Taxonomic affinities of the putative titanosaurs from the Late Jurassic Tendaguru Formation of Tanzania: phylogenetic and biogeographic implications for eusauropod dinosaur evolution

Abstract

The Late Jurassic Tendaguru Formation of Tanzania, southeastern Africa, records a rich sauropod fauna, including the diplodocoids Dicraeosaurus and Tornieria, and the brachiosaurid titanosauriform Giraffatitan. However, the taxonomic affinities of other sympatric sauropod taxa are poorly understood. Here, we critically reassess and redescribe these problematic taxa, and present the largest phylogenetic analysis for sauropods (117 taxa scored for 542 characters) to explore their placement within Eusauropoda. Janenschia robusta has played a prominent role in discussions of titanosaur origins, with various authors referring at least some remains to Titanosauria, a clade otherwise known only from the Cretaceous. Re-description of the holotype of Janenschia, and all referable remains, supports its validity and placement as a non-neosauropod eusauropod. It forms a clade with Haestasaurus, from the earliest Cretaceous of the UK, and the Middle/Late Jurassic Chinese sauropod Bellusaurus. Phylogenetic analysis and CT scans of the internal pneumatic tissue structure of Australodocus bohetii tentatively support a non-titanosaurian somphospondylan identification, making it the only known pre-Cretaceous representative of that clade. New information on the internal pneumatic tissue structure of the dorsal vertebrae of the enigmatic Tendaguria tanzaniensis, coupled with a full re-description, results in its novel placement as a turiasaur. Tendaguria is the sister taxon of Moabosaurus, from the Early Cretaceous of North America, and is the first turiasaur recognised from Gondwana. A previously referred caudal sequence cannot be assigned to Janenschia and displays several features that indicate a close relationship with Middle-Late Jurassic East Asian mamenchisaurids. It can be diagnosed by six autapomorphies, and we erect the new taxon Wamweracaudia keranjei gen. et sp. nov. The presence of a mamenchisaurid in the Late Jurassic of southern Gondwana indicates an earlier and more widespread diversification of this clade than previously realised, prior to the geographic isolation of East Asia. Our revised phylogenetic dataset sheds light on the evolutionary history of Eusauropoda, including supporting a basal diplodocoid placement for Haplocanthosaurus, and elucidating the interrelationships of rebbachisaurids. The Tendaguru Formation shares representatives of nearly all sauropod lineages with Middle Jurassic-earliest Cretaceous global faunas, but displays a greater range of diversity than any of those faunas considered individually. Biogeographic analysis indicates that the Tendaguru sauropod fauna was assembled as a result of three main phenomena during the late Early and/or Middle Jurassic: (1) invasions from Euramerica (brachiosaurids, turiasaurs); (2) endemism in west Gondwana (dicraeosaurids, diplodocids); and (3) regional extinctions that restricted the ranges of once widespread groups (mamenchisaurids, the Janenschia lineage). Multiple dispersals across the Central Gondwanan Desert are required to explain the distributions ...

Peer Review #2 of "New titanosauriform (Dinosauria: Sauropoda) specimens from the Upper Cretaceous Daijiaping Formation of southern China (v0.1)"

“…Many authors have suggested some degree of endemicity among eastern Asian sauropods in general, and have proposed the existence of putative endemic eastern Asian titanosauriform clades including Euhelopodidae (Wilson & Upchurch 2009;D'Emic, 2012), Nemegtosauridae (Wilson 2005) and Opisthocoelicaudiinae (You et al 2004). Recent phylogenies support the validity of Euhelopodidae, but the validity of Nemegtosauridae and Opisthocoelicaudiinae remains controversial (Upchurch, Mannion & Taylor 2015;Poropat et al 2016;González Riga et al 2018;Mannion et al, 2019). Arriving at a clearer understanding of titanosauriform phylogeny will undoubtedly require more extensive description of some of the lesser-studied Cretaceous eastern Asia taxa, ideally based in some cases on much more complete specimens than are presently available.…”

Supplemental Material for 'Reassessment of a historical collection of sauropod dinosaurs from the northern Morrison Formation of Wyoming, with implications for sauropod biogeography. (Bulletin of the American Museum of Natural History, no. 437)'

“…Two species are currently considered valid: H. priscus and H. delfsi. Very few phylogenetic analyses include both species (Calvo and Salgado, 1995;Gallina and Apesteguía, 2005;Mannion et al, 2019). In all but one analysis of Mannion et al (2019; using an equal-weighting approach), the two species do not form a monophyletic clade (including a second analysis of Mannion et al, 2019, that used extended implied weighting).…”

Reassessment of a Historical Collection of Sauropod Dinosaurs from the Northern Morrison Formation of Wyoming, with Implications for Sauropod Biogeography

“…Two species are currently considered valid: H. priscus and H. delfsi. Very few phylo¬ genetic analyses include both species (Calvo and Salgado, 1995;Gallina and Apesteguia, 2005;Mannion et al, 2019). In all but one analysis of Mannion et al (2019;using an equal-weighting approach), the two species do not form a monophyletic clade (including a second analysis of Mannion et al, 2019, that used extended implied weighting).…”

“…Very few phylo¬ genetic analyses include both species (Calvo and Salgado, 1995;Gallina and Apesteguia, 2005;Mannion et al, 2019). In all but one analysis of Mannion et al (2019;using an equal-weighting approach), the two species do not form a monophyletic clade (including a second analysis of Mannion et al, 2019, that used extended implied weighting). Both Haplocanthosaurus species have frequently been recovered within Diplodocoidea (Whitlock, 2011a;Mannion et al, 2012Mannion et al, , 2019Tschopp et al, 2015a), though they are also commonly positioned within Macronaria (Gallina and Apesteguia, 2005;Carballido et al, 2012;Royo-Torres et al, 2017).…”