Abstract
Although skeletal remains of the iconic oldest known avialian Archaeopteryx have been known for almost 150 years, several aspects of the cranial anatomy of this taxon have remained enigmatic, mainly because of the strongly flattened and often fractured and incomplete nature of available skull materials. New investigation of the skulls of the recently described, excellently preserved tenth (Thermopolis) and the seventh (Munich) specimens revealed several previously unrecognized characters and helps to resolve some problematic issues. Thus, the nasal of Archaeopteryx shows a lateral notch for the lacrimal, as is found in many other saurischian dinosaurs, the maxilla clearly participates in the margin of the external nares, and there seems to be a pneumatic foramen in the lacrimal, comparable to the lacrimal fenestra found in many non-avian theropods. In the braincase, Archaeopteryx shows pneumatic features reminiscent of non-avian theropods, including a ventral basisphenoid recess and an anterior tympanic recess that is laterally incised into the basisphenoid/prootic. Most importantly, however, the postorbital process of the jugal shows a facet for the suture with the postorbital, thus resolving the question of whether Archaeopteryx had a closed postorbital bar. A new reconstruction of the skull of Archaeopteryx is presented, making the skull of this taxon even more theropod-like than previously recognized. Furthermore, the closed postorbital bar and the configuration of the bones of the skull roof cast serious doubt on claims that an avian-style cranial kinesis was present in this taxon.
Kurzfassung
Obwohl Skelettreste des ältesten bekannten Vogels Archaeopteryx seit nun 150 Jahren bekannt sind, sind einige Aspekte der Schädelanatomie dieses Taxon weiter ungewiss, vor allem da die meisten bekannten Schädelreste stark komprimiert und meist zerbrochen und unvollständig sind. Neue Untersuchungen am Schädel des kürzlich beschriebenen und hervorragend erhaltenen 10. (Thermopolis) und des 7. (Münchener) Exemplares zeigen einige bisher unerkannte Merkmale der Schädelanatomie und helfen, andere bisher umstrittene Fragen zu lösen. So zeigt das Nasale von Archaeopteryx einen lateralen Einschnitt für die Sutur mit dem Lacrimale, wie er bei vielen Saurischia vorhanden ist, das Maxillare hat Anteil am Rand der externen Nares und das Lacrimale hat offenbar ein großes, pneumatisches Foramen, das in seiner Position dem Lacrimal-Fenster vieler basalerer Theropoden entspricht. Im Hirnschädel zeigt Archaeopteryx Merkmale die an jene basalerer Theropoden erinnern, so etwa einen Rezessus basisphenoidalis und einen anterioren tympanischen Rezessus, der von lateral in das Basisphenoid und das Prooticum einschneidet. Insbesondere zeigt jedoch der Postorbital-Fortsatz des Jugale eine Facette für die Sutur mit dem Postorbitale, was die Frage klärt, ob Archaeopteryx eine geschlossene Postorbital-Spange besass. Eine neue Rekonstruktion des Schädels von Archaeopteryx macht diesen noch Theropoden-ähnlicher als bisher angenommen. Zudem stellt die geschlossene Postorbital-Spange und die Konfiguration der Knochen des Schädeldaches die angenommene Vogel-ähnliche Schädel-Kinetik bei Archaeopteryx in Frage.
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Acknowledgments
This article resulted from the Archaeopteryx event during the Munich Mineralientage in 2009, during which six of the original Archaeopteryx specimens were gathered together. Special thanks are therefore due to Christoph Keilmann, who made this event possible, and the institutions and private individuals who made their specimens of the Urvogel available during the event. Very special thanks are furthermore due to Burkhard Pohl for the loan of the Thermopolis specimen after the event and to Helmut Tischlinger for UV photography. The article benefited from discussions with Christian Foth, Xu Xing, and Adriana López-Arbarello, and from financial support by the Volkswagen Foundation under grant AZ I/84 640. Gerald Mayr is thanked for a critical review of the manuscript.
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Rauhut, O.W.M. New observations on the skull of Archaeopteryx . Paläontol Z 88, 211–221 (2014). https://doi.org/10.1007/s12542-013-0186-0
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DOI: https://doi.org/10.1007/s12542-013-0186-0