.news.com.au/story/0,20867,21665765-2702,00.html|title=Bones reveal Queensland's prehistoric titans |accessdate=2007-05-04 |last=Roberts |first=Greg |date=2007-05-03 |publisher=The Australian ] Four well preserved skeletons of a titanosaur species were found in Italy, a discovery first reported on May 2, 2006. [http://www.sciencedaily.com/upi/index.php?feed=Science&article=UPI-1-20060502-14331100-bc-italy-dinosaur.xml] Only Antarctica has yielded no titanosaur remains.Remains have also been recently discovered in New Zealand [http://www.nzherald.co.nz/section/1/story.cfm?c_id=1&objectid=10518111] .

Paleobiology

Diet

Fossilized dung associated with late Cretaceous titanosaurids has revealed phytoliths, silicified plant fragments, that offer clues to a broad, unselective plant diet. Besides the plant remains that might have been expected, such as cycads and conifers, discoveries published in 2005 [ [http://www.sciencemag.org/cgi/content/abstract/310/5751/1177 Dinosaur Coprolites and the Early Evolution of Grasses and Grazers - Prasad et al. 310 (5751): 1177 - Science ] ] revealed an unexpectedly wide range of monocotyledons, including palms and grasses (Poaceae), including ancestors of rice and bamboo, which has given rise to speculation that herbivorous dinosaurs and grasses co-evolved.

Nesting

A large titanosaurid nesting ground was discovered in Auca Mahuevot, in Patagonia, Argentina and another colony has reportedly been discovered in Spain. The small eggs, about 11–12 cm (4–5 in.) in diameter, contained fossilised embryos, complete with skin impressions (though there was no indication of feathers or dermal spines). Apparently several hundred female saltasaurs dug holes, laid their eggs and then buried them under dirt and vegetation. This gives evidence of herd behavior, which, along with their armor, may have been a defensive behavior against large predators like the "Abelisaurus".

ystematics

For such a widespread and successful group (they represent roughly a third of the total sauropod diversity known to date), the fossil record of titanosaurs is poor. Only recently have skulls or relatively complete skeletons (see "Rapetosaurus") of any of the roughly 50 species of titanosaur been discovered. Many are poorly known, and much of the material may either be deemed invalid or be reclassified as understanding of the clade grows.

The family Titanosauridae was named after and anchored on the poorly known genus "Titanosaurus", which was coined by Richard Lydekker in 1877, on the basis of a partial femur and two incomplete caudal vertebrae. Fourteen species have since been referred to "Titanosaurus", which distribute the genus across Argentina, Europe, Madagascar, India and Laos and throughout 60 million years of the Cretaceous Period. Despite its centrality to titanosaur systematics and biogeography, a re-evaluation of all "Titanosaurus" species recognises only five as diagnostic. The type species "T. indicus" is invalid, because it is based on 'obsolescent' characters - once diagnostic features that have gained a broader taxonomic distribution over time. Consequently, use of the genus "Titanosaurus" has largely been abandoned. The most well known "Titanosaurus" specimens have since been re-assigned to other genera, including "Isisaurus". However, if "Titanosaurus indicus" is redescribed in the future, on the basis of new finds, "Titanosaurus" itself becomes provisionally valid.

Some paleontologists (such as Sereno, 2005 [http://www.taxonsearch.org/dev/taxon_edit.php?Action=View&tax_id=316] ) have contended that "Titanosaurus" is too poorly known to use as a basis for classification, family names for which it is the type genus (e.g. Titanosaurinae, Titanosauridae, Titanosauroidea) should not have other genera referred to them. Weishampel "et al.", in the second edition of "The Dinosauria", also did not use the family Titanosauridae, and instead used several smaller titanosaur families such as Saltosauridae and Nemegtosauridae.Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.) (2004). The Dinosauria, Second Edition.. University of California Press., 861 pp.]

Taxonomy

Family-level taxonomy follows the definitions proposed by Paul Sereno in 2005, and referrals of genera to families in their individual descriptions.Sereno, P. C. 2005. [http://www.taxonsearch.org/Archive/stem-archosauria-1.0.php Stem Archosauria—TaxonSearch] [version 1.0, 2005 November 7] ]

* Superfamily Titanosauroidea
** Clade Titanosauria
*** "Uberabatitan" Salgado, L. and Carvalho, I. (2008). "Uberabatitan ribeiroi", a new titanosaur from the Marila Formation (Bauru Group, Upper Cretaceous), Minas Gerais, Brazil." "Palaeontology, 51(4): 881-901. DOI: 10.1111/j.1475-4983.2008.00781.x]
*** Family Andesauridae
**** "Andesaurus" (Argentina)
*** Family Titanosauridae (disused, =Clade Lithostrotia)
**** "Ampelosaurus" (France)
**** "Argentinosaurus" (Argentina)
**** "Austrosaurus" (Australia)
**** "Chubutisaurus" (Argentina)
**** "Epachthosaurus" (Argentina)
**** "Futalognkosaurus" (Argentina)
**** "Ligabuesaurus" (Argentina)
**** "Lirainosaurus" (Spain)
**** "Phuwiangosaurus" (Thailand)
**** "Tangvayosaurus" (Laos)
**** Family Antarctosauridae
***** "Antarctosaurus" (Argentina)
**** Family Nemegtosauridae
***** "Bonitasaura" (Argentina)
***** "Magyarosaurus" (Romania)
***** "Malawisaurus" (Malawi)
***** "Nemegtosaurus" (Mongolia)
***** "Rapetosaurus" (Madagascar)
***** "Trigonosaurus" (Brazil)
**** Family Saltasauridae
***** "Argyrosaurus" (Argentina)
***** "Bonatitan" (Argentina)
***** "Iuticosaurus" (UK)
***** "Lirainosaurus" (Spain)
***** "Maxakalisaurus" (Brazil)
***** "Pellegrinisaurus" (Argentina)
***** "Quaesitosaurus" (Mongolia)
***** "Rinconsaurus" (Argentina)
***** "Sonidosaurus" (China)
***** Subfamily Opisthocoelicaudiinae
****** "Alamosaurus" (USA)
****** "Borealosaurus" (China)
****** "Huabeisaurus"? {China)
****** "Isisaurus" (India)
****** "Opisthocoelicaudia" (Mongolia)
***** Subfamily Saltasaurinae
****** "Neuquensaurus" (Argentina)
****** "Saltasaurus" (Argentina, Uruguay)
****** Tribe Aeolosaurini
******* "Aeolosaurus" (Argentina)
******* "Gondwanatitan" (Brazil)
******* "Rocasaurus" (Argentina)
*** Uncertain Placement ("incertae sedis")
**** "Adamantisaurus" {Brazil)
**** "Aegyptosaurus" (Egypt, Niger)
**** "Amargatitanis" (Argentina)
**** "Baurutitan" (Brazil)
**** "Bruhathkayosaurus" (India)
**** "Gobititan" (China)
**** "Hypselosaurus" (Romania)
**** "Jainosaurus" (India)
**** "Jiangshanosaurus" (China)
**** "Karongasaurus" (Malawi)
**** "Laplatasaurus" (Argentina, Uruguay)
**** "Mendozasaurus" (Argentina)
**** "Paralititan" {Egypt)
**** "Puertasaurus" (Argentina)
**** "Titanosaurus" (India)
**** "Venenosaurus" (USA)

Phylogeny

In the second edition of "The Dinosauria", the clade Titanosauria was defined as all sauropods closer to "Saltasaurus" than to "Brachiosaurus", a definition followed by Upchurch "et al." (2004). A few scientists, such as Paul Sereno, have continued to use node-based definitions or definitions which exclude "Euhelopus" as well as "Brachiosaurus". [http://www.taxonsearch.org/dev/taxon_edit.php?Action=View&tax_id=316]

Relationships within the Titanosauria have historically been extremely variable from study to study, complicated by the fact that clade and rank names have been applied inconsistently by various scientists. One possible cladogram is presented here, and follows a 2007 analysis by Calvo and colleagues. The authors notably used the family Titanosauridae in a broader fashion than other recent studies, and coined the new clade name Lognkosauria.Calvo, J.O., Porfiri, J.D., González-Riga, B.J., and Kellner, A.W. (2007) "A new Cretaceous terrestrial ecosystem from Gondwana with the description of a new sauropod dinosaur". "Anais Academia Brasileira Ciencia", 79(3): 529-41. [http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=pubmed&dopt=AbstractPlus&list_uids=17768539] ]

clade| style=font-size:100%;line-height:80%
label1=Titanosauria
1=clade
1="Andesaurus"
label2=Titanosauridae
2=clade
label1=unnamed
1=clade
1="Malawisaurus"
label2=Lognkosauria
2=clade
1="Mendozasaurus"
2="Futalognkosaurus"
label2=unnamed
2=clade
1="Epachthosaurus"
label2=Eutitanosauria
2=clade
label1=unnamed
1=clade
1="Rapetosaurus"
label2=unnamed
2=clade
label1=Aeolosaurini
1=clade
1="Gondwanatitan"
2="Aeolosaurus"
label2=unnamed
2=clade
1="Rinconsaurus"
2=Loma Lindero sp.
label3=unnamed
3=clade
1="Lirainosaurus"
label2=unnamed
2=clade
label1=Opisthocoelicaudiinae
1=clade
1="Opisthocoelicaudia"
2="Alamosaurus"
label2=Saltasaurinae
2=clade
1="Neuquensaurus"
label2=unnamed
2=clade
1="Saltasaurus"
2="Rocasaurus"

References

External links

* [http://www.dinodata.org/index.php?option=com_content&task=view&id=544&Itemid=103 Titanosauria on DinoData]
* The Geological Society article " [http://www.geolsoc.org.uk/template.cfm?name=Rapetosaurus Best ever titanosaur skeleton discovered in Madagascar] ".
* National Geographic article, " [http://news.nationalgeographic.com/news/2001/09/0927_TVdinoeggs.html Eggs Hold Skulls of Titanosaur Embryos] ".
* Channel 4 article, " [http://www.channel4.com/history/microsites/B/big_monster_dig/programmes/titanosaur_eggs/ Titanosaur eggs in France] ".