Volkheimeria

''Volkheimeria'' is an extinct genus of sauropod dinosaurs that lived in what is now Argentina during the Early Jurassic, 178–179 million years ago. Its type and only species is ''Volkheimeria chubutensis''.

Discovery and naming

The only known specimen of ''Volkheimeria'' was discovered at the site of Cerro Cóndor Sur, roughly a kilometer west of the village of Cerro Cóndor in Chubut Province, Argentina. In 1979, José Bonaparte described it as representing a new genus and species, ''Volkheimeria chubutensis'', alongside two other species discovered in the same strata, ''Piatnitzkysaurus floresi'' and ''Patagosaurus fariasi''. The genus name ''Volkheimeria'' honors the Argentinean paleontologist Wolfgang Volkheimer.

Fossil record

Only a single specimen of ''Volkheimeria chubutensis'' is known: the holotype PVL 4077, a partial skeleton from the Cañadón Asfalto Formation of Argentina. This specimen consists of a partial cervical vertebra, two complete and two partial dorsal vertebrae, part of the sacrum, several incomplete caudal vertebrae, partial ilia, a pubis, an ischium, a femur, and a tibia. The specimen was not fully grown, but had probably reached sexual maturity. An isolated tooth found in the Cañadón Asfalto Formation, MPEF-PV 10860, may belong to ''Volkheimeria'', though this cannot be proven without more complete specimens.

Classification

''Volkheimeria'' was originally identified as a primitive sauropod, distinguishable from ''Patagosaurus''. Some phylogenetic analyses of the taxon have recovered it as a eusauropod, vulcanodontid, or primitive sauropod, though its position is variable due to its incomplete nature. The phylogenetic analysis of Pol and colleagues in 2022 recovered ''Volkheimeria'' as a non-eusauropod based on primitive features of the vertebrae, though alternative placements were identified as closer to either '' Amygdalodon'' or ''Archaeodontosaurus'', as shown below.

Classification history

Bonaparte initially regarded ''Volkheimeria'' as a primitive member of Cetiosauridae. He considered both it and ''Lapparentosaurus'' to represent an early stage in cetiosaurid evolution, more advanced than '' Vulcanodon'' but more primitive than ''Patagosaurus'' and '' Cetiosaurus''. In 1990, John S. McIntosh included both ''Volkheimeria'' and ''Lapparentosaurus'' in Brachiosauridae, albeit without providing anatomical evidence for classifying ''Volkheimeria'' as such. In 2004, Upchurch et al. regarded the affinities of ''Volkheimeria'' as uncertain, due to the lack of a phylogenetic analysis including the taxon. In 2011, Pol et al. included both ''Volkheimeria'' and ''Lapparentosaurus'' in a phylogenetic analysis, and recovered them as basal eusauropods, more derived than ''Shunosaurus'' but more basal than ''Barapasaurus'', with ''Volkheimeria'' more basal than ''Lapparentosaurus''. In 2017, Cerda et al. found ''Volkheimeria'' to be a non-eusauropod sauropod closely related to '' Tazoudasaurus''. In 2018, Holwerda and Pol found ''Volkheimeria'' to be a non-eusauropod sauropod, as the sister taxon of ''Spinophorosaurus''.

Evolution

''Volkheimeria'' lived during the Toarcian age of the Early Jurassic, 178-179 million years ago. The beginning of the Toarcian was a time of significant faunal turnover for sauropodomorphs, as all sauropodomorph lineages except for sauropods died out and eusauropods, which became the dominant sauropod group in the Middle Jurassic, began to diversify. ''Volkheimeria'' was not a member of the eusauropod radiation, and was probably a representative of a lineage that diverged from other sauropods in the earliest Jurassic or even the Triassic.

Paleoecology

The ecosystem represented by the Cañadón Asfalto Formation included at least four sauropods other than ''Volkheimeria chubutensis'', all of them eusauropods: '' Bagualia alba'', ''Patagosaurus fariasi'', an unnamed basal eusauropod, and a possible neosauropod.

References

Dinosaur genera
Middle Jurassic dinosaurs of South America
Jurassic Argentina
Fossils of Argentina
Cañadón Asfalto Formation
Fossil taxa described in 1979
Taxa named by José Bonaparte

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