Your Friends The Titanosaurs, part 20: Neuquensaurus, Normanniasaurus, and Notocolossus

The entrants this week come with both notability and downsides. Normanniasaurus genceyi is one of the few well-established Early Cretaceous titanosaurs, and Notocolossus gonzalezparejasi is one of the largest known titanosaurs. However, both are known from rather limited material to date. Neuquensaurus, on the other hand, has had no shortage of material referred to it, but is a historical mess. So far it has escaped the fate of Argyrosaurus superbus, Laplatasaurus araukanicus, and Titanosaurus indicus, historically significant names that have been re-analyzed and cut down to just a type specimen. There are still questions surrounding Neuquensaurus, but at least there are multiple specimens that can be assigned to it.

Neuquensaurus australis and robustus

Neuquensaurus as a taxonomic entity is complicated. Saltasaurs themselves are pretty straightforward: distinctive small-bodied titanosaurs with short, stocky limbs, better-developed armor than other titanosaurs, and heavily pneumatized skeletons (neck, back, ribs, most of the tail, shoulder girdle, ilium [Cerda et al. 2012], even chevrons [Zurriaguz et al. 2017] with air chambers). Neuquensaurus itself, though, checks off three boxes that ensure a bumpy ride: bonebeds, Friedrich von Huene, and being originally described as a species of Titanosaurus. To get to the beginning of the story, we have to go back to the original work on titanosaurs in South America, Lydekker (1893).

We've already encountered two of the species Lydekker described in 1893, Argyrosaurus superbus and Microcoelus patagonicus. The first species he described in the paper has so far turned out to be the success: Titanosaurus australis. Lydekker had "a large series of associated vertebrae from Neuquen mostly belonging to a single individual, together with bones of the fore and hind limbs, and some fragments of the pectoral and pelvic girdles", of which he decided that "The caudal vertebrae represented in plate i may, however, be taken as the actual types." So far, so good. (He also decided that a cervical and dorsal were too small to belong to an adult T. australis and named them Titanosaurus nanus, which figures occasionally in the Neuquensaurus story but is best left for the moment as a dubious titanosaur, as per Powell 2003 and Wilson and Upchurch 2003.)

Plate i from Lydekker (1893) shows the vertebrae he regarded as the type specimens of Titanosaurus australis. Note the biconvex specimen in the upper right, which becomes important later on.

The next significant discussion of these fossils came from von Huene (1929a), and as we saw earlier, one of the things he did was to separate some of Lydekker's fossils into new genus and species Laplatasaurus araukanicus. He then concluded that the remaining "Titanosaurus" material could be divided still further, into T. australis Lydekker and a more robust form which he named, logically enough, Titanosaurus robustus. There is nothing inherently wrong with his proposition that two morphs existed and represent two species, only the means; i.e., how did he determine which bones belonged to which species when all he had were disarticulated specimens, and T. australis was inconveniently based on vertebrae? However he did it, he had enough T. australis to put together the first skeletal reconstruction of a titanosaur, having no way of knowing that the particular titanosaur he reconstructed was actually not very representative of titanosaurs in general (saltasaurs making up only a small fraction of titanosaur diversity).

I originally wasn't going to show this figure a third time, but I couldn't resist because not only does it include two of the titanosaurs in this post (Neuquensaurus and Notocolossus), they are represented by respectively the smallest (a) and largest (j) humeri. Interestingly, despite the vast difference in size, both had notably robust humeri. (Figure 4 in González Riga et al. 2019). CC-BY-4.0.

Bonaparte and Gasparini (1979) made the next major contribution to the story by confirming the holotype for Titanosaurus australis and selecting lectotypes for T. robustus, in the process being kinder to von Huene than most future reviewers. For completeness, the type for T. australis is given as MLP 77-V-28-1 (Museo La Plata; the six caudals illustrated by Lydekker in Plate i), and the types for T. robustus are given as MLP 26-250 (right ulna, alternatively MLP-CS 1095), MLP 26-251 (left ulna, alternatively MLP-CS 1094), MLP 26-254 (left radius, alternatively MLP-CS 1171), and MLP 26-259 (left femur, alternatively MLP-CS 1480). MLP 77-V-28-1, also known as MLP Ly 1–6, was augmented by D'Emic and Wilson (2011), who included a sacrum (MLP Ly 7), which is important as we'll get to in a moment.

Powell (1986, 1992) proposed the name Neuquensaurus for "T." australis. Due in part to nomenclatural issues (Powell 1986 is a dissertation, and Powell 1992 is sometimes seen as not explicitly following rules designating a new taxon), it didn't catch on immediately. For example, McIntosh (1990) in The Dinosauria had both "T." australis and "T." robustus as species of Saltasaurus. By the time The Dinosauria II rolled around, Neuquensaurus australis was listed, but "T." robustus was still labeled as a species of Saltasaurus (perhaps due to being overlooked when the table was updated) (Upchurch et al. 2004). Further work produced the first associated partial skeleton (Salgado et al. 2005), a study of the appendicular bones (Otero 2010), a reanalysis of the holotype of N. australis and just what constitutes the genus and species (D'Emic and Wilson 2011), and an analysis of Neuquensaurus vertebrae to find out if there are multiple vertebral morphs as well (Zurriaguz 2015).

Neuquensaurus (and predecessor names Titanosaurus australis and T. robustus) became a handy receptacle over the years. Scores of bones representing all parts of the body except the skull have been attributed to these names, as can be followed through Lydekker (1893), von Huene (1929a), Powell (2003), Wilson and Upchurch (2003), Salgado et al. (2005), and Otero (2010). Inevitably, not all of these specimens can be firmly attributed to Neuquensaurus. For example, von Huene (1929b) placed some remains from Uruguay into "T." australis, but Powell (2003) found the Uruguayan fossils to be indeterminate at the genus and species levels. D'Emic and Wilson (2011) took an even more conservative tack, limiting N. australis to the holotype, a sacrum from the Saltasaurus loricatus type locality of El Brete, the "MCS 5" partial skeleton described by Salgado et al. (2005), and one of von Huene's (1929a) caudal series. This is certainly appealing from a rigorist point of view, but does leave behind a lot of orphaned fossils. As if by compensation, D'Emic and Wilson (2011) expanded the holotype to include a sacrum.

The sacrum thing is actually pretty important. One of the six vertebrae considered by Lydekker as the types of Titanosaurus australis has a ball on both ends (biconvex). This kind of vertebra is sometimes found as the first caudal in titanosaurs. D'Emic and Wilson found that Lydekker's biconvex "caudal" fit a sacrum and, moreover, had been incorporated into that sacrum rather than being a true caudal. There are two major upshots to this: Lydekker's type can be expanded to include something which is directly comparable to other sacra (which is quite helpful because there's not even any guarantee that Lydekker's six vertebrae came from the same individual); and Neuquensaurus australis has a very distinctive sacrum. It is seven vertebrae long instead of six (as in other titanosaurs), elongate in build, and the vertebral centra are significantly skinnier in the middle of the sacrum than at the ends. Salgado et al.'s MCS 5 skeleton has the same kind of sacrum, so it can be assigned to N. australis, and an El Brete sacrum shows the same characteristics. Of course, the El Brete sacrum also makes things more complicated because previously the locality was thought to have just one titanosaur species, Saltasaurus loricatus. Now there are two very similar species to be disentangled.

Figure 2 from D'Emic and Wilson (2011), showing Lydekker's biconvex vertebra (here s7) reunited with the sacrum in ventral view. Note how the centra of s3, s4, and s5 are so much narrower than the end vertebrae. (The sacrum is also pneumatic like just about everything else in a saltasaur, in case you were wondering.) CC-BY-4.0.

Figure 9 from D'Emic and Wilson (2011), showing PVL 4017-18 from the El Brete Saltasaurus locality, with seven vertebrae and the skinny middle. CC-BY-4.0.

Are there actually two species of Neuquensaurus? It's fair to say that in the sample referred to Neuquensaurus, N. australis, and N. robustus, some limb bones are noticeably more robust than others (not that the "gracile" morph is a delicate flower). Salgado et al. (2005) found some limb bones at the same site as the MCS 5 skeleton which they regarded as more robust examples of Neuquensaurus bones than the MCS 5 skeleton. D'Emic and Wilson (2011) attributed MCS 5 to N. australis based on the sacrum, so if you go in for N. robustus, this could mean that von Huene was right in considering australis the more gracile form. On the other hand, Zurriaguz (2015) found that at least two morphs could be distinguished in Neuquensaurus vertebrae, but could not correlate them cleanly with the australis/robustus division; instead, one corresponded to von Huene's material (both australis and robustus) and one to Salgado et al.'s material (considered to represent australis). Given the lack of association of most specimens assigned to Neuquensaurus, authors have generally regarded the species N. robustus as dubious or at least not firmly established (Powell 2003; Wilson and Upchurch 2003; Otero 2010), and this is probably the safest route until additional associated specimens are found.

Figure 10 from Otero (2010). The femur depicted as A is described as N. australis; B is referred to the N. robustus morph; and C is one of the lectotypes of N. robustus. Do the differences point to two species, sexual dimorphism, individual variation, or something else? CC-BY-4.0.

Speaking of sacra, Neuquensaurus and Saltasaurus are practically joined at the hip in phylogenetic analyses. It would be notable if someone published an analysis where they didn't turn out in close proximity to each other. In fact, your genericometer may consider them as species of the same genus, Saltasaurus (or Microcoelus if you're feeling perverse). (What you do with Rocasaurus muniozi, the other guaranteed saltasaur, is then up to you.)

Finally: femur length for MCS 5 is 85.0 cm (33.5 in; right) and 83.0 (32.7 in; left); and provenance varies. The type is from near Neuquén in Neuquén Province, with uncertain stratigraphy, but von Huene's specimens from the Cinco Saltos and General Roca areas of Río Negro Province are attributed to the Anacleto Formation (Otero 2010), MCS-5 is from the upper Anacleto near Cinco Saltos (Salgado et al. 2005), and the El Brete sacrum is from the Leche Formation of Salta Province (D'Emic and Wilson 2011). Note that with the significant changes in Upper Cretaceous geological nomenclature in Argentina over the past couple of decades, you can expect to see a lot of other formation names employed in older publications. The small size of saltasaurs is intriguing; unlike, say, Magyarosaurus, where we can point to small landmasses, it's not clear what the advantage of small body size was for saltasaurs. All we can tell is that it must have paid off somehow.

Figure 1 from Otero (2010). Part A shows the locations of Neuquén, Cinco Saltos, and General Roca in Argentina, Part B shows the mounted skeleton of Neuquensaurus at the Museo de La Plata, and Part C shows a restoration with reported appendicular bones highlighted and a human for scale (it's a bit chunkier than von Huene's restoration). CC-BY-4.0.

Normanniasaurus genceyi

The quest for pre-Late Cretaceous titanosaurs has so far produced a few examples of the genuine article and a lot of false leads, led by the fallen hope Janenschia (in which case the so-called titanosaur caudals were later removed to new genus Wamwerecaudia, which also wasn't a titanosaur). Europe has tried this game a few times, producing such immortals as Aepisaurus and Macrurosaurus. The dubious "Titanosaurus" valdensis, also known as Iuticosaurus, was about the best of these until Normanniasaurus genceyi.

N. genceyi is based on partial remains recovered from Bléville on the north side of Le Havre in Normandy, France by Pierre Gencey in 1990. The fossils were found in blocks of the Poudingue Ferrugineux, a lower to middle Albian unit of marine origin, but the living animal probably lived to the west on the Armorican Massif (Brittany and Lower Normandy). The genus name comes from Normannia, the Latin word for Normandy, and the species name honors Gencey, giving us "Pierre Gencey's Normandy lizard" (Le Loueff et al. 2013).

The holotype of N. genceyi is MHNH-2013.2.1.1 through .12 (Museum d'Historie Naturelle du Havre, France), including fragments of presacral vertebrae, partial sacrum, two caudals, a scapula, parts of both ilia and ischia, and the proximal ends of a femur and fibula. A caudal centrum collected years before from Bléville but apparently from a higher horizon may represent a specimen of another individual. Some other Albian-age vertebrae from Argonne and Villers Saint Barthélémy are also similar (Le Loueff et al. 2013).

One of N. genceyi's more notable anatomical characteristics is the presence of hyposphene–hypantrum articulations in the presacral vertebrae. Among titanosaurs, this is only known in the basal titanosaurs Andesaurus delgadoi and Epachthosaurus sciuttoi. On the other hand, the anterior caudal is strongly procoelous and the presacrals have typical titanosaurian cancellous (spongy) texture (Le Loueff et al. 2013). Although it is rather fragmentary, it has been included in several recent phylogenetic analyses. Interestingly, in some cases it turns up fairly far along into Titanosauria (Gorscak et al. 2017; Sallam et al. 2018; Gorscak and O'Connor 2019; Mannion et al. 2019). In others it ends up near the base of Titanosauria (Díez Díaz et al. 2018), where we might otherwise expect it.

Notocolossus gonzalezparejasi

After starting with the miniaturized Neuquensaurus, we now meet with a properly titanic titanosaur, Notocolossus gonzalezparejasi. Actually, there's a decent chance we've already met N. gonzalezparejasi, only traveling under the name "Antarctosaurus" giganteus. N. gonzalezparejasi is one of the less complete super-titanosaurs, and so is a bit of an also-ran in terms of familiarity, although it can boast the longest known titanosaur humerus at 1,760 mm (69.29 in) (González Riga et al. 2016, 2019).

The genus name is a combination of Greek "notos" for "southern" and Latin "colossus", which technically refers to a big statue but has become shorthand for any big thing, while the species name honors Dr. Jorge González Parejas, so loosely translated we have "Jorge González Parejas's southern giant". Two individuals are known, recovered from the basal Plottier Formation at Cerro Guillermo, Mendoza Province, Argentina. The holotype is UNCUYO-LD 301 (Laboratorio de Dinosaurios, Universidad Nacional de Cuyo, Mendoza), which consists of a dorsal, a caudal, part of a pubis, and the aforementioned humerus, found within an 8 m by 8 m area (26 ft by 26 ft). Second and smaller individual UNCUYO-LD 302 includes seven caudals with chevrons and a complete and articulated right foot with astragalus, found within a 5 m by 5 m area (16 ft by 16 ft), 403 m (1,322 ft) from the holotype at the same horizon. It was assigned to N. gonzalezparejasi because the caudals were almost the same as the caudal included in the type specimen (González Riga et al. 2016).

Honestly, you could have just skipped the previous two paragraphs and looked at this figure, and not have missed much except my deathless prose. This is Figure 1 in González Riga et al. (2016); in the skeletal reconstruction, green is the holotype and orange is the referred specimen. Regrettably, were you to map "Antarctosaurus" giganteus onto it, there would be almost no overlap except for the pubis (incomplete for both taxa). CC-BY-4.0.

Given the relative paucity of fossils, N. gonzalezparejasi is like the renowned Argentinosaurus huinculensis in that once you've finished marveling at its great size, there isn't much else to do with it. The humerus itself is appropriately beefy, which you can confirm for yourself from the handy González Riga et al. (2019) humerus diagram included above with Neuquensaurus (N. gonzalezparejasi is "j"). The single known dorsal vertebra of the holotype is also quite large, estimated at 1,500 mm (4.92 ft) wide across the diapophyses (on the transverse processes, making this the widest dimension of the vertebra) (González Riga et al. 2016). This is greater than in Argentinosaurus, although to be fair Argentinosaurus didn't get where it was by simply being broad across the transverse processes.

The presence of a complete foot in the smaller specimen is significant, because only a handful of complete titanosaur feet have been found; coincidentally enough, one of them belongs to another titanosaur from the Plottier Formation, the undescribed Agua del Padrillo titanosaur (UNCUYO-LD 313) (González Riga et al. 2016). (The Plottier does quite well for titanosaurs; in addition to N. gonzalezparejasi and "Antarctosaurus" giganteus, there's Petrobrasaurus puestohernandezi, an unnamed aeolosaur, the Agua del Padrillo titanosaur, and possibly Muyelensaurus pecheni. Even if you synonymize the two giants and banish M. pecheni back to the Portezuelo Formation, there's still four taxa.) The foot has two phalanges per all toes but the fifth, which has none, and the metacarpals are all relatively short and similar in size, so overall the foot was short and compact, which makes sense given the size of the animal. In addition, most sauropods had three distinct claws per foot, on the first three toes; the foot of N. gonzalezparejasi has three blunt and non-claw-like ungual phalanges instead (González Riga et al. 2016).

A closer look at the Notocolossus postcrania (A=humerus, B=pubic fragment, C=astragalus, D–F=elements of the foot). González Riga et al. 2016: Figure 4. CC-BY-4.0.

N. gonzalezparejasi was not found to be a lognkosaur at first (González Riga et al. 2016), but since then it has generally turned up there, along with most other super-titanosaurs. As for its size? González Riga et al. (2016) started off at approximately 60.4 metric tons (66.6 US tons) for the holotype, but then produced counter-arguments that could shave off as much as a third of that. Just as I was in the process of writing this, Paul (2019) produced an estimate of 50 to 55 metric tons (55 to 61 US tons) for this species.

References

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