Detection of lost calamus challenges identity of isolated Archaeopteryx feather

Abstract

In 1862, a fossil feather from the Solnhofen quarries was described as the holotype of the iconic Archaeopteryx lithographica. The isolated feather's identification has been problematic, and the fossil was considered either a primary, secondary or, most recently, a primary covert. The specimen is surrounded by the 'mystery of the missing quill'. The calamus described in the original paper is unseen today, even under x-ray fluorescence and UV imaging, challenging its original existence. We answer this question using Laser-Stimulated Fluorescence (LSF) through the recovery of the geochemical halo from the original calamus matching the published description. Our study therefore shows that new techniques applied to well-studied iconic fossils can still provide valuable insights. The morphology of the complete feather excludes it as a primary, secondary or tail feather of Archaeopteryx. However, it could be a covert or a contour feather, especially since the latter are not well known in Archaeopteryx. The possibility remains that it stems from a different feathered dinosaur that lived in the Solnhofen Archipelago. The most recent analysis of the isolated feather considers it to be a primary covert. If this is the case, it lacks a distinct s-shaped centerline found in modern primary coverts that appears to be documented here for the first time.

Figure 1

The isolated Archaeopteryx feather, Berlin specimen MB.Av.100. (A) As it looks today under white light (see Plates 1 & 5 [Fig. 1] of, Fig. 1A of and Plate 10 of). (B) Original drawing from 1862 by von Meyer. (C) Laser-Stimulated Fluorescence (LSF) showing the halo of the missing calamus (negative image). See Fig. S2 for additional images of the main slab, specimen BSP 1869 VIII 1 (‘Munich slab’). Scale bar 1 cm.

Figure 2

Overlay of the isolated feather MB.Av.100 scaled to the same size as the most similar secondary feather in the wing of the Berlin Archaeopteryx MB.Av.101. Significant foreshortening of the isolated feather does not support its association with Archaeopteryx.

Figure 3

Size-normalized centerline calamus-rachis traces for the primary coverts of 24 modern birds compared to the trace of the isolated feather (Berlin specimen, MB.Av.100). The blue line is the isolated feather’s trace whilst the orange line is from the common magpie (Pica pica, Fig. S3) whose wing has been cited as the isolated feather’s closest modern match^,. In brown is the centerline trace from a modern Undulated Tinamou (Crypturellus undulatus UWBM 71526, Fig. S4), which belongs to the only groups of extant palaeognaths with flight capabilities. The yellow zone represents the area covered by the traces of all 24 measured feathers, including a 1.5% error zone allowing for taphonomic flex (see Fig. S1). In all cases the isolated feathers centerline is a large departure from modern primary coverts.