Abstract
Dinosaurs with fossilized filamentous integument structures are usually preserved in a highly flattened state. Several different feather types have been described on this basis, but the two-dimensional preservation of specimens during fossilization makes the identification of single feather structures difficult due to overlapping feather structures in vivo. Morphological comparison with the diversity of recent feather types is therefore absolutely vital to avoid misinterpretation. To simulate the preservation process, a cadaver of recent Carduelis spinus (European siskin) was flattened in a printing press. Afterwards, the structure of the plumage was compared with the morphology of a single body feather from the same specimen. In comparison with the single feather, the body plumage of the flattened bird looked rather filamentous. It was almost impossible to identify single structures, and in their place, various artefacts were produced. The investigation of plumage in a specimen of the Mesozoic bird Confuciusornis sanctus reveals similar structures. This indicates that flattening of specimens during fossilization amplifies the effect of overlapping among feathers and also causes a loss of morphological detail which can lead to misinterpretations. The results are discussed in connection with some dubious feather morphologies in recently described theropods and basal birds. Based on recent feather morphology, the structure of so-called proximal ribbon-like pennaceous feathers (PRPFs) found in many basal birds is reinterpreted. Furthermore, the morphology of a very similar-looking feather type found in the forelimb and tail of an early juvenile oviraptorosaur is discussed and diagnosed as the first feather generation growing out of the feather sheath. Thus, the whole plumage of this theropod might represent neoptile plumage.
Kurzfassung
Dinosaurier mit fossilierten, filamentösen Integument-Strukturen sind in der Regel stark zerdrückt erhalten. Basierend auf diesen Funden wurden mehrere Federtypen beschrieben, allerdings ist die zweidimensionale Erhaltung während der Fossilisation die Identifikation von einzelnen Federstrukturen erschwert, da Federstrukturen in vivo einander überlappen. Des Weiteren ein morphologischer Vergleich mit der Fülle von rezenten Federtypen absolut wichtig ist, um Fehlinterpretationen zu vermeiden. Um diesen Prozess nachzuvollziehen wurde ein Kadaver von Carduelis spinus in einer Druckerpresse zerdrückt. Im Anschluss wurde die Struktur des Gefieders mit der Morphology einer einzelnen Körperfeder von Carduelis spinus verglichen. Im Vergleich zu der Einzelfeder ist das Gefieder des zerdrückten Vogels eher faserig. Einzelne Strukturen lassen sich schwer nachweisen, es können jedoch artifizielle Strukturen beobachtet werden. Die Untersuchung des Gefieders eines Exemplars des mesozoischen Vogels Confuciusornis sanctus führt zum ähnlichen Resultat. Das bedeutet, dass das Zerdrücken der Kadaver während der Fossilisation den Effekt der Überlappung verstärkt und ebenfalls zum Verlust von morphologischen Details führt, was zu Fehlinterpretationen verleiten kann. Die Ergebnisse werden im Zusammenhang mit einigen fragwürdigen Federmorphologien bei kürzlich beschriebenen Theropoda und basalen Vögeln diskutiert. Basierend auf der Morphologie von rezenten Federn wird der Aufbau von so genannten proximal ribbon-like pennaceous feathers (PRPFs), wie man sie bei vielen basalen Vögeln findet, neu interpretiert. Weiterhin wird die Morphologie eines ähnlichen aussehenden Federtyps, der an den Armen und am Schwanz bei einem sehr jungen Oviraptorosaurier ausgebildet ist, diskutiert und als erste Federgeneration, die gerade aus der Federscheide wächst, bestimmt. Daraus folgt, dass wahrscheinlich das gesamte Gefieder dieses Theropoden zum Neoptil-Gefieder gehört.
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Acknowledgments
I would like to thank Norma Schmitz and Ragnar Kinzelbach for access to the Zoological Collection of the University of Rostock; Felix Quade and Clemens Döring for organizing the printing press; Bastian Klußmann and Ole Sten Møller for taking the pictures of Carduelis spinus and Rhea americana; and Daniela Schwarz-Wings for access to the collection of the Natural History Museum of Humboldt University, Berlin. Further thanks go to Ole Sten Møller, Alexander Scheuerlein, Gerald Mayr, David Martill and one anonymous reviewer for very helpful comments on earlier versions of the manuscript; and to Lucy Cathrow and Jennifer Lane for improving the English.
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Foth, C. On the identification of feather structures in stem-line representatives of birds: evidence from fossils and actuopalaeontology. Paläontol Z 86, 91–102 (2012). https://doi.org/10.1007/s12542-011-0111-3
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DOI: https://doi.org/10.1007/s12542-011-0111-3