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.

Send in the nautiloids: Early Ordovician fossils of the National Park Service

Previously we looked at the National Park Service records of the late Cambrian and Late Ordovician. What comes between the late Cambrian and Late Ordovician? That's right, the Early Ordovician. (The Middle Ordovician also does, but at the moment I've got Early on my mind. You know, in North America it might actually be more practical to divide the period into Early and Late, based on the lowstand that separates the Sauk Sequence from the Tippecanoe Sequence; or, maybe not. Who knows? You start to think about things like that when contemplating the divisions of the geologic time scale; where would the lines have been placed if it had been initially developed somewhere other than northwestern Europe?)

The Early Ordovician is kind of a transitional episode; in some ways, it's like a tag to the end of the Cambrian, considering it's the wind-down of the Sauk Sequence. I get the feeling that this epoch was not necessarily the most pleasant 15 or so million years in North America, at least in some areas. For example, in the Upper Midwest the Early Ordovician is represented by our old friend the Prairie du Chien Group. The PdC was certainly not bereft of life, but a whole lot of that life was stromatolite-building cyanobacteria, and a general rule of thumb is that any non-Precambrian geologic unit that features intervals of wall-to-wall stromatolites was probably not that hospitable while being deposited. Otherwise, the groups most commonly reported from Lower Ordovician rocks in NPS areas are brachiopods, nautiloids, gastropods, trilobites, graptolites, and conodonts. Apart from the nautiloids, you might think you were back in the late Cambrian. The evolutionary flowering that is evident in Middle and especially Upper Ordovician rocks was just kind of simmering: mollusks and echinoderms were chugging (although a lot of those early echinoderms didn't catch on), but corals and bryozoans were in low gear.

By my count, as many as 15 NPS units and affiliated areas have fossiliferous Lower Ordovician rocks, although the records at several of these units are not known to be particularly impressive at this time. Four of the parks are represented by the good old PdC, with fossils at Effigy Mounds NM, MNRRA, Saint Croix National Scenic Riverway, and potentially one of the units of NPS-affiliated Ice Age National Scientific Reserve. The distribution is a decent match for Early Ordovician finds in the United States as a whole (compare to the Early Ordovician records in the Paleobiology Database, for example). The major holes are New Mexico/Oklahoma/Texas, the Hudson River Valley, and Utah; none of Utah's NPS units includes a classic Ibexian sequence, but Great Basin NP next door in Nevada is Ibexian-adjacent and no slouch itself. It hosts one of the more interesting Early Ordovician fossil records in the NPS, along with Chesapeake and Ohio Canal National Historical Park, Death Valley NP, and Pictured Rocks National Lakeshore.

As usual, click to embiggen. Our Early Ordovician parks are 1) Death Valley NP; 2) Great Basin NP; 3) Kobuk Valley NP; 4) Denali NP & Preserve; 5) Yukon-Charley Rivers NPres; 6) Wind Cave NP; 7) Mississippi National River and Recreation Area; 8) Saint Croix National Scenic Riverway; 9) Picture Rocks National Lakeshore; 10) Ice Age National Scientific Reserve (affiliated area); 11) Effigy Mounds NM; 12) Ozark National Scenic River; 13) Buffalo National Scenic River; 14) Great Smoky Mountains NP; 15) Chesapeake and Ohio Canal National Historical Park.

Chesapeake and Ohio Canal NHP preserves good examples of the standard Early Ordovician assemblage in the Stonehenge Limestone and overlying Rockdale Run Formation. The Early Ordovician of both Death Valley NP and Great Basin NP is represented by rocks of the Pogonip Group, although different formations are present at the two parks. (When considering Paleozoic paleontology, if Death Valley or Yukon-Charley Rivers don't have something, it might not be present in the NPS. In this case Death Valley has the better record.) Great Basin is distinguished for examples of some of the wacky echinoderms that proliferated during the Ordovician. Pictured Rocks National Lakeshore is noted for the oldest NPS vertebrate material (I reserve the right to be cagy about the exact placement of conodonts), consisting of armor attributed to Anatolepis (Miller et al. 2006; a pteraspidomorph, or ostracoderm in more old-timey lingo). Pictured Rocks, incidentally, has an interesting unresolved stratigraphic issue: the above specimens came from the Au Train Formation and were associated with other microfossils of Early Ordovician age (Miller et al. 2006). However, a dissertation (Oetking 1952) documented Au Train macrofossils from the lakeshore area that appear to be correlative to Platteville fossils (i.e., Late Ordovician). This all suggests to me that either the identifications of Oetking's fossils are overly generous, or that the rocks identified as the Au Train Formation are more complex than currently suspected (a cryptic unconformity, etc.).

References

Miller, J. F., R. L. Ethington, and R. Rosé. 2006. Stratigraphic implications of Lower Ordovician conodonts from the Munising and Au Train Formations at Pictured Rocks National Lakeshore, Upper Peninsula of Michigan. Palaios 21:227–237.

Oetking, P. F. 1952. The relation of the Lower Paleozoic to the older rocks in the northern peninsula of Michigan. Dissertation. University of Wisconsin, Madison, Wisconsin.