DNA content and distribution in ancient feathers and potential to reconstruct the plumage of extinct avian taxa

Abstract

Feathers are known to contain amplifiable DNA at their base (calamus) and have provided an important genetic source from museum specimens. However, feathers in subfossil deposits generally only preserve the upper shaft and feather 'vane' which are thought to be unsuitable for DNA analysis. We analyse subfossil moa feathers from Holocene New Zealand rockshelter sites and demonstrate that both ancient DNA and plumage information can be recovered from their upper portion, allowing species identification and a means to reconstruct the appearance of extinct taxa. These ancient DNA sequences indicate that the distal portions of feathers are an untapped resource for studies of museum, palaeontological and modern specimens. We investigate the potential to reconstruct the plumage of pre-historically extinct avian taxa using subfossil remains, rather than assuming morphological uniformity with closely related extant taxa. To test the notion of colour persistence in subfossil feathers, we perform digital comparisons of feathers of the red-crowned parakeet (Cyanoramphus novaezelandiae novaezelandiae) excavated from the same horizons as the moa feathers, with modern samples. The results suggest that the coloration of the moa feathers is authentic, and computer software is used to perform plumage reconstructions of moa based on subfossil remains.

Figure 1.

(a) Morphological structure of a palaeognathus feather, here shown by emu (Dromaius novaehollandiae). The main shaft (rachis) supports side branches (barbs) and together makes up the distal component of feathers. In vaned feathers, barbs are held together by small sub-branches termed barbules, which in turn are held together by interlocking hooks or barbicels. (b) A schematic representation of the distal feather components sampled in this study using a neo-avian feather to illustrate the role of barbules and barbicels in forming a vaned structure characteristic of flighted birds.

Figure 2.

Quantification of the amount of colour fading in subfossil red facial and green contour feathers of red-crowned parakeet (C. novaezelandiae novaezelandiae) from the Late Holocene Roxburgh Gorge rockshelter B with modern red-crowned parakeet feathers in RGB colour space. The graph indicates that the amount of colour fading in subfossil parakeet feathers is minimal. The colours of moa feathers from the same deposits are also likely to be relatively unmodified.

Figure 3.

Characteristic morphology and colour of moa feathers identified from ancient DNA sequences. (a) Feathers identified as upland moa (M. didinus), South Island giant moa (D. robustus), stout-legged moa (E. gravis) and heavy-footed moa (P. elephantopus) exhibited overlapping morphology and colour. The three best examples are shown. From left to right: upland moa (OM Av10793.1), upland moa (OM Av10791.1), South Island giant moa (OM Av10793.2). (b) White-tipped feather (A 06.49.18) identified as heavy-footed moa. Scale bar, 10 mm.

Figure 4.

(a) Plumage of brown kiwi (A. australis); (b) plumage of great-spotted kiwi (A. haastii); (c) plumage of little-spotted kiwi (A. oweni); (d) reconstruction of upland moa (M. didinus), South Island giant moa (D. robustus), stout-legged moa (E. gravis) and heavy-footed moa (P. elephantopus) plumage based on a dark feather; (e and f) reconstruction of upland moa and heavy footed moa plumage based on white-tipped feathers, (e) densely and (f) sparsely spaced.