Your Friends The Titanosaurs, part 24: Pitekunsaurus, Puertasaurus, and Qingxiusaurus

This time around there are two more from Argentina to close out a streak of five consecutive entries from Patagonia which we began last time, and then one from China. Puertasaurus reuili completes the set of super-titanosaurs and again overshadows the other two entries, Pitekunsaurus macayai and Qingxiusaurus youjiangensis.

Pitekunsaurus macayai

P. macayai is another titanosaur from the Anacleto Formation, also known for Antarctosaurus wichmannianus, Laplatasaurus araukanicus, Neuquensaurus australis, and a few lesser lights of dubious validity. It's not particularly widely known outside of titanosaur workers, although it does tend to slip into descriptions of other titanosaurs because the known fossils represent most of the parts of the body. It was named in 2008 by Filippi and Garrido, after having made a brief teaser appearance in Filippi and Garrido (2006).

The holotype is made up of eighteen complete bones or large portions of bones, plus rib pieces and fragments, catalogued as different numbers under MAU-Pv-AG-446 (Aguada Grande locality, Paleontología de Vertebrados section of the Museo Municipal "Argentino Urquiza" in Rincón de los Sauces, Neuquén, Argentina). These bones are: a braincase; a left frontal; a tooth; four anterior cervical vertebrae and one posterior cervical; two anterior dorsals and a posterior dorsal; an anterior caudal and three distal caudals; the right scapula and ulna; and the proximal left femur (Filippi and Garrido 2008). The holotype was found at Aguada Grande, about 6 km (4 miles) south of Rincón de los Sauces. The bones were found disarticulated but associated in fine-grained rocks interpreted as muddy floodplain deposits (Filippi and Garrido 2008). The genus name incorporates the Mapuche word "Pitëkun", which can be translated as "to discover", and the species name honors Luis Macaya, who reported discovering the specimen to the Museo Municipal in April 2004 (Filippi and Garrido 2008). In spirit, if not in exact fact, the name can be rendered as "lizard discovered by Luis Macaya".

The type individual seems to have been a titanosaur of smallish to middling size. The preserved part of the femur, which is broken below the fourth trochanter (a significant muscle attachment site about midway down the bone), is 57 cm long (22 inches) (Filippi and Garrido 2008), and based on titanosaurian proportions it seems unlikely that it would have much exceeded a meter in length (about 40 inches) when complete. The complete ulna is 48 cm long (19 inches) (Filippi and Garrido 2008), and the neural arches are fused to the centra, so the type individual wasn't particularly youthful. P. macayai hits many typical titanosaurian traits: the tooth is peg-like, the cervicals are long with large triangular neural spines running anterior-posterior, the anterior caudal is procoelous with the neural arch cheated to the front of the centrum, etc. One feature that isn't standard is the articulations of the posterior caudals, which include amphicoelous, biconvex, and procoelous articulations, reminiscent of Rinconsaurus caudamirus (Filippi and Garrido 2008).

Here we have fifteen sauropod scaps, one of which belongs to Pitekunsaurus macayai. Try to guess which one! Figure 2 in González Riga et al. (2019). CC-BY-4.0. (incidentally, it's "a".)

Like most titanosaurs, the position of P. macayai within the group is unresolved. Wilson et al. (2009) and Curry Rogers and Wilson (2014) found that its braincase is comparable to those of Jainosaurus septentrionalis, Muyelensaurus pecheni, and Vahiny depereti, which is kind of an odd assortment, but stranger things have happened (and oddly enough, this is not the only time Jainosaurus shows up in this post). Filippi and Garrido (2008) did not include a phylogenetic analysis and refrained from making a finer classification within the titanosaurs, beyond noting that P. macayai wasn't a saltasaur and mentioning the caudal similarity with Rinconsaurus. Despite the comparison, and the braincase similarities with rinconsaur Muyelensaurus, Pitekunsaurus and Rinconsaurus aren't frequently found hanging out with each other in phylogenetic analyses. Nor does Pitekunsaurus usually turn up with the aeolosaurs, as found by Coria et al. (2013). P. macayai can be best described as generally sorting out in the vast middle of Titanosauria.

Puertasaurus reuili

P. reuili is based on MPM 10002 (Museo Padre Molina, Río Gallegos, Santa Cruz, Argentina), which amounts to the grant total of a partial cervical, a complete second dorsal, and two caudal centra (Novas et al. 2005). The name honors two fossil hunters for their discovery and preparation of the bones: "Puerta" refers to Pablo Puerta and "reuili" refers to Santiago Reuil, so the name essentially means "Pablo Puerta's and Santiago Reuil's lizard". At the time of description, the specimen was reported as from the Pari Aike Formation (Novas et al. 2005). The name of the host formation is unsettled in the literature, with Cerro Fortaleza Formation (Lacovara et al. 2014) and middle Mata Amarilla Formation (Rozadilla et al. 2019) also used. Ages given by various authors span the entire Late Cretaceous, but Varela et al. (2012) have a middle Cenomanian date for the lower middle Mata Amarilla. The discovery locality is Cerro Los Hornos near La Leona River in Santa Cruz Province, where the bones were found in a lens of fine gray sandstone with carbonized cycad and conifer fossils (Novas et al. 2005).

Obviously the major attraction for P. reuili has been its size. As with some of the other super-titanosaurs, the small number of specimens limit what can be done with it after marveling at its great size. The cervical, although incomplete, is of historical note for being the first known cervical of a super-titanosaur. It is 118 cm long (46 in) and 140 cm (55 in) wide (fused ribs included). The neural arch is low but the spine itself is quite large, being wider than the centrum (which in itself is much wider than high). The dorsal is notable because the centrum is as wide as it is long (in all other titanosauriforms, the centra of the anterior dorsals are longer than wide). It also supports an enormous neural arch, giving the whole thing the appearance of wings or a roughly diamond-shaped sail. This vertebra is 106 cm tall (42 in) and a grandiose 168 cm wide (66 in, or only a few inches shorter than my own height), making it the widest known dinosaur vertebra (Novas et al. 2005). Presumably P. reuili put a lot of stock into having a strong, broad back. The caudals seem to be unremarkable procoelous titanosaurian caudals.

On the left, an Argentinosaurus huinculensis dorsal. On the right, the Puertasaurus reuili dorsal. Image found at Wikimedia Commons, which had been modified from a photo placed on Flicker by "Marco." CC-BY-2.0.

So, how big was P. reuili? That's kind of hard to say, given only there are only four bones. Novas et al. (2005) did not include any estimates of the entire animals, but press accounts at the time it was announced were pitching "115 to 131 feet (35 to 40 meters) long" and a weight between "88 and 110 tons (80 and 100 metric tons)". Some of this was due to our very incomplete understanding of titanosaur anatomy and proportions at the time. As unbelievable as it may seem, it was once thought that titanosaurs as a rule had short cervicals; go ahead, check "Titanosauridae" in "A Field Guide to Dinosaurs" (Lambert 1983) if you don't believe me. (This is what comes of only having wimpy saltasaur necks.) The discovery and description of Futalognkosaurus dukei made it apparent that P. reuili wasn't quite as extravagant as initially thought. Greg Paul's 2019 overview of super-titanosaurs noted that the dorsal of P. reuili is similar in size to those of Patagotitan mayorum, and placed it in a 45-to-55-metric-ton tier (50 to 61 US tons).

This will come as no surprise to anyone who's been following along, but P. reuili is a card-carrying lognkosaur. If a modern analysis were to find it outside of Lognkosauria, that would be a notable finding, the kind that would indicate either a serious mistake somewhere or a radical new interpretation of titanosaurs. It is known from the same formation as fellow lognkosaur and [my mistake; 2020-05-18] super-titanosaur Dreadnoughtus schrani, but the two have substantially different vertebrae (Lacovara et al. 2014).

Qingxiusaurus youjiangensis

Like Pitekunsaurus macayi, Qingxiusaurus youjiangensis was named in 2008, and is not widely known outside of specialist circles. Even among titanosaurs it's pretty obscure. Q. youjiangensis was described in Mo et al. (2008) for material including an anterior caudal neural spine, both sternal plates, and both humeri, catalogued as NHMG 8499 (Natural History Museum of Guangxi, in Nanning City, Guangxi, China). Mo et al. referred to the holotype as a "partial postcranial skeleton", so the optimist in me holds out hope that there is more material which was omitted from the initial description. "Qingxiu" refers to "a picturesque scenery of mountains and water in Guangxi", making this the first dinosaur named for scenery, and "youjiangensis" refers to a river near the discovery site. The combination produces something along the lines of "picturesque Guangxi scenery lizard from the Youjiang River".

At this time, there is not a lot to be said about the geology of Q. youjiangensis. NHMG 8499 was found in unnamed Upper Cretaceous red beds at the village of Dashi, a suburb of Nanning, in southeastern China (Mo et al. 2008). The neural spine is simple, without much in the way of laminae. It widens slightly from its base while having flat anterior and posterior surfaces, giving it a paddle shape (Mo et al. 2008). (It's not nearly as extreme as in the "Kweichow sauropod", but the two share the "wider than long" property.) The sternal plates have the typical crescentic or kidney-like shape, only being notable for being relatively small compared to the humeri for a titanosaur (length ratio of 0.65 versus the humeri compared to 0.75 or more in other titanosaurs). The slightly longer left humerus is 900 mm long (35 inches) (Mo et al. 2008), suggesting a smallish titanosaur.

Mo et al. (2008) suggested that Q. youjiangensis could a saltasaurid or closely related to Saltasauridae, based on the anatomy of the humerus. Wilson et al. (2009) noted that a humerus referred to Jainosaurus resembled those of Q. youjiangensis. Averianov and Sues (2017) agreed with a saltasaurid identity. Mannion et al. (2019), while agreeing that it was a titanosaur, did not attempt any finer placement.

References

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