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scientific correspondence allele dropout3. Consequently, this tech- The structure of Enantiornithine bird the expanded base and waisted crown typi- nique requires validation before use in skulls is poorly understood. Until now, the cal of all known toothed birds (Fig. 1g). forensic casework. We are currently investi- best known was Gobipteryx, of which there The ‘T’-shaped lacrimal is inclined post- gating a robust interpretation strategy for are fragmentary adult and embryonic eriorly. The braincase is expanded over that single-cell STR profiling. This work also skulls6 showing the absence of teeth, a in Archaeopteryx (Fig. 1 b,d) and this may raises issues about STR profiling low num- reduced antorbital fenestra and an reflect an increased brain size coupled with bers of cells and the need for stringent pre- Archaeopteryx-like quadrate. an improved shoulder girdle (keeled ster- cautions in collecting and processing to Cathayornis from the Early Cretaceous num) and presumably more sophisticated avoid contamination. of China has the typical elongated outer powers of flight in Cathayornis. There is a I. Findlay, A. Taylor, P. Quirke metacarpal and the characteristic shapes of bone in the posterior corner of the skull Department of Molecular Oncology, the scapula, coracoid, and distal tibiotarsus that might be a squamosal, but the Algernon Firth Building, University of Leeds, found in later enantiornithine birds3,7. quadrate articulation and basicranial Leeds LS2 9LN, UK Photographs of the skull have been pub- region is not preserved in our material, nor R. Frazier, A. Urquhart lished8 and a drawing of it as it is pre- is the quadratojugal and jugal. Forensic Science Service, Gooch Street North, served7, but there has been no detailed There is a well-preserved quadrate (Fig. Birmingham B5 6QQ, UK reconstruction of any enantiornithine skull 1f) lying disarticulated and behind one

1. van Oorschot, R. A. H. & Jones, M. K. Nature 387, 767 (1997). published to date. Our reconstruction (Fig. skull (IVPP, V10916). It is a long slender 2. Sparkes, R. et al. Int. J. Legal Med. 109, 195–204 (1996). 1) is based on the holotype of Cathayornis bone with a single small proximal head and 3. Findlay, I., Ray, P., Quirke, P., Rutherford, A. J. & Lilford, R. (specimen IVPP, V9769) and skulls from very little orbital process. It is similar to the Hum. Reprod. 10, 1609–1618 (1996) . two skeletons referred to that genus (IVPP, quadrate (Fig. 1e) of the London, Eichstätt V10896 and V10916). The latter two skulls and seventh Archaeopteryx specimens9 and provide information on the maxilla, to that of Gobipteryx. In Archaeopteryx the lacrimal and a lateral view of the quadrate. dorsal process of the jugal is too far back to Archaeopteryx-like skull The premaxilla bears four or five small contact a postorbital even if one were pre- teeth that are directed downwards or sent10. The reduction or loss of the post- in Enantiornithine bird slightly forwards. It is covered externally orbital frees the jugal bar for prokinesis and with large nutrient foramina. The dorsal may have occurred more than once in The bird Cathayornis from the Early Creta- process of the premaxilla extends posteri- avian evolution. Cathayornis lacks evidence ceous period gives the first evidence for a orly slightly beyond the edge of the nares for a postorbital but one is present in Con- post-Jurassic survival of an Archaeopteryx- (nostrils). It is slightly shorter in fuciusornis. The flattened nature of the like skull in birds. This skull combines Archaeopteryx (Fig. 1 c,d). The nares meet nasal and the nasal process of the premax- short, toothed premaxillaries, nasals meet- on the midline as in Archaeopteryx and are illa7 may also indicate the presence of ing at the midline and submaxillary fossae overlapped by the premaxillaries on their prokinesis in Cathayornis. in the antorbital fenestra. anterior process. If Archaeopteryx and the Enantiornithes During the late Mesozoic era, from the The premaxillaries are toothed and are united into a monophyletic Sauriurae1, Early Cretaceous to the latest Cretaceous about one-third the length of the skull then the presence of a primitive Archaeo- (Maestrichtian), two distinct groups of compared to about one-quarter in Archaeo- pteryx-like skull in Cathayornis, after the birds co-existed as separate lineages1,2. One pteryx, and the nasals are shortened. The derived postcranial differences between of these, the ornithurine birds, survived antorbital fenestra is large and triangular enantiornithine and ornithurine birds was into the Cenozoic era to give rise to all with two distinct anterior maxillary fossae. established, indicates that the modern modern birds3,4. The other lineage, the The maxillary is toothed. Teeth are set in ornithurine skull and ‘typical avian kinesis’ Enantiornithes, became extinct along with sockets indicating that the individuals are was developed independently by ornith- dinosaurs at the end of the Cretaceous3,5. mature. The teeth are not serrated and have urine birds. Larry D. Martin a fr b pa fr Zhonghe Zhou* na na Natural History Museum oc pm pm and Department of Systematics and Ecology, la University of Kansas, Lawrence, pa 5mm Kansas 66045, USA q ma *and Institute of Vertebrate Paleontology and dn fr 1mm la na Paleoanthropology, pm c 5mm pa Chinese Academy of Sciences, PO Box 643, fr Beijing 100044, China oc pa e-mail: [email protected] 5mm d na g 1. Hou, L., Martin, L. D., Zhou, Z. & Feduccia, A. Science 274, la pm 1164–1167 (1996). 2. Martin, L. D. in Origin of the Higher Groups of Tetrapods (eds j Schultze, H. P. & Trueb, L.) 485–540 (Comstock, Ithaca, 1991). q 1mm 1mm ma 3. Martin, L. D. Cour. Forschungsinst. Senckenberg 181, 23–36 qj sa (1995). e f 4. Feduccia, A. The Origin and Evolution of Birds (Yale Univ. Press, dn 5mm New Haven, 1996). art an 5. Chiappe, L. M. Nature 378, 349–355 (1995). 6. Elzanowski, A. Paleontol. Polon. 42, 147–179 (1981). Figure 1 Reconstruction of skull structures of Cathayornis and Archaeopteryx. a, Lateral view of Cathayor- 7. Zhou, Z. Cour. Forschungsinst. Senckenberg 181, 9–22 (1995). nis. b, Dorsal view of Cathayornis. c, Lateral view of Archaeopteryx. d, Dorsal view of Archaeopteryx. e, 8. Zhou, Z., Jin, F. & Zhang, J. Chinese Sci. Bull. 37, 1365–1368 Quadrate of Archaeopteryx. f, Quadrate of Cathayornis. g, Labial view of tooth from the maxillary of Cathay- (1992). 9. Wellnhofer, P. Archaeopteryx 11, 1–47 (1993). ornis. Abbreviations: an, angular; art, articular; dn, dentary; fr, frontal; j, jugal; la, lacrimal; ma, maxillary; na, 10.Elzanowski, A. & Wellnhofer, P. J. Vert. Paleontol. 16, 81–94 nasal; oc, occipital; pa, parietal; pm, premaxillary; q, quadrate; qj, quadratojugal; sa, surangular. (1996).