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Jurassic Archosaur Is a Non-Dinosaurian Bird Jurassic archosaur is a non-dinosaurian bird Stephen A. Czerkas & Alan Feduccia Journal of Ornithology ISSN 2193-7192 Volume 155 Number 4 J Ornithol (2014) 155:841-851 DOI 10.1007/s10336-014-1098-9 1 23 Your article is protected by copyright and all rights are held exclusively by Dt. Ornithologen-Gesellschaft e.V.. This e-offprint is for personal use only and shall not be self- archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy J Ornithol (2014) 155:841–851 DOI 10.1007/s10336-014-1098-9 ORIGINAL ARTICLE Jurassic archosaur is a non-dinosaurian bird Stephen A. Czerkas • Alan Feduccia Received: 17 April 2014 / Revised: 4 June 2014 / Accepted: 13 June 2014 / Published online: 9 July 2014 Ó Dt. Ornithologen-Gesellschaft e.V. 2014 Abstract Re-examination utilizing Keyence 3D digital Keywords Scansoriopteryx Á Epidendrosaurus Á microscopy and low angled illumination of the fossil Theropod Á Archosaur Á Daohugou Biota Á Jurassic Scansoriopteryx, a problematic sparrow-size pre-Archae- opteryx specimen from the Jurassic Daohugou Biotas, pro- Zusammenfassung vides new evidence which challenges the widely accepted hypothesis that birds are derived from dinosaurs in which Archosaurier aus dem Jura ist ein nicht-dinosaurischer avian flight originated from cursorial forms. Contrary to Vogel previous interpretations in which Scansoriopteryx was con- sidered to be a coelurosaurian theropod dinosaur, the absence Eine erneute Untersuchung mittels Keyence-3D-Digi- of fundamental dinosaurian characteristics demonstrates that talmikroskopie und Dunkelfeldbeleuchtung des fossilen it was not derived from a dinosaurian ancestry and should not Scansoriopteryx, eines zweifelhaften sperlingsgroßen pra¨- be considered as a theropod dinosaur. Furthermore, the Archaeopteryx-Beleges aus den jurassischen Daohugou- combination in which highly plesiomorphic non-dinosaurian Schichten, liefert neue Hinweise, welche die weithin ane- traits are retained along with highly derived features, yet only rkannte Hypothese in Frage stellen, dass Vo¨gel von Di- the beginnings of salient birdlike characteristics, indicates nosauriern abstammen und sich der Vogelflug u¨ber that the basal origins of Aves stemmed from outside the laufende Formen entwickelte. Im Widerspruch zu fru¨heren Dinosauria and further back to basal archosaurs. Impressions Deutungen, die Scansoriopteryx als Coelurosaurier, also of primitive elongate feathers on the forelimbs and hindlimbs einen theropoden Dinosaurier, betrachteten, zeigt das suggest that Scansoriopteryx represents a basal form of Fehlen grundlegender Dinosaurier-Eigenschaften, dass er ‘‘tetrapteryx’’ in which incipient aerodynamics involving nicht von Dinosauriervorfahren abstammt und somit auch parachuting or gliding was possible. Along with unique nicht als theropoder Dinosaurier angesehen werden sollte. adaptations for an arboreal lifestyle, Scansoriopteryx fulfills Außerdem deuten die in Kombination mit stark abgeleite- predictions from the early twentieth century that the ances- ten Merkmalen erhaltenen deutlich plesiomorphen Nicht- tors of birds did not evolve from dinosaurs, and instead were dinosaurier-Eigenschaften bei gleichzeitig erst in Ansa¨tzen derived from earlier arboreal archosaurs which originated vorhandenen vogelartigen Auspra¨gungen darauf hin, dass flight according to the traditional trees-down scenario. die tieferen Urspru¨nge der Aves außerhalb der Dinosaurier liegen und weiter zuru¨ck zu den basalen Archosauriern reichen. Abdru¨cke primitiver verla¨ngerter Federn an den Communicated by F. Bairlein. Vorder- und Hinterextremita¨ten legen nahe, dass Scanso- S. A. Czerkas riopteryx eine basale Form eines ,,Tetrapteryx‘‘war, bei der The Dinosaur Museum, Blanding, UT 84511, USA beginnende Aerodynamik in Gestalt von Segel- oder Gleitflug mo¨glich war. In Verbindung mit einzigartigen & A. Feduccia ( ) Anpassungen an eine baumbewohnende Lebensweise er- Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA fu¨llt Scansoriopteryx Vorhersagen aus dem fru¨hen 20. e-mail: [email protected] Jahrhundert, die besagen, dass sich die Vorfahren der 123 Author's personal copy 842 J Ornithol (2014) 155:841–851 Vo¨gel nicht aus Dinosauriern entwickelten, sondern essentially as exaptations, through a complex series of stattdessen von fru¨heren baumbewohnenden Archosauriern biophysically improbable events from a completely cur- abstammen, bei denen sich der Flug gema¨ß der tradition- sorial lifestyle. While not the only possible scenario for ellen Baumtheorie entwickelte. how birds evolved, the cursorial ground–up model has been firmly embraced by paleontologists using phylogenetic analyses to support their conclusions (Chiappe 2007). Scansoriopteryx represents the opposite hypothesis in Introduction which birds are derived from non-dinosaurian archosaurs that were already small and had adapted to an arboreal The search for a suitable prototype for avian ancestry has lifestyle. Jumping, parachuting, and gliding are all pre- intensified with the opening of the Chinese Lower Creta- dictable incipient stages of flight behavior, each totally ceous Jehol Biota during the past two decades, but atten- adaptive, which are readily seen in some extant reptiles, as tion is now shifting to the older components of the well as rarer examples in the fossil record, some of which Daohugou Biota of Jurassic age, considered variously as date back to the Triassic or Upper Permian (McGuire and troodontid feathered dinosaurs or early birds (Feduccia Dudley 2011; Frey et al. 1997). That the origin of birds 2012, 2013). Among the most intriguing, but still poorly would have involved some manner of jumping, parachut- understood, older elements are the scansoriopterygids, ing, and gliding is substantiated by this re-examination of Scansoriopteryx (=Epidendrosaurus) (Czerkas and Yuan Scansoriopteryx and fulfills predictions from the early 2002; Zhang et al. 2002). twentieth century that the ancestor of birds was a small, Previous interpretations from independent studies are in arboreal basal archosaur (Steiner 1918) and a ‘‘tetrapteryx’’ agreement that scansoriopterygids (Scansoriopteryx/Epi- glider (Beebe 1915). The impressions of feathered wings in dendrosaurus and Epidexipteryx) are more plesiomorphic Scansoriopteryx are consistent with its basal level of avian than Archaeopteryx and are probably very close to the status and provide important insights towards understand- origin of birds (Zhang et al. 2008; Xu et al. 2010; Sullivan ing how birds first achieved the ability to fly. et al. 2014). These studies have also independently con- The non-dinosaurian and basal avian status of Scanso- cluded that Scansoriopteryx was arboreal. However, there riopteryx presents challenges for phylogenetic interpreta- is disagreement as to what Scansoriopteryx should be tions which must account for maniraptorans having regarded as either a coelurosaurian theropod dinosaur or an characteristics that appear to look avian. Either they are avian ancestor derived from non-dinosaurian archosaurs. dinosaurs with exaptations of flight-related anatomy as For more than three decades, since the discovery of interpreted within the constraints of cladistic analyses, or Deinonychus and the use of cladistics employed towards more likely that they are basal forms of secondarily deciphering dinosaurian phylogenetics and how birds are flightless birds derived from birds which had at least some related to them, an essential criterion has been that bird- incipient ability to fly. Variations of this last option were like dinosaurs were non-avian, primarily based on their proposed as early as the mid-1980s (Paul 2002; Olshevsky obvious inability to fly and the assumption that they were 1992), but have been largely ignored especially by phylo- not derived from volant ancestors. This non-avian status is genetic analyses. As interpreted in this paper, the second- crucial to the hypothesis that birds are derived from such ary flightless scenario necessitates that maniraptorans are dinosaurs represented by maniraptorans (dromaeosaurs, not true theropods or dinosaurs because they would have troodontids, oviraptorosaurids) in that their avian-looking been derived from birds more or less at the evolutionary characteristics are accounted for as exaptations which were level seen in Scansoriopteryx, or at a slightly more not originally used for flight. Under this premise, the origin advanced stages. If so, then similarities linking manira- of birds supposedly evolved at least a rudimentary form of ptorans to dinosaurs are mistaken interpretations due to flight anatomy indirectly from behavior not associated with convergence, examples of which are revealed by this re- flight. As improbable as this might be, these non-avian examination of Scansoriopteryx. forms then had to evolve into relatively tiny sizes in which While palaeontologists have in recent decades embraced the exaptations could eventually be co-opted into being the view that birds are
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