''Mnyamawamtuka'' (pronounced "Mm-nya-ma-wah-mm-too-ka" ; meaning "beast of the Mtuka river drainage" in Kiswahili) is a genus of

lithostrotia 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'' an ...

titanosaur Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still th ...

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

from the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

Galula Formation in

Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands and ...

. The type and only species is ''M. moyowamkia''.

Discovery and naming

In 2004, a sauropod skeleton was found at the Mtuka River, twenty kilometres from

Lake Rukwa Lake Rukwa is an endorheic lake located the Rukwa Valley of Rukwa Region, Songwe Region and Katavi Region in southwestern Tanzania. The lake is the third largest inland body of water in the country. Geography The alkaline Lake Rukwa lies midw ...

. It was excavated between 2005 and 2008. In 2019, the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

''Mnyamawamtuka moyowamkia'' was named and described by Eric Gorscak and Patrick M. O’Connor. The generic name is a contraction of the

Kiswahili Swahili, also known by its local name , is the native language of the Swahili people, who are found primarily in Tanzania, Kenya and Mozambique (along the East African coast and adjacent litoral islands). It is a Bantu language, though Swahili ...

''Mnyama wa Mtuka'', the "Beast of the Mtuka". The describers made explicit that they considered "beast" to be an apt name for a member of the Titanosauria. The specific name is a contraction of ''moyo wa mkia'', meaning the "heart of the tail" in Kiswahili, a reference to the heart-shaped cross-section of the rear facet of the middle tail vertebrae. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

, RRBP 05834, was found in a layer of the Mtuka Member of the Galula Formation dating from the

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

, most likely between 110 and 100 million years old. It consists of a partial skeleton lacking the skull. It contains a neural arch of a front neck vertebra, centra of four neck vertebrae, seven back vertebrae, seven neural arches and seven centra of tail vertebrae, four chevrons, numerous rib pieces, a right shoulder blade, a right breastbone, both humeri, a left ulna, a right first metacarpal, a left third metacarpal, the left ischium, the right pubic bone, both thighbones, both shinbones, the left calfbone, the left metatarsus, two toe phalanges and a foot claw. The skeleton was not articulated. Despite the missing skull it represents one of the most complete known skeletons of early titanosaurs.

Description

The holotype individual had an estimated length of 7.6 metres and a weight of 1.5 tonnes. It probably was not fully grown. The describing authors indicated some distinguishing traits. Five of these are

autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...

, unique derived characters. The middle and rear dorsal (back) vertebrae have an accessory ridge or ''lamina'', forked at the top, located between the normal ridge connecting the front articular processes, and the neural channel. The rear back vertebrae lack a ridge connecting the rear articular processes because the ridge on the rear of the neural process runs all the way down to the neural channel. The middle tail vertebrae have a vertebral body of which the rear face is widened to above and sideways, resulting in a heart-shape. The upper inner side of the front edge of the shoulder blade, the part touching the coracoid, features a curved crest running parallel to a groove. Each of the paired breast bone plates is exceptionally small, equalling just 42% of the length of the humerus.

Phylogeny

''Mnyamawamtuka'' was placed in the

Titanosauria Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...

in 2019.

Cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

analyses indicated several possible positions in the evolutionary tree. ''Mnyamawamtuka'' was sometimes recovered outside of the

Lithostrotia 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'' an ...

. Alternatively, it was positioned in a basal position within the lithostrotians, as

sister species In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

of ''

Malawisaurus ''Malawisaurus'' (meaning "Malawi lizard") is an extinct genus of titanosaurian sauropod dinosaur. It is known from the Dinosaur Beds of northern Malawi, which probably date to the Aptian stage of the Early Cretaceous. The type species is ''M. di ...

''.

References

{{Portal bar, Dinosaurs, Cretaceous, Tanzania Lithostrotians Late Cretaceous dinosaurs of Africa Aptian life Cenomanian life Fossil taxa described in 2019 Aptian genus first appearances Cenomanian genus extinctions