Your Friends The Titanosaurs, part 31: Trigonosaurus, Uberabatitan, and Vahiny

As we close in on the end of the alphabet, we drop by Brazil for the last time (for now) for a double feature (Trigonosaurus pricei and Uberabatitan ribeiroi), then head over to Madagascar for Vahiny depereti. Oddly enough, we've already had the last entry from Argentina.

Trigonosaurus pricei

Trigonosaurus pricei is not one of the more famous titanosaurs, but it *is* one of the more significant: it is known from one of the more complete titanosaurian vertebral series, making it a key reference taxon for a group in which vertebrae are critical. Befitting this noteworthy status, it has a long pre-description history under nicknames. If you're going back through the literature, its other aliases include "Series B" (sometimes with a "Brazil" or "DGM" attached), and the "Peirópolis titanosaur".

The history of T. pricei begins with a quarry opened by paleontologist Llewellyn Ivor Price (so no points for guessing the meaning of the species name) at the Săo Luís Farm, Veadinho Hill, just north of Peirópolis in Uberaba Municipality, Minas Gerais State, Brazil (Campos et al. 2005); Uberaba of course also figures later on in today's post. Known as the Caieira quarry, the site was worked between 1949 and 1961 (Kellner et al. 2005). It produced a number of sauropod fossils (Price in Lamego 1959), including what became known as "Series B" and "Series C" (=holotype of Baurutitan britoi), but the fossils were not described in any detail until Powell (1987; revised as Powell 2003). For the record, there was also a "Series A", but it was from a different site and figures in the Uberabatitan story, so we'll catch up with it later. The Caierira site is in sandstone of the Serra da Galga Member of the Maastrichtian-aged Marília Formation (Campos et al. 2005), and as the quarry map in Kellner et al. (2005) shows, it's another one of those sites where titanosaurs belonging to multiple taxa have seemingly exploded. The limb and girdle bones can't be sorted at this time, but fortuitously enough, there are those couple of long sequences of vertebrae. I don't think the other bones have been described in the formal literature to date, although there are a dissertation and abstract (Trotta 2002a, 2002b). The Marília Formation is interpreted as a terrestrial unit "deposited in alluvial fans, braided fluvial systems, alluvial plains and ephemeral lakes under a hot, dry climate," with long dry seasons (Salgado and Carvalho 2008).

T. pricei has for a holotype MCT 1488-R (Museu de Ciências da Terra, Rio de Janeiro), consisting of five cervical vertebrae, ten dorsals, six sacrals, and the left ilium. The last cervical through to the end of the dorsal series were found articulated, and the sacrals and ilium as well (Campos et al. 2005). An additional ten caudals, catalogued as MCT 1719-R, were designated a paratype (Campos et al. 2005); Price and Powell considered that they belonged to the same individual as MCT 1488-R, but Campos et al. (2005) could not find evidence to confirm or reject this proposal. They *are* about the right size (Campos et al. 2005), and a quick visual comparison shows they didn't come from Baurutitan britoi, at least. The genus name is a reference to the "Triângulo Mineiro" region of Minas Gerais, and the species name is, of course, in honor of Price (Campos et al. 2005), giving us something like "Llewellyn Ivor Price's Triângulo Mineiro lizard".

Figure 4b from Brusatte et al. (2017), showing the Trigonosaurus holotype plus referred caudals. The scale bars in each box are 10 cm (4 in). The caudals are quite distinct from those named Baurutitan, found in the same quarry. CC BY-NC 4.0.

The cervicals and dorsals are on the elongate side. The cervical neural spines are relatively low. The dorsal neural spines are posteriorly inclined, while the anterior caudal neural spines are anteriorly inclined (one of the most obvious differences from Baurutitan). Like all good titanosaurian hips, the ilium has the requisite broad lateral flare.

It is worth taking a moment to comment on the holotypes of Trigonosaurus and Baurutitan, given how much fun titanosaur bonebeds have been. Although the holotype of Baurutitan and the tail referred to Trigonosaurus are quite distinct, the holotype of Trigonosaurus only overlaps the holotype of Baurutitan in one element: the last sacral. The last sacral of Trigonosaurus is fused to the rest of the sacrum and the ilium, limiting how much can be seen. However, it differs very obviously from the Baurutitan sacral: it is strongly posteriorly convex, whereas the Baurutitan sacral has a concave posterior articulation surface. Furthermore, the centrum of the T. pricei sacral is flatter dorso-ventrally, and the neural spine is expanded dorsally and more inclined posteriorly (Kellner et al. 2005). This at least guarantees that the Baurutitan holotype cannot be a tail of Trigonosaurus, although it still leaves open a slight possibility that the referred Trigonosaurus caudals belong to a third titanosaur taxon. Price appears to have assigned the caudals to what became Trigonosaurus based on compatible size and morphology (Kellner and Campos 1999; Campos et al. 2005).

T. pricei appears in most titanosaur phylogenies, with its earliest usage predating its formal naming: note "Brazil Series B" in Curry Rogers (2005). Numerous potential placements have been presented. Among them in recent papers are: adjacent to the saltasaurs (González Riga et al. 2016); in a small clade with Brazilian titanosaurs Maxakalisaurus and Tapuiasaurus (Bandeira et al. 2016); at the root of a clade also including Alamosaurus, Opisthocoelicaudia, and the saltasaurs (Carballido and Sander 2014; Averianov and Skutschas 2017; Carvalho et al. 2017; Filippini et al. 2017; Torcida Fernández-Baldor et al. 2017; Simón et al. 2018); or nested among the aeolosaurs (Gorscak et al. 2017; Sallam et al. 2018; Gorscak and O'Connor 2019; Hechenleitner et al. 2020).

Juárez Valieri and Ríos Díaz (2013) assigned an additional specimen from a Peirópolis site, the posterior dorsal vert CCP 494 (Centro de Pesquisas Paleontológicas Llewelyn Ivor Price, Peirópolis) to T. pricei. As before, it was from the Serra da Galga Member of the Marília Formation. This specimen had been previously reported by Santucci and Bertini (2006) as an unnamed large titanosaur and by Salgado and Carvalho (2008) as potentially Uberabatitan or something similar. Juárez Valieri and Ríos Díaz (2013) instead interpreted it as a 10th dorsal of a larger, older T. pricei. Admittedly CCP 494 does look like D10 of MCT 1488-R, although it is interesting that the upper margin of the neural spine is gently tilted anteriorly in MCT 1488-R while being more steeply tilted posteriorly in CCP 494.

Uberabatitan ribeiroi

We don't have to go far for Uberabatitan ribeiroi, just down the road more or less to Uberaba. We're even still in the same member of the same formation as Trigonosaurus pricei, albeit higher in section. The genus name refers to Uberaba, while the species name honors Luis Carlos Borges Ribeiro, the director of the Centro de Pesquisas Paleontológicas Llewellyn Ivor Price (Salgado and Carvalho 2008), giving us something like "Luis Carlos Borges Ribeiro's Uberaba titan".

U. ribeiroi is represented by yet another von Huene's puzzle of a bonebed. Most of the skeleton is represented by at least one bone, making it one of the most completely known titanosaurs (assuming of course that all of the bones actually pertain to U. ribeiroi, which no one has yet disagreed with). At the time that Salgado and Carvalho (2008) named the genus and species, 62 bones thought to represent three individuals were known from the discovery site. When Silva Junior et al. (2019) redescribed it, an additional six bones had been recovered, and the number of individuals had gone up from three to at least five based on the presence of three left femora of similar size, a much larger cervical, and juvenile material. This does tend to play havoc with type specimens. Salgado and Carvalho (2008) designated a group of bones as the type individual including cervical vertebrae and ribs, a dorsal vertebra and neural arch, a dorsal rib, a sacral centrum, caudal vertebrae, chevrons, a sternal plate, a right coracoid, a left humerus and radius, a right radius, a right metacarpal, left and right pubic bones, and a left tibia, fibula, and astragalus (various numbers under CPP-UrHo). Silva Junior et al. (2019) restricted the type to the tibia, fibula, and astragalus, although retaining the rest of the bonebed as Uberabatitan. Silva Junior et al. also noted similarities in the caudals [correction 2021/05/21: cervicals] of U. ribeiroi and "DGM Series A", which they interpreted as evidence that "Series A" is either U. ribeiroi or a similar species.

U. ribeiroi swings to the more robust side of the titanosaur continuum, with limb and girdle bones being notably robust. One of the more unusual features is a flange on the fibula that fits in a groove on the tibia between the cnemial crest and a prominent protuberance (Salgado and Carvalho 2008; Silva Junior et al. 2019). Although its vertebrae are reportedly less pneumatic than other Brazilian titanosaurs (Silva Junior et al. 2019), that doesn't mean it didn't have pneumatic fun; also, a U. ribeiroi vertebrae has served as a test case for studying the influence of taphonomy on evidence of pneumaticity (Aureliano et al. 2020). Among the individuals, one is estimated at a healthy 26 m long (85 ft), although most of the bones are indicative of animals between 10 and 15 m long (33 and 49 ft); the longest femur pertains to one of these more modest individuals, and is 66.29 cm long (26.10 inches) (Silva Junior et al. 2019).

U. ribeiroi has not appeared in a lot of phylogenies to date, with little resolution. It has ended up as the sister taxon to Laplatasaurus (Gallina and Otero 2015), as the sister of Brasilotitan within the saltasaurs (Bandeira et al. 2016), and as an aeolosaur (Hechenleitner et al. 2020). Silva Junior et al. (2019) re-scored and re-ran U. ribeiroi in three existing matrices and got three different results within the middle of Titanosauria. Although the authors noted an affinity for Brasilotitan, I found it interesting that it also tended to show up in the vicinity of Rapetosaurus. This might be an effect of Rapetosaurus being one of the few titanosaur taxa that can rival it for completeness.

Vahiny depereti

Finally, after going through Rapetosaurus krausei and "Titanosaurus" madagascariensis, we get to the *other*, other Maevarano titanosaur. The short story is that a small amount of the Maevarano titanosaur material, less than 10% of the vertebrae, limb bones, and girdle bones, represents something other than R. krausei (Curry Rogers and Wilson 2014). For a little over a decade, this taxon was known informally as Malagasy Taxon B. As was explained with "T." madagascariensis, you might think that Taxon B should be some new genus using madagascariensis, but that is not how things have worked out. On the one hand, Vahiny depereti could be construed as an overabundance of taxonomic caution. On the other hand, since when have disassociated titanosaur bones played fair?

The "T." madagascariensis type caudal that isn't Rapetosaurus, clipped from Depéret (1896). Does that make it Vahiny depereti? (Or Vahiny madagascariensis?)

Not feeling comfortable resurrecting madagascariensis, Curry Rogers and Wilson (2014) instead chose to designate an entirely new genus and species, based on partial braincase UA 9940 (Université d'Antananarivo, Antananarivo, Madagascar). An additional braincase fragment from a juvenile was referred to it. Braincases tend to be full of informative features, which made choosing one for a holotype a logical move. This does, though, leave the rest of bits known as Malagasy Taxon B waiting for a more complete specimen to unite them. The genus name is a Malagasy word meaning "traveler" or "visitor", in reference to its rarity compared to R. krausei, and the species name honors Charles Depéret for his work describing the first dinosaur fossils from Madagascar, as well as first proposing that titanosaurs had armor (Curry Rogers and Wilson 2014). Thus, we get something like "Charles Depéret's traveler." Incidentally, the "y" at the end of Vahiny is silent (Curry Rogers and Wilson 2014); such is transliteration.

Curry Rogers and Wilson (2014) noted similarities between the braincases of V. depereti and Jainosaurus septentrionalis. They did not run a phylogenetic analysis, though. The only publication I know of that includes both, Mannion et al. (2019), did indeed find the two in a sister-group relationship. Coincidentally enough, we also know that there are "T." madagascariensis-type caudals in the Lameta Formation, although if they were to turn out to belong to Jainosaurus, that doesn't seem to help the "Jainosaurus is really Titanosaurus indicus" hypothesis. Further applying the "Transitive Property of Indo-Malagasy Titanosaurs", since we're more than a hundred sauropods into this thing and might as well indulge in some baseless speculation, it is also interesting to note that Isisaurus and Rapetosaurus also have a tendency to show up adjacent to each other in titanosaur phylogenies, albeit not a super-strong tendency. (Note that "Malagasy Taxon B" in the Curry Rogers 2005 phylogeny is not based on Vahiny as we know it, because it is only scored for postcranial material such as sacral ribs, caudal vertebrae, and shoulder girdle bones.)

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