Your Friends The Titanosaurs, part 16: Malarguesaurus and Magyarosaurus

We've entered the "M"s, where we'll be for the next few entries. This entry features quasi-titanosaur Malarguesaurus florenciae and distinguished miniaturized sauropod Magyarosaurus dacus plus whatever else is in (or out of) Magyarosaurus. Before getting into the discussion, you may be interested to know of two recent freely available titanosaur publications, González Riga et al. (2019) and Mannion et al. (2019). González Riga et al. (2019) is an overview of the limb and girdle bones of South American titanosaurs, and names a clade Colossosauria for Lognkosauria plus Rinconsauria. Mannion et al. (2019) redescribes Dongyangosaurus sinensis and Jiangshanosaurus lixianensis, and finds them and a couple other taxa (Baotianmansaurus henanensis and Yongjinglong datangi) to be outside of Titanosauria (which required a few notes to be added to previous entries).

Malarguesaurus florenciae

We come now to a question: Why Malarguesaurus and not Ligabuesaurus? What special insight compelled me to cover M. florenciae as a true titanosaur but not L. leanzai? Likelihood, mostly. From my notes covering titanosaurian phylogenetic analyses over the past few years (and including multiple results in the same paper), M. florenciae shows up as a true titanosaur in seven, a polytomic titanosaur in six (where the base of Titanosauria has turned into a blob of sauropods, including many that are otherwise considered euhelopodids or what-have-you), and more or less the sister to Titanosauria in two. L. leanzai shows up in more results because it's based on better material. Its numbers break down as follows: a titanosaur in four, a polytomic titanosaur in five, and outside of Titanosauria in twelve. It's not the most elegant way of making a decision, but there you go.

M. florenciae would actually be more interesting as a non-titanosaur than a titanosaur, because it would be that rarest of rare birds, a post-Cenomanian sauropod that's not a titanosaur. About the best we have at the moment are some stray euhelopodids (if I say "Gannansaurus" and you do anything but look at me blankly, you're probably as bad off as myself) and some marginally informative bits and pieces. For whatever reasons, titanosaurs managed a very thorough takeover of sauropod niches shortly after the beginning of the Late Cretaceous. (No particular reason for bringing it up, but when considering the flowering plant revolution of the Cretaceous, paleontologists often note the rise of ceratopsians and hadrosaurs. There's a third group of large herbivores that seems to have taken to the new situation, too; no points for guessing what it is. Seems like something that someone ought to mention.)

Enough on M. florenciae as a name that shows up in a cladogram. Let's get back to M. florenciae the animal. It is based on a partial skeleton collected in 2005 from the Quebrada Norte site in the Paso de las Bardas area of Mendoza Province, Argentina (González Riga et al. 2009; the publication actually showed up online in 2008, but it was not published in physical form until the next year). This specimen was found in massive red mudstones of the Portezuelo Formation (González Riga et al. 2009), a rock unit which has also yielded the somewhat more famous Futalognkosaurus dukei (and Baalsaurus mansillai). González Riga et al. (2009) interpreted the mudstone as floodplain deposits within a meandering river system. For a change, the skeleton was not jumbled with a bunch of other skeletons; instead, there appears to be the remains of only one individual, associated within an area about 16 m square (170 square feet, which seems like a lot, but that's a square about 4 m or 13 ft on a side). The bones were weathered before burial and do not show evidence of orientation or size selection (González Riga et al. 2009).

This map, Figure 1 in Previtera (2017), not only shows where Pas de las Bardas is, but also shows several other localities that have come up or will come up, such as Rincon de los Sauces and General Roca. CC-BY-3.0.

González Riga et al. (2009) named the genus for the Malargüe Department of Mendoza Province, where it was found, and used the species name to honor the discoverer, Florencia Fernández Favarón, giving us something like "Florencia Fernández Favarón's Malargüe Department lizard". The type specimen is reposited by the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, Colección Paleovertebrados in Mendoza as IANIGLA-PV 110. It includes caudal vertebrae, chevrons, ribs, a partial humerus and femur, and bits. González Riga et al. (2009) also referred a couple of caudals and a fibula (IANIGLA-PV 111) from the Cerro La Torre site 600 m (1,700 ft) south of the Quebrada Norte quarry to the species.

Unlike most of the titanosaurs we've seen, the caudals of M. florenciae are not particularly procoelous until you get into the distal tail. Most of the distinctive features are concentrated on the neural spines, which start off vertical and with a straight anterior margin but a strongly curved posterior margin. By the distal caudals, there's this skewed thing going on where the prezygapophyses are pointed up and the postzygapophyses are pointed down with respect to the centra, both by as much as about 45 degrees. The femur is robust and not particularly unusual for a titanosauriform (González Riga et al. 2009). González Riga et al. (2009) originally found it to be just outside of Titanosauria, but as noted above, it's tended to show up just within Titanosauria more frequently as of late. M. florenciae has not featured in many publications, although Previtera (2017) did publish a study on histology and taphonomy of the site, finding that the type individual was not fully grown at the time of death.

Magyarosaurus dacus and company

Didn't we just do a miniature European titanosaur? No matter; Magyarosaurus is the *classic* miniature European titanosaur, albeit sometimes obscured by being sunk into Hypselosaurus or Titanosaurus. There's just one slight problem, though, which you might be able to guess from the section heading: it's not entirely clear what constitutes Magyarosaurus. Does it contain one, two, or three species? (And how is Paludititan nalatzensis involved in all of this?) Magyarosaurus is known from copious disarticulated material. (This seems like it should mean something: why should, say, the Morrison, or various Jurassic Chinese formations, yield nice partial sauropod skeletons, whereas it seems like winning the lottery to get an associated titanosaur skeleton without some other titanosaur mixed in?) It's almost a reflex to note that Magyarosaurus is in serious need of revision (e.g., McIntosh 1990, Le Loeuff 1993, Wilson and Upchurch 2003, Upchurch et al. 2004, Dalla Vecchia 2006, Benton et al. 2010, Csiki et al. 2010, Grellet-Tinner et al. 2012, Csiki-Sava et al. 2015, Díez Díaz et al. 2018). This does make it a bit difficult to write about the anatomy of Magyarosaurus, at least until a revision is published (how can you know if you're writing about Magyarosaurus if you aren't sure what it is?), but there's plenty of other stuff to discuss.

Magyarosaurus began printed life as another species of Titanosaurus, part of the collections made by Baron Franz Nopcsa in the Haţeg Basin of Transylvania. Either the Baron was more interested in the ornithopods (today's Zalmoxes and Telmatosaurus) and armored dinosaurs (Struthiosaurus), or he couldn't make much out of the disarticulated sauropod remains, but the only paper in which he gave much attention to his Transylvanian titanosaurs was Nopcsa (1915). In this paper, he named and briefly described and illustrated Titanosaurus dacus, "Dacian titan lizard", Dacia being the old Roman name for the region. He had a number of different bones representing much of the body, including dorsals, sacrals, caudals, ribs (notably pneumatic), scapulae, pelvic bones, all of the long bones of the limbs, and claws. The caudals are typically procoelous and strongly grooved on the underside. He estimated that T. dacus was at most 5 to 6 m long (16 to 20 ft). In a bit of trivia, Nopcsa briefly digressed to mention that he disagreed with the infamous lizard-legged Diplodocus of Tornier.

In the introduction to the paper Nopcsa apologized that he did not know when the full monograph he had planned could be completed, due to external circumstances (World War I, one result of which being Transylvania was transferred from Hungary to Romania). Although he later returned to several of the other taxa, he never quite made it back to T. dacus, leaving it in the hands of Friedrich von Huene. By now you know the drill for when von Huene had disassociated titanosaur remains to assess.

This plate illustrates some of Nopcsa's Titanosaurus dacus material (items 4a, 4b, 4c, 5, 8a, and 8b). 4 and 5 are caudals, presented "backward" from how we usually orient them, and 8 is a claw. Other taxa include "Orthomerus" (=Telmatosaurus; 1, 2, and 3), Struthiosaurus (9), and "Megalosaurus" (spoiler: it's not Megalosaurus; 6, 7). 

In 1932, after he'd gotten through with the titanosaur bonebeds of Argentina but before the publication of his findings on the titanosaur bonebeds of India, our frequent guest von Huene addressed T. dacus in his monograph on saurischian dinosaurs. Sensibly enough, he moved dacus out of Titanosaurus and into a new genus, which he named Magyarosaurus, "Magyar lizard" (in the process, intentionally or not, making a statement about the status of Transylvania). He then added two more species, M. hungaricus and M. transsylvanicus ("Hungarian Magyar lizard" and "Transylvanian Magyar lizard"). He regarded M. dacus as having more robust caudals than M. transsylvanicus, and so also assigned the more robust limb elements to it, but refrained from assigning any bones to a species if they were only represented by single examples. For the material assigned to M. transsylvanicus, he took a stab at determining male and female caudal vertebrae, which is an admirably forward-thinking thing to do but seems like the kind of thing you'd want to save until after you have a few associated skeletons, not before. He recognized that M. hungaricus, based on a fibula, was larger than the other two species, and was not entirely certain that it belonged to the same genus. He suspected that a few other large bones belonged to it, but again refrained from assigning them.

The paleontological community apparently decided that this time von Huene had gone too far and jammed it all back into Titanosaurus, or Hypselosaurus (because if you can't put Titanosaurus on every continent, you can at least put every smallish European titanosaur into that paragon of completeness, Hypselosaurus). There matters rested until Magyarosaurus was revived around 1990. Inasmuch as anything solid can be said about von Huene's three species, the last reference to say anything about M. transsylvanicus regarded it as probably a synonym of M. dacus (Grigorescu 2010), while "M." hungaricus seems to be a large-bodied outlier (Grigorescu 2010; Stein et al. 2010; see more below).

As mentioned, Magyarosaurus is known from the Haţeg Basin of Transylvania. Two approximately contemporaneous Maastrichtian-aged formations are known from this basin: the Densuş-Ciula Formation in the northwest part of the basin, and the Sânpetru Formation along the Râul Mare and Sibisel river valleys (Benton et al. 2010; Nopcsa originally thought he was dealing with the Danian, a.k.a. the earliest Paleocene, but this has since been revised). The major difference between the two is that the Densuş-Ciula Formation has volcaniclastic rocks (sediments of volcanic origin) and the Sânpetru Formation mostly lacks them (Benton et al. 2010). Nopcsa was the first to suggest that the Haţeg Basin was an island in the Cretaceous. He based this in part on the dinosaurs being smaller than usual, which he attributed to insular dwarfism (the phenomenon of big species evolving to a smaller size due to being on a small landmass). Nopcsa's inference looks to have been on the money, but living pre-plate-tectonics he would have had a hard time knowing just how complex Cretaceous Europe was. Haţeg Island is thought to have been a landmass on the order of the size of Hispaniola, around 80,000 square km (31,000 square miles) (Benton et al. 2010).

Part A of Figure 1, Grellet-Tinner et al. (2012), to give you an idea of the geography (green areas are Maastrichtian rocks, red dots correspond to amount of volcanic influence). CC-BY-4.0.

The exact nature and extent of dwarfing of Magyarosaurus have been discussed in several papers since Nopcsa. Jianu and Weishampel (1999), using regression analyses, interpreted M. dacus as a paedomorphic dwarf (basically, it never grew up; it matured while still having the traits and body size of a juvenile titanosaur). Le Loeuff (2005) challenged the idea that M. dacus was any kind of dwarf by reporting on much larger Transylvanian specimens, including a partial humerus he interpreted as belonging to an animal 10 to 15 m long (30 to 50 ft). He suggested that what looked like juvenile-sized adults was just the result of taphonomic biases toward actual juveniles. Stein et al. (2010), looking at osteology, came to a different conclusion. After sampling a series of limb bones, they found that *all* of the small limb bones from the Haţeg Basin in their sample were from fully grown animals. The large humerus, though, was a ringer, which they attributed to von Huene's old "M." hungaricus. Shades of the occasional full-sized M. columbi found among the pygmy mammoth fosssils of Channel Islands National Park, it could represent a stray from a larger landmass, an individual in a pre-dwarfing population, or a period in time when the island itself was larger.

Titanosaur eggs are also known from the Haţeg Basin (Grellet-Tinner et al. 2012), although some eggs than have been assigned to titanosaurs in the past have turned out to be hadrosaur eggs (Grigorescu 2017). Befitting dwarfed titanosaurs, the eggs are in relatively small clutches (four on average), and are only 12 cm (4.7 in) in diameter. One includes embryonic integument impressions (Grellet-Tinner et al. 2012). Given the uncertainties of Haţeg Basin sauropods, they could have been laid by Magyarosaurus or Paludititan.

References

Benton, M. J., Z. Csiki, D. Grigorescu, R. Redelstorff, P. M. Sander, K. Stein, and D. B. Weishampel. 2010. Dinosaurs and the island rule: The dwarfed dinosaurs from Haţeg Island. Palaeogeography, Palaeoclimatology, Palaeoecology 293(3):438–454. doi:10.1016/j.palaeo.2010.01.026.

Csiki, Z. 1999. New evidence of armoured titanosaurids in the Late Cretaceous–Magyarosaurus dacus from the Hateg Basin (Romania). Oryctos 2:93–99.

Csiki, Z., V. Codrea, C. Jipa-Murzea, and P. Godefroit. 2010. A partial titanosaur (Sauropoda, Dinosauria) skeleton from the Maastrichtian of Nǎlaţ-Vad, Haţeg Basin, Romania. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 258(3):297–324. doi:10.1127/0077-7749/2010/0098.

Csiki-Sava, Z., E. Buffetaut, A. Ősi, X. Pereda-Suberbiola, and S. L. Brusatte. 2015. Island life in the Cretaceous - faunal composition, biogeography, evolution, and extinction of land-living vertebrates on the Late Cretaceous European archipelago. Zookeys 469:1–161. doi:10.3897/zookeys.469.8439.

Dalla Vecchia, F. M. 2006. Telmatosaurus and the other hadrosaurids of the Cretaceous European Archipelago. An overview. Natura Nascosta 32:1–55.

Díez Díaz, V., G. Garcia, X. Pereda Suberbiola, B. Jentgen-Ceschino, K. Stein, P. Godefroit, and X. Valentin. 2018. The titanosaurian dinosaur Atsinganosaurus velauciensis (Sauropoda) from the Upper Cretaceous of southern France: new material, phylogenetic affinities, and palaeobiogeographical implications. Cretaceous Research 91:429–456. doi:10.1016/j.cretres.2018.06.015.

González Riga, B. J., E. Previtera, and C. A. Pirrone. 2009. Malarguesaurus florenciae gen. et sp. nov., a new titanosauriform (Dinosauria, Sauropoda) from the Upper Cretaceous of Mendoza, Argentina. Cretaceous Research 30(1):135–148.

González Riga, B. J., M. C. Lamanna, A. Otero, L. D. Ortiz David, A. W. A. Kellner, and L. M. Ibiricu. 2019. An overview of the appendicular skeletal anatomy of South American titanosaurian sauropods, with definition of a newly recognized clade. Academia Brasileira de Ciências 91(Supp. 2): e20180374. doi:10.1590/0001-3765201920180374.

Grellet-Tinner, G, V. Codrea, A. Folie, A. Higa and T. Smith. 2012. First evidence of reproductive adaptation to "island effect" of a dwarf Cretaceous Romanian titanosaur, with embryonic integument in ovo. PLoS ONE 7(3):e32051. doi:10.1371/journal.pone.0032051.

Grigorescu, D. 2010. The latest Cretaceous fauna with dinosaurs and mammals from the Haţeg Basin – a historical overview. Palaeogeography, Palaeoclimatology, Palaeoecology 293:271–282.

Grigorescu, D. 2017. The "Tustea puzzle" revisited: Late Cretaceous (Maastrichtian) Megaloolithus eggs associated with Telmatosaurus hatchlings in the Hateg Basin. Historical Biology 29(5):627–640.

Huene, F. von. 1932. Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und Geschichte [plates]. Mongraphien zur Geologie und Palaeontologie 4(1).

Jianu, C.-M., and D. B. Weishampel. 1999. The smallest of the largest: a new look at possible dwarfing in sauropod dinosaurs. Geologie en Mijnbouw 78:335–343.

Le Loeuff, J. 1993. European titanosaurids. Revue de Paléobiologie 7:105–117.

Le Loeuff, J. 2005. Romanian Late Cretaceous dinosaurs: big dwarfs or small giants? Historical Biology 17:15–17.

Mannion, P. D., P. Upchurch, X. Jin, and W. Zheng. 2019. New information on the Cretaceous sauropods of Zhejiang Province, China: impact on Laurasian titanosauriform phylogeny and biogeography. Royal Society Open Science 6(8):191057. doi:10.1098/rsos.191057. 

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.

Nopcsa, F. 1915. Die Dinosaurier der siebenbürgischen Landesteile Ungarns. Mitteilungen aus dem Jahrbuche der Kgl. Ungarischen Geologischen Reichsanstalt 23:1–24 plus four plates.
Previtera, E. 2017. Bone microstructure and diagenesis of saurischian dinosaurs from the upper Cretaceous (Neuquén group), Argentina. Andean Geology 44(1):39–58. doi:10.5027/andgeoV44n1-a03.

Stein, K., Z. Csiki, K. Curry Rogers, D. B. Weishampel, R. Redelstorff, J. L. Carballidoa, and P. M. Sandera. 2010. Small body size and extreme cortical bone remodeling indicate phyletic dwarfism in Magyarosaurus dacus (Sauropoda: Titanosauria). Proceedings of the National Academy of Sciences of the United States of America 107(20):9258–9263.

Upchurch, P., P. M. Barrett, and P. Dodson. 2004. Sauropoda. Pages 259–322 in D. Weishampel, P. Dodson, and H. Osmólska, editors. The Dinosauria (2nd ed.). University of California Press, Berkeley, California.

Wilson, J. A., and P. Upchurch. 2003. A revision of Titanosaurus Lydekker (Dinosauria – Sauropoda), the first dinosaur genus with a "Gondwanan" distribution. Journal of Systematic Palaeontology 1(3):125–160.