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:
Aeolosaurus rionegrinusAeolosaurus 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 colhuehuapensisAeolosaurus 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 maximusThe 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 this 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 Lago Colhué Huapi Formation 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.
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