Sunday, July 15, 2018

Your Friends The Titanosaurs, part 2: Aeolosaurus

Aeolosaurus is one of those dinosaurs that is referenced fairly often in the literature, but has not left a strong impression with non-specialists, kind of like a character actor who's appeared in dozens of movies and TV shows over the years. The name rings a bell, but it's hard to recall much detail. It's easily the least familiar dinosaur to have both a namesake clade (Aeolosauridae/Aeolosaurinae/Aeolosaurini, depending on your taste, with the last being the most commonly used) and three valid species. It's not Aeolosaurus's fault, after all, unless you want to blame it for its habit of bequeathing only bits of tails to posterity. If you saw one amble by, you would definitely remember it.

However, there are good reasons why Aeolosaurus keeps on making cameo appearances: it and its closest relatives have very distinctive caudal vertebrae, and these vertebrae are fairly common in rocks covering the last 15+ million years of Argentina and southern Brazil. Because of my caution regarding titanosaur divisions, I haven't added a formal Aeolosaurini to my own files, but there certainly appears to be a group of South American titanosaurs with distinctive Aeolosaurus-like caudal vertebrae. For the purposes of this post I'm happy to refer to them as aeolosaurinids. I'm not going to get into detailed diagnoses, but I *will* briefly describe these caudals. If nothing else, they're the thing to remember about Aeolosaurus and aeolosaurinids:

In titanosauriformes, the neural arches of the caudal vertebrae have a tendency to creep up on the anterior part of the centra, rather than being centered. Aeolosaurinids take this even farther, with the articulating processes, the prezygapophyses and postzygapophyses, swept forward by the general excitement and the neural spines sometimes directed anteriorly as well. In Aeolosaurus this can be exaggerated to the point that the postzygapophyses are as far forward as the anterior margin of the centrum (Martinelli et al. 2011), which means that the prezygapophyses have to be stretched over nearly the entire preceding centrum to reach their articulations with the postzygapophyses (the exact positions of the processes vary along the tail; Santucci and de Arruda-Campos 2011). You might think of the prezygapophyses as something like stereotypical Frankenstein arms or sleepwalker arms, sticking way out in front of the rest of a vertebra. The figure below probably does a much better job of demonstrating:

Caudals from several aeolosaurinids, from Martinelli et al. (2011), showing how the neural arch and its processes are shifted to the anterior end of the centrum. It also shows the procoelous nature of titanosaurian caudals, a style of ball-and-socket articulation with the socket in front and ball in back. In Aeolosaurus this is not a perfect ball, but skewed dorsally. Anterior is left and posterior is right, in case you need the orientation. "MPMA\without number" is actually part of the holotype of Aeolosaurus maximus, so all three named species are supposedly included, but the specimen labeled here as "MPMA\without number" actually appears to be CPP 248 (supposedly C) per an earlier figure in the publication. Could C and D be mixed up?

Aeolosaurus rionegrinus

Aeolosaurus rionegrinus, which starts the whole thing, kicked around in the abstract-and-dissertation circuit for a couple of years before formally appearing in Powell (1987). Not having Powell's publication at hand, I am going off of Glut (1997) and Santucci and de Arruda-Campos (2011) for this description of the type specimen and locality. The holotype and only known specimen is MJG-R 1 (MJG=Museo "Jorge Gerhold"), a partial postcranial skeleton including seven caudals, parts of both scapulae, both humeri, ulnae, and radii, five metacarpals, both ischia, the right fibula and tibia, an astragalus, and bits and pieces. The girdle elements are robust, like in Saltasaurus. This specimen was collected from the Angostura Colorada Formation of Casa de Piedra in Río Negro Province, Argentina. The name Aeolosaurus is a reference to windy Patagonia, "Aeolos" being a mythological Greek "keeper of the winds". (By the way, when you say "Aeolosaurus", you don't pronounce the "A"; same thing as Aegyptosaurus, come to think of it.) "Rionegrinus" refers to Río Negro Province.

Aeolosaurus rionegrinus, or Aeolosaurus at all for that matter, did not catch on immediately. The species is mentioned briefly in at least the 1992 paperback edition of The Dinosauria, albeit with no paragraph of discussion (McIntosh 1990), but inexplicably the index is under the impression that it's a stegosaurian. If you find it on page 453, let me know. Powell produced a second, more detailed description in 2003.

Powell (1987, 2003) also described a second specimen consisting of 15 articulated caudals, MACN-RN 147 (Museo Argentio de Ciencias Naturales Bernardino Rivadavia), as Aeolosaurus rionegrinus?, from the Los Alamitos Formation of Patagonia. This specimen is now generally regarded as something other than Aeolosaurus (Salgado and Coria 1993; Salgado et al. 1997; Juárez Valieri and Calvo 2011).

Aeolosaurus colhuehuapensis

Aeolosaurus colhuehuapensis is not as hard to spell as it looks.

No, really, just sound out "colhuehuapensis" to yourself a few times. It looks more intimidating than it is. (Same thing for Opisthocoelicaudia, which is not nearly as difficult as its type species, skarzynskii, where you have to remember "y"s versus "i"s and how many "i"s to put at the end.)

A. colhuehuapensis was named in 2007 by Casal et al. for UNPSJB-PV 959/1 to 959/27 (vertebrate paleontology collections of Universidad Nacional de la Patagonia San Juan Bosco), 21 articulated caudals and associated chevrons collected at a temporarily emergent island in the southeast part of Lake Colhué Huapi, which neatly explains the name. The lake is located in the Sarmiento Department of Chubut Province, Argentina. The vertebrae are unfortunately somewhat eroded. Originally the find was attributed to the upper member of the Bajo Barreal Formation, but Casal et al. (2014) reevaluated the stratigraphy as representing an unnamed unit described informally as the "strata of Lake Colhé Huapi" (since formalized as the Lago Colhué Huapi Formation; Casal et al. 2015). Casal et al. (2014) also described the taphonomy of the specimen, interpreting the depositional setting as fluvial overbank, and commented on an opisthotonic curve to the articulated tail.

A view of the lake and surrounding exposures; photo taken by Gonce, found on Wikimedia Commons.

Aeolosaurus maximus

The most recent addition to the Aeolosaurus stable is A. maximus, named in 2011 by Santucci and de Arruda-Campos. It's also notable as the first species of Aeolosaurus named from Brazil, although by no means the first fossil from Brazil attributed to Aeolosaurus (see "Aeolosaurus sp." below). It is based on a partial associated skeleton collected in 1997 and 1998 by staff of the Museu de Paleontologia de Monte Alto, mentioned as early as Santucci and Bertini (2001). The skeleton, MPMA 12-0001-97, includes two partial posterior cervicals, fragments of several dorsals, parts of nine caudals, seven partial cervical ribs, twelve partial dorsal ribs, eight chevrons, a fragmentary scapula and arm bones, the left and partial right femur, the left ischium, and fragments. This specimen was found in sandstone at the top of the Adamantina Formation 12 km (7.5 mi) southwest of Monte Alto in São Paulo State. Croc and theropod teeth were found with the titanosaur, but no tooth marks were observed (Santucci and de Arruda-Campos 2011). Brusatte et al. (2017) mentioned that some fossils previously reported from the Adamantina Formation may have come from the Presidente Prudente Formation, which overlies the lower Adamantina and interfingers with the upper Adamantina, but it looks like we're safe with A. maximus, which was found some distance from the areas mapped as the Presidente Prudente in Brusatte et al.'s map.

Part of the future holotype of Aeolosaurus maximus (A), plus indeterminate aeolosaurinid vertebrae (CPP 248 is clearly the same as D in the first figure used in the post). From Martinelli et al. (2011).

The type individual was on the order of 14 to 15 m long (46 to 49 ft) (Brusatte et al. 2017), which may not strike you as "maximus" for a sauropod, but Aeolosaurus seems to have been among the wing of smaller titanosaurs; Novas (2009) estimated Aeolosaurus as about 10 m (33 ft long). The complete femur measures 1.55 m (5.09 ft) long, but is slender for its size. "Maximus" is relative.

Of course, with dinosaurs there is a particular risk that the species you described as belonging to a known genus will later wind up in its own genus, and A. maximus is already a decent potential candidate for future removal from Aeolosaurus. Several years before it was described, Martinelli et al. (2011) regarded the caudal vertebrae of the type specimen ("MPMA/without number") as belonging to an indeterminate aeolosaurinid (the other parts were not then described). The authors noted that the caudals were more like those of other Brazilian aeolosaurinids than Aeolosaurus, a distinction observed quantitatively in Filippi et al. (2013): A. maximus plots with the great unwashed masses of aeolosaurinids rather than A. rionegrinus and A. colhuehuapensis in some details of placement of vertebral features. Bandeira et al. (2016), in their description of Austroposeidon magnificus, found A. maximus to plot rather distantly from the other two Aeolosaurus species in their phylogenetic analysis, and therefore referred to it as "A." maximus throughout the paper. Frankly, I would not be surprised to see A. maximus under a different genus sometime in the next 10–20 years.

Aeolosaurus sp.

Normally, I wouldn't have a section for undetermined finds, but there's been a lot more Aeolosaurus sp. floating around than Aeolosaurus of the three named species. Aeolosaurus sp. has proven very popular as an assignment for titanosaur fossils in Argentina and Brazil, primarily Aeolosaurus-type caudal vertebrae. However, as time goes on and more aeolosaurinids are described, the popularity of Aeolosaurus sp. has declined in favor of the less-exclusive "Aeolosaurini indet." or something similar, as in Martinelli et al. (2011) and Filippi et al. (2013).

So far, we've seen three species from three specimens, representing three formations, three provinces or states, and two nations: A. rionegrinus from the Angostura Colorada Formation of Río Negro Province, Argentina; A. colhuehuapensis from the "strata of Lake Colhé Huapi" of Chubut Province, Argentina; and A. maximus from the Adamantina Formation of São Paulo State, Brazil. South American Cretaceous formations have historically been difficult to firmly date, but these units are regarded as Campanian–Maastrichtian in age, or between about 84 and 66 million years old. In fact, Aeolosaurus as a genus, or aeolosaurinids in general, may be a biostratigraphic marker for Campanian and Maastrichtian formations in Argentina and Brazil (Santucci and de Arruda-Campos 2011; Brusatte et al. 2017). With Aeolosaurus sp., we have the potential to expand the known stratigraphic and geographic range of the genus, as well as fill in other bits of the anatomy. What do we have?

Aside from the Los Alamitos Formation Aeolosaurus rionegrinus? dealt with previously, the Los Alamitos Formation of Río Negro Province has yielded MPCA 27100 (Museo Provincial de Cipolletti), which includes four caudals, two partial sternal plates, several limb bones from the left side of the body (humerus, femur, tibia, fibula, astragalus, and four metatarsals), and two metacarpals. As with A. rionegrinus, the limb bones are robust (Salgado et al. 1997).

There is a fair amount of A. sp. material from the Salitral Moreno locality in the Allen Formation of Río Negro Province, under several MPCA collection numbers (Salgado and Coria 1993; García and Salgado 2013). In 1993 these included MPCA 27174, five caudals, a right ulna, a metacarpal, a left pubis, and a right ischium; MPCA 27175, a right ulna and radius; and MPCA 27176 and 27177, osteoderms (Salgado and Coria 1993). By 2013 MPCA-Pv 27175 was a left ulna only, with the radius apparently going to MPCA-Pv 27174; there were also MPCA-Pv 27178 (metatarsal I), MPCA-Pv 27179 (chevron), and MPCA-Pv 27180 (another left ulna); and, bizarrely, without comment MPCA-Pv 27176 was now a left humerus and MPCA-Pv 27177 was now a left femur, and the figures show that neither could be remotely mistaken for armor. (Just to confuse things further, the same femur is identified as MPCA-Pv 27177 and MPCA-Pv 27174 in different figure captions.) Meanwhile, MPCA-Pv 27176 the osteoderm goes on its way in the literature as Aeolosaurus sp. armor (Salgado 2003; D'Emic et al. 2009; Cerda et al. 2015; Zurriaguz 2017). Perhaps some numbers got mixed up in García and Salgado 2013?

Finally, there are several reports from the Adamantina and Marília formations of Brazil, but they have been contentious. First reported by Santucci and Bertini (2001), Brazilian A. sp. records are primarily caudal vertebrae. Candeira (2010) accepted the occurrences as A. sp., but a more detailed examination by Martinelli et al. (2011) found several errors and interpreted none of the putative Aeolosaurus fossils from Brazil known at that time as Aeolosaurus, instead assessing them as indeterminate aeolosaurinids or titanosaurs (including the future type of A. maximus), or distinct named genera and species. Brazilian Aeolosaurus also gets into the argument that Gondwanatitan faustoi is a species of Aeolosaurus. This hypothesis appears to be defunct, but we can go over it in more detail when we get to that species.

References


Bandeira, K. L. N., F. Medeiros Simbras, E. Batista Machado, D. de Almeida Campos, G. R. Oliveira, and A. W. A. Kellner. 2016. A new giant Titanosauria (Dinosauria: Sauropoda) from the Late Cretaceous Bauru Group, Brazil. PLoS ONE 11(10):e0163373.

Brusatte, S. L. C. R. A. Candeiro, and F. M. Simbras. 2017. The last dinosaurs of Brazil: the Bauru Group and its implications for the end-Cretaceous mass extinction. Anais de Academia Brasileira de Ciências 89(3):1465–1485.

Candeiro, C. R. A. 2010. Record of the genus Aeolosaurus (Sauropoda, Titanosauria) in the Late Cretaceous of South America: paleogeographic implications. Estudios Geologicos 66(2):243–253.

Casal, G., R. D. Martinez, M. Luna, J. C. Sciutto, and M. C. Lamanna. 2007. Aeolosaurus colhuehuapensis sp. nov. (Sauropoda, Titanosauria) de la Formacion Bajo Barreal, Cretacicosuperior de Argentina. Revista Brasileira de Paleontologia 10(1):53–62.

Casal, G. A., L. M. Ibiricu, J. O. Allard, R. D. Martínez, M. Luna, and B. J. González Riga. 2014. Tafonomía del titanosaurio Aeolosaurus colhuehuapensis, Cretácico Superior, Patagonia central, Argentina: un ejemplo de preservación en facies fluviales de desbordamiento [Taphonomy of the titanosaur Aeolosaurus colhuehuapensis, Upper Cretaceous, central Patagonia, Argentina: an example of preservation in overbank fluvial facies]. Revista Mexicana de Ciencias Geológicas 31(2):163–173.

Casal, G. A., J. O. Allard, and N. Foix. 2015. Análisis estratigráfico y paleontológico de afloramientos del Cretácico Superior en la cuenca del Golfo San Jorge: propuesta de nueva unidad litoestratigráfica para el Grupo Chubut. Revista de la Asociación Geológica Argentina 72:81–99.

Cerda, A. I., R. A. García, J. E. Powell, and O. Lopez. 2015. Morphology, microanatomy and histology of titanosaur (Dinosauria, Sauropoda) osteoderms from the Upper Cretaceous of Patagonia. Journal of Vertebrate Paleontology 35(1):e905791.

D'Emic, M. D, J. A. Wilson, and S. Chatterjee. 2009. The titanosaur (Dinosauria: Sauropoda) osteoderm record review and first definitive specimen from India. Journal of Vertebrate Paleontology 29(1):165–177.

Filippi, L. S., A. G. Martinelli, and A. C. Garrido. 2013. Registro de un dinosaurio Aeolosaurini (Sauropoda, Titanosauria) en el Cretácico Superior (Formación Plottier) del norte de la provincia de Neuquén, Argentina, y comentarios sobre los Aeolosaurini Sudamericanos [Record of an Aeolosaurini dinosaur (Sauropoda, Titanosauria) in the Upper Cretaceous (Plottier Formation) of northern Neuquén Province, Argentina, and comments on the South American Aeolosaurini]. Revista Brasileira de Paleontologia 16(1):147–156.

García, R. A., and L. Salgado. 2013. The titanosaur sauropods from the late Campanian-early Maastrichtian Allen Formation of Salitral Moreno, Río Negro, Argentina. Acta Palaeontologica Polonica 58(2):269–284.

Glut, D. F. 1997. Aeolosaurus. Pages 84–86 in Dinosaurs: The Encyclopedia. McFarland & Company, Inc., Jefferson, North Carolina.

Juárez Valieri, R. D., and J. O. Calvo. 2011. Revision of MUCPv 204, a Senonian basal titanosaur from northern Patagonia. Paleontología y Dinosaurios y desde América Latina. Anales del III Congreso Latinoamericano de Paleontología: 143–152.

Martinelli, A. G., D. Riff, and R. P. Lopes. 2011. Discussion about the occurrence of the genus Aeolosaurus Powell 1987 (Dinosauria, Titanosauria) in the Upper Cretaceous of Brazil. Gaea 7(1):34–40.

McIntosh, J. S. 1990. Sauropoda. Pages 345–401 in D. B. Weishampel, P. Dodson, and H. Osmólska, editors. The Dinosauria. University of California Press, Berkeley, California.

Novas, F. E. 2009. The Age of Dinosaurs in South America. Indiana University Press, Bloomington and Indianapolis, Indiana.

Powell, J. E. 1987. The Late Cretaceous fauna of Los Alamitos, Patagonia, Argentina. Part VI—the titanosaurids. Revista del Museo Argentino de Ciencias Naturales 3(3):147–153.

Powell, J. E. 2003. Revision of South American titanosaurid dinosaurs: palaeobiological, palaeobiogeographical, and phylogenetic aspects. Records of the Queen Victoria Museum 111.

Salgado, L. 2003. Considerations on the bony plates assigned to titanosaurs (Dinosauria, Sauropoda). Ameghiniana 40:441–456.

Salgado, L., and R. A. Coria. 1993. El género Aeolosaurus (Sauropoda, Titanosauridae) en la Formación Allen (Campaniano-Maastrichtiano) de la provincia de Río Negro, Argentina. Ameghiniana 30:119–128.

Salgado, L., R. A. Coria, and J. O. Calvo. 1997. Presencia del género Aeolosaurus (Sauropoda, Titanosauridae) en la Formación Los Alamitos, Cretácico Superior de la provincia de Río Negro, Argentina. Geociências 2:44–49.

Santucci, R. M., and R. J. Bertini. 2001. Distribuição paleogeográfica e biocronológica dos titanossauros (Saurischia, Sauropoda) do Grupo Bauru, Cretáceo Superior do sudeste brasileiro. Revista Brasileira de Geociências 31(3):307–314.

Santucci, R. M., and A. C. de Arruda-Campos. 2011. A new sauropod (Macronaria, Titanosauria) from the Adamantina Formation, Bauru Group, Upper Cretaceous of Brazil and the phylogenetic relationships of Aeolosaurini. Zootaxa 3085:1–33.

Zurriaguz, V. 2017. New record of titanosaurian (Dinosauria: Sauropodomorpha) osteoderms from the Upper Cretaceous of North Patagonia. Cretaceous Research 74:175–180.

7 comments:

  1. It continues to be good to see titanosaurs getting this kind of love, they certainly need it. Aeolosaurus in particular--I wonder what those freakish caudal vertebrae were for. I realize now that I've been pronouncing Aeolosaurus wrong, too, so I guess I learned something today.

    Regarding the Bandeira et al. paper which found Aeolosaurus maximus to not clade with Aeolosaurus proper: that phylogenetic analysis is a strong contender for the worst one I've ever seen. Unless I'm crazy, there are several taxa scored incorrectly for more than 50% of the characters they can be scored for! A. maximus itself is, at a glance, clearly scored incorrectly for some characters and is scored for several things that aren't even preserved (e.g. the sacrum and tibia)!

    That said, A. maximus is definitely the outlier in Aeolosaurus, so despite doubting Bandeira et al.'s assessment, I wouldn't be surprised if it got split out soon too. A. colhuehuapensis is already more closely related to A. rionegrinus than A. maximus is.

    ReplyDelete
    Replies
    1. Thank you! Oddly, it seems like errors of specimen numbering are also disconcertingly common in the literature for Aeolosaurus, such as Martinelli et al. (2011)'s misidentified vertebrae (the same article that devotes about a column of text to the errors in Candeiro 2010) and whatever happened with MACNPv 27176 and 27177 in García and Salgado (2013).

      Re: the caudals: seems like there might be a thesis there—what are the biomechanical implications of aeolosaurinid caudal specializations?

      Delete
    2. There probably is a thesis there.

      One thing that just occured to me is that aeolosaurs aren't the only titanosaurs with weirdly displaced zygapophyses somewhere on their bodies. Saltasaurus cervical vertebrae have prezygs that don't extend as far forward as in other titanosaurs and long postzygs--pretty much like some sort of mirror image of Aeolosaurus's caudals. I wonder if there's some connection there, like how titanosaurs have procoelous tails and opisthocoelous necks for similar mechanical reasons.

      Delete
  2. Nice article, on a genus that deserves more attention.
    MACN-RN 147 includes an amphicoelous caudal as the last preserved caudal in the series (Powell, 2003 - illustrated in Plate 6). The presence of an amphicoelous caudal vertebra may warrant this specimen's transfer to a new genus or species.

    ReplyDelete
    Replies
    1. Having just re-read Juárez Valieri and Calvo (2011), maybe 'amphicoelous' is not the best term (should be 'procoelous-opisthoplatyan'?):
      "An articulated caudal sequence assigned to Aeolosaurus rionegrinus? was recovered from Los Alamitos Formation (MACN-RN 147, Powell, 1987, 2003), late Campanian to early Maastrichtian preserves fifteen elements, all procoelous except the last vertebra, which was reported as amphicoelic, although in the terminology used here is better described as procoelous-opisthoplatyan."

      Delete
    2. Surprisingly (well, surprisingly because titanosaurs are so abundant in the LK of Argentina), there seems to be no named titanosaurs in the Los Alamitos Formation, so there's no obvious candidate to take in MACN-RN 147.

      Delete
    3. *no named titanosaur *species*, that is.

      Delete