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Mnyamawamtuka moyowamkia
Gorscak & O’Connor. 2019 |
Abstract
The African terrestrial fossil record has been limited in its contribution to our understanding of both regional and global Cretaceous paleobiogeography, an interval of significant geologic and macroevolutionary change. A common component in Cretaceous African faunas, titanosaurian sauropods diversified into one of the most specious groups of dinosaurs worldwide. Here we describe the new titanosaurian Mnyamawamtuka moyowamkia gen. et sp. nov. from the Mtuka Member of the Galula Formation in southwest Tanzania. The new specimen preserves teeth, elements from all regions of the postcranial axial skeleton, parts of both appendicular girdles, and portions of both limbs including a complete metatarsus. Unique traits of M. moyowamkia include the lack of an interpostzygapophyseal lamina in posterior dorsal vertebrae, pronounced posterolateral expansion of middle caudal centra, and an unusually small sternal plate. Phylogenetic analyses consistently place M. moyowamkia as either a close relative to lithostrotian titanosaurians (e.g., parsimony, uncalibrated Bayesian analyses) or as a lithostrotian and sister taxon to Malawisaurus dixeyi from the nearby Aptian? Dinosaur Beds of Malawi (e.g., tip-dating Bayesian analyses). M. moyowamkia shares a few features with M. dixeyi, including semi-spatulate teeth and a median lamina between the neural canal and interpostzygapophyseal lamina in anterior dorsal vertebrae. Both comparative morphology and phylogenetic analyses support Mnyamawamtuka as a distinct and distant relative to Rukwatitan bisepultus and Shingopanasongwensis from the younger Namba Member of the Galula Formation with these results largely congruent with newly constrained ages for the Mtuka Member (Aptian–Cenomanian) and Namba Member (Campanian). Coupled with recent discoveries from the Dahkla Oasis, Egypt (e.g., Mansourasaurus shahinae) and other parts of continental Afro-Arabia, the Tanzania titanosaurians refine perspectives on the development of African terrestrial faunas throughout the Cretaceous—a critical step in understanding non-marine paleobiogeographic patterns of Africa that have remained elusive until the past few years.
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Systematic paleontology
DINOSAURIA
SAURISCHIA
SAUROPODA
TITANOSAURIFORMES
TITANOSAURIA
LITHOSTROTIA
MNYAMAWAMTUKA MOYOWAMKIA, gen. et sp. nov.
Etymology: Mnyamawamtuka (Mm-nya-ma-wah-mm-too-ka), ‘mnyama’ is the Kiswahili word for ‘animal’ or ‘beast’ and acts as a conceptual proxy to the titans in Titanosauria, and ‘wa Mtuka' is Kiswahili for ‘of the Mtuka’ in reference to the river drainage that yielded the type specimen. Moyowamkia (Mm-oh-yo-wa-mm-key-ah), ‘moyo’ is the Kiswahili word for heart and ‘wa mkia’ is Kiswahili for ‘of the tail’, in reference to the posterolateral expansion of the posterior centrum on the middle caudal vertebrae that gives the posterior centrum surface a heart-shape outline.
Holotype: RRBP 05834, a partial skeleton including an anterior cervical vertebral neural arch and four cervical vertebral centra, seven partial dorsal vertebrae, a sacral neural arch, three partial sacral centra, three sacral ribs, seven caudal vertebral neural arches and seven centra, four chevrons, numerous dorsal rib fragments, a right scapula, a right sternal plate, a partial left humerus and distal right humerus, partial left ulna, right metacarpal I and left metacarpal III, a partial left ischium, a partial right pubis, partial left and right femora, left tibia and partial right tibia, a left fibula, left metatarsal I, left metatarsal II, right metatarsal III, left metatarsal IV, left metatarsal V, two pedal phalanges, a left ungual, and numerous unidentifiable fragments. The majority of the fossils were prepared at the Ohio University Fossil Preparation Facility, with some of the first-discovered elements prepared by J. P. Cavigelli. Preperation used standard manual and technical techniques including hand tools and pneumatic air scribes. Repository information of RRBP 05834 is the Rukwa Rift Basin Project, Tanzanian Antiquities Unit, Dar es Salaam, Tanzania. The fossils are, at time of publication, on temporary loan and deposited at Ohio University in Athens, Ohio. All of the fossils are accessible by request. Research casts will permanently be housed at Ohio University and in the collections at Denver Museum of Science and Nature.
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| Fig 1. Map of research area. Map of Africa, A, with expanded regional map of the Rukwa Rift Basin of Tanzania, B, with the type localities of Mnyamawamtuka moyowamkia and Rukwatitan bisepultus quarry near the Galula study area, C, and the Shingopana songwensis quarry near the Nsungwe study area, D. Malawi Dinosaur Beds (DB) marked in B to demonstrate the proximity of the deposits to the Galula Formation. |
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Fig 2. Quarry map of the Mtuka bonebed locality RRBP 2004–06. Recovered elements of Mnyamawamtuka moyowamkia are color-coded and separated by dashed lines according to the year they were collected. The quarry map is represented as a four-by-six-meter grid. Unmarked elements on the map are either fragments or unidentified.
Abbreviations: cac, caudal vertebral centrum; cana, caudal vertebral neural arch; cr, cervical rib; cvc, cervical vertebral centrum; dc, dorsal vertebral centrum; dic, distal caudal vertebra; dr, dorsal rib; dv, dorsal vertebra; fem, femur; fib, fibula; ha, haemal arch; hum, humerus; isc, ischium; mtc I, metacarpal I; sac, sacral centrum; scap, scapula; sp, sternal plate; sr, sacral rib; tib, tibia; ul, ulna; un, ungual. |
Type locality and horizon: The specimen was recovered in the Mtuka Member of the Cretaceous Galula Formation. The Mtuka Member is dominated by coarse sandstone fluvial deposits and abundant overbank siltstone and mudstone lenses within an extensive fluvial braidplain system. The holotype of M. moyowamkia was recovered from a quarry developed along the Mtuka River drainage in southwestern Tanzania (Fig 1). The quarry is roughly 20 kilometers south of Lake Rukwa near the coordinates of 32° 34’ E and 8° 34’ S. The initial discovery was made in 2004 at locality RRBP 2004–06, with additional elements recovered sequentially during the 2005–2008 field seasons by the Rukwa Rift Basin Project field teams (Fig 2). Generally, larger and more complete elements, such as appendicular remains, were recovered in the western part of the quarry whereas smaller and more fragmented elements were recovered from the eastern part of the quarry, indicating short-distance transport (Fig 2). Excavation permits were issued by The United Republic of Tanzania, Ministry of Natural Resources and Tourism, Antiquities Unit, P.O. Box 2280, Dar es Salaam, Tanzania to P. M. O’Connor under the specific permit numbers: 14–2004; EA 402/605/01; EA 402/605/01/78; EA 402/605/01/20; and EA 402/604/01/7. In a broader context, the M. moyowamkia discovery and excavation was made in the early years of the Rukwa Rift Basin Project with the aim of addressing the paucity of fossils recovered from the Cretaceous of sub-Saharan Africa.
Age and distribution: The materials were recovered from the Mtuka Member of the Galula Formation of the Red Sandstone Group, Rukwa Rift Basin, southwestern Tanzania. Based on previous lines of evidence, including faunal data within the overlying Namba Member, the age of the Galula Formation was best constrained to the middle Cretaceous (Aptian–Cenomanian) with potential dates of 100–110 Ma. However, new paleomagnetic data place the Mtuka Member (i.e., the specific unit from which M. moyowamkia was recovered) within the Cretaceous long normal with estimates of Aptian–Cenomanian for the unit and a younger date for the overlying Namba Member as either Campanian or Cenomanian–Santonian.
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Fig 3. Teeth associated with Mnyamawamtuka moyowamkia skeleton.
Teeth recovered from the Mnyamawamtuka moyowamkia quarry. A–D, tooth Morph A; E–F, tooth Morph B; and G–J, tooth Morph C. A, G, distal; B, E, H, labial; C, I, mesial; D, J, lingual; and F, occlusal views. Abbreviations: labwf, labial wear facet; linwf, lingual wear facet. Scale bar equals 1 cm. |
Diagnosis:
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Mnyamawamtuka moyowamkia is diagnosed by the following suite of autapomorphies: (1) middle and posterior dorsal vertebrae with vertical lamina between neural canal and interprezygapophyseal lamina that bifurcates dorsally; (2) posterior dorsal vertebra with no interpostzygapophyseal lamina as the postspinal lamina continues to the dorsal margin of the neural canal; (3) prominent dorsolateral expansion on the posterior centrum of the middle caudal vertebra; (4) curved crest with accompanying fossa within the dorsomedial region of the proximal scapular blade; (5) sternal plate unusually small, estimated to be, at most, 42% of humerus length.
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Eric Gorscak and Patrick M. O’Connor. 2019. A New African Titanosaurian Sauropod Dinosaur from the middle Cretaceous Galula Formation (Mtuka Member), Rukwa Rift Basin, Southwestern Tanzania.
PLoS ONE. 14(2): e0211412. DOI:
10.1371/journal.pone.0211412
