Historical Biology, 2005; 17: 15–17
Romanian late cretaceous dinosaurs: Big dwarfs or small giants?
JEAN LE LOEUFF Muse´e des Dinosaures, 11260 Espe´raza, France
Abstract It has been argued that the Late Cretaceous dinosaurs from Transylvania were affected by dwarfism as a consequence of their evolution in an insular habit. However, several bones from Nopcsa’s collections housed in London and Budapest shows that some Transylvanian saltasaurids reached lengths of 10– 15 m. These multi-ton animals can hardly be considered as dwarfs, even by dinosaurian standards. It is suggested here that taphonomical biases, possibly linked to the existence of age-classed communities among sauropod populations, explain why the vast majority of recovered bones are of young individuals.
Keywords: Dinosauria, Sauropoda, Romania, Late Cretaceous, social behaviour, dwarfism
Introduction The Late Cretaceous dinosaurs from Romania were first described by Nopcsa at the end of the nineteenth century. Between 1899 and 1915, Nopcsa described a hadrosaurid (Telmatosaurus transsylvanicus), a rhabdodontid (Zalmoxes robustus) and the saltasaurid Magyarosaurus dacus and he suggested (Nopcsa 1914) that the small size of the dinosaurs from Romania might have been related to the insularity of Transylvania during the latest Cretaceous. Most recent authors (Weishampel et al. 1991; Csiki and Grigorescu 1998; Jianu and Weishampel 1999) have defended this conclusion. In their work on M. dacus, Jianu and Weishampel (1999) noted that its humeri “appear to be more similar to those of subadults than to adults of other taxa” and they concluded “this ‘juvenile’ morphology may constitute dwarfing in M. dacus by heterochronic paedomorphosis”. Description Nopcsa’s collections are now housed at the Natural History Museum in London (BMNH) and at the Geological Survey of Hungary in Budapest (MAFI). I had the opportunity to visit both collections in 1991, and I observed a few large, albeit broken bones. In Budapest, a large sauropod humerus (MAFI V13491) from Valiora (Figure 1(a)) is only partially preserved.
Its total length is 450 mm. Its mediolateral midshaft width is of 129 mm; a complete small humerus (MAFI V13492; Figure 1(b)) has a transverse width at its narrowest point of 50 mm and a total length of 365 mm. To estimate the original length of MAFI V13491, I used Jianu & Weishampel’s RMA (Reduced major axis regression) analyses (Figure 7 of Jianu and Weishampel 1999). I calculated a total length of 800–900 mm for MAFI V13491. A 800–900 mm humerus like MAFI V13491 would belong to a 10–15 m long titanosaur that could not be considered a dwarf. In London, I also observed several large femoral condyles (BMNH R3859, BMNH R11106, BMNH R11107); BMNH R11107 is a broken lateral condyle of a right femur which total length can be estimated around 1000 mm. A 580 mm long ulna (BMNH R11123) is also present in the London collection (Figure 2). These bones apparently have not been considered by other researchers. These elements also indicate the existence of some large individuals among the Romanian titanosaur assemblage.
Discussion The conclusions of Jianu and Weishampel (1999) and other authors are no longer tenable in the light of these new data. I suggest that the juvenile morphology reported by Jianu and Weishampel (1999) for M. dacus
Correspondence: J. Le Loeuff, Muse´e des Dinosaures, 11260 Espe´raza, France. E-mail:
[email protected] ISSN 0891-2963 print/ISSN 1029-2381 online q 2005 Taylor & Francis DOI: 10.1080/08912960500376210
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J. le Loeuff
Figure 1. M. dacus, Valiora, humerus MAFI V13491: (a) and V13492; (b) in caudal view; scale bar: 50 mm.
Figure 2. M. dacus, ulna BMNH R11123; total length: 580 mm.
simply reflects a high proportion of juvenile specimens in their sample: most of the bones in the collections belong to young individuals, but adults could become much bigger as is attested by the fragmentary femora from London and the humerus from Budapest. How can we explain why most dinosaur bones excavated in Romania are small or even very small? It is possible that both taphonomical biasing as well as sampling bias are responsible for this apparent dwarfism. Taphonomical biases might be related to palaeoethological features: juvenile sauropods might have constituted herds independent of adults during their early years when their food was certainly different from adult food (this was simply linked to the height of browsing: a hatchling dinosaur could hardly eat the same leaves as a 4 –5 m tall adult). This palaeoethological hypothesis finds support in palaeoichnological data: juvenile sauropod trackways are sometimes found associated with parallel trackways without the presence of adult tracks (see Lockley and Meyer 1994 for an example of subadult sauropods heading in the same direction in Cabo Espichel, Late Jurassic of Portugal). The abundance of juvenile remains in Transylvania would thus reflect the existence of ageclassed communities among sauropod populations Regarding the sampling bias, relatively few Late Cretaceous dinosaur bones are known from Transylvania and a predominance of small sized remains may be an artefact of a reduced data set: the key of the “mystery” of small sauropods probably resides in further large-scale excavations in Transylvania. Another point worthy of interest is that the presence of such large dinosaurs on a very small island is surprising. The exact surface of the Hateg emergent area in the Maastrichtian is imprecisely known as the palaeogeography of this part of the world is obscured by the alpine deformation and post Cretaceous sedimentation (Dercourt et al. 1993). Weishampel et al. (1991) suggested that its surface was of only 7500 km2 and that it was separated from other central European islands by 200 – 300 km of shallow sea. Conversely, Jianu and Boekschoten (1999) have suggested that it would have occupied much of the Mesozoic Carpathians and the Apulian plate, being intermittently interconnected with other landmasses both to the east and west. This suggests that this landmass would have sometimes reached as much as 100,000 km2 in area (see map in Csiki and Grigorescu 2001). The western “Ibero-Armorican” landmass covered between 600,000 and 1,500,000 km2 during the Late Cretaceous (being sometimes connected to a large central European island on present day Germany and Poland). This area contained quite large dinosaurs: the biggest Ampelosaurus atacis bones from southern France suggest the existence of 20 m long titanosaurs. Thus, considering that the Hateg area was only a small part of a much larger emergent area (albeit intermittently isolated during marine transgressions),
Romanian dinosaurs it is not inconceivable that rather large dinosaurs existed on it (however, they reach large sizes). Conclusions The small size of most of the Hateg dinosaurs bones is here considered to represent juveniles rather than being the result of heterochronic dwarfism. The true surface area of the “Transylvanian island” in the Late Cretaceous has probably been underestimated. An abundance of juvenile remains is tentatively considered to reflect the existence of age-classed communities among dinosaur populations but sample size bias may have played a role. Thus no conclusive evidence exists of island-related dwarfism among dinosaurs. Acknowledgements I thank Dr Angela Milner (Natural History Museum, London) and Dr Laszlo Kordos (Geological Survey of Hungary, Budapest) for allowing me to study the Transylvanian dinosaurs housed in their institutions. Thanks to Dan Grigorescu, Zoltan Csiki, Coralia
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Jianu, David Weishampel, Eric Buffetaut for stimulating discussions on dwarfism and Romanian dinosaurs.
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