Hi all — I am now in La Plata, and have been since Sunday. The only reason I have not posted anything from here yet is that I still have not finished studying either of the dinosaurs that are housed here that I wanted to see… That said, I do have something to show in the meantime.

On my last day in Buenos Aires, it occurred to me that I had not gone through the displays at the Museo Argentino de Ciencias Naturales (MACN) properly. I failed to do so during my 2013 visit too, and I decided to remedy that this time. I would have taken far better photos than you will see here had I been able take my tripod in; sadly, I was not allowed. 

The dinosaur and reptile hall in the MACN is like a greatest hits album of Argentinian Mesozoic fossils — almost all of the classics are there. For the most part, I’ll let the photos (and captions) speak for themselves, and will hopefully report on an Antarctic dinosaur tomorrow!

Dinosaurs reign supreme in Antarctica today. Sounds weird, doesn't it? But it’s true! The reason? Every bird braving the frigid southern continent, be it a waddling penguin or a wandering albatross, is a living, breathing, highly derived theropod dinosaur. You might then wonder: Are the birds of modern day Antarctica continuing an ancient legacy? Did dinosaurs reign supreme in Antarctica during the Mesozoic Era? The answer to both questions, as has become clear in the last three decades or so, is emphatically yes.

To date, Antarctica has only produced evidence of dinosaurs from the Jurassic and Cretaceous periods. All of the Jurassic specimens (of which I am aware) are held in institutions in the USA. However, fortunately for me, almost all of the Cretaceous-aged dinosaur specimens collected from Antarctica are housed here in Argentina. Next week, at Museo de La Plata, I will have the opportunity to study two of these. Earlier this week, however, I was privileged to be able to study the most recently named dinosaur from Antarctica — Morrosaurus antarcticus.

In the last two blog posts, I was able to provide a fair bit of information about the collection history of the other dinosaurs I studied at the Museo Argentino de Ciencias Naturales — Loncosaurus argentinus and Chubutisaurus insignis. This was largely possible because such details were published as part of the papers in which these specimens were described. Frustratingly, a similar level of information was not easily available for Morrosaurus! All I found out is that it was collected by geologists Juan M. Lirio and Héctor Nuñez during 2002 (or perhaps a year or two prior), based on an abstract published in Ameghiniana by them — in conjunction with Fernando Novas and Andrea Cambiaso — that year.

The type specimen of Morrosaurus (MACN 19777) comprises bits and pieces of a right hind leg. The shafts of the femur (thighbone) and the tibia and fibula (shinbones) are missing, but at least their top and bottom ends are preserved (only one end in the case of the fibula). By contrast, the metatarsals (the upper toe bones in the foot bound in flesh) are almost complete. In fact, I suspect that the only reason that they are incomplete is because of repeated freezing and thawing of the specimen: the part of Antarctica from which Morrosaurus derives is, in the modern day, covered by ice in winter but not summer. The metatarsals are quite distinctive: the middle one was evidently massive, whereas the flanking metatarsals are distinctly compressed, meaning that the metatarsus as a whole would have comprised a tightly-packed bundle of bones. Whether Morrosaurus possessed a rudimentary first and/or fifth toe is unknown based on the available material.

The first description of MACN 19777 was produced by Andrea Cambiaso and included as part of her 2007 Ph.D. dissertation. However, Cambiaso never published on this specimen, and evidently did not consider it worthy of a name since she did not give it one. Finally, in 2016, Sebastian Rozadilla and colleagues (including Novas and Lirio) decided that it was worth naming MACN 19777, and they dubbed it Morrosaurus antarcticus.

When I first saw the type specimen of Morrosaurus, I was struck by how large it was (well, relatively speaking; large for a small ornithopod, if you will). In fact, the same was true of Loncosaurus — both it and Morrosaurus were evidently quite a bit larger than even the largest of the known Cretaceous ornithopods from Victoria (Leaellynasaura, Atlascopcosaurus, Qantassaurus and Diluvicursor were quite titchy by comparison). Once I have seen Talenkauen and Macrogryphosaurus — both of which are larger still — I might ponder the significance of that size discrepancy further… for now though, I’ll press on.

Argentina was home to huge diversity of long- (and even some short-) necked sauropods during the Cretaceous Period (145–66 Ma). Indeed, the first dinosaurs named and described from Argentina were all sauropods — I might write more on them next week, since many of those specimens are housed at Museo de La Plata; that said, while there I have bigger (albeit literally smaller) fish to fry...

It is fair to say that the true abundance and diversity of sauropods in the Argentinian Cretaceous has only really been revealed in the last thirty years or so, with the late Jaime Powell’s 1986 Ph.D. thesis (published in full in 2003) catalysing much of the subsequent research on titanosaurs in particular. Nevertheless, some very important Argentinian sauropods were named before Powell’s monumental manuscript, and one of these was Chubutisaurus insignis.

Starting in February 1965, agronomical engineer Julio Fernández Duque and palaeontologist Guillermo del Corro spent 30 days excavating fossilised dinosaur bones from a site near Cerro Barcino and Cerro Winches in Chubut Province. The bones, which were first discovered by a local rancher named Mr Martínez (whose widow had informed Duque of their existence), were preserved in such hard rock that Duque and del Corro had to use dynamite in order to extract them. A substantial quantity of fossil material was recovered from the site, and all of the bones appeared to belong to a single sauropod dinosaur — except for five theropod teeth, which were named Megalosaurus inexpectatus by del Corro in 1966. All of these bones were deposited in the collections of the Museo Argentino de Ciencias Naturales in Buenos Aires, with the exception of two fragmentary limb bones that were donated to the Museo Provincial de Ciencias Naturales y Oceanografía in the 1970s.

Ten years after the excavations took place, del Corro described and named the sauropod from Chubut ​as Chubutisaurus insignis (the “notable Chubut lizard”), which he classified in its own family, Chubutisauridae. However, del Corro illustrated only a small subset of the available material and misinterpreted several specimens. He also suggested that Chubutisaurus was Late Cretaceous in age, but provided little evidence to support this interpretation. His paper — preliminary by his own admission — would need to be followed up by a more comprehensive work down the line.

In 1978, José Bonaparte and Zulma Gasparini highlighted the fact that Chubutisaurus was more “primitive” anatomically than the titanosaurs that were so characteristic of South America during the Late Cretaceous (100.5–66 Ma). Consequently, they suggested that Chubutisaurus was actually substantially older than suspected by del Corro; based on microfossils from the same formation that had been interpreted as Aptian in age (125–113 Ma), they suggested Chubutisaurus was actually from the Early Cretaceous.

Twelve years later, in the Sauropoda chapter of The Dinosauria, John McIntosh illustrated several of Chubutisaurus’ limb bones and suggested that it was a brachiosaurid. However, it was not until 1993 that a more comprehensive, albeit still abbreviate, description was published by Leonardo Salgado. He suggested against classifying Chubutisaurus as a brachiosaurid, because he considered the anatomical features that McIntosh had used to link the two as shared “primitive” characters. However, Salgado did identify some features that could be used to link brachiosaurids, Chubutisaurus and titanosaurs, indicating a possible relationship between all three. 

​In 1991, a few years before Salgado’s paper on Chubutisaurus was published, the Museo Paleontológico Egidio Feruglio (MPEF) launched a field trip to try to relocate Duque and Del Corro’s quarry. They were able to do so with the help of Mr Martínez’s son, who had been present when Duque and del Corro excavated the site in 1965. In 1991, and in 2007 as well, the MPEF team collected more material of Chubutisaurus — some of which had been transported some distance from their original positions by the force of the 1965 dynamite blasts. All of the material collected by the MPEF came to reside in the Museum in Trelew, meaning that the only known specimen of Chubutisaurus is now divided between three separate museums!

A complete description of Chubutisaurus was only published relatively recently (2011) by José Carballido, Diego Pol, Ignacio Cerda and Leonardo Salgado. These authors concluded that Chubutisaurus was of Cenomanian age (~100.5–93.9 Ma) and that it was more closely related to titanosaurs than to brachiosaurs. Indeed, in both their analysis and in most recent analyses of sauropod interrelationships, Chubutisaurus is resolved as a basal somphospondylan — a close relative of titanosaurs, but not a true titanosaur itself.
​
The material on which Chubutisaurus is based — which derives from the Bayo Overo Member of the Cerro Barcino Formation, Chubut Province — is extremely incomplete, although in fairness that is not a rarity for sauropods. The few thoracic vertebrae preserved suggest that those situated near the front of the chest — and therefore at the base of the neck — were quite short front-to-back but tall top-to-bottom. Further back in the sequence, the inverse holds true. Although no neck vertebrae were found, it can be inferred that the neck was quite long — partly because Chubutisaurus was a sauropod, for which long necks were the norm, but also because the short vertebrae at the front of the thorax were probably so short front-to-back (relatively speaking) to cope with the stresses imposed upon them by the movements of a long neck. By contrast, the tail of Chubutisaurus — although nowhere near complete — was presumably shorter than the neck: all of the tail vertebrae known are (again, relatively) short front-to-back.

​The tail vertebrae of Chubutisaurus are interesting for another reason: they are not procoelous. The centra (vertebral bodies) of procoelous vertebrae are concave on the front articular face and convex on the back one. However, those of Chubutisaurus are shallowly concave on the front face but essentially flat on the back face. This easily distinguishes the tail vertebrae of Chubutisaurus from those of most titanosaurs, the sauropods for which Argentina has become famous, because almost all of them have procoelous tail vertebrae; only in the most basal titanosaurs are the tail vertebrae not procoelous (as in the Australian Savannasaurus) or only incipiently so (as in the basalmost titanosaur by definition, Andesaurus).

That'll do for now; once I have had a look at the girdle and limb bones of Chubutisaurus, I might have more to say... in the immediate future, however, I need to move on to another dinosaur — one from the southernmost continent of all!

References

​Bonaparte, J.F. & Gasparini, Z.B., 1978. Los sauropodós de los Grupos Neuquén y Chubut, y sus relaciones cronológicas. Actas del VII Congreso Geológico Argentino, Neuquén, 1978 2, 393–406.

Carballido, J.L., Pol, D., Cerda, I. & Salgado, L., 2011. The osteology of Chubutisaurus insignis Del Corro, 1975 (Dinosauria: Neosauropoda) from the ‘Middle’ Cretaceous of Central Patagonia, Argentina. Journal of Vertebrate Paleontology 31, 93–110.

Del Corro, G., 1966. Un nuevo dinosaurio carnívoro del Chubut (Argentina). Museo Argentino de Ciencias Naturales (Bernardino Rivadavia), Communicaciones Paleontología 1, 1–4.

Del Corro, G., 1975. Un nuevo saurópodo del Cretácico Superior, Chubutisaurus insignis gen. et sp. nov. (Saurischia, Chubutisauridae nov.) del Cretácico Superior (Chubutiano), Chubut, Argentina. Actas I Congreso Argentino de Paleontología y Biostratigrafía, 229–240.

McIntosh, J.S., 1990. Sauropoda. In The Dinosauria. Weishampel, D.B., Dodson, P. & Osmólska, H., eds, University of California Press, Berkeley, 345–401.

Powell, J.E., 1986. Revisión de los titanosauridos de América del Sur. Ph.D. thesis. Universidad Nacional de Tucumán, Tucumán, Argentina, 472 pp. (unpublished).

Powell, J.E., 2003. Revision of South American titanosaurid dinosaurs: palaeobiological, palaeobiogeographical and phylogenetic aspects. Records of the Queen Victoria Museum 111, 1–173.

As an Australian palaeontologist, I am all too familiar with dinosaur taxa named on the basis of a single bone.  The theropods Rapator, Walgettosuchus, Ozraptor, Kakuru, Nanantius and Timimus. The ornithopod Fulgurotherium. The ulna known as Serendipaceratops, whatever that is. Let us kick off, then, in familiar territory, with an Argentinian dinosaur named on the basis of a single incomplete bone. Meet Loncosaurus argentinus (MACN 11269; often (?mis)transcribed as MACN 1269).

Florentino Ameghino (1854–1911) was a pioneer of Argentinian palaeontology. Although he was not the first to report dinosaurs from Argentina, Ameghino did make what he considered to be the first report of a theropod dinosaur from the Republic. In 1899, on the basis of an incomplete femur and a tooth (MACN 10985) — discovered by Carlos Ameghino, Florentino’s brother — Ameghino declared that a relative of the English theropod Megalosaurus bucklandii lived in Argentina during the Cretaceous Period.
 
For the next three decades, Loncosaurus received relatively little attention from palaeontologists. However, that changed in 1929, when Friedrich von Huene (1875–1969) published what was, for many decades after, the definitive work on Argentinian dinosaurs: Los Saurisquios y Ornitisquios del Cretáceo Argentina. In this monumental paper, von Huene included a brief assessment of Loncosaurus: he seemed satisfied that the femur belonged to a coelurosaurian theropod dinosaur, and even went so far as to say that it compared favourably with ostrich dinosaurs — ornithomimids. Critically, he also illustrated the femur, showing the prominent fourth trochanter and the hollow nature of the shaft, but also highlighting just how incomplete the specimen was. Von Huene also illustrated and briefly appraised the tooth found with the femur, demonstrating beyond doubt that it, too, pertained to a theropod.

Once von Huene was done, however, the dust again settled on Loncosaurus. Although often included in dinosaur lists as a theropod — sometimes as a synonym of Genyodectes — it was not until 1980 that Loncosaurus received a new lease on life. Ralph Molnar, in a paper reviewing Australian Late Mesozoic terrestrial tetrapods, also listed the terrestrial tetrapods from the other Gondwanan continents. In so doing, he listed Loncosaurus as a hypsilophodontid ornithopod, with the following footnote appended: “Loncosaurus is represented by the proximal portion of the right femur and teeth… The teeth…are clearly theropod…[but]…The prominent fourth trochanter (partially missing) and the strong posterior development of the greater trochanter of the femur contraindicate theropod affinities. Both features are found in hypsilophodont femora…and for this reason the femur is here tentatively considered to pertain to a small ornithopod.” (Molnar, 1980:140).

Molnar was the first to call into question the association of the tooth with the femur, and in so doing he took the femur — which undoubtedly was not from a theropod — out of the shadow of the tooth — which undoubtedly was — and appraised it in its own right. His interpretation appears to have received broad acceptance: in both editions of The Dinosauria, Loncosaurus is listed as an iguanodontian (albeit as a nomen dubium). Molnar’s interpretation was reaffirmed by Rodolfo Coria and Leonardo Salgado in 1996, when they redescribed and illustrated the specimen, confirming beyond any reasonable doubt that it was an ornithopod. So really, Ameghino hadn’t just announced the first Argentinian theropod back in 1899; he’d also inadvertently, and unknowingly, made the first report of an Argentinian ornithopod too.

Loncosaurus was found at Pari-Aike on the Río Sehuen, in Santa Cruz Province. It derives from the Mata Amarilla Formation, which dates to the Cenomanian–Santonian (~100.5–83.6 Ma). Further fossil hunting in this rock unit has turned up another ornithopod — the wonderfully preserved Talenkauen santacrucensis, which I intend to see later on this trip — but no more specimens referable to Loncosaurus are yet known. Hopefully, in time, that will change.

References

Ameghino, F. 1899. Nota preliminar sobre el Loncasaurus[sic] argentinus, un representante de la familia de los Megalosauridae en la República Argentina. Annales Societas Ciencias 47:61–62.

Cambiaso, A. V. 2007. Los ornitópodos e iguanodontes basales (Dinosauria, Ornithischia) del Cretácico de Argentina y Antártida: In Facultad de Ciencias Exactas y Naturales, Vol. Ph.D., pp. 410. Universidad de Buenos Aires, Buenos Aires, Argentina.

Coria, R. A., and A. V. Cambiaso. 2007. Ornithischia; pp. 167–187 in Z. Gasparini, L. Salgado, and R. A. Coria (eds.), Patagonian Mesozoic Reptiles. Indiana University Press, Bloomington & Indianapolis, IA.

Coria, R. A., and L. Salgado. 1996. "Loncosaurus argentinus" Ameghino, 1899 (Ornithischia, Ornithopoda): a revised description with comments on its phylogenetic relationships. Ameghiniana 33:373–376.

Ezcurra, M. D., and F. L. Agnolín. 2017. Gondwanan perspectives: theropod dinosaurs from western Gondwana. A brief historical overview on the research of Mesozoic theropods in Gondwana. Ameghiniana 54:483–487.

Huene, F. v. 1929. Los Saurisquios y Ornitisquios del Cretáceo Argentina. Anales Museo de La Plata 3:1–196.

Molnar, R. 1980. Australian late Mesozoic terrestrial tetrapods: some implications. Mémoires de la Société Géologique de France (Nouvelle Série) 139:131–143.

Norman, D. B. 2004. Basal Iguanodontia; pp. 413–437 in D. B. Weishampel, P. Dodson, and H. Osmólska (eds.), The Dinosauria: Second Edition. University of California Press, Berkeley.

Norman, D. B., and D. B. Weishampel. 1990. Iguanodontidae and Related Ornithopods; pp. 510–533 in D. B. Weishampel, P. Dodson, and H. Osmólska (eds.), The Dinosauria. University of California Press, Berkeley.