Titanosauridae
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Lithostrotia is a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
of derived titanosaur sauropods that lived during the
Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145  Ma to 100.5 Ma. Geology Pro ...
and Late Cretaceous. The group was defined by Upchurch ''et al.'' in 2004 as the most recent common ancestor of '' Malawisaurus'' and '' Saltasaurus'' and all the descendants of that ancestor. Lithostrotia is derived from the Ancient Greek , meaning "inlaid with stones", referring to the fact that many known lithostrotians are preserved with osteoderms. However, osteoderms are not a distinguishing feature of the group, as the two noted by Unchurch ''et al.'' include
caudal vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
with strongly concave front faces (procoely), although the farthest vertebrae are not procoelous.


History of research

In 1895, Richard Lydekker named the family Titanosauridae to summarize sauropods with procoelous (concave on the front) caudal vertebrae. The name Titanosauridae has since been widely used, and was defined by Salgado and colleagues (1997), Gonzalaz-Riga (2003), and Salgado (2003) as a node-based taxon. According to a proposal by Wilson and Upchurch (2003) looks today much of the research on the use of that name from: Wilson and Upchurch published a revision of the genus '' Titanosaurus'' and declare the type species ''Titanosaurus indicus'' as invalid because it is based only on two vertebrae of the tail, showing no diagnostically usable features. Consistently these authors consider ranking groups that are based on ''Titanosaurus'' as the nominal taxon, Titanosauridae, Titanosaurinae and Titanosauroidea - also considered invalid. In 2004 Upchurch and colleagues presented the new group Lithostrotia to describe the same group as Titanosauridae, but instead it was not based upon a specific taxon. The name Lithostrotia is not currently recognized by all researchers.


Definition and synapomorphies

Upchurch and colleagues (2004) define the Lithostrotia as a node-based taxon that includes the last common ancestor of '' Malawisaurus'' and '' Saltasaurus'' and all descendants of that ancestor. According to this definition the Lithostrotia includes all forms that are more
derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...
than ''Malawisaurus'' in phylogenies. In addition to defining the group, Upchurch and colleagues gave two common derived features (
synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...
), which serve to distinguish the group from non-members. The first is that all
caudal vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
apart from the farthest
distal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
were procoelous, meaning their front face was concave. Also, the front (proximal) caudal vertebrae were particularly strong procoelous. This first feature is also shared with Mamenchisauridae. Unchurch ''et al.'' named Lithostrotia based on the presence of osteoderms in many members, but the eponymous osteoderms do not represent synapomorphy, as the evolutionary history of osteoderms is unknown within the titanosaurs. It may be this trait has developed multiple times independently within the titanosaurs and Lithostrotia, as osteoderms are known in many saltasaurids, ''
Mendozasaurus ''Mendozasaurus'' is a genus of titanosaurian sauropod dinosaur. It was a member of Titanosauria, which were massive sauropods that were common on the southern landmasses during the Cretaceous. It is represented by several partial skeletons from ...
'', '' Aeolosaurus'', ''
Ampelosaurus ''Ampelosaurus'' ( ; meaning "vine lizard") is a titanosaurian sauropod dinosaur from the Late Cretaceous Period of what is now France. Its type species is ''A. atacis'', named by Le Loeuff in 1995. A possible unnamed species has given ''Ampel ...
'', and various other genera both within and outside Lithostrotia with different morphologies.


Systematics

Lithostrotia is a derived group of titanosaurs, excluding primitive forms such as '' Andesaurus'' and '' Phuwiangosaurus''. The possibly equivalent clade Titanosauridae was positioned in a phylogenetic analysis by Calvo ''et al.'' (2007), where it included all titanosaurs apart from '' Andesaurus'', though multiple primitive forms were not analyzed. Other phylogenies, by Unchurch ''et al.'' (2015), instead have found a few, non-lithostrotian titanosaurs, or nearly all non-brachiosaurid titanosauriformes within the group. Poropat ''et al.'' (2015) conducted a similar analysis to one of Unchurch ''et al.'' (2015). This analysis found that ''Andesaurus'', '' Argentinosaurus'' and '' Epachthosaurus'' were within Titanosauria but outside Lithostrotia, and the latter group included '' Malawisaurus'', '' Nemegtosaurus'', ''
Diamantinasaurus ''Diamantinasaurus'' is a genus of titanosaurian sauropod from Australia that lived during the early Late Cretaceous, about 94 million years ago. The type species of the genus is ''D. matildae'', first described and named in 2009 in paleontology, ...
'', ''
Tapuiasaurus ''Tapuiasaurus'' (meaning " Tapuia lizard") is a genus of titanosaur which lived during the Lower Cretaceous period (Aptian age) in what is now Minas Gerais, Brazil. Its fossils, including a partial skeleton with a nearly complete skull, ha ...
'' and ''
Alamosaurus ''Alamosaurus'' (; meaning "Ojo Alamo lizard") is a genus of opisthocoelicaudiine titanosaurian sauropod dinosaurs, containing a single known species, ''Alamosaurus sanjuanensis'', from the late Cretaceous Period of what is now southern North Am ...
'' as basal lithostrotians outside
Saltasauridae Saltasauridae (named after the Salta region of Argentina where they were first found) is a family of armored herbivorous sauropods from the Upper Cretaceous. They are known from fossils found in South America, Asia, North America, and Europe. Th ...
. Another phylogenetic analysis by Poropat and colleagues in 2016, partially reproduced below, found ''
Diamantinasaurus ''Diamantinasaurus'' is a genus of titanosaurian sauropod from Australia that lived during the early Late Cretaceous, about 94 million years ago. The type species of the genus is ''D. matildae'', first described and named in 2009 in paleontology, ...
'' as a non-lithostrotian titanosaur and the sister taxon of the contemporary ''
Savannasaurus ''Savannasaurus'' is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous Winton Formation of Queensland, Australia. It contains one species, ''Savannasaurus elliottorum'', named in 2016 by Stephen Poropat and colleagues. The holot ...
''. The cladogram below follows Mocho ''et al.'' (2019) with the new subgroup called Lirainosaurinae.Mocho P, Páramo A, Escaso F, Marcos-Fernández F, Vidal D, Ortega F. 2019. Titanosaurs from Lo Hueco (Campanian-Maastrichtian) reveal new information about the evolutionary history of European titanosaurs, pp. 111. In: The Palaeontological Association (ed.), 63rd Annual Meeting, 15th–21st December 2019, University of Valencia, Spain, Programme Abstracts, AGM papers Poropat ''et al.'' (2016) Mocho ''et al.'' (2019) While the clade Lithostrotia has been used in many different phylogenetic analyses as a description for a clade of titanosaurs, its use is not universal. The clade has been omitted from results as it has been considered a synonym of Titanosauria, or it has been used as either a very large clade encompassing almost all titanosaurs, or a smaller clade that excludes the taxa of
Colossosauria Colossosauria is a clade of titanosaur sauropods from the latest Early Cretaceous through the Late Cretaceous of South America. The group was originally named by Bernardo González-Riga ''et al.'' in 2019 in paleontology, 2019 and defined as the ...
. These incongruent results are because of the instability of the defining taxon ''Malawisaurus'', which may in fact represent a chimaeric assemblage of remains and requires re-evaluation to determine what Lithostrotia includes.


References

{{Portal bar, Dinosaurs Cretaceous dinosaurs Fossil taxa described in 2004