brief communications of three, with correspondingly larger energy Palaeontology penalties2,8. Each pair of fused pentagons in a neutral fullerene cage carries an energy The ‘feathers’ of ǁ penalty of 70–90 kJ mol 1 with respect to Longisquama the structure of C60 (ref. 8). Two candidate structures (isomers 6,140 and 6,275) have he elongated dorsal appendages of the the minimum three fused pentagon pairs; reptile Longisquama insignis, from the all others in the set have from 6 to 15 penta- TTriassic of Kyrgyzstan1, have recently gon fusions. been reinterpreted as the first record of We confirmed the qualitative preference feathers in a non-avian tetrapod2 — long for isomers with low numbers of fused pen- predating the feathers of the oldest known tagons using model calculations that treat bird, Archaeopteryx. Here we present evi- the cage as an empty fullerene capable of dence that the dorsal scales of Longisquama accepting electrons from a central reservoir. are not feathers, and that they are in fact At the density-functional tight binding strikingly different from avian feathers. We level of computation9, with full geometry conclude that Archaeopteryx remains the optimization of a closed-shell electron con- oldest known feathered tetrapod. figuration, the empty cage 6,140 is stabi- Longisquama is a small diapsid reptile lized by 120 kJ molǁ1 with respect to its with an uncertain phylogenetic position. It nearest rival, with a 12-line NMR spectrum is known from an incomplete skeleton with and the minimal three pentagon adjacen- integumentary appendages and isolated cies (isomer 6,275). As between two and six appendages. Appendage PIN (for Palaeon- excess electrons are added to the cage, to tological Institute of the Russian Academy simulate the range of likely charge transfer of Sciences) 2584/7, preserved as part and from the encapsulated cluster, isomer 6,140 counterpart, retains an infilling of fine- becomes increasingly favoured over all grained sediment and high-fidelity impres- other empty cages in the set. In view of this sions of the external left and right surfaces consistent preference, we propose a struc- of the appendage (Fig. 1). This infilling, ture for Sc3N@C68 (Fig. 2) consisting of the preserved either on one side of the speci- encapsulated Sc3N cluster in the C68 (D3) men or on the counterpart, shows that the three-fold symmetric isomer 6,140 cage. tubular configuration described for the Figure 1 Part and counterpart of an elongated dorsal scale of

The encapsulated Sc3N cluster is shown proximal portion extends along the entire Longisquama insignis (PIN 2584/7). Where the sedimentary infill- with the Sc atoms on C2 axes, but from the length of the appendage, although the distal ing (black circles) is not preserved, sharp impressions of the cor- 45Sc NMR it is also possible that these repre- portion is expanded anteroposteriorly and rugated external surface of the structure are visible (white circles). sent time-averaged orientations. flattened transversely. This indicates that in Arrows point to corresponding patches of sedimentary infilling on S. Stevenson*, P. W. Fowler†, T. Heine‡, life the two external surfaces were separated part and counterpart. ab, anterior smooth band; c, corrugations; J. C. Duchamp§, G. Rice*, T. Glass*, from each other by an intervening space v, median ‘vein’. K. Harich*, E. Hajdu||, R. Bible||, H. C. Dorn* (now sediment-filled). *Department of Chemistry, Virginia Tech, There are no feather-like features on the and counterparts of feather impressions in Blacksburg, Virginia 24061, USA distal portion of the appendage. Here, two Archaeopteryx are concave and convex, e-mail: [email protected] corrugated membrane-like surfaces touch respectively. †School of Chemistry, University of Exeter, along their leading and trailing edges to form We believe that the dorsal appendages of Stocker Road, Exeter EX4 4QD, UK wide, smooth bands. The two membranes Longisquama are highly modified scales, as ‡Dipartimento di Chemica ‘G. Ciamician’, were apparently supported by a median vein- suggested previously1,3, rather than feathers. Università di Bologna, via Selmi 2, like structure extending the length of the Examination of the holotype of L. insignis Bologna I-40126, Italy appendage. This has been proposed as the (PIN 2584/4) suggests that they were §Department of Chemistry, Emory and Henry homologue of the rhachis of avian feathers2. anchored in the skin or epaxial muscles. College, Emory, Virginia 24327-0943, USA On either side of this ‘vein’, the external sur- Robert R. Reisz*, Hans-Dieter Sues† ||Searle, 4901 Searle Parkway, Skokie, faces of the appendage are corrugated. This *Department of Biology, University of Toronto in Illinois 60077, USA corrugation varies along the appendage: Mississauga, 3359 Mississauga Road, Mississauga, 1. Kroto, H. W. Nature 329, 529–531 (1987). proximally, individual rugae are relatively Ontario L5L 1C6, Canada 2. Kobayashi, K., Nagase, S., Yoshida, M. & Osawa, E. large and widely spaced, but in the distal e-mail: [email protected] J. Am. Chem. Soc. 119, 12693–12694 (1997). 3. Dorn, H. C. et al. in Fullerenes: Recent Advances in the portion they are smaller and densely packed. †Department of Palaeobiology, Royal Ontario Chemistry and Physics of Fullerenes and Related Materials (eds The densely arranged distal corrugations Museum, 100 Queen’s Park, Toronto, Kadish, K. M. & Ruoff, R. S.) 990–1002 (Electrochemical have been compared to the pinnae of avian Ontario M5S 2C6, Canada Society, Pennington, 1998). 2 e-mail: [email protected] 4. Butenschön, H. Angew. Int. Edn Engl. 36, 1695–1697 feathers , but the fossils indicate that these (1997). are formed on a membrane-like structure on 1. Sharov, A. G. Paleontol. Zhur. 1970, 127–130 (1970). 5. Krätschmer, W., Fostiropoulos, K. & Huffman, D. R. Chem. either side of the ‘vein’. 2. Jones, T. et al. Science 288, 2202–2205 (2000). Phys. Lett. 170, 167–170 (1990). The fossils were split into part and coun- 3. Feduccia, A. The Origin and Evolution of Birds (Yale Univ. Press, 6. Stevenson, S. et al. Nature 401, 55–57 (1999). New Haven, 1996). 7. Fowler, P. W. & Manoloupoulos, D. E. An Atlas of Fullerenes terpart during collecting, and most of the (Oxford Univ. Press, Oxford, 1995). appendages are now preserved as impres- 8. Albertazzi, E. et al. Phys. Chem. Chem. Phys. 1, 2913–2919 sions of their left and right sides, without Correction (1999). the intervening sediment core. The surfaces Detection of preinvasive cancer cells 9. Seifert, G., Porezag, D. & Frauenheim, T. Int. J. Quantum Chem. 58, 185–192 (1996). of both the part and counterpart impres- V. Backman et al. sions of individual appendages are concave, Nature 406, 35–36 (2000) Supplementary information is available on Nature’s World-Wide Web site (http://www.nature.com) or as paper copy from the an indication that these structures are The name of the tenth author of this communication is London editorial office of Nature. three-dimensional. In contrast, the parts J. A. McGilligan (not T. McGillican as published). © 2000 Macmillan Magazines Ltd 428 NATURE | VOL 408 | 23 NOVEMBER 2000 | www.nature.com