Your Friends The Titanosaurs, part 29.5: Bravasaurus and Punatitan

No sooner do I announce that Titanosaurus is up next for the titanosaurs than a couple of gate-crashers show up to butt in line: Bravasaurus arrierosorum and Punatitan coughlini. These two taxa were described in the same paper (Hechenleitner et al. 2020) and from the same locality (Quebrada de Santo Domingo) and stratigraphic unit (Ciénaga del Río Huaco Formation), albeit from different levels. They are from Argentina, but not Patagonia; instead, they are from the western, Andean part of the northwestern province of La Rioja, becoming the first named titanosaurs from this province. They are also the first titanosaurs named from the Ciénaga del Río Huaco Formation. The age of this formation has not yet been tightly constrained but is regarded as Campanian–Maastrichtian. In addition to the titanosaur bones, at least three laterally extensive horizons of eggs attributed to titanosaurs were found, between the two bone-bearing levels.

Part of Figure 1 from Hechenleitner et al. (2020), featuring reconstructions of Punatitan coughlini (c) and Bravasaurus arrierosorum (d), with red highlights showing known fossils (scale bar = 1 m). CC-BY-4.0.

Bravasaurus arrierosorum

Bravasaurus arrierosorum is somewhat better represented than Punatitan coughlini, and quite a bit smaller. Its genus name is derived from Laguna Brava, a lake in the vicinity of Quebrada de Santo Domingo which is the centerpiece of a provincial reserve, while "arriero" is a Spanish term for a muleteer or muleskinner, who in this particular case were wrangling cattle across the Andes (Hechenleitner et al. 2020). A rough translation would be "the arrieros' Laguna Brava lizard". It is known from two specimens. The holotype, CRILAR-Pv 612 (Paleovertebrate Collection of Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja, Argentina), includes a right quadrate and quadratojugal, four cervical vertebrae, five dorsals, and three caudals, some dorsal ribs, three chevrons, the left humerus, a fragmentary ulna, a fourth metacarpal, a partial left ilium with attached sacral ribs, the right pubis, a partial ischium, the left femur, and both fibulae. A second specimen, CRILAR-Pv 613, includes a tooth, dorsal ribs, the right ilium, and the right femur (Hechenleitner et al. 2020).

The stratigraphic horizon for B. arrierosorum is in the lower part of the Ciénaga del Río Huaco Formation. Both CRILAR-Pv 612 and 613 were found about 34 m up (110 ft), about 240 m apart (790 ft), in moderately to poorly sorted medium-grained sandstone interpreted as crevasse splay deposits. A quarry map (in the supplemental information) shows the association and partial articulation of the type specimen (Hechenleitner et al. 2020).

Part of Supplementary Figure 1 of Hechenleitner et al. (2020), showing the general geography, geology, and stratigraphy of the two titanosaurs and egg horizons. CC-BY-4.0.

B. arrierosorum is among the smallest known titanosaurs. For the type specimen, the humerus is 53 cm long (21 in) and the femur is 68 cm long (27 in), while the neural arches of the vertebrae are completely fused to their centra, indicating it was not a young animal when it died. Hechenleitner et al. (2020) estimated that it weighed in the neighborhood of 2.89 metric tons (3.19 US tons), which the authors put above the likes of Lirainosaurus and Magyarosaurus but below Neuquensaurus and Saltasaurus. Like some other small-bodied titanosaurs, particularly saltasaurs, B. arrierosorum had robust limb bones (except for the unusually gracile fibulae). However, despite the stocky limb bones, its small body size, and geographic location in a part of South America area known for saltasaurs, B. arrierosorum does not appear to have been closely related to them. Instead, it plots within another group of titanosaurs with some notably small members, the aeolosaurs (Hechenleitner et al. 2020). (In case your mind was wandering toward the idea of B. arrierosorum as a small, mountain-adapted titanosaur, the Andean Orogeny was in progress, but the Andes weren't quite *The Andes* yet. It would certainly be interesting to find titanosaurs adapted to getting around in areas with relatively steep topography and higher elevation.)

Punatitan coughlini

Punatitan coughlini is rather more typically sized for a titanosaur. The genus name incorporates "puna", "the local name that distinguishes the oxygen-depleted atmosphere of the high Andes", and the species name honors geologist Tim Coughlin, who first reported dinosaur fossils from this area (Hechenleitner et al. 2020); this can be translated roughly as "Tim Coughlin's Andean titan". The type and only known specimen is CRILAR-Pv 614, which includes a partial posterior cervical, two middle dorsals, a partial sacrum, 13 articulated caudals with some articulated chevrons, dorsal ribs, the right pubis, and the left ischium (Hechenleitner et al. 2020).

P. coughlini comes from much higher in the formation than B. arrierosorum, about 170 m up (560 ft). In fact, there is an argument that this horizon should actually be attributed to the overlying Puesto La Flecha Formation, which has an arbitrary, transitional contact with the Ciénaga del Río Huaco Formation. The upper beds are interpreted as part of an ephemeral lake setting. CRILAR-Pv 614 was found in a small area, partially articulated and stacked, in what is thought to be a sandy lobe (Hechenleitner et al. 2020).

In the absence of long bones, the size of Punatitan coughlini cannot be estimated with great precision. CRILAR-Pv 614 is larger than small saltasaurs and aeolosaurs such as Neuquensaurus, Overosaurus, Saltasaurus, and Trigonosaurus, but smaller than Aeolosaurus (A. rionegrinus and A. maximus, which Hechenleitner et al. regard as a potentially distinct genus) and Mendozasaurus, being most similar in size to the holotype of Uberabatitan (which we haven't gotten to yet). As with B. arrierosorum, the neural arches are fused to the centra, so the type was not a young animal (Hechenleitner et al. 2020).

P. coughlini also plots as an aeolosaur, in its case right smack between "A." maximus and A. rionegrinus, which means your genericometer may prefer it as a species of Aeolosaurus, but I digress. The caudals are somewhat more stereotypically aeolosaur than those of B. arrierosorum, but then again there are only three caudals known for B. arrierosorum.

Figure 5 in Hechenleitner et al. (2020), which combines a phylogeny with color coding for latitude in South America (which actually hasn't changed all that much since the Late Cretaceous). CC-BY-4.0.

References

Hechenleitner, E. M., L. Leuzinger, A. G. Martinelli, S. Rocher, L. E. Fiorelli, J. R. A. Taborda, and L. Salgado. 2020. Two Late Cretaceous sauropods reveal titanosaurian dispersal across South America. Communications Biology 3:article number 622. doi:10.1038/s42003-020-01338-w.