Your Friends The Titanosaurs: Menucocelsior arriagadai

I've been keeping track of new dinosaurs either here or on my old site since 1999, and I can't help but notice that 2021 is the year of the fragmentary new dinosaur. Is this a reflection of COVID restrictions at museums and so forth, i.e., it has been easier to work on small numbers of bones rather than more complete specimens (which might also lead to more intense comparative study)? Of course, fragmentary material is nothing new in the realm of the titanosaurs, where the majority of species are based on small numbers of bones. (2021 has been pretty good for titanosaurs.) Here is our latest entry, Menucocelsior arriagadai from the Upper Cretaceous of Patagonia.

Genus and Species: Menucocelsior arriagadai. "Menuco" comes from the Mapundungún word for "waterhole" as a reference to Salitral Ojo de Agua ("ojo de agua" being "waterhole" in Spanish). "Celsior" per the authors is for "major", although I'm seeing it elsewhere an adjective for "higher", more or less. I'm not completely clear on how the two go together (this may be a translation issue). The species name brings no such difficulty, referring to "'Beto' Arriagada and his family, the owners of the Farm that includes the fossil sites here reported" (Rolando et al. 2021).

Citation: Rolando, M. A., J. A. Garcia Marsà, F. L. Agnolín, M. J. Motta, S. Rozadilla, and F. E. Novas. 2021. The sauropod record of Salitral Ojo del Agua: An Upper Cretaceous (Allen Formation) fossiliferous locality from northern Patagonia, Argentina. Cretaceous Research 105029. doi: 10.1016/j.cretres.2021.105029.

Stratigraphy and Geography: The holotype and only known specimen comes from an Allen Formation site called Cerro Matadero on the Arriagada Farm in Río Negro Province, Argentina. The area is known as Salitral Ojo de Agua (Rolando et al. 2021). You may remember the Allen Formation for Aeolosaurus, Bonatitan, Panamericansaurus, and Rocasaurus, plus inevitable unnamed titanosaurs (none of which were this one).

Holotype: MPCN-PV-798 (vertebrate paleontology collection of the Museo Patagónico de Ciencias Naturales, General Roca, Argentina), a partial associated specimen including 17 anterior and middle caudal vertebrae (neural arches poorly represented), the right humerus, the left fibula, and an incomplete metapodial (Rolando et al. 2021).

Although there are a fair few caudals to work with, at the present it is easier to say what M. arriagadai isn't than what it is. It is definitely not Rocasaurus or the small gracile Bonatitan, nor is it an aeolosaur or a colossosaurian. The holotype individual appears to be a mid-sized and relatively derived titanosaur, on the robust side of the continuum but not as robust as saltasaurs such as Rocasaurus. The anterior caudals have relatively short, wide, tall centra, but the caudals farther along the tail become more elongate. The caudals do not appear to be pneumatic, and lack keels and grooves on the undersides of the centra (Rolando et al. 2021). For now, M. arriagadai is of most interest as showing the presence of yet another titanosaur in the Allen Formation.

But that is not where the paper ends, not at all. M. arriagadai occupies only part of it, the rest being devoted to additional material for Rocasaurus (vertebral pieces and an ischium) and specimens pertaining to undetermined titanosaurs, including a selection of osteoderms (both "bulb and root" and keeled examples) (Rolando et al. 2021). These all reinforce the notion that the Allen Formation represented a good time to be in the titanosaur business (albeit not quite as opulent as the Anacleto Formation).

References

Rolando, M. A., J. A. Garcia Marsà, F. L. Agnolín, M. J. Motta, S. Rozadilla, and F. E. Novas. 2021. The sauropod record of Salitral Ojo del Agua: An Upper Cretaceous (Allen Formation) fossiliferous locality from northern Patagonia, Argentina. Cretaceous Research 105029. doi: 10.1016/j.cretres.2021.105029.