Titanosaurs (or titanosaurians; members of the groupTitanosauria) were a diverse group ofsauropoddinosaurs, including genera from every continent. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thriving at the time of theextinction event at the end of theCretaceous. This group includes some of thelargest land animals known to have ever existed, such asPatagotitan, estimated at 37 m (121 ft) long[15] with a mass of 69 tonnes (76 tons),[16] and the comparably-sizedArgentinosaurus andPuertasaurus from thesame region.
The group's name alludes to the mythologicalTitans of ancientGreek mythology, via the typegenus (now considered anomen dubium)Titanosaurus. Together with thebrachiosaurids and relatives, titanosaurs make up the larger sauropodcladeTitanosauriformes. Titanosaurs have long been a poorly-known group, and the relationships between titanosaur species are still not well-understood.
Due to the near-global distribution of titanosaurs during the Cretaceous, titanosaur fossils have been found on every continent, including Antarctica.[17] However, titanosaurs have the least complete fossil record of any major sauropodomorph group.[18] No complete titanosaur skeletons are known, and many species are only known from a few bones. Titanosaur skulls are especially rare. Though fragmentary cranial remains are known for several titanosaur genera, nearly complete skulls have been described for only four:Nemegtosaurus,Rapetosaurus,Sarmientosaurus, andTapuiasaurus.[19] As is the case in most other sauropod groups, there are few titanosaur specimens with complete necks preserving all of thecervical vertebrae in sequence.
Only three complete titanosaur necks are known: the holotype ofFutalognkosaurus and two undescribed specimens from Argentina. A fourth specimen, of an unidentified titanosaur from Brazil, preserves a nearly complete neck, with only theatlas, the tiny vertebra forming the joint between the skull and neck, missing.[20] Only five titanosaur specimens preserve complete, articulated hind feet.[21] This incompleteness is especially significant for giant titanosaurs, which are generally known from disarticulated and fragmentary remains.[21]
Titanosaurs are one of the few groups of dinosaurs for which fossil eggs are known.[22] The fossil site of Auca Mahuevo preserves a titanosaur nesting ground. Some titanosaur eggs have been found containing fossilembryos, which even preserve fossil skin.[23] These fossil embryos are among the few titanosaur specimens to preserve complete skulls.[24]
Titanosauria have the largest range of body size of any sauropod clade, and includes both the largest known sauropods and some of the smallest.[25] One of the largest titanosaurs,Patagotitan, had a body mass estimated to be 69 tonnes (76 tons), whereas one of the smallest,Magyarosaurus, had a body mass of approximately 900 kilograms (2,000 lb).[16][26] Even relatively closely related titanosaurs could have very different body sizes, as the smallrinconsaurs were closely related to the giganticlognkosaurs.[16] Fossils from perhaps the largest dinosaur ever found were discovered in 2021 in the Neuquén Province of northwest Patagonia, Argentina. It is believed that they are from a titanosaur.[27][28] Some of smallest titanosaurs, such asMagyarosaurus, inhabited Europe, which was largely made up of islands during the Cretaceous, and were likely island dwarfs. Another taxon of tiny titanosaurs,Ibirania, lived a non-insular context in Upper Creaceous Brazil, and is an example ofnanism resultant from other ecological pressures.[29]
The heads of titanosaurs are poorly known. However, several different cranial morphologies are apparent. In some species, such asSarmientosaurus, the head resembled that ofbrachiosaurids.[19] In others, such asRapetosaurus andNemegtosaurus, the head resembled that ofdiplodocids. In some titanosaurs, the skull was especially diplodocid-like due to square-shaped jaws;[30] the titanosaurAntarctosaurus is especially similar to therebbachisauridNigersaurus.[31] Titanosaurs had small heads, even when compared with other sauropods. The head was also wide, similar to the heads ofCamarasaurus andBrachiosaurus, though somewhat more elongated. Titanosaurian nostrils were large ("macronarian") and all had crests formed by the nasal bones. Their teeth were either somewhat spatulate (spoon-like) or like pegs or pencils, but were always very small.
Titanosaur necks were of average length for sauropods, and theirtails were whip-like though not as long as in thediplodocids. While thepelvis was slimmer than some sauropods, the pectoral (chest) area was much wider, giving them a uniquely "wide-legged" stance. As a result, thefossilized trackways of titanosaurs are distinctly broader than other sauropods. Their forelimbs were also stocky, and often longer than their hind limbs. Unlike other sauropods, some titanosaurs had no digits, walking only on horseshoe-shaped "stumps" made up of the columnar metacarpal bones.[32][33] Theirvertebrae (back bones) were solid (not hollowed-out), which may be a reversal to more basalsaurischian characteristics. Their spinal column was relatively flexible, likely making them more agile than other sauropods, though at the expense of rearing on their hind legs compared to the Diplodocoids. One of the most characteristic features shared by most titanosaurs were their procoelous caudal vertebrae, with ball-and-socket articulations between the vertebral centra.
Thedorsal vertebrae of titanosaurs show multiple derived features among sauropods. Similarly to the Rebbachisauridae, titanosaurs lost thehyposphene-hypantrum articulations, a set of surfaces between vertebrae that prevent additional rotation of the bones.Andesaurus, one of the most basal titanosaurs, shows a normal hyposphene. The same area is reduced inArgentinosaurus to only two ridges, and is fully absent in taxa likeOpisthocoelicaudia andSaltasaurus. BothArgentinosaurus andEpachthosaurus bear similar intermediate "hyposphenal ridges", which suggests they represent a more primitive form of dorsal vertebrae.[34]
Sauropod hands already are highly derived from other dinosaurs, being reduced into columnarmetacarpals and blockyphalanges with fewer claws. However, titanosaurs evolved the manus even further, completely losing the phalanges and heavily modifying the metacarpals.Argyrosaurus is the only titanosaur known to possesscarpals. Other taxa likeEpachthosaurus show a reduction of phalanges to one or two bones.Opisthoeoclicaudia shows even more reduction of the hand than other titanosaurs, with both carpals and phalanges completely absent.[35] However,Diamantinasaurus, while lacking carpals, preserves a manual formula of2–1–1–1–1, including a thumb claw and phalanges on all other digits. This, coupled with the preservation of a single phalanx on digit IV ofEpachthosaurus and potentiallyOpisthocoelicaudia (further study is necessary), show that preservation biases may be responsible for the lack of hand phalanges in these taxa. This suggests thatAlamosaurus,Neuquensaurus,Saltasaurus andRapetosaurus - all known from imperfect or disarticulated remains previously associated with a lack of phalanges - may have had phalanges but lost them after death.[36]
Titanosaurs have a poor fossil record of theirpedes (feet), only being complete in five definitive titanosaurs. Among these,Notocolossus is the largest, and also has the most specialized pes: like all titanosaurs, its pes is composed of short, thickmetatarsals of approximately the same lengths; however, metatarsals I and V are notably more robust than in other taxa.[37]
From skin impressions found withfossils, it has been determined that the skin of many titanosaurs wasarmored with a small mosaic of small, bead-likescales surrounding larger scales.[23] While most titanosaurs were very large animals, many were fairly average in size compared to other giant dinosaurs. Some island-dwelling dwarf titanosaurs, such asMagyarosaurus, were probably the result ofallopatric speciation andinsular dwarfism.
Some titanosaurs hadosteoderms. Osteoderms were first confirmed in the genusSaltasaurus but are now known to have been present in a variety of titanosaurs within the clade Lithostrotia.[38] The exact arrangement of osteoderms on the body of a titanosaur is not known, but some paleontologists consider it likely that the osteoderms were arranged in two parallel rows on the animal's back, an arrangement similar to the plates ofstegosaurs.[39] Several other arrangements have been proposed, such as a single row along the midline, and it is possible that different species had different arrangements. The osteoderms were certainly far more sparse than those ofankylosaurs, and did not completely cover the back in scutes. Because of their sparse arrangement, it was unlikely that they served a significant role in defense. However, they may have played an important role in nutrient storage for titanosaurs living in highly seasonal climates and for female titanosaurs laying eggs.[40][41] Osteoderms were present on both large and small species, so they were not solely used by smaller species as protection against predators.[42] New evidence published in 2021 suggests there were indeed some defensive purposes in titanosaur osteoderms; simulated bite marks from both baurusuchid crocodylomorphs and abelisaurids on titanosaurid osteoderms suggest they could be useful for protecting the animals as well as functioning in mineral storage.[43]
| Phylogenetic position of Titanosauria withinEusauropoda[44] |
Titanosaurs are classified assauropoddinosaurs. This highly diverse group forms the dominant clade of Cretaceous sauropods.[45] Within Sauropoda, titanosaurs were once classified as close relatives ofDiplodocidae due to their shared characteristic of narrow teeth, but this is now known to be the result of convergent evolution.[46] Titanosaurs are now known to be most closely related toeuhelopodids andbrachiosaurids; together they form a clade named Titanosauriformes.[47]
For much of the 20th century, most known species of titanosaurs were classified in the family Titanosauridae, which is no longer in widespread use.[7] Titanosauria was first proposed in 1993 as a taxon to encompass titanosaurids and their close relatives.[48] It has been phylogenetically defined as the clade composed of the most recent common ancestor ofSaltasaurus andAndesaurus and all of its descendants.[46][7][49][50][38][47] The relationships of species within Titanosauria remain largely unresolved, and it is considered one of the most poorly-understood areas of dinosaur classification. One of the few areas of agreement is that the majority of titanosaurs exceptAndesaurus and some other basal species form a clade calledLithostrotia, which some researchers consider equivalent to the deprecated Titanosauridae.[7][51][50] Lithostrotians include titanosaurs such asAlamosaurus,Isisaurus,Malawisaurus,Rapetosaurus, andSaltasaurus.[51]
Titanosaurus indicus was first named by BritishpaleontologistRichard Lydekker in1877, as a new taxon of dinosaur based on two caudals and a femur collected on different occasions at the same location inIndia.[52] While it was later given a position as a sauropod withinCetiosauridae by Lydekker in1888,[53] he named the newsauropod familyTitanosauridae for the genus in1893, which included onlyTitanosaurus andArgyrosaurus, united byprocoelous caudals,opisthocoelous presacrals, a lack of pleurocoels and open chevrons.[54] Following this, Austro-Hungarian paleontologistFranz Nopcsa reviewed reptile genera in1928, and provided a short classification of Sauropoda, where he placed theTitanosaurinae (a reranking of Lydekker's Titanosauridae) inMorosauridae, and included the generaTitanosaurus,Hypselosaurus andMacrurosaurus because they all had strongly procoelous caudals.[55]
German paleontologistFriedrich von Huene provided a significant revision of Titanosauridae the following year in1929, where he reviewed the dinosaurs ofCretaceousArgentina, and named multiple new genera. Huene included multiple species ofTitanosaurus from India,England,France,Romania,Madagascar and Argentina,Hypselosaurus andAepisaurus from France,Macrurosaurus from England,Alamosaurus fromUnited States, andArgyrosaurus,Antarctosaurus, andLaplatasaurus from Argentina. The material between them represented almost all regions of the skeleton, which showed they were derived sauropods Huene interpreted as closest toPleurocoelus of the various non-titanosaurid genera.[56]
For his1986 thesis, Argentinian paleontologistJaime Powell described and classified many new genera of South American titanosaurs. Using the family Titanosauridae to include them all, he grouped the genera into Titanosaurinae,Saltasaurinae,Antarctosaurinae,Argyrosaurinae and Titanosauridae indet. Titanosaurinae includedTitanosaurus and the new genusAeolosaurus, united by multiple features of the caudal vertebrae; the new clade Saltasaurinae was created to includeSaltasaurus and the new genusNeuquensaurus, united by very distinct dorsals, caudals, and ilia; the new clade Antarctosaurinae was created to includeAntarctosaurus, distinguished by large size, a different form ofbraincase, more elongate girdle bones, and more robust limb bones; and Argyrosaurinae was created forArgyrosaurus, bearing a more robust forelimb and hand and more primitive dorsals. The new genusEpachthosaurus was named for a more basal titanosaurid classified as Titanosauridae indet. along with unnamed specimens,Clasmodosaurus andCampylodoniscus.[57]
John Stanton McIntosh provided a synopsis of sauropod relationships in1990, using Titanosauridae as the group to contain all taxa like previous authors.Opisthocoelicaudia was placed inOpisthocoelicaudiinae withinCamarasauridae, following its original description and not later works, andNemegtosaurus andQuaesitosaurus were placed withinDicraeosaurinae. Titanosauridae included many previously named genera, plus taxa likeTornieria andJanenschia.[58]Saltasaurus included the species previously known asTitanosaurus australis andT. robustus, which were namedNeuquensaurus by Powell in 1986.[7] McIntosh provided a large diagnosis of the family: "dorsals with irregularly shaped pleurocoels and spines directed strongly backward; transverse processes directed dorsally as well as laterally, very robust in shoulder region; a second dorsosacral, its rib fused to ilium; caudals strongly procoelous with a prominent ball on distal end of centrum throughout tail; caudal arches on front half of centrum; sternal plates large; preacetabular process of ilium swept outward to become almost horizontal", but stressed that the relationships of titanosaurids to other sauropod groups couldn't be determined due to a lack of cranial material.[58]
A brief review of putative titanosaurids from Europe was authored byJean Le Loeuff in1993, and covered the supposed genera known so far. TheBarremian (middle Early Cretaceous) speciesTitanosaurus valdensis, named decades previous by Huene, was kept as the oldest of the titanosaurid and given the new genus nameIuticosaurus. The French taxonAepisaurus was removed from the family and placed in undetermined Sauropoda.Macrurosaurus was considered achimaera of titanosaurid and non-titanosaurid material because of the presence of both procoelous andamphicoelous caudals. Huene's speciesTitanosaurus lydekkeri was left as anomen dubium, but left within Titanosauridae.Maastrichtian fossils from France andSpain were removed fromHypselosaurus andTitanosaurus, withHypselosaurus being declared dubious likeT. lydekkeri. The variety of Romanian fossils named asMagyarosaurus by Huene were also moved into the same species again,M. dacus as originally named by Nopcsa.[59]
José Bonaparte and Rodolfo Coria in1993 concluded that a new clade of derived sauropods was necessary becauseArgentinosaurus,Andesaurus andEpachthosaurus were distinct from Titanosauridae as they possessedhyposphene-hypantrum articulations, but were still very closely related to the titanosaurids. The taxa that possessed the articulations were united within the new familyAndesauridae, and the two families were grouped together within the new clade Titanosauria. The titanosaurs were diagnosed by possessing smallpleurocoels centered within an anteroposteriorly elongate depression and the presence of two well defined depressions on the posterior face of the neural arch. The entire group was compared favourably withcetiosaurids likePatagosaurus andVolkheimeria.[48]
Overlooking the naming of Titanosauria,Paul Upchurch in1995 named the cladeTitanosauroidea, to includeOpisthocoelicaudia and the more derived Titanosauridae (Malawisaurus,Alamosaurus andSaltasaurus). United by: caudals with anteriorly-shifted neural spines, extremely robust forearm bones, a prominent concavity on theulna for articulation with the humerus, a laterally flared and flattenedilium, and a less robust pubis; Upchurch considered the clade sister taxon toDiplodocoidea, because of their shared dental anatomy, although he noted that peg-like teeth might have been independently evolved.[60] This was followed up by Upchurch's1998 study on sauropod phylogenetics, which additionally recoveredPhuwiangosaurus andAndesaurus within Titanosauroidea and resolvedOpisthocoelicaudia as the sister ofSaltasaurus instead of the most basal titanosauroid. This result places Titanosauroidea in a group withCamarasaurus andBrachiosaurus, althoughNemegtosauridae (Nemegtosaurus andQuaesitosaurus) was still classified as the basalmost family of diplodocoids. Upchurch chose to use Titanosauroidea as a replacement name for Titanosauria due to the recommended use ofLinnean taxonomy and ranks.[61]
In1997, Leonardo Salgadoet al. published a phylogenetic study onTitanosauriformes, including relationships within Titanosauria. They provided a definition for the clade of "including the most recent common ancestor ofAndesaurus delgadoi and Titanosauridae and all of its descendants". Titanosauria resolved including the same two subclades as Bonaparte & Coria (1993), where Andesauridae was monotypic, only including the name genus, and Titanosauridae was all other titanosaurs. Titanosauria was additionally rediagnosed, with eye-shaped pleurocoels, forked infradiapophyseallaminae, centro-parapophyseal laminae, procoelous anterior caudals, and a significantly longerpubis thanischium. Titanosauridae was less strongly defined because of the polytomy betweenMalawisaurus andEpachthosaurus, so some diagnostic features couldn't be resolved. Saltasaurinae was defined as the most recent ancestor ofNeuquensaurus,Saltasaurus and its descendants, and diagnosed by short cervicalprezygapophyses, vertically compressed anterior caudals, and a posteriorly shifted anterior caudal neural spine.[46]
| Titanosauria |
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Contributing additional work to the systematics of titanosaurs, Spanish paleontologistJosé Sanzet al. published an additional study in1999, utilizing both the names Titanosauria and Titanosauroidea in displaying their results. Similar to Upchurch (1995), Sanzet al. recoveredOpisthocoelicaudia as a titanosauroid outside Titanosauria, while Titanosauria was redefined to include only the taxa classified by their study.Eutitanosauria was proposed as a name for the titanosaurs more derived thanEpachthosaurus, and noted the presence ofosteoderms as a probablesynapomorphy of this clade.Aeolosaurus,Alamosaurus,Ampelosaurus andMagyarosaurus were looked at using their character list, but were considered too incomplete to add to the final study.[62]
Argentinian paleontologist Jaime Powell published his 1986 thesis in2003, with revisions to bring his old work up to date, including the addition of more phylogenetics and the recognition of Titanosauria as a clade name. Using the datamatrix of Sanzet al. (1999) and modifying it to include additional taxa and some character changes, Powell found that titanosaurs formed mostly a single gradual radiation beginning withEpachthosaurus as the most basal titanosaur, andAmpelosaurus andIsisaurus as the most derived. Titanosauroidea (following Upchurch 1995), was distinguished by pre- and post-spinal laminae in anterior caudals, a laterally flared ilium, a lateral expansion of the upper femur, and strongly opisthocoelous posterior dorsals. Less inclusive, Titanosauria was diagnosed by horizontally facing dorsaldiapophyses, prominent procoelous anterior caudals, and a ridge on thesternal plates. Within Titanosauria, Eutitanosauria was characterized by the absence of a hyposphene-hypantrum, no femoral fourth trochanter, and osteoderms. A small clade ofAlamosaurus,Lirainosaurus and the "Peirópolis titanosaur" (Trigonosaurus) was resolved, and diagnosed by only a rotation of the tibia so the proximal end is perpendicular to the distal end. More derived clades, while resolved, were only weakly supported, or characterized by reversions of diagnostic traits of larger groups (below and left).[63]
Powell (2003)
| Curry-Rogers & Forster (2001)
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Rapetosaurus was described in2001 byKristina Curry-Rogers andCatherine Forster, who additionally provided a new phylogenetic analysis ofTitanosauriformes (above and right). Titanosauria was strongly supported, distinguished by up to 20 characters depending on unknown traits in basal taxa. Similarly, Saltasaurinae was characterised by up to 16 traits, and the clade ofRapetosaurus and related taxa possessed four unique features.Nemegtosaurus andQuaesitosaurus were resolved within Titanosauria for the first time, after being placed in Diplodocoidea by multiple other analyses, becauseRapetosaurus provided the first significant titanosaur cranial material with associated postcrania. All three genera were resolved in a clade together, although Curry-Rogers & Forster noted that it was possible the group was only resolved because no other titanosaurs had comparable cranial material.Opisthocoelicaudia was also nested deeply in Saltasaurinae, though a further investigation of titanosaur interrelationships was proposed.[64]
American paleontologist Jeff Wilson presented another revision of overall sauropod phylogeny in2002, resolving strong support for most groups, and a similar result to Upchurch (1998) although withEuhelopus closest to titanosaurs instead of outsideNeosauropoda. More internal clades were resolved for Titanosauria, withNemegtosaurus andRapetosaurus united within Nemegtosauridae, andSaltasauridae including two subfamilies, Opisthocoelicaudiinae and Saltasaurinae. Saltasauridae was defined as a node-stem triplet, where everything descended from the common ancestor ofOpisthocoelicaudia andSaltasaurus was within Saltasauridae, and the subfamilies Saltasaurinae and Opisthocoelicaudiinae were for every taxon on one branch of the saltasaurid tree or the other.[31]
Wilson and Paul Upchurch followed this study up in2003 with a significant revision of the type genusTitanosaurus, and revisited all the material that had been assigned to the genus while reviewing titanosaur inter-relationships. Because they foundTitanosaurus to be adubious name, they proposed thatLinnaean-named groups Titanosauridae and Titanosauroidea should be considered invalid as well. Wilson & Upchurch (2003) supported the definition of Salgadoet al. (1997) for Titanosauria, since it was oldest and most similar to the original content of the group when named by Bonaparte & Coria (1993).Lithostrotia (Upchurchet al. 2004) was defined to beMalawisaurus and all more derived titanosaurs, and the cladeEutitanosauria (Sanzet al. 1999) was considered a possible synonym ofSaltasauridae. Wilson & Upchurch (2003) presented a reduced cladogram of Titanosauria, including only the most commonly-analyzed taxa from previous studies, resulting in a tree similar to that of Wilson (2002) but withRapetosaurus andNemegtosaurus excluded andEpachthosaurus included.Alamosaurus andOpisthocoelicaudia were united within Opisthocoelicaudiinae,Neuquensaurus andSaltasaurus formed Saltasaurinae, andIsisaurus placed as the next most derived titanosaurid.[7]
At the same time as Wilson & Upchurch redescribing the species ofTitanosaurus, Saldago (2003) looked over the potential invalidity of the family Titanosauridae and redefined the internal clades of Titanosauria.[7][65] Titanosauria was defined as more inclusive than Titanosauroidea, contrasting with earlier used by Upchurch (1995) and Sanzet al. (1999), as all taxa inSomphospondyli closer toSaltasaurus thanEuhelopus. In order to create additional stability, Saldago also definedAndesauroidea for onlyAndesaurus, as every titanosaur closer to that genus thanSaltasaurus, and also it's opposite Titanosauroidea as every titanosaur closer toSaltasaurus thanAndesaurus. Next most inclusive, Salgado revitalised Titanosauridae to include everything descended from the ancestor ofEpachthosaurus andSaltasaurus, and to replace the node-stem triplet of Saltasauridae, defined the cladesEpachthosaurinae and Eutitanosauria asEpachthosaurus>Saltasaurus andSaltasaurus<Epachthosaurus respectively. Saltasaurinae and Opisthocoelicaudiinae were retained with their original definitions, but Lithostrotia was considered a synonym of Titanosauridae, and Titanosaurinae was considered aparaphyletic clade of unrelated titanosaurids.[65]
Following the clade definitions proposed in previous Salgado studies,Bernardo González-Riga published two papers in 2003 describing new taxa in Titanosauria:Mendozasaurus, andRinconsaurus (withJorge O. Calvo). In both studies, the new taxa formed clades within Titanosauridae, although neither were named, and new diagnostic features were proposed for the family.[66][67] ForMendozasaurus, the new genus grouped withMalawisaurus as basal within Titanosauridae, but because of the features of caudal vertebrae in these basal taxa, González-Riga recommended revising the diagnosis of the family, instead of changing the content.[66] The situation of caudals inRinconsaurus also suggested procoelous caudals were no longer diagnostic, because in the tail ofRinconsaurus the vertebrae regularly changed their articular surfaces, being from procoelous caudals interspersed with amphicoelous, opisthocoelous and biconvex vertebrae.[67]Rinconsaurus was then included inAeolosaurini, a clade named the following year by Aldirene Franco-Rosaset al. containing everything closer toAeolosaurus andGondwanatitan thanSaltasaurus orOpisthocoelicaudia. Only the three genera and various intermediate specimens were included in Aeolosaurini in their2004 paper, with the tribe being considered to be within Saltasaurinae.[68]
The second edition ofThe Dinosauria, published in2004, included newly described titanosaurs and other taxa reidentified as titanosaurs. Written by Upchurch,Paul Barrett andPeter Dodson, a review of Sauropoda included a more expansive Titanosauria for sauropods more derived than brachiosaurids. Titanosauria, defined as everything closer toSaltasaurus thanBrachiosaurus, included a very large variety of taxa, and the new cladeLithostrotia was named for a large number of more derived taxa, although Nemegtosauridae was placed in Diplodocoidea following earlier publications of Upchurch.[51] Lithostrotia adopted the distinguishing feature of strongly procoelous caudals, previously used for Titanosauria.[7][51]
In2005, Curry-Rogers proposed a new phylogenetic analysis that focused on the inter-relationships of Titanosauria and included the most expansive character and taxon list of any study before it. 364 characters were selected from all previous phylogenetic analyses and scored across 29 probable titanosaurs, ranging from theLate Jurassic AfricanJanenschia to the large variety of Late Cretaceous global genera. Proposing her analysis as the basis for a new phylogenetic framework of Titanosauria, Curry-Rogers recommended only using named for clades that were very strongly supported. For the strict consensus, every taxon more derived thanBrachiosaurus was in an unresolved polytomy except for a clade ofRapetosaurus andNemegtosaurus, and one of Saltasaurinae. Within the recommended results, she only named Titanosauria, Lithostrotia, Saltasauridae, Saltasaurinae and Opisthocoelicaudiinae, because of the weakness of support (below and left).[49]
Curry-Rogers (2005)
| Carballidoet al. (2017)
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Another form of composite matrix was created by Calvo, González-Riga andJuan Porfiri in2007, based upon multiple previous studies between 1997 and 2003. The final analysis included 15 titanosaurs and 65 characters, and the typical titanosaur subclades were resolved, Titanosauridae being used over Lithostrotia following Salgado (2003), and the new cladeRinconsauria for the clade ofRinconsaurus andMuyelensaurus. The new clade (defined asRinconsaurus andMuyelensaurus) was placed as the sister taxon of Aeolosaurini, which together grouped withRapetosaurus as sister to Saltasauridae.[50] In the same year, Calvoet al. published another paper, describing the basal titanosaurFutalognkosaurus. The only difference in the resulting phylogeny, based on the matrix of the Calvo, González-Riga & Porfiri (2007), was the addition ofFutalognkosaurus as the sister taxon toMendozasaurus in a clade Calvoet al. namedLognkosauria, defined by the two genera classified within it.[69] A very similar result was also recovered by González-Rigaet al. in2009 in a phylogenetic analysis based partially on that of Calvoet al. (2007), althoughEpachthosaurus was nested withRapetosaurus outside the clades of aeolosaurines.[70] Further updates and modifications were then made by Palbo Gallina & Apesteguía in2011, with the additions ofLigabuesaurus,Antarctosaurus,Nemegtosaurus andBonitasaura and character updates to match, bringing the total to 77 characters and 22 taxa. Significantly contrasting the earlier results, internal relationships of Titanosauria were rearranged.Malawisaurus nested withAndesaurus in a clade of the basalmost titanosaurs outside Titanosauroidea, whereLirainosaurus, instead of being the basal member of the saltasaur-branch was instead basalmost titanosauroid. Lognkosauria moved to be within rinconsaurs, while Nemegtosauridae was resolved as the sister ofAeolosaurus andGondwanatitan, and the rinconsaur-lognkosaur branch.Antarctosaurus was unstable, but placed in a polytomy with the lognkosaurs and rinconsaurs before being excluded. Saltasaurinae and its relationship withOpisthocoelicaudia remained the same.[71]
Nemegtosauridae was additionally revised by Hussam Zaheret al. (2011) with the description ofTapuiasaurus, which nested closer toRapetosaurus thanNemegtosaurus, with all three forming a clade of derived lithostrotians. Using the matrix of Wilson (2002), following the additions of a few cranial characters andDiamantinasaurus,Tangvayosaurus andPhuwiangosaurus, remained the same as originally found by Wilson but withDiamantinasaurus sister to Saltasauridae and the other two genera as basal titanosaurs outside Lithostrotia, since Titanosauria, while undefined, was labelled to include all taxa closer toSaltasaurus thanEuhelopus.[72] Following a revision of the skull ofTapuiasaurus, Wilsonet al. (2016) rescored the analysis of Zaheret al. and recovered similar results for everything but Nemegtosauridae, where the family dissolved into a more basalTapuiasaurus outside Lithostrota andNemegtosaurus outside Saltasauridae. While non-titanosaur phylogeny remained identical in every single result, the topology within Titanosauria was very labile and prone to change with minor adjustments.[73]
Also following the 2002 analysis of Wilson, José Carballido and colleagues published a redescription ofChubutisaurus in 2011, and utilized an updated Wilson matrix, expanded to 289 characters across 41 taxa, including 15 titanosaurs. The primary focus of the analysis was on the basal titanosauriform taxa, but Titanosauria was defined, as the most recent common ancestor ofAndesaurus delgadoi andSaltasaurus loricatus, and all its descendants, although the only autapomorphy of the group recovered was the absence of a prominent ventral process on the scapula.[74] This same matrix and basis of characters was further utilized and expanded for analyses onTehuelchesaurus,Comahuesaurus and related rebbachisaurs,Europasaurus, andPadillasaurus, before being expanded upon once again in2017 by Carballidoet al. during the description ofPatagotitan to 405 characters and 87 taxa, including 28 titanosaurs (above and right).[75][76][77][78][79] The definition of Titanosauria was preserved following Salgadoet al. (1997) asAndesaurus plusSaltasaurus. Eutitanosauria (closer toSaltasaurus thanEpachthosaurus) was resolved as a very inclusive clade composed of two distinct branches, one leading to the larger-bodied lognkosaurs and the other to the smaller-bodied saltasaurs. On the lognkosaur branch of Eutitanosauria, there is a branch of lognkosaurs and one of Rinconsauria. Following Calvo, González-Riga and Porfiri (2007), Rinconsauria was defined asMuyelensaurus plusRinconsaurus, and Lognkosauria was defined asMendozasaurus plusFutalognkosaurus. Rinconsauria included taxa typically found within Aeolosaurini as well, so Aeolosaurini was redefined asAeolosaurus rionegrinus plusGondwanatitan to preserve the original restricted content, otherwise the entire rinconsaur-lognkosaur branch would be classified within Aeolosaurini. Lithostrotia, Saltasauridae and Saltasaurinae had their definitions preserved from earlier studies, and included their typical content.[79]
Philip Mannion and colleagues redescribedLusotitan in2013, creating a new analysis of 279 characters drawn from significant previous analyses by Upchurch and Wilson supplemented by other studies. 63 sauropods were included, focusing on non-titanosaurian sauropods, although 14 probable titanosaurs were included. Unique to Mannionet al., continuous characters were distinguished in a run of the matrix, which resolved almost all ofSomphospondyli within Titanosauria because ofAndesaurus placing very basal in a large group of Andesauroidea. Titanosauroidea was tentatively retained as the opposite clade of titanosaurs, which included all other traditional titanosaurs, although it was noted because of the invalidity ofTitanosaurus, Titanosauroidea should be considered an invalid name as well.[47] While the original analysis didn't focus on titanosaurs, it was utilised during the descriptions ofSavannasaurus andDiamantinasaurus,Yongjinglong, an osteology ofMendozasaurus, and redescribingTendaguria.[36][80][81][82][44] From these updates, an analysis of 548 characters and 124 taxa was published by Mannionet al. in2019 for a redescription ofJiangshanosaurus andDongyangosaurus, and additional revisions ofRuyangosaurus were made. No differentiation between continuous and discrete characters was made like performed by Mannionet al. (2013), but a large clade of Andesauroidea was still resolved with implied weights. Both redescribed Asian taxa, as well asYongjinglong, previously considered derived titanosaurs related to Saltasauridae, were removed to outside the clade.[83]
| Titanosauria | |
In the description ofMansourasaurus, Sallamet al. (2017) published a phylogenetic analysis of Titanosauria including the most taxa of any analysis of the clade.[84] In an updated version of the analysis, with the taxonMnyamawamtuka added, Gorscak & O'Connor (2019) got similar results, with slightly different relationships within small clades.[14]
| Titanosauria | |
Fossilized dung associated with late Cretaceous titanosaurids from India has revealedphytoliths, silicified plant fragments, that offer clues to a broad, unselective plant diet. Besides the plant remains that might have been expected, such ascycads andconifers, discoveries published in 2005[85] revealed an unexpectedly wide range ofmonocotyledons, includingpalms and grasses (Poaceae), including ancestors ofrice andbamboo, which has given rise to speculation that herbivorous dinosaurs and grassesco-evolved.[86][87][88][89]
A large titanosauridnesting ground was discovered in Auca Mahuevo, inPatagonia, Argentina and another colony has reportedly been discovered in Spain. Several hundred femalesaltasaurs dug holes with their back feet, laid eggs in clutches averaging around 25 eggs each, and buried the nests under dirt and vegetation. The smalleggs, about 11–12 centimetres (4.3–4.7 in) indiameter, containedfossilisedembryos, complete withskin impressions. The impressions showed that titanosaurs were covered in a mosaic armour of small bead-like scales.[23] The huge number of individuals gives evidence ofherd behavior, which, along with their armor, could have helped provide protection against large predators such asAbelisaurus.[90]
The titanosaurs were the last great group of sauropods, which existed from about 136[91] to 66million years ago, before theCretaceous–Paleogene extinction event, and were the dominantherbivores of their time.[citation needed] The fossil evidence suggests they replaced the other sauropods, like thediplodocids and thebrachiosaurids, which died out between the lateJurassic and the mid-Cretaceous Periods.
Titanosaurs were widespread. In December 2011, Argentine scientists announced titanosaur fossils had been found on Antarctica[17]—meaning that titanosaur fossils have been found on all continents. They are especially numerous in the southern continents (then part of thesupercontinent ofGondwana). Australia had titanosaurs around 96 million years ago: fossils have been discovered inQueensland of a creature around 25 metres (82 ft) long.[92][93] Remains have also been discovered in New Zealand.[94] One of the largest ever titanosaur footprints was discovered in theGobi Desert in 2016.[95] One of the oldest remains of this group was described byGhilardi et al. (2016).[96] It was found from theValley of the Dinosaurs,Paraíba state ofBrazil, representing a 136-million-year-old subadult individual.[91]
Ibirania, a nanoid titanosaur fossil from Brazil suggests that individuals of various genera were susceptible to diseases such asosteomyelitis and parasite infestations. The specimen hails from the late cretaceousSão José do Rio Preto Formation,Bauru Basin, and was described in the journalCretaceous Research byAureliano et al. (2021).[97] Examination of the titanosaur's bones revealed what appear to be parasitic blood worms similar to the prehistoricPaleoleishmania but are 10-100 times larger, that seemed to have caused the osteomyelitis. The fossil is the first known instance of an aggressive case of osteomyelitis being caused by blood worms in an extinct animal.[98][99][100]
{{cite journal}}: CS1 maint: multiple names: authors list (link){{cite journal}}: CS1 maint: multiple names: authors list (link)Titanosauria at theEncyclopædia Britannica
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