Patagotitan mayorumHere comes Patagotitan mayorum, here to save us all from Argentinosaurus huinculensis as the biggest titanosaur, only it doesn't quite pull it off (see also Paul 2019). Not that it doesn't give a darn good performance, though, as anyone who has seen the skeletal mounts at the American Museum of Natural History and Field Museum of Natural History can relate. These are based in large part on actual Patagotitan material. In contrast, the skeletal mount of A. huinculensis is mostly extrapolated from other titanosaurs out of necessity, so if you want to see a super-titanosaur in its proper trappings, P. mayorum is your best bet.
|Here it is filling out the Field Museum, from Wikimedia Commons (photo by Zissoudisctrucker). CC-BY-4.0.|
P. mayorum made its grand entrance in 2017, but of course the process of discovery and description began some time before. As described in the supplementary information for Carballido et al. (2017), the first fossils were found by Aurelio Hernandez on "La Flecha" Farm in 2010. The Museo Paleontológico Egidio Feruglio (MPEF) first investigated in 2012 and excavated seven times between January 2013 and February 2015, collecting almost 130 sauropod bones and 57 theropod teeth. The collected sauropod bones are all attributed to P. mayorum and were obtained from three horizons at the same quarry, with more sauropod specimens found nearby but not collected at the time of description. The lowest horizon (FLV1) yielded one associated specimen (MPEF-PV3399) and isolated bones of at least two more slightly smaller individuals. The second horizon (FLV2) is 1 m (3 ft) above FLV1 and produced only a few isolated specimens. The third horizon (FLV3) begins 0.4 m (1.3 ft) above FLV2 and yielded the holotype (MPEF-PV 3400) and scattered bones of at least one more individual. Taphonomically, the site is interpreted as low-energy, compared to the floodplain of a meandering stream or river, with less flow energy than needed to move large bones. The bones have varying degrees of association and states of preservation, suggesting at least some of them sat out for a while. Geologically, the quarry is at the top of the Cerro Castaño Member of the Cerro Barcino Formation, just below the base of the Las Plumas Member. Detrital zircons indicate a maximum age of 101.62 ± 0.18 Ma for a level between FLV1 and FLV2, suggesting a latest Albian age (Carballido et al. 2017).
The genus name "Patagotitan" refers to Patagonia, and the species name honors the Mayo family, owners of "La Flecha", for their hospitality, giving something like "the Mayo family's Patagonian titan". As mentioned, the holotype is MPEF-PV 3400, which consists of three cervical vertebrae, seven dorsals, six anterior caudals, dorsal ribs, three chevrons, both sternal plates, the right scapulocoracoid, both pubic bones, and both femora. The other specimens from the quarry are regarded as paratypes, and add more cervicals, humeri, forearm bones, a fibula, ischia, and more caudals. Most of the sections of the skeleton are represented by something, with the exception of the skull, hands, feet, ilium, and sacrum. Interestingly, in light of the Argentinosaurus hyposphene–hypantrum controversy, Patagotitan has an H–H, but only between the third and fourth dorsals. This is about where the shoulders would brace against the body, so this could a structural reinforcement. The dorsal neural spines are relatively tall and vertical, compared to the shorter and less vertical spines of other super-titanosaurs. The anterior caudals have unusual neural arches, with high transverse processes and neural spines that are both notably tall and broad, suggesting a lot of real estate for muscle attachment (Carballido et al. 2017). Despite its size, P. mayorum did not have especially robust limb bones; in fact, its femur was relatively slender (González Riga et al. 2019). (I will spare us another use of the humerus comparison figure.)
Just how big was it? Carballido et al. (2017) estimated a mass of 69 metric tons (76 US tons) for the holotype, while Paul (2019) produced a range of 50 to 55 metric tons (55 to 61 US tons). The longest femur is a healthy 238 cm long (7.80 ft) (Carballido et al. 2017). Carballido et al. did not give an overall length, but for what it's worth, scaling from their Figure 1 indicates they had in mind an animal about 38 m long (125 ft) (and the femur seems to line up within the error of pixels). Histological analyses of the holotype and other specimens indicate that their growth was slowing but had not stopped (Carballido et al. 2017), so there's a little room to pack on a ton or two.
Carballido et al. (2017) found P. mayorum to be a lognkosaurian, fittingly enough the sister taxon to Argentinosaurus huinculensis. This is carried through in practically every other analysis, except in the variable-rates tip dating Bayesian analysis of Gorscak and O'Connor (2019), where it ends up in a sort of middle-of-the-titanosaur-pack position.
|Or perhaps you may prefer it looming over puny humans in a dark and mysterious setting at the AMNH? Photo from Wikimedia Commons (photo by D. Benjamin Miller, modified and lightened by MathKnight). CC-BY-4.0.|
Pellegrinisaurus powelliPellegrinisaurus powelli would like you to know that it's also a big sauropod, even if you don't think about it very often. Novas (2009) included an estimate of 20 to 25 m long (66 to 82 ft).
The type and only known specimen of P. powelli was discovered and excavated in 1975 by a team from the Museo Provincial Cipolletti "Carlos Ameghino" (MPCA) under Roberto Abel (Powell 1986; Salgado 1996). It was then briefly described by Powell in 1986 as cf. Epachthosaurus sp. After another decade, it became a new genus and species in Salgado (1996). The discovery locality is south of Lago Pellegrini in northern Río Negro Province, Argentina, northeast of Cinco Saltos (Salgado 1996). Salgado (1996) described the horizon as the lower member of the Allen Formation, which is now known as the Anacleto Formation (Novas 2009). Our other Anacleto titanosaurs have been Antarctosaurus wichmannianus, Barrosasaurus casamiquelai, Laplatasaurus araukanicus, Narambuenatitan palomoi, and Neuquensaurus australis (potentially including "Titanosaurus" robustus and probably at least part of Loricosaurus scutatus), with Pitekunsaurus macayai yet to be featured, making this a rather crowded place in terms of titanosaurs. (Whether they all are distinct has yet to be determined.)
You can probably guess what Pellegrinisaurus powelli means; a rough translation is "Jaime Powell's Lago Pellegrini lizard". The type specimen is MPCA 1500, which includes four dorsal centra, 26 incomplete caudals, and a partial right femur. The dorsals are probably from the posterior part of the back (think "lumbar" if dinosaurs had lumbar regions) and their centra are significantly wider than tall (about twice as much, apparently a natural feature and not due to crushing). The neural arches of the caudals are set quite low, and the neural spines are quite low and long going back; in fact, by about the 15th caudal the neural spine is so low and extended so far back that it become an additional point of articulation for the prezygapophyses of the next vertebra back, restricting movement.
In terms of placement, three options have shown up in recent years: 1) in the vicinity of Epachthosaurus as a basal titanosaur (Bandeira et al. 2016); 2) the sister taxon to Epachthosaurus and a much more derived titanosaur (majority-rule consensus result in Gorscak and O'Connor 2019); and a member of a clade which also embraces Alamosaurus, Baurutitan, and Dreadnoughtus (Gorscak et al. 2017; Sallam et al. 2018; other results in Gorscak and O'Connor 2019).
Petrobrasaurus puestohernandeziSometimes it's obvious why a particular dinosaur species hasn't attracted much attention; maybe it's only known from a single bone, for example. In other cases, it's not as easy to see. From the amount of press Petrobrasaurus puestohernandezi has gathered (it does not appear to have made it to a single published phylogenetic analysis, for example [correction, 2020/04/19: one, one of the two analyses included in the 2013 original description of Overosaurus paradasorum, randomly enough; see comments]), you might suspect it's based on a single metacarpal or something like that. Nope—there's actually a fair part of an associated skeleton, certainly more than the average titanosaur.
First things first. The type and only known specimen of P. puestohernandezi was recovered from the middle-upper Plottier Formation in 2006–2007. The site is in the Puesto Hernández oil field of the Petrobras oil company, about 25 km (16 mi) northwest of Rincón de los Sauces, northern Neuquén, Patagonia, Argentina. Rocks of the Plottier Formation here are alternating beds of white quartz-rich sandstone and reddish mudstone deposited in a fluvial system. P. puestohernandezi was found at the base of one of the mudstone beds, in an area of about 60 square meters (650 square feet). The bones are all appropriate for one individual and appear to have undergone little transport, but the presence of five theropod tooth crowns suggests scavenging (Filippi et al. 2011).
You can probably figure out the meaning of the name from the previous paragraph; the genus name refers to Petrobras and the species name to the locality, producing something like "Petrobras lizard from the Puesto Hernández oil field" (-ensis or -icus would have made more sense than -i, I think, but you get the idea). The type specimen is a series of bones cataloged under MAU-Pv-PH-449/1 through 37 (Museo Argentino Urquiza, Paleontología de Vertebrados, Puesto Hernández collection). They include a couple of teeth, a partial cervical, fragments of cervical ribs, parts of five dorsals, dorsal ribs, six caudals, chevron fragments, both sternal plates, the right humerus, four metacarpals, a fragment of an ilium, the left pubis, both femora, parts of both tibiae, and fragments (Filippi et al. 2011).
|This is better than it gets for most titanosaurs, if a bit light on the all-important vertebrae. The scale is 1 m for the skeleton and 1 cm for the teeth in the inset. Figure 3 in Filippi et al. (2011). CC-BY-4.0.|
Together, these bones define a titanosaur of respectable but not overwhelming size, with the marginally longer left femur at 1575 mm long (62.01 in) (comparable to Andesaurus) and the humerus 1200 mm long (47.24 in) (Filippi et al. 2011). It was not one of the more robust titanosaurs; González Riga et al. (2019) described its humerus, femur, and pubis as relatively slender. The teeth are of the slender "pencil-like" morph (Filippi et al. 2011). Filippi et al. (2011) mentioned running the species through an existing analysis but receiving a polytomy at the base of Eutitanosauria. They opted not try to place P. puestohernandezi more firmly, but noted similarities with Mendozasaurus neguyelap, making it a potential lognkosaurian.
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