Sunday, June 21, 2020

Your Friends The Titanosaurs, part 25: Quaesitosaurus, Quetecsaurus, and Rapetosaurus

Here we are, June 2020, and this is not only the 300th post at Equatorial Minnesota, but also the second anniversary of "Your Friends The Titanosaurs". It seems fitting enough that the two should coincide. This particular set of three titanosaurs covers a pretty broad spread, geographically, from Mongolia to Argentina to Madagascar.

Quaesitosaurus orientalis

It may seem like an odd thing, given the famous rarity of sauropod skulls, but Quaesitosaurus orientalis is the forgotten skull-based sauropod. This situation can be laid squarely at the feet of Nemegtosaurus mongoliensis, because quite literally everything that Q. orientalis does, N. mongoliensis does better (and did first, to boot), with one exception: Q. orientalis is the first classic dinosaur with a genus name beginning with "Q". (Oddly, out of the 11 "Q" names so far given to classic dinosaurs, three of them were given to titanosaurs.) Nemegtosaurus mongoliensis is known from a mostly complete skull from Upper Cretaceous rocks in south-central Mongolia, and Quaesitosaurus orientalis is known from a less complete and very similar skull from Upper Cretaceous rocks in south-central Mongolia. Bearing in mind that Q. orientalis has historically clung like a barnacle to Nemegtosaurus, we don't need to reiterate the whole historical discussion of "nemegtosaurs can never be titanosaurs and here's why", although certainly feel free to go back and re-read if the mood strikes you.

Q. orientalis was described in Kurzanov and Bannikov (1983), although the actual credit is Bannikov and Kurzanov in Kurzanov and Bannikov (1983). (I have no idea why the authorship should be reversed.) The name is derived from the Latin "quaesitus" meaning abnormal and "orientalis" meaning "eastern", giving us something like "eastern abnormal lizard". The type specimen is PIN 3906/2 (Russian Academy of Sciences), a partial skull and mandible; the mandible's all there but the skull is missing the middle. Although the illustration omits the teeth, the text describes their features (they're of the skinny cylindrical variety), with sockets for 13 teeth per half of the upper jaw (four in the premaxilla and nine in the maxilla) and 13 per half of the mandible, crowded to the front of the jaw (Kurzanov and Bannikov 1983).

Kurzanov and Bannikov (1983) reported the discovery site as Shara-Tsav in the Barungoyot Formation (a.k.a. the Barun Goyot Formation). Usually the site is now spelled as Shar Tsav (see for example Maryańska 2000 or Currie et al. 2018). The stratigraphy is a bit less certain. Kurzanov and Bannikov (1983) described the site as Barun Goyot in part because they also found Gallimimus sp. and Avimimus portentosus specimens there. If you have a soft spot for Avimimus, you might find that to be an odd statement, because A. portentosus is *not* typical of the Barun Goyot. Watabe et al. (2010) suggested that instead the site is within the Nemegt Formation.

As to why Kurzanov and Bannikov thought their beast was "abnormal", the obvious candidate feature is the "abnormally large cavity of the middle ear, formed by the quadrate bones". They interpreted this as evidence of very sensitive hearing and terrestrial habits. A later review (Wilson 2005) would show that the apparent size of this "resonator depression" is due to damage and incomplete preservation (see below). Kurzanov and Bannikov contrasted this with their interpretation of the jaws as suited for gathering large amounts of soft vegetation from the water. (This is close to the end of the "swamp sauropod" model being used in serious scientific reports.) Something that's much more intriguing now than it was in 1983 is the suggestion that parts of the lower jaw were covered with a horny surface. Could this be an anticipation of the keratinous "guillotine" crest of Bonitasaura?

Does Q. orientalis represent the same genus as Nemegtosaurus, or even the same species as N. mongoliensis? There is not a lot to separate them, actually, and recent phylogenetic analyses have neglected Q. orientalis. As analyzed in Wilson (2005), the features used to distinguish the two taxa over the years are not that great. Many of them are due to different deformation histories: the N. mongoliensis holotype skull underwent compression from the sides as well as some shear, while the Q. orientalis type skull was compressed in a dorso-ventral direction. This can explain, for example, the apparent broader snout of Q. orientalis. The loss or partial loss of certain bones of the Q. orientalis skull also led to apparent differences. The "resonator depression" of Kurzanov and Bannikov (1983) is an example. It is actually an artifact of incomplete preservation: the squamosal and quadratojugal, which are supposed to cover the quadrate fossa, are incompletely preserved (former bone) or altogether missing (latter bone) (Wilson 2005). Wilson (2005) was able to find some subtle differences, but ultimately suggested that separation or synonymization were both arbitrary in this case and elected to keep them separate in case of future discoveries (and because of the differing stratigraphy). Note, though, that this was on the basis of Q. orientalis being from the Barun Goyot and N. mongoliensis being from the Nemegt. The stratigraphic situation is a bit more confused now, with N. mongoliensis being from interfingering Barun Goyot/Nemegt beds (Currie et al. 2018) and Q. orientalis possibly from the Nemegt. (What if Q. orientalis is indeed a distinct taxon, but is actually the skull of Opisthocoelicaudia instead of that honor going to N. mongoliensis?)

Quetecsaurus rusconii

Quetecsaurus rusconii has not yet had much time to percolate into the scientific scene, having only been named in 2014, but it seems like a taxon that might prove useful because its type specimen is an associated skeleton including bones from a variety of parts of the skeleton. Granted, although there are a variety of bones, there isn't a lot of depth in any one area (one dorsal, one caudal, etc.) and they tend to be fragmentary, but just getting an associated specimen seems like a triumph of no small magnitude following bonebed after bonebed!

The holotype and only known specimen of Q. rusconii was discovered during a mining project in Mendoza Province, Argentina, at Cañada del Pichanal (not a great distance from Rincon de los Sauces, in Neuquén Province). It was found in the Cerro Lisandro Formation, a Turonian unit. At the discovery site this unit is represented primarily by "massive and laminated red-purple mudstones" interpreted as a muddy floodplain. The skeleton was associated but mostly disarticulated, with no preferential orientation of long bones (González Riga and Ortiz David 2014).

The name is derived from the Milcayac word "Quetec", meaning "fire", and honors Carlos Rusconi, a naturalist who had worked in Mendoza Province and had also been the director of the Museum of Natural Sciences "Juan Cornelio Moyano", giving us "Carlos Rusconi's fire lizard" (González Riga and Ortiz David 2014). (It seems like there should be a story behind the choice of "fire lizard", but it's not in the description.) The holotype is UNCUYO-LD-300 (Universidad Nacional de Cuyo, Instituto de Ciencias Básicas, Laboratorio de Dinosaurios, Mendoza, Argentina). It consists of (deep breath) "postorbital, two teeth, atlas, one posterior cervical vertebra, one incomplete anterior dorsal vertebra, one incomplete anterior dorsal vertebra, one anterior caudal centrum, eight dorsal ribs, a coracoid, an incomplete humerus, distal fragments of a radius and an ulna, and five metacarpals" (González Riga and Ortiz David 2014). We're looking mostly at part of the torso and an arm, in other words.

The teeth are of the "chisel" variety. The posterior cervical has the fashionable tall titanosaurian neural arch with triangular profile, and a fairly squat centrum. The dorsal is fragmentary, and the caudal centrum is your typical procoelous titanosaurian caudal centrum. The coracoid has a quadrangular shape akin to what saltasaurs and Rinconsaurus have. The partial humerus is robust and has a distinctive curve to its proximal end (González Riga and Ortiz David 2014). No size comparison here from me; there's not a lot of complete bones to work from. The authors ran their new species through a phylogenetic analysis and found it to land just outside of Lognkosauria (González Riga and Ortiz David 2014). Q. rusconii has only been considered in a few analyses since then, ending up as 1) a fairly basal titanosaur just beyond Lognkosauria (Bandeira et al. 2016), 2) about the same place as González Riga and Ortiz David found it (Tykoski and Fiorillo 2017, which is not too surprising since they were using the same matrix), and 3) within Logknosauria (Carballido et al. 2017).

Rapetosaurus krausei

The 1990s were a time when sauropod researchers had thrown over many old ideas about how to classify the great beasts, but were still a long way from consensus on replacements. (It may seem like we haven't made much progress, but we have!) One of the outstanding issues was no one knew what the heck a titanosaur really looked like. There were plenty of bones, but they came from bonebeds representing multiple individuals (and sometimes multiple titanosaur species). Furthermore, these titanosaurs had almost invariably forgotten to pack their skulls for their trip through time, and those that had brought skulls forgot to pack their bodies and thus were thought to be diplodocids/oids. Into this breach came the exceptionally well-timed discovery of Rapetosaurus krausei.

Rapetosaurus, being attacked by some theropod.

R. krausei was formally described in 2001 (Curry Rogers and Forster 2001), but it was known for several years before then; I first saw it in an episode of "Paleoworld" aired in 1996. To R. krausei goes the honors of one of the two most complete individual titanosaur skeletons (can't forget Opisthocoelicaudia), the first unquestioned titanosaur skull, and the first skull material clearly associated with a skeleton. These honors, plus the absence of any obvious major skeletal oddities, have given R. krausei a position as a "basic" titanosaur. Of course, as always, there is a caveat when trying to find a "basic" titanosaur: the mostly complete skeleton is from a partially grown individual, which means that R. krausei has a touch of Camarasaurus Syndrome (the phenomenon wherein the best skeleton of a dinosaur is from a young individual, leading people to think of it as small).

Fittingly, R. krausei is also one of the most thoroughly described titanosaurs. For a basic bibliography, here's what you need:
  • Curry Rogers and Forster (2001), the original description
  • Curry Rogers and Forster (2004), the description of the skull material
  • Curry Rogers (2009), the postcranial osteology
  • Curry Rogers et al. (2011), a description of an osteoderm
  • Curry Rogers et al. (2016), a description of a very young individual
  • Curry Rogers and Kulik (2018), a description of osteohistology
Rapetosaurus krausei is named after "Rapeto", "a mischievous giant of Malagasy folklore", and the species name honors paleontologist David W. Krause (Curry Rogers and Forster 2001), giving us something like "mischievous giant lizard of David Krause". The type specimen is UA 8698 (Université d' Antananarivo), most of an adult skull and mandible. This specimen and the other specimens come from the Anembalemba Member of the Maastrichtian-aged Maevarano Formation, in the Mahajanga Basin of northwestern Madagascar (Curry Rogers and Forster 2001). R. krausei is not the only titanosaur known from these rocks; there's also rare Vahiny depereti (Curry Rogers and Wilson 2014) and chimeric "Titanosaurus" madagascariensis. A fact of life commonly mentioned in these papers is the strongly seasonal and semi-arid paleoenvironment.

Still getting attacked.

The skull of R. krausei established the long, drawn-out snout of titanosaurs, with the prominent step up from the tooth row. If you're used to Morrison sauropods, it looks strange, with the hitch in the jawline, the long, banana-shaped antorbital fenestra, and the jaw joint slung forward. The lower jaw has the U-shaped form rather than the squared form. The teeth are of the cylindrical form, and are not crowded as far forward as in some titanosaurs.

Rapetosaurus krausei, slightly restored (E), and some titanosauriform friends (Giraffatitan [A], Abydosaurus [B], Sarmientosaurus [C], Nemegtosaurus [D], Rapetosaurus [E], and Tapuiasaurus [F]). Figure 33 in Martínez et al. (2016). CC-BY-4.0.

The major published basis for our knowledge of the postcranial skeleton is FMNH PR 2209 (Field Museum of Natural History), a largely complete, disarticulated, associated skeleton of a partially grown individual. You may notice two restoration "morphs" out there: the older style seen in the publications and a more recent, more upwardly oriented style as exemplified by Scott Hartman's restoration. The differences are mostly related to the position of the shoulder girdle and the length of individual vertebrae of the incomplete neck. Still, R. krausei is not noted for the length of its arms, so even with the shoulders up high, the back is close to level. The cervicals have tall and long neural arches, atop long cylindrical centra. The dorsals are much shorter, and the spines are lower until past the middle of the back. The anterior caudals have the typical procoelous articulation and anteriorly placed neural arches. The ulna is robust and about 70% the length of the humerus, which in turn is about 80% the length of the femur. No ossified carpals were found, nor were any manual phalanges, although Curry Rogers (2009) reported the presence of articular surfaces that would imply their existence. The ilium flares out behind the torso, and the pubis is much longer than the ischium. The hind limb is on the gracile side and not especially notable. No osteoderms were found with FMNH PR 2209 (Curry Rogers 2009), but single osteoderms have been found with another juvenile and an adult specimen (Curry Rogers et al. 2011). The adult osteoderm, found near a pair of ischia, is the famously empty specimen we discussed last June as evidence of titanosaur osteoderms being used as mineral reservoirs.

A variety of differently aged individuals are known for R. krausei. Of course, the FMNH PR 2209 skeleton comes from a half-grown individual: the femur of this specimen is 65.7 cm long (25.9 in), not even half the length of the largest known R. krausei femur (FMNH PR 2255, 143.4 cm or 56.46 in long). Curry Rogers and Kulik (2018) interpreted this individual as an adult but with some room for growth. For comparison, the skeleton of Opisthocoelicaudia has a femur just shy of 140 cm long, and in its neckless state is about 8.5 m long (28 ft). With a neck and a slightly more impressive tail, a 14–16 m (46 to 52 ft) range seems quite reasonable for FMNH PR 2255. At the other end of the scale, Curry Rogers et al. (2016) published a brief description of UA 9998, an individual whose life span was measured in weeks. This tiny sauropod was estimated as 35 cm tall (14 in) at the hip and 40 kg (88 lb) in mass. Features of the bone structure attest to the harsh climate affecting its growth; it likely died of starvation, or at least was starving at the time of death. Despite its age, its limbs had similar proportions to grown individuals (isometric growth).

Part of the juvenile R. krausei material on temporary display at the Science Museum of Minnesota back in 2016.

Surprisingly, although R. krausei is well-known, well-represented, and thoroughly described, and is included in every phylogeny, its position is not particularly stable from paper to paper. It tends to show up in the company of Isisaurus and/or Nemegtosaurus and/or aeolosaurs, without committing to any one position. We can safely guess that the instability is more the fault of the other titanosaurs than R. krausei.


Bandeira, K. L., F. M. Simbras, E. B. Machado, D. de Almeida Campos, G. R. Oliveira, and A. W. A. Kellner. 2016. A new giant Titanosauria (Dinosauria: Sauropoda) from the Late Cretaceous Bauru Group, Brazil. PLoS ONE 11(10):e0163373. doi:10.1371/journal.pone.0163373.

Carballido, J. L., D. Pol, A. Otero, I. A. Cerda, L. Salgado, A. C. Garrido, J. Ramezani, N. R. Cúneo, and J. M. Krause. 2017. A new giant titanosaur sheds light on body mass evolution among sauropod dinosaurs. Proceedings of the Royal Society B: Biological Sciences 284(1860):20171219. doi:10.1098/rspb.2017.1219.

Currie, P. J., J. A. Wilson, F. Fanti, B. Mainbayar, and K. Tsogtbaatar. 2018. Rediscovery of the type localities of the Late Cretaceous Mongolian sauropods Nemegtosaurus mongoliensis and Opisthocoelicaudia skarzynskii: Stratigraphic and taxonomic implications. Palaeogeography, Palaeoclimatology, Palaeoecology 494:5–13. doi:10.1016/j.palaeo.2017.10.035.

Curry Rogers, K. 2009. The postcranial osteology of Rapetosaurus krausei (Sauropoda: Titanosauria) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology 29(4):1046–1086.

Curry Rogers, K., and C. A. Forster. 2001. The last of the dinosaur titans: a new sauropod from Madagascar. Nature 412 (6846):530–534.

Curry Rogers, K., and C. A. Forster. 2004. The skull of Rapetosaurus krausei (Sauropoda: Titanosauria) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology 24(1):121–144.

Curry Rogers, K., and J. A. Wilson. 2014. Vahiny depereti, gen. et sp. nov., a new titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous Maevarano Formation, Madagascar. Journal of Vertebrate Paleontology 34(3):606–617.

Curry Rogers, K., and Z. Kulik. 2018. Osteohistology of Rapetosaurus krausei (Sauropoda: Titanosauria) from the Upper Cretaceous of Madagascar. Journal of Vertebrate Paleontology 38(4):e1493689. doi:10.1080/02724634.2018.1493689.

Curry Rogers, K., M. D. D’Emic, M. Vickaryous, and A. Cagan. 2011. Sauropod dinosaur osteoderms from the Late Cretaceous of Madagascar. Nature Communications 2:564. doi:10.1038/ ncomms1578.

Curry Rogers, K., M. Whitney, M. D’Emic, and B. Bagley. 2016. Precocity in a tiny titanosaur from the Cretaceous of Madagascar. Science 352(6284):450-453.

González Riga, B. J., and L. Ortiz David. 2014. A new titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous (Cerro Lisandro Formation) of Mendoza Province, Argentina. Ameghiniana 51(1):3–25.

Kurzanov, S., and A. Bannikov. 1983. A new sauropod from the Upper Cretaceous of Mongolia. Paleontologicheskii Zhurnal 2:90–96.

Maryańska, T. 2000. Sauropods from Mongolia and the former Soviet Union. Pages 456–461 in M. J. Benton, M. A. Shishkin, D. M. Unwin, and E. N. Kurochkin, editors. The age of dinosaurs in Russia and Mongolia. Cambridge University Press, Cambridge, United Kingdom.

Tykoski, R. S., and A. R. Fiorillo. 2017. An articulated cervical series of Alamosaurus sanjuanensis Gilmore, 1922 (Dinosauria, Sauropoda) from Texas: new perspective on the relationships of North America's last giant sauropod. Journal of Systematic Palaeontology 15(5):339–364. doi:10.1080/14772019.2016.1183150.

Watabe, M., K. H. Tsogtbaatar, S. Suzuki, and M. Saneyoshi. 2010. Geology of dinosaur-fossil-bearing localities (Jurassic and Cretaceous: Mesozoic) in the Gobi Desert: Results of the HMNS-MPC Joint Paleontological Expedition. Hayashibara Museum of Natural Sciences Research Bulletin 3:41–118.

Wilson, J. A. 2005. Redescription of the Mongolian sauropod Nemegtosaurus mongoliensis Nowinski (Dinosauria: Saurischia) and comments on Late Cretaceous sauropod diversity. Journal of Systematic Palaeontology 3(3):283–318.

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