Your Friends The Titanosaurs, part 7: Barrosasaurus, Baurutitan, and Bonatitan

We come now to a sauropod that acts as a titanosaurian frame of reference (Baurutitan britoi), a sauropod that gets overshadowed by another sauropod with a very similar name (Bonatitan reigi), and Barrosasaurus casamiquelai, which is kind of stuck waiting for the rest of Titanosauria to get sorted out.

Barrosasaurus casamiquelai

Barrosasaurus casamiquelai is working against the double whammy of a recent description and limited material, and consequently has yet to make much of an impression in the literature. In fact, once you get past the original description (Salgado and Coria 2009), there's not much else to add.

B. casamiquelai was discovered at Sierra Barrosa, Neuquén Province, west-central Argentina, in red fluvial sandstone of the lower Anacleto Formation (Salgado and Coria 2009). Given the reshuffling of Upper Cretaceous formations in Argentina, I had to check and for a moment thought that the discovery site might have been transferred to the Sierra Barrosa Formation, which produced the theropod Murusraptor barrosaensis from the same area (Coria and Currie 2016). However, multiple formations are exposed at the Sierra Barrosa locality (Salgado and Coria 2009; Coria and Currie 2016). (Which also means the Paleobiology Database's pages for the Sierra Barrosa locality and Murusraptor barrosaensis need a tweak to remove Murusraptor from the Anacleto.) "Barrosasaurus" refers to Sierra Barrosa, and "casamiquelai" honors the late Argentine earth scientist Rodolfo Casamiquela (Salgado and Coria 2009), so all together it's approximately "Rodolfo Casamiquela's lizard from Sierra Barrosa".

B. casamiquelai is based on three dorsal vertebrae, discovered adjacent to each other and thought to represent one individual. These vertebrae are cataloged as MCF-PVPH-447/1, -447/2, and -447/3 (Museo "Carmen Funes", Colección Paleontologia de Vertebrados, Plaza Huincul, Neuquén). They may be the seventh or eighth, ninth or tenth, and third dorsal vertebrae, respectively. Although none has a complete neural arch, we can tell from the centra that this was a large animal, with the two more complete vertebrae having centra 230 and 270 mm long (9.1 and 10.6 in), and 270 and 280 mm across (10.6 and 11.0 in) (Salgado and Coria 2009). It was certainly significantly larger than Neuquensaurus australis, also of the Anacleto Formation; see for example the specimen described in Salgado et al. (2005), in which the dorsal centra top out at about half the length. Preservation is very good, with fragile laminae still present (Salgado and Coria 2009).

There is enough material to show that B. casamiquelai is clearly not the same as other titanosaurs for which dorsal vertebrae are known, at least those known in 2009, but unfortunately not enough material (for this species and the other titanosaurs) for Salgado and Coria (2009) to make a detailed classification. There are a few features, such as the presence of certain laminae, that are consistent with a fairly basal position in Titanosauria (Salgado and Coria 2009). With its distinctive vertebral anatomy and good preservation of fine details, it should be possible to classify B. casamiquelai more precisely once titanosaur classification becomes clearer and there is a sufficient sample of titanosaur dorsals for comparison.

Baurutitan britoi

For being a 2005 description, Baurutitan britoi shows up regularly in the titanosaur literature. Its secret? It is represented by an articulated string of 19 vertebrae, including the last sacral vertebra and the first 18 caudals, almost all of which are complete. (Chevrons, a.k.a. hemal [or haemal] arches, are also present, but hardly anyone ever talks about those unless the year is around 1985 and you're arguing that a random skid-like chevron is evidence for a diplodocid in an un-diplodocid time and place.) A tail like this is very useful for comparative purposes, especially in Titanosauria, where the caudal is the coin of the realm. It show the variation of vertebrae along the tail, which helps researchers determine where in a titanosaur's tail an isolated caudal came from.

Eighteen caudal vertebrae from one Baurutitan britoi, plus chevrons in box a2 (Brusatte et al. 2017). C1, the first caudal, has a biconvex centrum, and the rest of the centra are procoelous (concave anterior, convex posterior), a classic titanosaurian feature. The scale bar is 10 cm (4 in), so these caudals compare favorably in size to the Neuquensaurus australis caudals in Salgado et al. (2005), making this another smallish titanosaur (Kellner et al. 2005 suggested 12 to 14 m long, or 39 to 46 ft).

The fossils that came to be named Baurutitan britoi were uncovered and excavated in 1957 by Llewellyn Ivor Price and his crew from the well-known Peirópolis site in Minas Gerais State, southeastern Brazil. This site also produced the titanosaur Trigonosaurus pricei, a future guest of this series. The bones were found in medium-grained white and yellow sandstones of the Serra da Galga Member of the Maastrichtian-aged Marília Formation (Kellner et al. 2005). Reportedly the crew worked manually through as much as an astonishing 18 m (59 ft) of overburden at the site. Quarry maps for the site can be seen in Campos and Kellner (1999) and Kellner et al. (2005). Price did not end up describing the caudals, but recognized that they established the presence of a second titanosaur taxon at Peirópolis (Lamego 1959). Jaime Powell (1987, 2003) later evaluated the Peirópolis material, designating the partial tail as Titanosaurus sp. "Series C".

It still remained to formally describe the material, which was accomplished in Kellner et al. (2005). The authors chose "Bauru" because the Marília Formation is part of the Bauru Group, and "britoi" honors Ignacio Aureliano Machado Brito, a Brazilian paleontologist who'd advised two of the authors, making this "Ignacio Aureliano Machado Brito's Bauru Group titan." The bones are all under one catalog number, MCT 1490-R (Museu de Ciências da Terra, Rio de Janeiro).

Before it had been named, the fossils that became B. britoi had already embarked on a career as a comparative specimen, which will probably continue until we have many more titanosaur tails. In terms of classification, it has been included in several phylogenetic analyses, ending up all over Titanosauria (and once outside; Bandeira et al. 2016). The vertebrae are distinct from aeolosaur-type caudals, as can be seen by comparisons using Kellner et al. (2005) and Martinelli et al. (2011), so it probably isn't one of them, although some of the caudal centra do have a slight "heart" shape to the posterior surface, similar to Gondwanatitan.

Bonatitan reigi

The first thing to remember here is to not confuse Bonatitan reigi with Bonitasaura salgadoi. This can be easier said than done: both are smallish Upper Cretaceous titanosaurs from Río Negro Province, Argentina, and both are known from fossils that include skull material. The shorthand is that Bonitasaura is the one with the beak. (Also, for some reason Bonitasaura either gets restored with a heavily shrink-wrapped skull, or, thanks to Jurassic World: The Game, as some kind of neon-purple-blue nightmare beast.)

But enough about Bonitasaura, which gets its own time next month provided no one comes up with three additional titanosaurs between it and Bonatitan. It's Bonatitan's misfortune that although its fossils certainly do include skull bones, they aren't the facial bones; they're the bones of the braincase, which are deeply informative to people who speak Braincase but otherwise are difficult for the layperson to use to build up some kind of mental illustration.

From Figure 7 of Martinelli and Forasiepi (2004): a braincase of Bonatitan reigi. Top is dorsal, middle is posterior, bottom is left lateral. If it helps to orient you, "Fr" denotes the frontal bones, "P" denotes the parietals, and "Bo" denotes the basioccipital, making up the occipital condyle (the ball that articulates with the neck)

Of course, when you get braincases, you can do neat things like the paleo-neurological study of Paulina Carabajal (2012). In case you're curious, the endocast (a cast of the space occupied by the brain) is 59 mm long (2.3 in), 45 mm tall (1.8 in), and 37 mm wide (1.5), and occupies a volume of 25 mL (0.85 oz) without the pituitary space. Also, it seems that titanosaurs did not devote much to the olfactory system, and the structure of the inner ear suggests a decreased range of head movements compared to other sauropods (Paulina Carabajal 2012). Although there were flowers in the Late Cretaceous, titanosaurs seem unlikely to enjoyed stopping to smell them.

The braincase of Bonatitan reigi, as depicted in Figure 1 from Carabajal (2012); go here to see the full caption. A is left lateral, B is dorsal, and C is posterior, with the green being the bone ,the yellow being the endocast, and the purple being the inner ear.

Bonatitan reigi was described in Martinelli and Forasiepi (2004) for a collection of disarticulated titanosaur fossils from lower Allen Formation rocks of Bajo de Santa Rosa (also given as Salitral de Santa Rosa) in Río Negro Province, Argentina. The lower Allen Formation is thought to represent a brackish lagoonal to supratidal setting (Salgado et al. 2007). Martinelli and Forasiepi (2004) is actually about much more than the sauropod: the Bajo de Santo Rosa site has yielded fossils of a great number of vertebrates. These included chondrichthyans, several kinds of teleosts, lungfish, frogs, turtles, sphenodontians, elasmosaurid plesiosaurs, apparent carcharodontosaurids, and hadrosaurids, plus sauropod eggs and eggshells (Martinelli and Forasiepi 2004; if you'd like to further explore the eggs, there's Salgado et al. 2007 and 2009). Later, the dromaeosaurid Austroraptor cabezai would be described from the same site (Novas et al. 2009), and in fact the same stratigraphic level (Salgado et al. 2014). The bulk of the material described by Martinelli and Forasiepi came from B. reigi. The genus name refers to paleontologist José Bonaparte, while the species name refers to another notable figure in South American paleontology, Osvaldo Reig. The formulation is a little awkward, but you could read it as "Bonaparte and Reig's titan" (or "Reig's Bonaparte's titan").

Altogether, the sauropod remains described by Martinelli and Forasiepi (2004) amounted to two braincases, an incomplete cervical, a dorsal, a couple of partial caudals, some incomplete chevrons, a left humerus, a left radius, a left ulna, a piece of metacarpal, three femora, three tibiae, a left fibula, two calcaneums, and two metatarsals. Martinelli and Forasiepi used size to sort the material into holotype MACN-PV RN 821 and smaller individual MACN-PV RN 1061 (Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" of Buenos Aires, PV for the vertebrate paleontology collection, RN for the Río Negro collection). Salgado et al. (2014), in their redescription of the taxon, came to a rather different conclusion. They decided that five individuals were represented, although to be fair most of MACN-PV RN 821 ended up as their Individual B and most of MACN-PV RN 1061 became their individual D. They also restricted the holotype to the braincase from MACN-PV RN 821, but opted not to renumber the various specimens. Inevitably, some bones were also re-identified ("ulna" as a metatarsal, "calcaneum" as an astragalus) or added (sacral rib, elements of the hands and feet).

Although the type braincase is smaller than the braincase in MACN-PV RN 1061, the 1061 braincase came from an animal that was not as skeletally mature, because the "sutures are not obscured by fusion" (Salgado et al. 2014). Martinelli and Forasiepi (2004) interpreted the occipital condyle as being oriented posteriorly as in Rapetosaurus, but it actually has a more typical posterio-ventral orientation (Paulina Carabajal 2012; Salgado et al. 2014). The limb bones are on the gracile side, unlike the stocky limbs of Neuquensaurus and Saltasaurus (Martinelli and Forasiepi 2004; Salgado et al. 2014).

A reconstructed mount of B. reigi is on display at the Museo Argentino de Ciencias Naturales; as noted by Victoria Arbour, it's a little sauropod. Per Martinelli and Forasiepi (2004), the largest femur is 585 mm long (23.0 in). However, the taxon could have gotten larger than the known material, because the braincases are considered to be subadult (Paulina Carabajal 2012).

Although B. reigi is better represented than most titanosaurs, it hasn't shown up in many phylogenetic analyses. Martinelli and Forasiepi (2004) described it as a saltasaurine, and Filippi et al. (2011) found it in Saltasaurinae in their phylogenetic analysis, while Salgado et al. (2015) and Díez Díaz et al. (2018), which used the Salgado et al. matrix, found it to be more basal in Titanosauria.

References

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