An unusual from the Late of Romania and the island rule

Hans-Dieter Sues1 Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560

sland faunas are natural laboratories First, the postcranial skeleton of Bal- of evolutionary change and have long daur differs from that of other known I fascinated biologists. The peculiar dromaeosaurids in numerous features. ecological conditions on islands have The hand of Baldaur shows extensive fu- frequently led to the of endemic sion of the carpals and metacarpals, and taxa that differ dramatically in body size there are only two functional digits, unlike and/or morphology from their mainland the three-fingered grasping hand in other relatives. Many large tend to be- dromaeosaurids. The foot retains a large, come smaller on islands, and small ones functional first digit, unlike the much generally become larger—a phenomenon reduced digit in most derived theropod known as the island rule (1, 2). Perhaps . This digit is very similar in size the best-known examples from the fossil and shape to the second pedal digit, which, record are the pony-sized elephants and as in other dromaeosaurids, carries pig-sized hippopotami that populated a greatly enlarged, strongly curved claw Crete and various other Mediterranean that had a considerable arc of motion. islands during the Pleistocene and Holo- Thus, each foot of Baldaur sported cene (3). Other examples include the a double set of these large claws, which Miocene Deinogalerix from Italy, Fig. 1. Reconstructed paleogeography of the were likely used for seizing and dis- which attained a body length of about European archipelago in the western Tethys and emboweling prey. The robust hind limb 70 cm (4), and the prehistoric rat Cor- adjacent regions during the , with shows extensive fusion of bones in its yphomys from East Timor, which may have selected present day coastlines superimposed to proportionately short distal portion, facilitate orientation. Simplified from refs. 10 and tipped the scales at 6 kg (5). Insular gi- 14. White areas denote land. Black circle indicates with formation of a tibiotarsus and a tar- gantism has also been found in certain position of Hatxeg region. AD, Adriatic-Dinaric sometatarsus. These unusual features groups of birds such as owls (6). Platform; C, Crimea; IB, Iberia; T, Tisia-Dacia Block. suggest that Baldaur was capable of de- In the early decades of the last century, livering powerful strikes with its feet. Franz Baron Nopcsa reported a distinctive Based on what is known about insular (Maastrichtian) verte- related to counterclockwise rotation and faunas past and present, Csiki et al. (11) brate assemblage from the Hatxeg Basin northward motion of the African conti- hypothesize that the peculiar body plan of Transylvania (now part of Romania). nental plate. Subduction resulted in vol- of this predatory dinosaur is probably This assemblage was dominated by several canic activity, which, in turn, led to the caused by the island effect. The body size endemic taxa of dinosaurs that attained formation of islands. The largest of these of Baldaur is comparable with that of significantly smaller body size than related Cretaceous islands covered much of the most other known dromaeosaurids. forms elsewhere. Impressed by this present day Iberian Peninsula and France Csiki et al. (11) conduct a thorough dwarfing, Nopcsa argued that the Hatxeg and extended well into central Europe. phylogenetic analysis of dromaeosaurid fauna represented an island biota (7). The Hatxeg Basin was located on a smaller theropods and find that Baldaur is most However, his work and conclusions were island in an archipelago that extended closely related to Velociraptor from the largely ignored until there was a resur- from the region now occupied by the Eu- Upper Cretaceous of Mongolia and China. gence of interest in the Late Cretaceous ropean Alps eastward to present day One of the unresolved issues concerning vertebrates from Transylvania in the late southwest Asia. the Late Cretaceous Hatxeg biota had 1970s (8). Since then, studies of the bone In recent years, fieldwork in various been its origin: was the Hatxeg region histology in the hadrosauroid dinosaur parts of Europe has resulted in many dis- a refugium for survivors of ancient line- (9) and the titanosaurian coveries of dinosaurs and other terrestrial ages that had been in place for millions sauropod Magyarosaurus (10) from the vertebrates, which are finally beginning ofyearsordidsomeofthetaxaindicate x ’ Hateg Basin have supported Nopcsa s hy- to shed light on the diversity of Late Cre- faunal connections with neighboring continents late into the Cretaceous? pothesis that both taxa have undergone an taceous island ecosystems in this region. The phylogenetic relationships of the evolutionary decrease in body size (nan- One of the most exciting discoveries, ism). Discoveries of additional vertebrate small hadrosauroids Telmatosaurus and reported by Csiki et al. (11) in PNAS, is fossils from the Late Cretaceous of the Tethyshadros (from the Maastrichtian a previously unknown taxon of theropod Hatxeg Basin have further underscored the Adriatic-Dinaric Island) suggest faunal distinctive nature of the Hatxeg biota. In dinosaur, Baldaur bondoc. Baldaur (named connections to Asia (12–14), and the PNAS, Csiki et al. (11) report on one of using an ancient Romanian word for discovery of Baldaur now lends further the most remarkable finds to date—an dragon) is referable to the Dromaeosaur- support to this hypothesis. The recently “ ” unusual theropod dinosaur. idae (the raptors of Park fame), described basal ceratopsian dinosaur During the Late Cretaceous, a shallow which are the closest relatives of birds. epicontinental sea dotted with variously The holotype of Baldaur bondoc is an ar- sized islands covered most of what is now ticulated partial postcranial skeleton. It Author contributions: H.-D.S. wrote the paper. Europe (Fig. 1). This topography reflected represents the most complete dromaeo- The author declares no conflict of interest. complex tectonic activities along the saurid fossil from Europe to date, but its See companion article on page 15357. northern margin of the western Tethys real scientific importance lies elsewhere. 1E-mail: [email protected].

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Ajkaceratops from the early Late Creta- graphic link between Europe and Asia. arrived from the Asiamerican landmass ceous (Santonian) of Hungary (15) seems Presumably, the ancestors of these dino- by island hopping, especially during times to represent yet another paleobiogeo- saurs (and possibly other vertebrates) of lower sea levels (14).

1. Foster JB (1964) Evolution of on islands. Na- 7. Nopcsa F (1914) Die Lebensbedingungen der obercre- Late Cretaceous of Romania. Proc Natl Acad Sci USA ture 202:234–235. tacischen Dinosaurier Siebenbürgens. Centralbl Min- 107:15357–15361. 2. Lomolino MV, et al. (2006) The island rule and a re- eral Geol Paläontol 1914:564–574. 12. Weishampel DB, Norman DB, Grigorescu D (1993) Tel- search agenda for studying ecogeographical patterns. 8. Weishampel DB, Grigorescu D, Norman DB (1991) matosaurus transsylvanicus from the Late Cretaceous – J Biogeogr 33:1503 1510. Thedinosaurs of Transylvania. Natl Geogr Res 7:196– of Romania: The most basal hadrosaurid dinosaur. Pa- 3. Sondaar PY (1994) Paleoecology and evolutionary pat- laeontology 36:361–385. 215. terns in horses and island mammals. Hist Biol 8:1–13. 13. Sues H-D, Averianov A (2009) A new basal hadrosau- 9. Benton MJ, et al. (2010) Dinosaurs and the island rule: 4. Butler PM (1980) The giant erinaceoid insectivore, De- roid dinosaur from the Late Cretaceous of Uzbekistan The dwarfed dinosaurs from Hatxeg Island. Palaeogeogr inogalerix Freudenthal, from the Upper Miocene of and the early radiation of duck-billed dinosaurs. Proc Palaeoclimatol Palaeoecol 293:438–454. Italy. Scripta Geol 57:1–72. Biol Sci 276:2549–2555. 10. Stein K, et al. (2010) Small body size and extreme cor- 5. Aplin K, Helgen KM (2010) Quaternary murid rodents 14. Dalla Vecchia FM (2009) Tethyshadros insularis, a new fi of Timor. Part I: New material of Coryphomys buehleri tical bone remodeling indicate phyletic dwar sm in hadrosauroid dinosaur () from the Upper Schaub, 1937, and description of a second species of Magyarosaurus dacus (Sauropoda: Titanosauria). Proc Cretaceous of Italy. J Vertebr Paleontol 29:1100–1116. the . Bull Am Mus Nat Hist 341:1–80. Natl Acad Sci USA 107:9258–9263. 15. Ösi A, Butler RJ, Weishampel DB (2010) A Late Creta- 6. Arredondo O (1976) The great predatory birds of the Pleis- 11. Csiki Z, Vremir M, Brusatte SL, Norell MA (2010) An ceous ceratopsian dinosaur from Europe with Asian tocene of Cuba. Smithsonian Contr Paleobiol 27:169–187. aberrant island-dwelling theropod dinosaur from the affinities. Nature 465:466–468.

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