Your Friends The Titanosaurs, part 9: "Campylodon", Clasmodosaurus, Choconsaurus, and Daxiatitan

I've come up against some judgement calls at this point. There are two varieties for this exercise. The first includes a group of names based on poor material that have had little study but which are sometimes/often stuck into Titanosauria, usually from historical inertia or the "provenance argument". The provenance argument goes something like this: "the only described sauropods from this time and place are titanosaurs, ergo this is a titanosaur". The provenance argument is a seductive bit of taxonomic stereotyping, but I'm wary of it. For one thing, the implicit flip side is "therefore there cannot be anything else here than titanosaurs". When the provenance argument is correct, it's not because you put in any effort or had any kind of insight, and when it isn't, you look stupid for being lazy. When confronted with this dilemma and, say, a handful of teeth which have no particular characteristics that would put them in one group or another, I don't see what's wrong with "indeterminate sauropod". The other type of judgement call includes the frustrating taxa that sometimes end up in a clade and sometimes end up outside of it, generally because they are in that fuzzy transitional zone.

For this particular entry, I had cause to consider examples of both types: in the historical orphan bin are "Campylodon" ameghinoi (=Campylodoniscus) and Clasmodosaurus spatula, and in the fuzzy clade bin is Chubutisaurus insignis. I decided that the position of Chubutisaurus is too unstable to be confident it's a titanosaur at this point, and so left it out. We can always cover it later on, with some of its similarly ambivalent cronies. As of this writing, others in a similar equivocal position which I currently have outside of Titanosauria include Angolatitan adamastor, the two Huanghetitan species, Ligabuesaurus leanzai, Mongolosaurus haplodon, Phuwiangosaurus sirindhornae, Tastavinsaurus sanzi, Triunfosaurus leonardii, and Wintonotitan wattsi. Two things they almost all have in common: late Early Cretaceous age, and when they do show up in Titanosauria they're just barely over the line. The other two were more problematic because there's not much material and they've never attracted much interest. I decided to cover them here together as examples.

"Campylodon" ameghinoi and Clasmodosaurus spatula

Let's start on a positive note: "Campylodon" ameghinoi, also known as Campylodoniscus, is one of the few titanosaur-ish sauropods known from skull material. That's good! Unfortunately, that skull material consists only of a maxilla fragment a few cm across. I present it below in all its glory.

The mortal remains of "Campylodon" ameghinoi in lateral (C), medial (D), and ventral (E) views, with a 5 cm scale bar (2 in). Cropped from Martínez et al. (2016) Figure 31, with a neighboring caption erased.

"C." ameghinoi was named in von Huene's massive 1929 monograph for a left maxilla he found in Florentino Ameghino's collections. The specimen, MACN A-IOR63 (Museo Argentino de Ciencias Naturales), was found at San Bernardo Hill west of Lake Musters in Chubut Province, Argentina, in either the Castillo Formation or overlying Bajo Barreal Formation (Novas 2009). Eventually it became clear that Campylodon was already in use, for a fish named by Cuvier and Valenciennes way back in 1832, so Kuhn (1961) substituted Campylodoniscus for the dinosaur. This means "Campylodon-like". What does "Campylodon" mean? It means "a fish named by Cuvier and Valenciennes way back in 1832", but von Huene missed that. (Either that, or "curved tooth"; Greek is funny that way. Take your pick.) The species name honors Ameghino. Meanwhile, in these parts the -iscus goes for naught, because I use the house rules of The Dinosauria: <spoiler> dubious species </spoiler> revert to the earliest genus name, so it's "Campylodon" rather than Campylodoniscus.

"C." ameghinoi has been basically forgotten, although in principle Campylodoniscus could be resurrected with a better sample size of titanosaur-ish maxillae for comparison or the discovery of a more complete skull with a matching maxilla. (I'm not holding my breath, either.) Von Huene (1929) described this species as having teeth intermediate between the pegs of Diplodocus and the broad-crowned teeth of Camarasaurus, which is consistent with a basal titanosaur. Bonaparte and Gasparini (1979) called it a nomen vanum ("empty name"), and Powell (2003) and Upchurch et al. (2004) considered it a nomen dubium. McIntosh (1990), in perhaps the kindliest revision, regarded it as valid but Sauropoda incertae sedis, which in hindsight might have been due to the belief at the time that titanosaurs had sloping diplodocid-like skulls to go with their diplodocid-like teeth, and "C." ameghinoi's maxilla is from a sauropod with a taller, boxier skull bearing not-quite-so-peglike teeth. Novas (2009) grouped it among the titanosaurs but still considered it a nomen vanum, and Martínez et al. (2016) had it with "titanosaurs and possible titanosaurs". As of the moment, though, nobody has presented an anatomical or phylogenetic case for classifying it within or outside of Titanosauria.

Clasmodosaurus spatula is more of the same, only there isn't even a maxilla to get excited about, just teeth. Probably the only real claim to fame for C. spatula (which is one more claim than "Campylodon" ameghinoi has going for it, actually) is that it's among the first non-avian dinosaurs named from South America. They are: Argyrosaurus superbus, Microcoelus patagonicus, Titanosaurus australis, Titanosaurus nanus (all Lydekker 1893), Loncosaurus argentinus (Ameghino 1899a), and Clasmodosaurus spatula (Ameghino 1899b). This is not the most auspicious beginning, but things got better.

Ameghino based this taxon on three partial teeth (uncatalogued) with compressed conical tips and longitudinal grooves (Powell 2003), from Santa Cruz Province at the southern end of Argentina, now attributed to the Mata Amarilla Formation (Novas 2009). Thirty years after Ameghino, Von Huene (1929), in one of the odder moments of his career, spent several paragraphs first establishing that C. spatula was not in fact a sauropod, but instead was most like Labrosaurus stechowi (with the miracle of hindsight, I suspect von Huene had in mind what later became the holotype tooth of the spinosaurid Ostafrikasaurus crassiseratus, which isn't quite your standard theropod tooth), and then going on to find it unlikely that it was the same as Loncosaurus because a tooth found with L. argentinus was more carnosaur-like. To be fair, it was a long monograph, and he was probably seeing fossils with crossed eyes by the time he got around to Clasmodosaurus.

Concerning whether C. spatula was a titanosaur, in the absence of more fossils than three teeth, the main argument to invoke is the provenance argument, as Powell (2003) did. It does share a feature with Bonitasaura salgadoi: teeth with polygonal cross-sections (Gallina and Apesteguía 2011).

Choconsaurus baileywillisi

Choconsaurus baileywillisi gets to play the one "sure thing" titanosaur in this entry. There aren't a lot of references to it in the literature to date because it was only formally published in 2018 (Simón et al. 2018). You may see some sources using 2017 as the publication date; this is because the online version was posted in August 2017, while the hard copy is given as published in February 2018. Either way, this is one of the most recently described titanosaurs and is basically only known from its original description. It did manage to sneak into the description of Baalsaurus mansillai (Calvo and Gonzalez Riga 2018) because there's some dentary material available for comparison.

C. baileywillisi is represented by fossils found at the "La Antena" site near Villa El Chocón and the north end of the Ezequiel Ramos Mexia Reservoir in eastern Neuquén Province, west-central Argentina. The site was primarily worked between 1996–2002 by the Museo Paleontológico Municipal "Ernesto Bachmann" of Villa El Chocón (MMCh-Pv) and the Geology and Paleontology Museum of the Universidad Nacional del Comahue (MUCPv) (Simón et al. 2018). The fossils came from the lower Huincul Formation (Simón et al. 2018); you may remember that the Huincul Formation also produced Argentinosaurus huinculensis. The Huincul of this particular area is rather more productive of rebbachisaurds, including specimens of Cathartesaura anaerobica and Limaysaurus tessonei. In addition, the type specimen of Andesaurus delgadoi was found nearby, but in the underlying Candeleros Formation (Simón et al. 2018). (Skorpiovenator bustingorryi also comes from the Huincul of this area, and Giganotosaurus carolinii from the Candeleros, but somebody else can have the theropods.)

The "Chocon" of Choconsaurus baileywillisi refers to Villa El Chocón, while the species name honors Bailey Willis (1857–1949), an American geologist who worked extensively in Patagonia. This gives us "Bailey Willis's Villa El Chocón lizard". The holotype specimen is a group of separately numbered elements, found articulated or closely associated: MMCH-PV 44/1–9, nine dorsal vertebrae, or almost all of the sequence 1 through 10 or 11 except for the fifth; MMCh-PV 44/10 and 11, the right scapulocoracoid and sternal plate; and MUCPv 244/5–9, the right metacarpus. The other macronarian fossils found in the same area were designated paratypes, and include a left premaxilla, a right dentary, various teeth, four cervical vertebrae, four rib fragments, nineteen caudal vertebrae, and a chevron (Simón et al. 2018). It's a good haul for a titanosaur, with almost all of the dorsal vertebrae plus some cervicals and caudals, and even a bit of skull material.

The premaxilla does not angle down in lateral view, instead making a straight margin and a blunt snout. The lower jaw is not squared off but U-shaped when viewed from above or below, and the teeth are intermediate between the broader teeth of more basal macronarians and the peg-like teeth of more derived titanosaurs. Unlike most titanosaurs, with the exception of Andesaurus delgadoi, the dorsal vertebrae have hyposphene-hypantrum articulations. These articulations are also found in the caudals, apparently a unique feature. The anterior caudals are distinctly procoelous, unlike in Andesaurus, but this doesn't continue into the middle of the tail as in more derived titanosaurs (Simón et al. 2018). Simón et al. found it to be a fairly basal titanosaur, which is consistent with its anatomy and age.

Just to confuse things a bit, C. baileywillisi is not the same as the El Chocón titanosaur tail previously thought to belong to Andesaurus (Otero et al. 2006; Mannion and Calvo 2011; Otero et al. 2011), from the underlying Candeleros Formation, but fossils eventually assigned to C. baileywillisi were mentioned in Calvo (1999).

Daxiatitan binglingi

Daxiatitan binglingi is somewhat uncomfortable here because it is sometimes pulled into the orbit of Euhelopus* (for example D'Emic 2012, Saegusa and Ikeda 2014, Sassani and Bivens 2017, and Moore et al. 2018). Generally, though, it has come out as a titanosaur in recent analyses (Mannion et al. 2013, 2017; Poropat et al. 2016; Averianov and Sues 2017; Averianov and Efimov 2018; Averianov et al. 2018; Gonzàlez Riga et al. 2018; Sallam et al. 2018 [some analyses]; Gorscak and O'Connor 2019).

*Euhelopdidae is kind of odd. It seems like every couple of decades someone puts Euhelopodidae forward only for it to collapse, although the iteration put forward by D'Emic (2012) is still viable.

Anyway, D. binglingi is one of a few obscure but colossal titanosaur-ish sauropods from the late Early Cretaceous of China (see also: "Huanghetitan" ruyangensis and Ruyangosaurus giganteus; titanosaur-ish sauropods were happy to reach titanic dimensions whenever they got the chance, but the "middle" Cretaceous was a particularly good time for this). It was described by You et al. in 2008 based on fossils found in Gansu Province. "Daxia" in the name refers to the Daxia River, a tributary of the Yellow River running in the area where the fossils were found. "Binglingi" is a reference to the Bingling Temple, also located in Gansu (You et al. 2008). Therefore, you get something like "the Bingling Temple's Daxia River titan". The holotype and only known specimen comes from the Lower Cretaceous Hekou Group of the Lanzhou Basin in southeastern Gansu (You et al. 2008); a more refined age hasn't been pinned down, though. The type specimen is GSLTZP03-001 (Fossil Research and Development Center of the Third Geology and Mineral Resources Exploration Academy of Gansu Province), and consists of the last ten cervicals, ten dorsals, two caudals, some partial ribs, a chevron, the right scapulocoracoid, and the right femur (You et al. 2008). There's not much for the limbs, but you can still get an impressive mount out of it.

By "Tiouraren", from Wikimedia Commons. CC BY-SA 3.0.

At the time of its description, You et al. (2008) considered D. binglingi the largest sauropod known from Asia. It seems to have focused on its vertebrae rather than its limbs: the femur is a respectable but not unheard-of 177 cm long (just shy of 70 in), but the largest cervical is 91 cm long (36 in) and has a posterior articulation surface which is 28 cm wide (11 in) and 31 cm tall (12 in). For comparison, the longest cervical of famously long-necked Mamenchisaurus hochuanensis is 73 cm long and the posterior articulation surface is 14 cm wide by 30 cm tall (5.5 in by 12 in), which also incidentally shows that D. binglingi had a neck that was basically round in cross-section by comparison (You et al. 2008). You et al. (2008) compared the necks of D. binglingi and Euhelopus zdanskyi, scaling D. binglingi's neck at slightly more than three times that of E. zdanskyi to reach an estimate of a 12.20 m long neck (40.03 ft). This assumes that D. binglingi is "Super Euhelopus" in proportions, but even without that the length of the last nine cervicals is 6.1 m (20 ft) (You et al. 2008). Aside from its enormous neck, D. binglingi is also notable for its strongly "wide-gauge" femora, which could correspond to wide-gauge sauropod tracks in the upper Hekou Group. The scapula also has a strongly defined process on its dorsal margin (You et al. 2008).

Figure 16 from Li et al. (2014), showing a group of sauropod scapulocoracoids (scale bar in lower right is 200 mm [65.6 in]); you can check out the figure there to see the whole caption, but we're currently interested in "Db" in the upper left, which is a line drawing of the scapulocoracoid of D. binglingi, showing the hooked process. It's going to be a while before we get to Yongjinglong...

Per some artifacts in the text, Daxiatitan was at one point going to be named Gansutitan, presumably for Gansu Province. The version I have must be partially corrected, because Daxiatitan is used in the phylogeny, but the type species is still listed at one point as "G. binglingi". As someone who's worked on a few publications and a lot of internal reports, I can tell you that captions and figures are some of the easiest places to commit mistakes, because they tend to get forgotten. You prepare your figures, lock them in, and move on, and then after several rounds of edits, whoops, you realize they don't reflect the text anymore, or you spelled "theropod" "therapod", or something like that. Other places where this creeps in: units, such as your microns becoming millimeters, or a decimal place migrates; and any kind of directional wording. It's incredibly easy for, say "west" to become "east". If you're lucky, an editor or reviewer will catch it.

(Since I'm already in the middle of a digression, here's something related: students, if you're preparing your very first poster presentation, know that no matter how well you think you've proofread your poster, when you've got it in front of you at the conference you will find a typo, or at the very least something you wish you could change. The best thing to do it to take it in stride. Something similar often happens in oral presentations, where you also will often be faced with that one moment where you lose your train of thought.)

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