Abstract
The historic fossil feather from the Jurassic Solnhofen has played a pivotal but controversial role in our evolutionary understanding of dinosaurs and birds. Recently, a study confirmed the diagnostic morphology of the feather’s original calamus, but nonetheless challenged the proposed identity as an Archaeopteryx covert. However, there are errors in the results and interpretations presented. Here we show that the feather is most likely an upper major primary covert, based on its long calamus (23.3% total length) and eight other anatomical attributes. Critically, this hypothesis is independently supported by evidence of similar primary coverts in multiple specimens of Archaeopteryx–including from the same fossil site and horizon as the isolated feather. We also provide additional insights, such as an updated colour reconstruction of the entire feather as matte black, with 90% probability. Given the isolated nature of the fossil feather, we can never know the anatomical and taxonomic provenance with 100% certainty. However, based on all available evidence, the most empirical and parsimonious conclusion is that this feather represents a primary covert from the ancient wing of Archaeopteryx.
Highlights
What anatomical identity is most supported? We evaluate the isolated feather across nine attributes, the relative calamus length
Including the diagnostic relative calamus length, all nine anatomical attributes of the isolated feather are most consistent with an identity as a upper major primary covert (UMPC), to the exclusion of all other candidate feather tracts
By virtue of the fossil feather’s isolated nature, we can never know the exact follicle or species from which the Urfeder originated with complete certainty
Summary
Including the diagnostic relative calamus length, all nine anatomical attributes of the isolated feather are most consistent with an identity as a UMPC, to the exclusion of all other candidate feather tracts. Attributes of the isolated feather that support it being a distal member of the UMPC tract include the relative calamus length being more similar (as mentioned above), vanes that are relatively asymmetric, and the angled distal tip; lack of an S-shaped centerline is more consistent with distal UMPCs in some modern birds (e.g., compare these traits in distal vs proximal members in Supplementary Fig. S6)[9,11,15,16,21]. If we consider all anatomical attributes aside from the relative calamus length, the most-supported identity of the isolated feather would still be a primary covert, albeit from a ventral tract–an under major primary covert (uMPC).
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