Your Friends The Titanosaurs: Abditosaurus kuehnei

Today we add Abditosaurus kuehnei to the long-running "Your Friends The Titanosaurs" series. January was pretty slow around here as far as new non-avian dinosaurs go, but coincidentally enough the dinosaur to break the dry spell was a titanosaur. Since then, we've also gotten Guemesia ochoai, an abelisaurid, which is very nice if you enjoy theropods. (It did make entry #1600 in the dinosaur sheet of The Compact Thescelosaurus.)

Genus and Species: Abditosaurus kuehnei. "Abditus" is Latin for "concealed", referring to the long gap between discovery and description, making this a comrade of our friend Thescelosaurus neglectus. "Kuehnei" honors the discoverer, Walter Georg Kühne (Vila et al. 2022). Together we get something like "Walter Georg Kühne's concealed lizard".

Citation: Vila, B., A. Sellés, M. Moreno-Azanza, N. L. Razzolini, A. Gil-Delgado, J. Canudo, and A. Galobart. 2022. A titanosaurian sauropod with Gondwanan affinities in the latest Cretaceous of Europe. Nature Ecology & Evolution. doi:10.1038/s41559-021-01651-5.

Stratigraphy and Geography: The type and only known specimen comes from the lower Conques Formation at a locality identified as Orcau-1 (also known as "Barranco de Orcau" or "Orcau"). This location is about 6 km (4 mi) east of Tremp, in the county of Pallars Jussà, Catalonia, Spain (Vila et al. 2022).

Holotype: The holotype is not catalogued as a unitary specimen. Instead, the bones are held at the Museo Nacional de Ciencias Naturales in Madrid (MNCN) and the Museu de la Conca Dellà in Isona (MCD) and catalogued under a variety of numbers. The bones pertain to an associated and semi-articulated partial skeleton found over an area about 6 m by 4 m (20 ft by 13 ft) and include: isolated teeth, 12 partial articulated cervical vertebrae, 7 anterior and middle dorsals, cervical and dorsal ribs, 3 chevrons, the right and partial left scapula, right coracoid, left sternal plate, a sternal rib (a titanosaurian rarity), a fragment of the left ilium, parts of both humeri, partial right radius, part of the right femur, the right tibia and fibula, and partial left fibula with attached calcaneum (another titanosaurian rarity). Some other material has gone missing (Vila et al. 2022).

Abditosaurus kuehnei, as its name suggests, is one of those dinosaurs that was not described until decades after it had been discovered. The history of the specimen is described in the supplementary information to the paper (here; ten times longer than the paper, so yeah, necessary stuff!). The abridged Abditosaurus story is that Kühne discovered the fossils September 25, 1954 while prospecting for Cretaceous mammals. Over the next couple of weeks he collected a few bones and jacketed a few more for later collection. He made a return trip in 1955 and collected more bones. Plans for additional collection were scuppered by lack of funds. Lapparent and Aguirre (1956) proposed that Kühne's sauropod was a new species of Hypselosaurus, which is what you did in 1956. The locality was revisited in the mid-1980s, but not fully collected until a series of expeditions 2012–2014 (Vila et al. 2022 supplementary information).

A few anatomical notes: The humerus is notably robust while the tibia is gracile. The ilium is pneumatized. There are several osteological indications of age, such as the presence of a sternal rib and a calcaneum, thought to have only ossified with great age (Vila et al. 2022). (Also, the cervical ribs are fused to their vertebrae.) In the supplementary information Vila et al. describe osteological samples from the limb bones that indicate the type individual had reached skeletal senility (histological ontogenetic stage HOS-14). Vila et al. estimated that the sauropod was 17.5 m (57.4 ft) long and a shade more than 14 metric tons (15.4 US tons) in body mass. These figures would make A. kuehnei somewhat larger than a typical titanosaur, and definitely larger than your typical subcompact European titanosaur.

The size of A. kuehnei is one of the major talking points. Along with its lengthy history, this species comes equipped with a full suite of implications. While titanosaurs seem to be big fans of some kind of phylogenetic uncertainty principle, in this case A. kuehnei shows no indication of clading with other European titanosaurs. Instead, it hangs out in the general vicinity of saltasaurs and its phylogenetic best friend appears to be the even larger Paralititan stromeri from the Cenomanian of Egypt. Vila et al. (2022) posited a scenario in which North African titanosaurs arrived in Ibero-Amorica during an early Maastrichtian marine lowstand via a loop through the various smaller landmasses then dotting the narrow Tethys Ocean. They tied this to an early Maastrichtian faunal turnover in which the previous mini-titanosaurs were replaced, and suggested something similar happened in Romania. Let the fossil record show that large(ish) titanosaurs in the Haţeg Basin fauna of Romania have been reported by Le Loeuff (2005), Stein et al. (2010), and Mannion et al. (2019).

I've mentioned this before, but I suspect that sauropods were excellent at dispersal over water, similar to elephants. They were big, full of air and fermenting plant gases, and had long necks that could have been held well above the water. Get 'em out to sea, and they could probably have gone a long way. Postulate that your traveling sauropod was a gravid female, and given what we know about the number of eggs a sauropod could lay, you've got a pretty good scenario for populating any landmass that was large enough to support sauropods and a reasonable distance from a landmass that already had sauropods.

References

Lapparent, A. F., and E. Aguirre. 1956. Présence de dinosauriens dans le Crétacé supérieur du bassin de Tremp (province de Lérida, Espagne). Comptes Rendus Sommaires de la Société Geólogique de France 14:261–262.

Le Loeuff, J. 2005. Romanian Late Cretaceous dinosaurs: big dwarfs or small giants? Historical Biology 17:15–17.

Mannion, P., V. Díez Díaz, Z. Ciski-Sava, P. Upchurch, and A. Cuff. 2019. Dwarfs among giants: resolving the systematics of the titanosaurian sauropod dinosaurs from the latest Cretaceous of Romania. Journal of Vertebrate Paleontology, Program and Abstracts, 2019:148.

Stein, K., Z. Csiki, K. Curry Rogers, D. B. Weishampel, R. Redelstorff, J. L. Carballidoa, and P. M. Sandera. 2010. Small body size and extreme cortical bone remodeling indicate phyletic dwarfism in Magyarosaurus dacus (Sauropoda: Titanosauria). Proceedings of the National Academy of Sciences of the United States of America 107(20):9258–9263.

Vila, B., A. Sellés, M. Moreno-Azanza, N. L. Razzolini, A. Gil-Delgado, J. Canudo, and A. Galobart. 2022. A titanosaurian sauropod with Gondwanan affinities in the latest Cretaceous of Europe. Nature Ecology & Evolution. doi:10.1038/s41559-021-01651-5.