}} Titanosaurs are classified as
sauropod dinosaurs. This highly diverse group forms the dominant clade of Cretaceous sauropods. Within Sauropoda, titanosaurs were once classified as close relatives of
Diplodocidae due to their shared characteristic of narrow teeth, but this is now known to be the result of convergent evolution. While it was later given a position as a sauropod within
Cetiosauridae by Lydekker in
1888, he named the new
sauropod family
Titanosauridae for the genus in
1893, which included only
Titanosaurus and
Argyrosaurus, united by caudals, presacrals, a lack of pleurocoels and open chevrons. Following this, Austro-Hungarian paleontologist
Franz Nopcsa reviewed reptile genera in
1928, and provided a short classification of Sauropoda, where he placed the
Titanosaurinae (a reranking of Lydekker's Titanosauridae) in
Morosauridae, and included the genera
Titanosaurus,
Hypselosaurus and
Macrurosaurus because they all had strongly procoelous caudals. German paleontologist
Friedrich von Huene provided a significant revision of Titanosauridae the following year in
1929, where he reviewed the dinosaurs of
Cretaceous Argentina, and named multiple new genera. Huene included multiple species of
Titanosaurus from India,
England,
France,
Romania,
Madagascar and Argentina,
Hypselosaurus and
Aepisaurus from France,
Macrurosaurus from England,
Alamosaurus from
United States, and
Argyrosaurus,
Antarctosaurus, and
Laplatasaurus from Argentina. The material between them represented almost all regions of the skeleton, which showed they were derived sauropods Huene interpreted as closest to
Pleurocoelus of the various non-titanosaurid genera. '' For his
1986 thesis, Argentinian paleontologist
Jaime 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 included
Titanosaurus and the new genus
Aeolosaurus, united by multiple features of the caudal vertebrae; the new clade Saltasaurinae was created to include
Saltasaurus and the new genus
Neuquensaurus, united by very distinct dorsals, caudals, and ilia; the new clade Antarctosaurinae was created to include
Antarctosaurus, distinguished by large size, a different form of
braincase, more elongate girdle bones, and more robust limb bones; and Argyrosaurinae was created for
Argyrosaurus, bearing a more robust forelimb and hand and more primitive dorsals. The new genus
Epachthosaurus was named for a more basal titanosaurid classified as Titanosauridae indet. along with unnamed specimens,
Clasmodosaurus and
Campylodoniscus.
John Stanton McIntosh provided a synopsis of sauropod relationships in
1990, using Titanosauridae as the group to contain all taxa like previous authors.
Opisthocoelicaudia was placed in
Opisthocoelicaudiinae within
Camarasauridae, following its original description and not later works, and
Nemegtosaurus and
Quaesitosaurus were placed within
Dicraeosaurinae. Titanosauridae included many previously named genera, plus taxa like
Tornieria and
Janenschia. A brief review of putative titanosaurids from Europe was authored by
Jean Le Loeuff in
1993, and covered the supposed genera known so far. The
Barremian (middle Early Cretaceous) species
Titanosaurus valdensis, named decades previous by Huene, was kept as the oldest of the titanosaurid and given the new genus name
Iuticosaurus. The French taxon
Aepisaurus was removed from the family and placed in undetermined Sauropoda.
Macrurosaurus was considered a
chimaera of titanosaurid and non-titanosaurid material because of the presence of both procoelous and caudals. Huene's species
Titanosaurus lydekkeri was left as a
nomen dubium, but left within Titanosauridae.
Maastrichtian fossils from France and
Spain were removed from
Hypselosaurus and
Titanosaurus, with
Hypselosaurus being declared dubious like
T. lydekkeri. The variety of Romanian fossils named as
Magyarosaurus by Huene were also moved into the same species again,
M. dacus as originally named by Nopcsa.
Titanosauria named José Bonaparte and Rodolfo Coria in
1993 concluded that a new clade of derived sauropods was necessary because
Argentinosaurus,
Andesaurus and
Epachthosaurus were distinct from Titanosauridae as they possessed , but were still very closely related to the titanosaurids. The taxa that possessed the articulations were united within the new family
Andesauridae, and the two families were grouped together within the new clade Titanosauria. The titanosaurs were diagnosed by possessing small 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 with
cetiosaurids like
Patagosaurus and
Volkheimeria. Overlooking the naming of Titanosauria,
Paul Upchurch in
1995 named the clade
Titanosauroidea, to include
Opisthocoelicaudia and the more derived Titanosauridae (
Malawisaurus,
Alamosaurus and
Saltasaurus). United by: caudals with anteriorly-shifted neural spines, extremely robust forearm bones, a prominent concavity on the
ulna for articulation with the humerus, a laterally flared and flattened
ilium, and a less robust pubis; Upchurch considered the clade sister taxon to
Diplodocoidea, because of their shared dental anatomy, although he noted that peg-like teeth might have been independently evolved. This was followed up by Upchurch's
1998 study on sauropod phylogenetics, which additionally recovered
Phuwiangosaurus and
Andesaurus within Titanosauroidea and resolved
Opisthocoelicaudia as the sister of
Saltasaurus instead of the most basal titanosauroid. This result places Titanosauroidea in a group with
Camarasaurus and
Brachiosaurus, although
Nemegtosauridae (
Nemegtosaurus and
Quaesitosaurus) 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 of
Linnean taxonomy and ranks. In
1997, Leonardo Salgado
et al. published a phylogenetic study on
Titanosauriformes, including relationships within Titanosauria. They provided a definition for the clade of "including the most recent common ancestor of
Andesaurus 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 infradiapophyseal , centro-parapophyseal laminae, procoelous anterior caudals, and a significantly longer
pubis than
ischium. Titanosauridae was less strongly defined because of the polytomy between
Malawisaurus and
Epachthosaurus, so some diagnostic features couldn't be resolved. Saltasaurinae was defined as the most recent ancestor of
Neuquensaurus,
Saltasaurus and its descendants, and diagnosed by short cervical , vertically compressed anterior caudals, and a posteriorly shifted anterior caudal neural spine. '' }} Contributing additional work to the systematics of titanosaurs, Spanish paleontologist
José Sanz et al. published an additional study in
1999, utilizing both the names Titanosauria and Titanosauroidea in displaying their results. Similar to Upchurch (1995), Sanz
et al. recovered
Opisthocoelicaudia 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 than
Epachthosaurus, and noted the presence of
osteoderms as a probable
synapomorphy of this clade.
Aeolosaurus,
Alamosaurus,
Ampelosaurus and
Magyarosaurus were looked at using their character list, but were considered too incomplete to add to the final study. Argentinian paleontologist Jaime Powell published his 1986 thesis in
2003, 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 Sanz
et al. (1999) and modifying it to include additional taxa and some character changes, Powell found that titanosaurs formed mostly a single gradual radiation beginning with
Epachthosaurus as the most basal titanosaur, and
Ampelosaurus and
Isisaurus 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 dorsal , prominent procoelous anterior caudals, and a ridge on the
sternal plates. Within Titanosauria, Eutitanosauria was characterized by the absence of a hyposphene-hypantrum, no femoral fourth trochanter, and osteoderms. A small clade of
Alamosaurus,
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).
Powell (2003) }}
Curry-Rogers & Forster (2001) }}
Rapetosaurus was described in
2001 by
Kristina Curry-Rogers and
Catherine Forster, who additionally provided a new phylogenetic analysis of
Titanosauriformes (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 of
Rapetosaurus and related taxa possessed four unique features.
Nemegtosaurus and
Quaesitosaurus were resolved within Titanosauria for the first time, after being placed in Diplodocoidea by multiple other analyses, because
Rapetosaurus 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. '' American paleontologist Jeff Wilson presented another revision of overall sauropod phylogeny in
2002, resolving strong support for most groups, and a similar result to Upchurch (1998) although with
Euhelopus closest to titanosaurs instead of outside
Neosauropoda. More internal clades were resolved for Titanosauria, with
Nemegtosaurus and
Rapetosaurus united within Nemegtosauridae, and
Saltasauridae including two subfamilies, Opisthocoelicaudiinae and Saltasaurinae. Saltasauridae was defined as a node-stem triplet, where everything descended from the common ancestor of
Opisthocoelicaudia and
Saltasaurus was within Saltasauridae, and the subfamilies Saltasaurinae and Opisthocoelicaudiinae were for every taxon on one branch of the saltasaurid tree or the other. Wilson and Paul Upchurch followed this study up in
2003 with a significant revision of the type genus
Titanosaurus, and revisited all the material that had been assigned to the genus while reviewing titanosaur inter-relationships. Because they found
Titanosaurus to be a
dubious name, they proposed that
Linnaean-named groups Titanosauridae and Titanosauroidea should be considered invalid as well. Wilson & Upchurch (2003) supported the definition of Salgado
et 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 (Upchurch
et al. 2004) was defined to be
Malawisaurus and all more derived titanosaurs, and the clade
Eutitanosauria (Sanz
et al. 1999) was considered a possible synonym of
Saltasauridae. 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 with
Rapetosaurus and
Nemegtosaurus excluded and
Epachthosaurus included.
Alamosaurus and
Opisthocoelicaudia were united within Opisthocoelicaudiinae,
Neuquensaurus and
Saltasaurus formed Saltasaurinae, and
Isisaurus placed as the next most derived titanosaurid. '' At the same time as Wilson & Upchurch redescribing the species of
Titanosaurus, Saldago (2003) looked over the potential invalidity of the family Titanosauridae and redefined the internal clades of Titanosauria. Titanosauria was defined as more inclusive than Titanosauroidea, contrasting with earlier used by Upchurch (1995) and Sanz
et al. (1999), as all taxa in
Somphospondyli closer to
Saltasaurus than
Euhelopus. In order to create additional stability, Saldago also defined
Andesauroidea for only
Andesaurus, as every titanosaur closer to that genus than
Saltasaurus, and also it's opposite Titanosauroidea as every titanosaur closer to
Saltasaurus than
Andesaurus. Next most inclusive, Salgado revitalised Titanosauridae to include everything descended from the ancestor of
Epachthosaurus and
Saltasaurus, and to replace the node-stem triplet of Saltasauridae, defined the clades
Epachthosaurinae and Eutitanosauria as
Epachthosaurus>
Saltasaurus and
Saltasaurus<
Epachthosaurus respectively. Saltasaurinae and Opisthocoelicaudiinae were retained with their original definitions, but Lithostrotia was considered a synonym of Titanosauridae, and Titanosaurinae was considered a
paraphyletic clade of unrelated titanosaurids. For
Mendozasaurus, the new genus grouped with
Malawisaurus 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. The second edition of
The Dinosauria, published in
2004, included newly described titanosaurs and other taxa reidentified as titanosaurs. Written by Upchurch,
Paul Barrett and
Peter Dodson, a review of Sauropoda included a more expansive Titanosauria for sauropods more derived than brachiosaurids. Titanosauria, defined as everything closer to
Saltasaurus than
Brachiosaurus, included a very large variety of taxa, and the new clade
Lithostrotia was named for a large number of more derived taxa, although Nemegtosauridae was placed in Diplodocoidea following earlier publications of Upchurch. Lithostrotia adopted the distinguishing feature of strongly procoelous caudals, previously used for Titanosauria.
Curry-Rogers (2005) }} '
Carballido et al.
(2017)' }} Another form of composite matrix was created by Calvo, González-Riga and
Juan Porfiri in
2007, 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 clade
Rinconsauria for the clade of
Rinconsaurus and
Muyelensaurus. The new clade (defined as
Rinconsaurus and
Muyelensaurus) was placed as the sister taxon of Aeolosaurini, which together grouped with
Rapetosaurus as sister to Saltasauridae. In the same year, Calvo
et al. published another paper, describing the basal titanosaur
Futalognkosaurus. The only difference in the resulting phylogeny, based on the matrix of the Calvo, González-Riga & Porfiri (2007), was the addition of
Futalognkosaurus as the sister taxon to
Mendozasaurus in a clade Calvo
et al. named
Lognkosauria, defined by the two genera classified within it. A very similar result was also recovered by González-Riga
et al. in
2009 in a phylogenetic analysis based partially on that of Calvo
et al. (2007), although
Epachthosaurus was nested with
Rapetosaurus outside the clades of aeolosaurines. Further updates and modifications were then made by Palbo Gallina & Apesteguía in
2011, with the additions of
Ligabuesaurus,
Antarctosaurus,
Nemegtosaurus and
Bonitasaura 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 with
Andesaurus in a clade of the basalmost titanosaurs outside Titanosauroidea, where
Lirainosaurus, 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 of
Aeolosaurus and
Gondwanatitan, 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 with
Opisthocoelicaudia remained the same. '' Nemegtosauridae was additionally revised by Hussam Zaher
et al. (2011) with the description of
Tapuiasaurus, which nested closer to
Rapetosaurus than
Nemegtosaurus, with all three forming a clade of derived lithostrotians. Using the matrix of Wilson (2002), following the additions of a few cranial characters and
Diamantinasaurus,
Tangvayosaurus and
Phuwiangosaurus, remained the same as originally found by Wilson but with
Diamantinasaurus sister to Saltasauridae and the other two genera as basal titanosaurs outside Lithostrotia, since Titanosauria, while undefined, was labelled to include all taxa closer to
Saltasaurus than
Euhelopus. Following a revision of the skull of
Tapuiasaurus, Wilson
et al. (
2016) rescored the analysis of Zaher
et al. and recovered similar results for everything but Nemegtosauridae, where the family dissolved into a more basal
Tapuiasaurus outside Lithostrota and
Nemegtosaurus 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. '',
Royal Ontario Museum Also following the 2002 analysis of Wilson, José Carballido and colleagues published a redescription of
Chubutisaurus 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 of
Andesaurus delgadoi and
Saltasaurus loricatus, and all its descendants, although the only autapomorphy of the group recovered was the absence of a prominent ventral process on the scapula. This same matrix and basis of characters was further utilized and expanded for analyses on
Tehuelchesaurus,
Comahuesaurus and related rebbachisaurs,
Europasaurus, and
Padillasaurus, before being expanded upon once again in
2017 by Carballido
et al. during the description of
Patagotitan to 405 characters and 87 taxa, including 28 titanosaurs (above and right). The definition of Titanosauria was preserved following Salgado
et al. (1997) as
Andesaurus plus
Saltasaurus. Eutitanosauria (closer to
Saltasaurus than
Epachthosaurus) 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 as
Muyelensaurus plus
Rinconsaurus, and Lognkosauria was defined as
Mendozasaurus plus
Futalognkosaurus. Rinconsauria included taxa typically found within Aeolosaurini as well, so Aeolosaurini was redefined as
Aeolosaurus rionegrinus plus
Gondwanatitan 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. While the original analysis didn't focus on titanosaurs, it was utilised during the descriptions of
Savannasaurus and
Diamantinasaurus,
Yongjinglong, an osteology of
Mendozasaurus, and redescribing
Tendaguria. From these updates, an analysis of 548 characters and 124 taxa was published by Mannion
et al. in
2019 for a redescription of
Jiangshanosaurus and
Dongyangosaurus, and additional revisions of
Ruyangosaurus were made. No differentiation between continuous and discrete characters was made like performed by Mannion
et al. (2013), but a large clade of Andesauroidea was still resolved with implied weights. Both redescribed Asian taxa, as well as
Yongjinglong, previously considered derived titanosaurs related to Saltasauridae, were removed to outside the clade. }} In the description of
Mansourasaurus, Sallam
et al. (2017) published a phylogenetic analysis of Titanosauria including the most taxa of any analysis of the clade. In an updated version of the analysis, with the taxon
Mnyamawamtuka added, Gorscak & O'Connor (2019) got similar results, with slightly different relationships within small clades.
(left) and Magyarosaurus (right), and femora of (left to right) Magyarosaurus, Lirainosaurus and Ampelosaurus'' }} ==Paleobiology==