Sunday, March 24, 2019

Your Friends The Titanosaurs, part 10: Diamantinasaurus, Dongyangosaurus, and Dreadnoughtus

For this week's post, we have two of the best represented titanosaur species, plus Dongyangosaurus sinensis, which isn't quite so well-represented but has some unusual features going for it. Our other guests are Diamantinasaurus matildae, one of a small number of Australian titanosaurs and titanosaur-like sauropods which lived close in time to the Early–Late Cretaceous boundary, and Dreadnoughtus schrani, controversial contender for the heavyweight crown.

Before we turn to this post's guests, you may be interested to know of a further twist in the story of the Balochistan titanosaurs. This isn't really the occasion to cover it in detail (I'm thinking the Isisaurus/Jainosaurus part of the alphabet), but building on the hypothesized reductions discussed in his recent work, M. Sadiq Malkani has sunk several of his titanosaur species (several items from February). The trims would leave the pre-existing Isisaurus colberti (including Sulaimanisaurus gingerichi) to join Pakisaurus balochistani, Gspsaurus pakistani (including Maojandino alami and Marisaurus jeffi), and Saraikimasoom vitakri (including Balochisaurus malkani and Nicksaurus razashahi). I. colberti and P. balochistani are described as medium to large slender forms, G. pakistani as a medium stocky form, and S. vitakri as a small stocky form.

Diamantinasaurus matildae

With Austrosaurus mckillopi playing coy about its identity as always (Poropat et al. 2017) (I think it's been classified in every major sauropod group over the years), Diamantinasaurus matildae gets the honor of being the first of the small group of middle Cretaceous Australian titanosaurs to be covered here. Although the Australian Cretaceous dinosaur scene is notable for being jam-packed with "hypsilophodont"-type dinosaurs, titanosaurs were also a significant component. (Not necessarily in the same places at the same times, though; sauropod remains have so far not been found in the "hypsilophodont" strongholds of Aptian–Albian Victoria, as noted by Poropat et al. 2015.) Titanosaurs are thought to have arrived in Australia from South America via Antarctica during the Early Cretaceous (Poropat et al. 2016).

D. matildae is known from two partial skeletons discovered in the Winton Formation of Queensland, Australia. The genus name is a reference to the Diamantina River, which runs near the type locality, and the species name "matildae" refers to Matilda of "Waltzing Matilda" (incidentally, if you're only familiar with the title of the song, "Matilda" isn't a person but a slang term for a bedroll) (Hocknull et al. 2009). The type locality is known informally as the "Matilda site" (Hocknull et al. 2009), and the type individual of D. matildae is also nicknamed "Matilda".

Diamantinasaurus matildae coming and going: left and right sides of the type individual AODF 603, clipped from Figure 2 of Hocknull et al. (2009), by T. Tischler, Australian Age of Dinosaurs Museum of Natural History. What is given as a left sternal plate is actually part of the right coracoid (Poropat et al. 2015). CC-BY-2.5.

The type individual is a little complicated. Holotype and paratype specimens are cataloged as AODF 603 (Australian Age of Dinosaurs Museum, Winton, Queensland, Australia) and are thought to represent the same individual. All in all, they encompass two incomplete dorsal verts, four sacrals, three partial cervical ribs, dorsal ribs, the right shoulder girdle, arm, and most of the hand (plus manual phalanges), the left humerus and left metacarpal I, most of the pelvis except the right ilium, and the right leg minus the foot (Poropat et al. 2016). These bones were found associated at the Matilda site, AODL 85, at Elderslie Sheep Station (Poropat et al. 2015). The same locality produced the type specimen of the theropod Australovenator wintonensis (Hocknull et al. 2009). Initially the age of the site was given as late Albian (Hocknull et al. 2009), but it has since been given as Cenomanian (Poropat et al. 2015). A second individual, AODF 836, includes the left squamosal, most of the braincase, right surangular, miscellaneous skull fragments, seven cervicals (including the atlas and axis), three dorsals, partial sacrum, dorsal ribs, the pelvis missing most of the ilia, and fragments (Poropat et al. 2016). It was found at AODL 127, the "Elliot site" (Poropat et al. 2016). AODF 836 has been used on its own in some cladograms (Poropat et al. 2016; Mannion et al. 2017; Averianov and Efimov 2018; González Riga et al. 2018), but always is found knotted up with D. matildae and another Australian titanosaur, Savannasaurus.

Anatomically, D. matildae seems to have been a fairly typical mid-sized titanosaur. The girdle bones were relatively robust (Poropat et al. 2015, 2016), and the ilium has pneumatic features, as seen in a few other titanosaur and titanosaur relatives (Poropat et al. 2015). The ulnae are particularly robust (Poropat et al. 2015). The femur length for the type individual is given as 1330 mm (52.4 in) (Hocknull et al. 2009). The type individual includes a nearly complete hand, if you do a bit of left-right mirroring. Included in this are phalanges, which show that the recent stereotype of titanosaurs lacking manual phalanges is exaggerated. Poropat et al. (2015) comment on this phenomenon and find the evidence that titanosaurs generally lacked "finger" bones to be weak, their rarity perhaps due to loss before burial. No wrist bones were found. The phalangeal formula for D. matildae is interpreted as 2-1-1-1-1, with digit I featuring the classic sauropod thumb claw (Poropat et al. 2015). Another notable feature, which has not drawn much comment, is the reported presence of gastralia ("belly ribs") (Hocknull et al. 2009; Poropat et al. 2015; but not Poropat et al. 2016), which are hardly ever reported for sauropods.

Dongyangosaurus sinensis

I can usually get hold of the original descriptions of these species one way or another, but so far Lü et al. (2008), the original description of Dongyangosaurus sinensis, has eluded me. Therefore, I've turned to the entry in Glut (2010) to make up for the shortfall. D. sinensis was reported from the Fangyan Formation at the village of Baidian, Dongyang County, Zhejiang Province, China. The Fangyan Formation is not noted for its dinosaurs at this time; in fact, outside of D. sinensis as obligatory titanosaur, I don't know of any others. This unit is considered to be of Cenomanian–Santonian age (Averianov and Sues 2017). However, it seems that the Fangyan may have been replaced by the Jinhua Formation (Xing et al. 2018; I know what the table says, but the text says "the Jinhua Formation was once regarded as Fangyan Formation" and Lü et al. 2008 is cited). The genus name refers to Dongyang County and the species refers to China, so together we get "Chinese Dongyang County lizard" or something similar, and yes, that's kind of awkward when translated. (Two geographic references in a name is probably one too many.)

D. sinensis is based on Dongyang Museum (DYM) 04888, a partial skeleton including ten dorsals, the sacrum, the first two caudals, partial ribs, both ilia, and a pubis and ischium. The bones are more or less articulated, although there's some displacement in the hip region that makes the spinal column diverge from the hips. The overall length of the type individual was estimated at around 15 m (49 ft). Lü et al. (2008) classified their new species as a basal titanosaurian similar in some ways to the noted titanosaurian non-conformist Opisthocoelicaudia. For example, both species have low divided neural spines on the dorsal vertebrae, low sacral neural spines, and simple transverse processes on the caudals. D. sinensis, though, does not have opisthocoelous caudals (actually amphicoelous), and its pubis is shorter than its ischium. Both of these traits, incidentally, are also different from the titanosaurian standard, and D. sinensis hasn't always come out as a titanosaur in phylogenetic analyses, flirting with Euhelopodidae in D'Emic (2012). D. sinensis may have also had rather intensely pneumatic dorsal vertebrae.

Imagine my surprise to find a photo of Dongyangosaurus on Wikimedia Commons. This is the better part of the holotype, although obscured somewhat by the angle. For orientation, the center of the photo is dominated by the pelvis: ilium above, pubis left, ischium right, acetabulum the dark patch between them. Dorsal and sacral vertebrae are visible behind.

As mentioned in the Baotianmansaurus henanensis post, D. sinensis and B. henanensis have a distinct tendency to show up in each other's company in phylogenetic analyses (Poropat et al. 2016; Mannion et al. 2017; Averianov and Efimov 2018; González Riga et al. 2018). D. sinensis once turned up as far out on the titanosaur tree as Saltasauridae (Mannion et al. 2013), but in the other quoted analyses it (and Baotianmansaurus) were very basal titanosaurs. Also as noted in the previous post, D. sinensis and its sidekick appear to be similar to an unnamed titanosaur from the Bissekty Formation of Uzbekistan (Averianov and Sues 2017).

Dreadnoughtus schrani

However big it actually was or wasn't, Dreadnoughtus schrani will always hold a footnote here for inspiring "On this occasion of receiving a new giant dinosaur". How big was it? If you only read the original description (Lacovara et al. 2014), the type individual had a mass of 59.3 metric tons (65.4 US tons) and a length of 26 m (85 ft). If you picked up Bates et al. (2015), it slimmed down considerably to between 22.1 and 38.3 metric tons (24.4 and 42.2 US tons), depending on the model. If you read SVPOW!, an animal on the order of 30 metric tons (33 US tons) is considered plausible, which rather neatly splits the difference in the estimates presented by Bates et al. (2015) six months before that paper was published. Going by the femur, this blog's standard unit for grasping the general size of a titanosaur, we're looking at a 191 cm (6.27 ft) thigh bone (Lacovara et al. 2014), which is big but still outclassed by titanosaurs such as "Antarctosaurus" giganteus or Patagotitan mayorum. The table of measurements in Lacovara et al. (2014) supports the general idea that D. schrani was big but not excessively so in comparison to other macronarians. On the other hand, the type individual may not have been fully grown (Lacovara et al. 2014), although it's kind of hard to say just what "fully grown" means for a dinosaur.

D. schrani is certainly among the most completely known large sauropods, and has become perhaps the most thoroughly described as well. Apart from the original description (Lacovara et al. 2014), the appendicular skeleton (Ullmann and Lacovara 2016) and dorsal vertebrae (Voegele et al. 2017) have also received their own papers.

The genus name comes from "dreadnought", Old English for "fearing nothing". It has a double meaning, in the sense of "this animal was so big as an adult it was essentially invulnerable" and as a reference to the dreadnoughts of the early 20th century. The species name "schrani" is for Adam Schran, who supported the research (Lacovara et al. 2014). Together, then, we get "Adam Schran's dreadnought".

The type specimen is MPM-PV 1156 (Museo Padre Molina, Rio Gallegos, Argentina), which includes a maxilla fragment, tooth, one cervical vert and some cervical ribs, dorsal verts and ribs, the sacrum, 32 caudals, 18 chevrons, the left shoulder girdle and arm minus the hand, both sternal plates, the pelvis, the left leg minus the foot, the right tibia, and two metatarsals and an ungual from the right foot. Paratype MPM-PV 3546, a smaller individual, includes a cervical vert, dorsal verts and ribs, sacrum, seven caudals, five chevrons, pelvis, and left femur (Lacovara et al. 2014). In other words, the majority of the skeleton is represented, although the skull, neck, hands, and feet are poorly known or altogether absent.

Dreadnoughtus schrani, strutting its stuff. Figure 2 of Lacovara et al. (2014); the torso seems to be a bit long. CC-BY-4.0.

D. schrani comes from the Cerro Fortaleza Formation, a Campanian–Maastrichtian age fluvial formation. This formation is occasionally confused with the Pari Aike or Mata Amarilla formations. The type locality, which yielded both individuals, is near Lago Viedma and Lago Argentino in southwestern Santa Cruz Province, Argentina. Both skeletons appear to have been buried in crevasse splay deposits, and we can assume there was a lot of sediment involved because one does not easily bury a large sauropod. At least one and maybe both known individuals appear to have been scavenged. The holotype was probably buried on its left side because the left appendages are better represented than the right (Lacovara et al. 2014). Interestingly, D. schrani isn't the only big titanosaur in the formation: the Cerro Fortaleza has also produced Puertasaurus reuili, notable for its robust vertebrae and broad neural spines, quite different from D. schrani (Lacovara et al. 2014).

One of the implications of D. schrani as a big titanosaur at the end of the Cretaceous, and the sprinkling of big titanosaurs in time and space and throughout Titanosauria, is that the basic titanosaur body plan appears to have had a sort of "reflex" for large sizes. Sauropods in general seem to have had a knack for reaching sizes in the neighborhood of 30 metric tons/25 m long when the opportunity presented itself, with the major exceptions being groups that apparently had some niche they fit best at smaller sizes, such as the dicraeosaurids, saltasaur-type titanosaurs, and rebbachisaurids (although Maraapunisaurus missed the memo).


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