This edition of "Your Friends The Titanosaurs" is a little different in that not only are we welcoming a new friend, we are saying goodbye to an old friend. The latter is something that should come as no surprise; with well over a hundred species, notorious for incomplete material, some of them are eventually going to turn out to be the same.
(Also, I should have mentioned this, but I moved the external links to a separate page to conserve space on the sidebar.)
We're going to need a refresher on some Brazilian titanosaurs before we get into the new stuff. This all goes back to Llewellyn Ivor Price's titanosaur material from Peirópolis. A quarry there ("Caieira" or "Ponto 1") yielded titanosaur specimens that included four significant series of vertebrae:
- Series A (MCT 1487-R; Museu de Ciências da Terra, Rio de Janeiro), 12 cervicals and 3 anterior dorsals. This specimen is now thought to represent Uberabatitan or something very similar (Silva Junior et al. 2019);
- Series B (MCT 1488-R), 5 cervicals, 10 dorsals, a sacrum, and ilium. This specimen is the holotype of Trigonosaurus pricei (Campos et al. 2005).
- Series C (MCT 1490-R), the last sacral, the first 18 caudals, and chevrons. This specimen is the holotype of Baurutitan britoi (Kellner et al. 2005).
- MCT 1719-R, 10 caudals. This specimen was designated the paratype of T. pricei (Campos et al. 2005). Although they are sometimes represented as part of Series B (e.g., Powell 1987, 2003), the caudals were not found in association with it (and were not found articulated with each other, for that matter); therefore, Campos et al. (2005) kept them separate from Series B, while noting that they were appropriately sized to belong to it.
|Anterior caudals of MCT 1719-R, which (spoiler) becomes the holotype of Caieiria allocaudata. Figure 21 from Silva Junior et al. (2022), which see for full caption. CC BY 4.0.|
If you've read practically any other post in the "YFTT" series, you are of course not surprised that there are multiple taxa at this quarry, but how many? For this we turn to the Peirópolis Titanosaur Transitive Property (PTTP). For the series with overlapping elements, Series A is pretty clearly not the same taxon as Series B, and Series C is not the same taxon as MCT 1719-R. If MCT 1719-R is the same taxon as Series B, then this taxon is not the same as Series C. That's as much as we can get out of the PTTP for the Caieira quarry: there is nothing directly comparable between Series A and Series C or MCT 1719-R, or Series B and MCT 1719-R, and Series B and Series C have only one point of overlap, the last sacral.
We always talk about needing more material. (Sometimes as an excuse, sometimes as a whine, sometimes more wistfully.) In this case, it turns out that there *is* more material, from the "Rodovia" quarry a few kilometers to the southeast in the same geological unit. Forty-four associated bones potentially representing one individual (yes, famous last words for titanosaur research) were excavated, plus a larger humerus regarded as belonging to something else. The haul included four cervicals, a cervical rib, six dorsals and a dorsal neural spine, four rib fragments, ten caudals, eight chevrons, right scapula and coracoid, right sternal plate, right humerus, a fragment of a left humerus, a right first metacarpal, a right and partial left ischium, and two left metatarsals. When studied, Silva Junior et al. (2022) found something interesting: the presacral vertebrae look like Trigonosaurus and the caudals look like Baurutitan. This gives us a few options, more if we stretch credulity:
- Baurutitan and Trigonosaurus (holotype only) are different ends of the same taxon.
- The material represents just one of the two (Baurutitan if we give Trigonosaurus MCT 1719-R), with resemblances to the other being coincidental.
- The material, cleverly mimicking one individual, actually represents two taxa and Rodovia, like Caieira, has produced fossils of the presacral verts of a Trigonosaurus and the tail of a Baurutitan.
- The Rodovia material represents a hitherto unsuspected titanosaur from the same formation as Baurutitan and Trigonosaurus that happens to have had presacral vertebrae strongly resembling Trigonosaurus and caudals strongly resembling Baurutitan.
Silva Junior et al. (2022) favored option 1, noting the association of the Rodovia material and the lack of evidence that MCT 1719-R indeed belongs to Series B. (I like their reasoning, but I do wish they'd spent a little longer on the single point of Series B/Series C overlap, the last sacral. There *are* some differences, most obviously in articulation: Series B's last sacral has a strongly convex articular surface for the tail, whereas Series C is the opposite, and the first caudal is biconvex. Are we proposing that one individual had the ball attach to the last sacral and the other had the ball attach to the first caudal, more or less?) There are several implications arising from their choice:
- One of the two names has to go, and although it's close (both B. britoi and T. pricei were published in the same volume), B. britoi wins by custom of page priority. (Which is a minor shame, because I liked Trigonosaurus as a name);
- B. britoi figuratively woke up on November 15, 2022 as one of the best-represented titanosaurs, augmented by Series B and the Rodovia material;
- The inclusion of postcrania in the Rodovia material gives the possibility of assigning some of postcrania at Caieira to B. britoi (or, alternatively, disallowing some);
- All these years we've accidentally been coding B. britoi as two taxa in phylogenies, one of which is actually chimeric ("T. pricei" plus somebody else's tail);
- MCT 1719-R needs somewhere else to go, because it is quite distinct from the tail of B. britoi.
This last bullet point is resolved by Silva Junior et al. (2022) with the new name Caieiria allocaudata.
Genus and Species: "Caieiria" refers to the site, and "allocaudata" is derived from the Greek word for "strange" and the Latin word for "tail" (Silva Junior et al. 2022), giving us something like "strange tail from Caieira".
Citation: Silva Junior, J. C. G, A. G. Martinelli, T. S. Marinho, J. I. da Silva, and M. C. Langer. 2022. New specimens of Baurutitan britoi and a taxonomic reassessment of the titanosaur dinosaur fauna (Sauropoda) from the Serra da Galga Formation (Late Cretaceous) of Brazil. PeerJ 10:e14333. doi:10.7717/peerj.14333.
Stratigraphy and Geography: C. allocaudata comes from the Serra da Galga Formation at the Caieira quarry a few kilometers north of Peirópolis in Minas Gerais State, Brazil (Silva Junior et al. 2022).
Holotype: MCT 1719-R, a group of ten anterior to middle caudals (Silva Junior et al. 2022).
We already spent some time with MCT 1719-R in the Trigonosaurus entry, so suffice it to say that these caudals are quite different from B. britoi's, most obviously in the neural spines. For C. allocaudata, the neural spines point slightly anteriorly or are vertical, whereas in B. britoi they point posteriorly. Despite this difference in polarity, both C. allocaudata and newly augmented B. britoi are found to be aeolosaurs (Silva Junior et al. 2022), a popular career choice among Brazilian titanosaurs.
|Middle caudals of MCT 1719-R (Caieiria allocaudata). Figure 22 in Silva Junior et al. (2022), which see for full caption. CC BY 4.0.|
Campos, D. d. A., A. W. A. Kellner, R. J. Bertini, and R. M. Santucci. 2005. On a titanosaurid (Dinosauria, Sauropoda) vertebral column from the Bauru Group, Late Cretaceous of Brazil. Arquivos do Museu Nacional, Rio de Janeiro 63(3):565–593.
Kellner, A. W. A., D. d. A. Campos, and M. N. F. Trotta. 2005. Description of a titanosaurid caudal series from the Bauru Group, Late Cretaceous of Brazil. Arquivos do Museu Nacional, Rio de Janeiro 63(3):529–564.
Powell, J. E. 1987. Morfología del esqueleto axial de los dinosaurios titanosauridos (Saurischia, Sauropoda) del Estado de Minas Gerais, Brasil. Anais do X Congress Brasileiro de Paleontologia, Rio de Janeiro:155–171.
Powell, J. E. 2003. Revision of South American titanosaurid dinosaurs: palaeobiological, palaeobiogeographical, and phylogenetic aspects. Records of the Queen Victoria Museum 111.
Silva Junior, J. C. G., T. S. Marinho, A. G. Martinelli, and M. C. Langer.
2019. Osteology and systematics of Uberabatitan ribeiroi (Dinosauria;
Sauropoda): a Late Cretaceous titanosaur from Minas Gerais, Brazil. Zootaxa
Silva Junior, J. C. G, A. G. Martinelli, T. S. Marinho, J. I. da Silva, and M. C. Langer. 2022. New specimens of Baurutitan britoi and a taxonomic reassessment of the titanosaur dinosaur fauna (Sauropoda) from the Serra da Galga Formation (Late Cretaceous) of Brazil. PeerJ 10:e14333. doi:10.7717/peerj.14333.