28-531: Lithostrotia is a clade of derived titanosaur sauropods that lived during the Early Cretaceous 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 lithostros , meaning "inlaid with stones", referring to
56-534: A clade (from Ancient Greek κλάδος (kládos) 'branch'), also known as a monophyletic group or natural group , is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree . In the taxonomical literature, sometimes the Latin form cladus (plural cladi ) is used rather than the English form. Clades are
84-479: A "ladder", with supposedly more "advanced" organisms at the top. Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming , this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a rank can be named) because not enough ranks exist to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it
112-623: A clade can be described based on two different reference points, crown age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. Ages of clades cannot be directly observed. They are inferred, either from stratigraphy of fossils , or from molecular clock estimates. Viruses , and particularly RNA viruses form clades. These are useful in tracking
140-686: 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 , Tapuiasaurus and Alamosaurus as basal lithostrotians outside Saltasauridae . Another phylogenetic analysis by Poropat and colleagues in 2016, partially reproduced below, found Diamantinasaurus as
168-1107: A non-lithostrotian titanosaur and the sister taxon of the contemporary Savannasaurus . The cladogram below follows Mocho et al. (2019) with the new subgroup called Lirainosaurinae . Poropat et al. (2016) Andesaurus Dongyangosaurus Baotianmansaurus Ligabuesaurus Savannasaurus Diamantinasaurus Xianshanosaurus Daxiatitan Malawisaurus Muyelensaurus Futalognkosaurus Epachthosaurus Tapuiasaurus Nemegtosaurus Isisaurus Saltasaurus Opisthocoelicaudia Jiangshanosaurus Alamosaurus Mocho et al. (2019) Malawisaurus Paludititan Lohuecotitan Epachthosaurus Alamosaurus Opisthocoelicaudia Neuquensaurus Rocasaurus Saltasaurus Lirainosaurus Atsinganosaurus Ampelosaurus Bonatitan Rapetosaurus Nemegtosaurus Gondwanatitan Aeolosaurus Rinconsaurus Muyelensaurus Bonitasaura Mendozasaurus Futalognkosaurus Clade In biological phylogenetics ,
196-457: A report in 2007.It is currently listed as "Titanosauria indet., possibly Malawisaurus .sp". Relatively small by sauropod standards, Malawisaurus reached lengths of about 15 metres (49 ft), and weighed about 10 tonnes (11 short tons). In 2020 it was given a smaller estimation of 11 meters (36 ft) and 2.8 tonnes (3.1 short tons). Like some other titanosaurs, ossicles have been found which are believed to represent dermal scutes that covered
224-422: A revised taxonomy based on a concept strongly resembling clades, although the term clade itself would not be coined until 1957 by his grandson, Julian Huxley . German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics . He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on
252-429: A suffix added should be e.g. "dracohortian". A clade is by definition monophyletic , meaning that it contains one ancestor which can be an organism, a population, or a species and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct. The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics ,
280-400: 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
308-499: Is also used with a similar meaning in other fields besides biology, such as historical linguistics ; see Cladistics § In disciplines other than biology . The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis , the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from Bernhard Rensch . Many commonly named groups – rodents and insects , for example – are clades because, in each case,
SECTION 10
#1732790288245336-400: 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
364-476: Is in turn included in the mammal, vertebrate and animal clades. The idea of a clade did not exist in pre- Darwinian Linnaean taxonomy , which was based by necessity only on internal or external morphological similarities between organisms. Many of the better known animal groups in Linnaeus's original Systema Naturae (mostly vertebrate groups) do represent clades. The phenomenon of convergent evolution
392-515: Is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life . The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. In 1876 Thomas Henry Huxley , an early advocate of evolutionary theory, proposed
420-489: Is still controversial. As an example, see the full current classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade Dracohors , which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort "; its form with
448-546: The Dinosaur Beds of northern Malawi, which probably date to the Aptian stage of the Early Cretaceous . The type species is M. dixeyi and the specific name honours Frederick Augustus Dixey . Malawisaurus dixeyi was originally described in 1928 by Sidney H. Haughton as a species of Gigantosaurus (an invalid name for the diplodocid currently known as Tornieria ). Haughton considered it closely related to
476-413: 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 with strongly concave front faces (procoely), although the farthest vertebrae are not procoelous. In 1895, Richard Lydekker named the family Titanosauridae to summarize sauropods with procoelous (concave on
504-458: 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
532-451: The fundamental unit of cladistics , a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population , or a species ( extinct or extant ). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over
560-546: The group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant , each of which consists of even smaller clades. The clade "rodent"
588-461: The group, Upchurch and colleagues gave two common derived features ( synapomorphies ), which serve to distinguish the group from non-members. The first is that all caudal vertebrae apart from the farthest distal 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
SECTION 20
#1732790288245616-590: The last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic . Some of the relationships between organisms that the molecular biology arm of cladistics has revealed include that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria , and multicellular organisms may have evolved from archaea. The term "clade"
644-518: The latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in phylogenetic nomenclature : node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions). The relationship between clades can be described in several ways: The age of
672-495: 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 , Aeolosaurus , Ampelosaurus , and various other genera both within and outside Lithostrotia with different morphologies. Lithostrotia
700-476: The species G. robustus (later the type species of Janenschia ). The holotype was discovered c. 1924 in the " Dinosaur Beds " of Malawi (then known as the Nyasaland Protectorate ), which are usually considered to be of Barremian - Aptian age based on K–Ar dating , though they have also been suggested to be Late Cretaceous in age based on the vertebrate assemblage. In 1993 it
728-514: The spread of viral infections . HIV , for example, has clades called subtypes, which vary in geographical prevalence. HIV subtype (clade) B, for example is predominant in Europe, the Americas and Japan, whereas subtype A is more common in east Africa. Malawisaurus Malawisaurus (meaning " Malawi lizard") is an extinct genus of titanosaurian sauropod dinosaur . It is known from
756-514: Was not based upon a specific taxon. The name Lithostrotia is not currently recognized by all researchers. 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 than Malawisaurus in phylogenies. In addition to defining
784-529: Was placed in the newly named genus Malawisaurus by Louis L. Jacobs and colleagues, based on newly collected material from the locality. The holotype is SAM 7405, a partial skeleton and its type locality is Mwakasyunguti . Malawisaurus is not known outside of Africa - however, an isolated tooth resembles those associated with Malawisaurus and was found in the Late Cretaceous ( Cenomanian )-aged Alcântara Formation of Brazil according to
#244755