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Tyrannosaurus Tyrannosaurid Skeletal Design First Evolved at Small Body Size Paul C. Sereno, et al. Science 326, 418 (2009); DOI: 10.1126/science.1177428 The following resources related to this article are available online at www.sciencemag.org (this information is current as of November 25, 2009 ): Updated information and services, including high-resolution figures, can be found in the online version of this article at: http://www.sciencemag.org/cgi/content/full/326/5951/418 Supporting Online Material can be found at: http://www.sciencemag.org/cgi/content/full/1177428/DC1 A list of selected additional articles on the Science Web sites related to this article can be found at: http://www.sciencemag.org/cgi/content/full/326/5951/418#related-content This article cites 21 articles, 2 of which can be accessed for free: http://www.sciencemag.org/cgi/content/full/326/5951/418#otherarticles This article has been cited by 1 articles hosted by HighWire Press; see: http://www.sciencemag.org/cgi/content/full/326/5951/418#otherarticles This article appears in the following subject collections: Paleontology http://www.sciencemag.org/cgi/collection/paleo on November 25, 2009 Information about obtaining reprints of this article or about obtaining permission to reproduce this article in whole or in part can be found at: http://www.sciencemag.org/about/permissions.dtl www.sciencemag.org Downloaded from Science (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. Copyright 2009 by the American Association for the Advancement of Science; all rights reserved. The title Science is a registered trademark of AAAS. REPORTS and China, including Guanlong (8), Dilong (5), Tyrannosaurid Skeletal Design First and Xiongguanlong (9) and the more fragmentary Eotyrannus (10), Stokesosaurus (11), Aviatyrannis Evolved at Small Body Size (12), and Proceratosaurus (13). With body lengths of only 2 to 5 m, these finds confirmed that Paul C. Sereno,1* Lin Tan,2 Stephen L. Brusatte,3 Henry J. Kriegstein,4 tyrannosaurids evolved from small-bodied, long- “ ” Xijin Zhao,5 Karen Cloward6 armed tyrannoraptors (1, 4, 10). Evidence link- ing these precursors to their oversized descendants Nearly all of the large-bodied predators (>2.5 tons) on northern continents during the Late has been limited to a relatively small set of derived Cretaceous were tyrannosaurid dinosaurs. We show that their most conspicuous functional features in the skull and skeleton (5, 8, 9). On the specializations—a proportionately large skull, incisiform premaxillary teeth, expanded jaw-closing other hand, it has been thought that the much musculature, diminutive forelimbs, and hindlimbs with cursorial proportions—were present in a greater range of truly tyrannosaurian characters, new, small-bodied, basal tyrannosauroid from Lower Cretaceous rocks in northeastern China. These particularly those in the skull and limbs, evolved specializations, which were later scaled up in Late Cretaceous tyrannosaurids with body masses only with body size increase in Late Cretaceous approaching 100 times greater, drove the most dominant radiation of macropredators of the tyrannosaurids (14). Mesozoic. We describe here a new small-bodied theropod, Raptorex kriegsteini nov. gen. nov. 1Department of Organismal Biology and Anatomy, University yrannosaurus rex is the best-known of sumed to have evolved for hypercarnivory (strict 2 several tyrannosaurid species (1), which carnivory) at large body size. Tyrannosaurids have of Chicago, Chicago, IL 60637, USA. Long Hao Institute of “ ” Geology and Paleontology, Bureau of Land and Resources, T were dominant in their role as multi-ton been viewed as heterochronic peramorphs (5), 010010 Hohhot, People’s Republic of China (PRC). 3Division predators on northern continents during the final the largest of which grew beyond the size and of Paleontology, American Museum of Natural History, New 25 million years of the Mesozoic (2–4). Hallmark form of smaller-bodied ancestors (6) via devel- York,NY10024,USA.43 Evergreeen Lane, Higham, MA 5 tyrannosaurid adaptations include a relatively large opmental acceleration (7). 02043, USA. Institute of Vertebrate Paleontology and Paleo- anthropology, Chinese Academy of Sciences, 100044 Beijing, skull with enhanced jaw-closing musculature, en- In the past decade, fossils pertaining to earlier PRC. 6Western Paleontological Laboratories, Lehi, UT 84043, larged olfactory bulbs, a relatively miniaturized fore- and more primitive tyrannosauroid species have USA. limb with only two functional digits, and a pinched been discovered in rocks of Middle Jurassic to *To whom correspondence should be addressed. E-mail: pedal structure common to cursors—features pre- Early Cretaceous age in North America, Europe, [email protected] on November 25, 2009 Fig. 1. Skull, endocast, and premaxillary teeth of the Early Cretaceous tyrannosauroid R. kriegsteini.Theskull reconstruction in (A) lateral and (B) dorsal views is shown. (C) Partial endocast in dorsal view showing the enlarged olfactory peduncles and swollen cerebral hemispheres. (D)Skullmodelcomposedofcastbones as seen in a computed tomography scan showing a cross section (red) of the snout at mid-length. (E)Right www.sciencemag.org premaxilla in lateral view. (F) Right premaxillary crowns in posteromedial view. Abbreviations: a, angular; afo, accessory fossa; am, articular surface for the maxilla; antfe, antorbital fenestra; apmf, anterior premaxillary foramen; ar, articular; asaf, anterior surangular fora- men; ch, cerebral hemisphere; d, dentary; d1, d6, and d15, dentary tooth 1, 6, and 15; emf, external mandib- ular fenestra; en, external naris; f, frontal; fo, foramen; Downloaded from j, jugal; jfl, jugal flange; jfo, jugal fossa; lcp, lacrimal cornualprocess;l,lacrimal;lfo,lacrimalfossa;m,max- illa;m1,m6,andm13,maxillarytooth1,6,and13; mfe, maxillary fenestra; n, nasal; nfo, narial fossa; olp, olfactory peduncle; p, parietal; pb, pathologic bone; pf, prefrontal; pl, palatine; pm, premaxilla; pm1 and pm4, premaxillary tooth 1 and 4; pmfe, promaxillary fenestra; po, postorbital; pofl, postorbital flange; ps, parasphenoid; q, quadrate; qj, quadratojugal; ri, ridge; rt, replacement tooth; sa, surangular; safe, surangular fenestra; sas, surangular shelf; sq, squamosal; stf, supra- temporal fenestra; stfo, supratemporal fossa; vg, vas- cular groove. Scale bars, 3 cm in (C), 2 cm in (E), and 1cmin(F). 418 16 OCTOBER 2009 VOL 326 SCIENCE www.sciencemag.org REPORTS sp. (15), that exhibits all major tyrannosaurid forelimb (Fig. 3). Discovered in the Lujiatun Jehol Group in northeast China (15, 16), Raptorex functional specializations in the skull and skel- Beds [Hauterivian-Barremian stages, ~130 mil- is known from an articulated skeleton of a sub- eton (Figs. 1 and 2), including a diminutive lion years ago (Ma)] of the Lower Cretaceous adult or young adult approximately 5 to 6 years old, with an adult body length of no more than 3m(16). Many features place Raptorex within Tyran- nosauroidea, a clade including Tyrannosauridae and their closest relatives (Fig. 4). In the skull, for example, the premaxilla is anteroposteriorly short and bears teeth with incisiform crowns, the maxilla has only 13 teeth, the internasal suture is fused, the jugal has a marked inflection along its ventral margin, and the retroarticular process of the lower jaw is short and transversely broad (Fig. 1, A and B, and D to F). In the postcra- nial skeleton, likewise, the scapula has a strap- shaped blade, and the forelimb and ilium are relatively short and long, respectively. The prin- cipal phylogenetic question, rather, is where Raptorex falls within Tyrannosauroidea. The skull is proportionately large as in tyran- nosaurids, measuring approximately 40% of trunk length (Fig. 2A). The skull in most other thero- pods, including the basal tyrannosauroid Guanlong (8), is relatively smaller, measuring about 30% or less of trunk length (16). Many additional cranial characters link Raptorex and large-bodied tyran- nosaurids. The functional significance of some on November 25, 2009 of these characters is poorly understood, such as the textured, highly vascularized nasals (also in Eotyrannus), the sutural contact between the lac- rimal and frontal along the orbital margin, the pneumatic invasion of the bodies of the lacrimal Fig. 2. Postcranial features of the Early Cretaceous tyrannosauroid R. kriegsteini.(A) Skeletal silhouette showing preserved bones (missing portions shown in red; the cast of the bones was used to eliminate and squamosal, or the enlarged surangular fora- color distractions). (B) Axis (C2) in left lateral view. (C) Midcervical vertebra (C5) in left lateral view. (D) men (Fig. 1, A and B) (16). Scapulocoracoid (left) in lateral view. (E) Ilium (left) in lateral view. (F) Humerus (left) in anterior view. Strengthening of the skull roof, on the (G) Ulna and radius (left) in medial view. (H)Manus(right)indorsalview.(I) Manual digit I (right) in other hand, is clearly the functional role of www.sciencemag.org medial view. (J) Co-ossified anterior gastral elements in ventral view. (K) Femur (left) in distal view. (L) another suite of advanced cranial characters Distal tibia and astragalus (left) in anterior view. (M) Distal metatarsal 3 (right) in posterior view. (N) linking Raptorex and large-bodied tyranno- Proximal ischium (left) in lateral view. Abbreviations: I-1, manual digit I
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