A Diverse Assemblage of Late Cretaceous Dinosaur and Bird Feathers From Canadian Amber

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A Diverse Assemblage of LateCretaceous Dinosaur and BirdFeathers from Canadian AmberRyan C. McKellar,1* Brian D. E. Chatterton,1 Alexander P. Wolfe,1 Philip J. Currie2

The fossil record of early feathers has relied on carbonized compressions that lack finestructural detail. Specimens in amber are preserved in greater detail, but they are rare. Late Cretaceouscoal-rich strata from western Canada provide the richest and most diverse Mesozoic featherassemblage yet reported from amber. The fossils include primitive structures closely matching theprotofeathers of nonavian dinosaurs, offering new insights into their structure and function.Additional derived morphologies confirm that plumage specialized for flight and underwaterdiving had evolved in Late Cretaceous birds. Because amber preserves feather structureand pigmentation in unmatched detail, these fossils provide novel insights regardingfeather evolution.

Although amber offers unparalleled pres-

ervation of feathers (14), only isolated

specimens of uncertain affinity have been

reported from the Late Cretaceous (5). This con-

trasts with the rich Early Cretaceous compressionassemblage from northeastern China (68), leav-

ing a substantial temporal gap in our understand-

ing of feather evolution. Late Cretaceous amber

from Grassy Lake, Alberta (late Campanian), is

derived from lowland cupressaceous conifer for-

ests that occupied the margin of the Western In-terior Seaway and is best known for its diverse

insect inclusions (9). Eleven feather or protofea-

ther specimens (10) were recovered by screening

over 4000 Grassy Lake amber inclusions pre-

dominantly within the Royal Tyrrell Museum of

Palaeontology (TMP) and University of Alberta

(UALVP) collections. These fossils have dis-

parate morphologies that span four evolutionary

stages for feathers (11, 12). Specimens include

filamentous structures similar to the protofeathers

of nonavian dinosaurs that are unknown in mod-

ern birds (1315), as well as derived bird feathersdisplaying pigmentation and adaptations for

flight and diving.

The currently accepted (11, 12) evolutionary-

developmental model forfeathers (Fig. 1A)consists

of a stage I morphology characterized by a sin-

gle filament: This unfurls into a tuft of fila-

ments (barbs) in stage II. In stage III, either some

tufted barbs coalesce to form a rachis (centra

shaft) (IIIa), or barbules (segmented secondary

1Department of Earth and Atmospheric Sciences, University oAlberta, Edmonton, Alberta T6G 2E3, Canada. 2Department oBiological Sciences, University of Alberta, Edmonton, AlbertaT6G 2E9, Canada.

*To whom correspondence should be addressed. [email protected]

Fig. 1. Feather evolutionary-developmental model (11), terminology (17), andstage I and II specimens from Canadian amber. (A) Feather stages outlined withintext. Green, calamus or equivalent; blue, barbs; purple, rachis; red, barbule inter-nodes; d.b., distal barbules; r., ramus; p.b., proximal barbules. (B) Field of fila-

ments cut obliquely(stage I), UALVP52821. (C) Filament clusters variablyoriented(stage II), UALVP 52822. (D) Close-up of (C), showing filaments that compriseclusters. Pigmentation coupledwith comparatively thickouter walls produces darkecolor than in isolated filaments. Scale bars, (B) and (C) 1 mm, (D) 0.1 mm (10)

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branches) stem from the barbs (IIIb); then, these

features combine to produce tertiary branching

(IIIa+b). Barbules later differentiate along the

length of each barb, producing distal barbules

with hooklets at each node to interlock adja-

cent barbs and form a closedpennaceous (vaned)

feather (stage IV). Stage V encompasses a wide

range of additional vane and subcomponent spe-

cializations. Most modern birds possess stage

IV or V feathers or secondary reductions from

these stages (11, 16). Modern feathers exhibit arange of morphologies that are associated with

their various functions and remain discernible

in some of their finest subunits, the barbules

(17). This is particularly important in the study

of amber-entombed feathers because preserva-

tion is biased toward feather subcomponents,

which provide the basis for our morphological

comparisons.

Stage I is represented by UALVP 52821,

which contains a dense forest of regularly spaced,

flexible filaments with a mean diameter of 16.4 T

4.2 mm (Fig. 1B and figs. S1 to S4). Filaments

are hollow with the internal cavity comprising

~60% of total diameter, have no obvious in-

ternal pith, and taper apically. Where surface

texture is observable, filaments bear a faint cross-

hatching pattern but lack surface topography.

The filaments are not plant or fungal remains

because they lack cell walls and are relatively

large. Comparatively small diameters and a

lack of cuticular scales imply that they are not

mammalian hairs, as does direct comparison to

a hair from this amber deposit. Their closest

morphological match is the filamentous cov-ering found of nonavian dinosaurs such as the

compsognathid Sinosauropteryx prima (18).

The amber-entombed specimens are slightly

finer than those ofSinosauropteryx, which may

have been distorted by compression and per-

mineralization. The amber filaments display a

wide range of pigmentation, ranging from nearly

transparent to dark (fig. S2). No larger-scale color

patterns are apparent. [Additional specimen de-

tails are provided in supporting online material

(SOM) text.]

The stage II morphotype (Figs. 1, C and D,

and fig. S5) consists of tightly adpressed clusters

approximately 0.2 mm in width and composed

of filaments that are otherwise similar to those

already discussed (10). Five clusters are pre-

served together in UALVP 52822. As in stage II

primitive feathers (11), filaments in each clus-

ter appear to diverge from a common basal re-

gion without branching, but no rachis is visible

where the clusters exit the amber. These fila-

ments bear some resemblance to fibrils that

compose pycnofibers (tufted filaments) in ptero

saur compression fossils (19), except the amberspecimens lack the secondary organization ob-

served in pycnofiber bundles. The most morphol-

ogically comparable compression fossils are

protofeathers associated with the dromaeosaurid

Sinornithosaurus millenii (10, 20). These clusters

exhibit generally comparable sizes and shapes to

the amber specimens and even have the more

loosely bundled appearance distally where indi

vidual filaments have more variable lengths.

In contrast to stages I and II, additional spec-

imens from Canadian amber have barbules spe-

cialized for discrete functions. In TMP 96.9.334

(Figs 2, A to C, and figs. S6 and S7) (10), a thick-

Fig. 2. Specialized bar-bules in Canadian am-ber. (A) Coiled barbulessurrounding thickened ra-chis (arrow), cut obliquely,TMP 96.9.334. (B) Close-up of coils in isolated bar-bule. (C) Semi-flattenedinternodes and weaklyexpanded node of (A).Diffuse, variable barbulepigmentation producespale overall color. (D) Iso-

lated barb with differ-entiated barbules andthickened ramus, in spi-ders web, UALVP 52820.(E) Barbules near distaltip of (D), with clearlydefined distal and prox-imal barbule series (leftand right sides of ramus,respectively). (F) Close-up of distal barbule in(E), showing nodal prongsand ventral tooth on ba-sal plate (arrow) adja-cent to abrupt transition

into pennulum. Bandedpattern of dark pigmen-tation within basal plate,and diffuse dark pigmen-tation within pennulum,suggest a gray or blackfeather (24). Scale bars,(A) 0.4 mm; (B), (D), and(E) 0.2 mm; (C) and (F)0.05 mm (10).

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ened rachis is surrounded by numerous barbules

with tightly coiled bases. The barbules undergo

three or more complete whorls and are com-

posed of semi-flattened internodes (~120 mm

long, 9 mm wide) separated by weakly expanded

nodes (~12 mm wide). This coiling cannot be

attributed to interaction between barbules and

resin during amber polymerization because it

only occurs at the base of each barbule. Mod-

ern seedsnipes and sandgrouse (21, 22) possess

belly feathers with similar basal barbule coil-

ing, which allows water to be retained for trans-

port to the nest for distribution to nestlings or for

cooling incubating eggs. Grebes also have coiled

barbules that absorb water into plumage, facili-

tating diving by modifying buoyancy, reducing

hydrodynamic turbulence, and improving insu-

lation (23). In all of these instances, the keratin of

coiled barbules interacts with water to uncoil and

absorb water through capillary action (22). The

high number of coils in TMP 96.9.334 is most

similar to that reported from grebes (23, 24)

implying that the Cretaceous barbules are related

to diving behavior.

Barbules displaying all characteristics neces-

sary for forming vaned feathers are also present

in Canadian amber (Fig. 2, D to F, and fig. S8)

Fig. 3. Pigmentation in Canadian amber feathers. (A to D) Semi-pennaceousfeathers, TMP 96.9.997: (A) six barbs; (B) close-up of box in (A), arrow indicatesunpigmented ramus; (C) detail of ramus and barbule bases; (D) dark-field micro-photograph of (C), showing brown coloration with ramus and basal internodesminimally pigmented. Density and distribution of pigments (24, 25) are con-sistent with medium- to dark-brown modern feathers. (E) Unpigmented downybarbules, TMP 79.16.12. (F to K) Poorly differentiated, flattened barbules: (F)partial overview of 16 pennaceous barbs, TMP 96.9.553; (G) close-up of (F),

showing variable, diffuse pigmentation within barbule bases (ventral platestranslucent, dorsal flanges pigmented); (H) unpigmented, isolated barb withjuvenile mite, TMP 96.9.546; (I) central portion of isolated barb, TMP 94.666.15(J) dark-field microphotograph of (I), showing overall color; (K) banded pig-mentation within basal plate of proximal barbule in (I), indicating 5 to 6 com-ponent internodes. (L) Reduced pennaceous barbs from non-interlocking regionof dark brown and white mottled chicken contour feather for comparison. Scale bars,(A) 0.5 mm; (B), (E), (F), (H) to (J), and (L) 0.2 mm; (C), (D), (G), and (K) 0.04 mm.

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(10). These were probably borne by an animal

capable of flight. Within UALVP 52820, bar-

bules of unequal lengths arise from either side

of the barb, producing a differentiated series of

longer proximal (~0.42 mm) and shorter distal

(~ 0.24 mm) elements, all having spinose nodal

projections. Barbules are widely spaced along a

thick ramus (barb shaft) adapted for rigidity and

are strongly differentiated to interlock with

adjacent barbs to form a vane (10).

On the basis of the presence of a rachis inTMP 96.9.334 and differentiated barbules in

UALVP 52820, these specimens can be assigned

conservatively to stages IV and V and are at-

tributed to Late Cretaceous birds. The remaining

six feathers are fragmentary downy and contour

feathers (Fig. 3). Although they offer limited in-

sight concerning the identity or behavior of their

bearer, their structure and pigmentation bear di-

rectly on feather evolutionary stages. Four of the

six feather fragments in TMP 96.9.997 (Fig. 3, A

to D, and fig. S9) are aligned. Superficially, these

exhibit an intermediate morphology (stage IIb)

proposed for an Early Cretaceous (late Albian)

French amber specimen (4). In the Canadian spec-imens, as in the French material, the main axis

preserved is short (3.7 mm) and weakly defined,

dorsoventrally flattened, and composed of fused

secondary branches in an opposite arrangement.

However, in the Canadian specimens intense pig-

mentation in each internode produces a beaded

appearance, highlighting segmentation that is oth-

erwise difficult to discern based on barbule di-

ameter variation (Fig. 3C). Segmentation identifies

the finest branches as barbules attached to narrow

rami, and not barb equivalents attached to a

rachis. This interpretation identifies these small

specimens as subcomponents of a larger feather,

such as basal barbs on a contour feather (17), andnot a distinct stage in feather evolution lacking

barbules (4). This interpretation probably extends

to the French material as well. Pigmentation is

preserved with fidelity in all additional speci-

mens. Although downy feathers are consistently

transparent, and would have been white in life,

pennaceous feathers are more variable, with dif-

fuse, transparent, and mottled patterns of pigmen-

tation (Fig. 3, E to L) that match those observed

in modern birds (10, 24, 25).

Although neither avian nor dinosaurian skel-

etal material has been found in direct association

with amber at the Grassy Lake locality, fossils of

both groups are present in adjacent stratigraphic

units. Hadrosaur footprints are found in close

association with the amber, and younger (late

Campanian and Maastrichtian) strata of western

Canada contain diverse nonavian dinosaur (26)

and avian (27, 28) remains. There is currently no

way to refer the feathers in amber with certainty

to either birds or the rare small theropods from

the area (26). However, the discovery of end-

members of the evolutionary-developmental spec-

trum in this time interval, and the overlap with

structures found only in nonavian dinosaur com-

pression fossils, strongly suggests that the proto-

feathers described here are from dinosaurs and not

birds. Given that stage I filaments were present

in densities relevant for thermoregulation and

protection, and that comparable structures are pre-

served as coronae surrounding compression fos-

sils, it becomes apparent that protofeathers had

important nonornamental functions. Specialized

barbule morphologies, including basal coiling, sug-

gest that Campanian feather-bearers had already

evolved highly specialized structures similar to those

of modern grebes to enhance diving efficiency.Canadian amber provides examples of stages I

through Vof Prums (11) evolutionary-developmental

model for feathers. None of the additional mor-

photypes observed in compression fossils of non-

avian dinosaurs (8, 15) or amber (4) were found

here, suggesting that some morphotypes may not

represent distinct evolutionary stages, or may not

have persisted into the Late Cretaceous. The snap-

shot of Campanian feather diversity fromCanadian

amber is biased toward smaller feathers, sub-

components of feathers, feathers that are molted

frequently, and feathers in body positions that

increase their likelihood of contacting resin on

tree trunks. Despite these limitations, the assem-blage demonstrates that numerous evolutionary

stages were present in the Late Cretaceous, and

that plumage already served a range of functions

in both dinosaurs and birds.

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(1995).

6. Q. Ji, P. J. Currie, M. A. Norell, S.-A. Ji, Nature 393,

39 (1998).7. M. Norell, X. Xu, Annu. Rev. Earth Planet. Sci. 33,

277 (2005).

8. X. Xu, Y. Guo, Vertebrata PalAsiatica 47, 311 (2009).

9. R. C. McKellar, A. P. Wolfe, in Biodiversity of Fossils in

Amber from the Major World Deposits, D. Penney, Ed.

(Siri Scientific Press, Manchester, 2010), pp. 149166.

10. Materials and methods are available as supporting

material on Science Online.

11. R. O. Prum, J. Exp. Zool. 285, 291 (1999).

12. R. O. Prum, A. H. Brush, Q. Rev. Biol. 77, 261 (2002).

13. A. H. Brush, Am. Zool. 40, 631 (2000).

14. P. J. Currie, P.-J. Chen, Can. J. Earth Sci. 38, 1705 (2001)

15. X. Xu, X. Zheng, H. You, Nature 464, 1338 (2010).

16. P. Stettenheim, Living Bird 12, 201 (1973).

17. A. M. Lucas, P. R. Stettenheim, Avian Anatomy:

Integument(U.S. Department of Agriculture, Washington

DC, 1972).

18. P.-J. Chen, Z.-M. Dong, S.-N. Zhen, Nature 391, 147

(1998).

19. A. W. A. Kellner et al., Proc. Biol. Sci. 277, 321 (2010)

20. X. Xu, Z.-H. Zhou, R. O. Prum, Nature 410, 200 (2001)

21. T. J. Cade, G. L. Maclean, Condor 69, 323 (1967).

22. G. L. MacLean, Bioscience 33, 365 (1983).

23. J. Fjelds, The Grebes: Podicipedidae (Oxford Univ. Press

New York, 2004).24. A. C. Chandler, Univ. Calif. Publ. Zool. 13, 243 (1916).25. C. J. Dove, Ornith. Mono. 51, 1 (2000).26. P. J. Currie, in Dinosaur Provincial Park: A Spectacular

Ancient Ecosystem Revealed, P. J. Currie, E. B. Koppelhus

Eds. (Indiana Univ. Press, Bloomington, 2005),

pp. 367397.27. N. Longrich, Cretac. Res. 30, 161 (2009).

28. E. Buffetaut, Geol. Mag. 147, 469 (2010).Acknowledgments: We thank the Leuck family and M. Schmid

(donated specimens); M. Caldwell, S. Ogg and M. Srayko

(microscopy); E. Koppelhus and H. Proctor (discussions); and

J. Gardner, B. Strilisky, A. Howell, and J. Hudon (TMP,

Redpath Museum, and Royal Alberta Museum collections).

Research was funded by Natural Sciences and Engineering

Research Council of Canada (NSERC) Discovery Grants to

B.D.E.C., A.P.W., and P.J.C. and NSERC and Alberta

Ingenuity Fund support to R.C.M.

Supporting Online Materialwww.sciencemag.org/cgi/content/full/333/6049/1619/DC1

Materials and Methods

SOM Text

Figs. S1 to S12

References (2949)

25 January 2011; accepted 22 July 2011

10.1126/science.1203344

Trace Metals as Biomarkers forEumelanin Pigment in the Fossil RecordR. A. Wogelius,1,2* P. L. Manning,1,2,3 H. E. Barden,1,2 N. P. Edwards,1,2 S. M. Webb,4

W. I. Sellers,5 K. G. Taylor,6 P. L. Larson,1,7 P. Dodson,3,8 H. You,9 L. Da-qing,10 U. Bergmann11

Well-preserved fossils of pivotal early bird and nonavian theropod species have providedunequivocal evidence for feathers and/or downlike integuments. Recent studies have reconstructedcolor on the basis of melanosome structure; however, the chemistry of these proposedmelanosomes has remained unknown. We applied synchrotron x-ray techniques to several fossiland extant organisms, including Confuciusornis sanctus, in order to map and characterize possiblechemical residues of melanin pigments. Results show that trace metals, such as copper, are presentin fossils as organometallic compounds most likely derived from original eumelanin. Thedistribution of these compounds provides a long-lived biomarker of melanin presence and densitywithin a range of fossilized organisms. Metal zoning patterns may be preserved long aftermelanosome structures have been destroyed.

Feather color in birds stems mostly from

chemical pigments, of which the most

widely used are melanins (1). Resolving

color patterns in extinct species may hold the

key to understanding selection processes that

acted during crucial evolutionary periods and

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www.sciencemag.org/cgi/content/full/333/6049/1619/DC1

Supporting Online Material for

A Diverse Assemblage of Late Cretaceous Dinosaur and Bird Feathers

from Canadian Amber

Ryan C. McKellar,* Brian D. E. Chatterton, Alexander P. Wolfe, Philip J. Currie

*To whom correspondence should be addressed. E-mail: [email protected]

Published 16 September 2011, Science333, 1619 (2010)

DOI: 10.1126/science.1203344

This PDF file includes:


SOM Text

Figs. S1 to S12

References (2949)


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Established methods were employed for the collection and preparation(29) of amber

inclusions. Epoxy-embedded amber nodules were slide-mounted and polished, and cover

slips were applied to optimize views and ensure long-term preservation of the inclusions.

Total slide thickness ranged from 1.8 mm to 8.5 mm, with the thickest mounts at timeschallenging the resolving power of compound microscopy. A suite of modern bird

feathers and hair samples were directly compared to the amber-entombed specimens, aswere morphological atlases on the microscopic structure of mammalian hairs (30, 31) and

feathers (24, 25). Modern comparative specimens were either epoxy-embedded or

examined unaltered, depending on the degree of magnification required. All specimens

were photographed using a Canon PowerShot A640 camera attached to a Zeiss StereoDiscovery.V8 microscope, or Zeiss Axio Imager.A1 compound microscope (b.f.

denotes bright field photographs, d.f. denotes dark field photographs). Images usually

encompass multiple focal planes and were compiled using Axiomat or Helicon Focussoftware. All measurements were taken either digitally using Axiomat, or on a Wild M5

dissecting microscope equipped with an ocular micrometer.The inherent limitations of working with amber governed our approach to theCanadian amber specimens, and consequently we focused our work on morphological

comparisons and morphometric analyses. The nature and rarity of these specimens

precludes destructive sampling until additional specimens are recovered. Potentially

contentious specimens, such as the Stage I and II morphotypes, were subjected toadditional non-destructive sampling. Spinning disk confocal microscopy (SDCM) and

laser scanning confocal microscopy (LSCM) were utilized. SDCM data were obtained

using a Hamamatsu Orca R2 camera on an inverted Olympus IX81 microscope with aYokogawa CSU-10 spinning disc confocal head (examining excitation at 491 nm and 561

nm). LSCM data were obtained with a Leica SP5 microscope using a 20x 0.5 Na

objective and acousto-optical tunable filters (examining excitation at 405 nm). Results ofthese analyses, as well as additional morphological details on all specimens are presented

here.Institutional abbreviations: TMP, Royal Tyrrell Museum of Palaeontology,

Drumheller, Alberta, Canada; RAM, Royal Alberta Museum, Edmonton, Alberta; RM,

Redpath Museum, McGill University, Montreal, Quebec, Canada, modern birdcollection; UALVP, University of Alberta Laboratory of Vertebrate Palaeontology,

Edmonton, Alberta.

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SOM Text

Additional details of Stage I and II morphotype identifications

A major concern regarding the specimens identified as Stage I or II morphotypes is

whether other possible interpretations are tenable. Within the main text we brieflysummarize these possibilities and the bases for their rejection. Here we provide full

details of the work underpinning our conclusions.

Comparison to modern mammalian hairs

In general, the Stage I and II morphotypes reported are of a smaller diameter than

most mammalian hairs and do not appear to possess cuticular scales. More specifically,the filaments measured from UALVP 52821 have a mean diameter of 16.44.2 m

(n=80), with minimum and maximum diameters of 6.2 m and 27.1 m, respectively. In

UALVP 52822, filaments have a mean diameter of 17.95.0 m (n=28), and rangebetween 10.7 m and 31.0 m. The UALVP 52822 filaments are loosely bundled into

five distinct clusters. The three clusters that have definite edges and appear to represent acomplete cross-section of the bundle measure 213 m, 233 m and 325 m in diameter attheir narrowest.

The diameters observed for Stage I and II filaments therefore fall just within the

lowest range of values known for modern mammal hair. Mammal hair has been studied

extensively, and the two main types that have been documented across a wide range oftaxa, with attention to both overall diameter and cuticular scale patterns, are underhairs

(understory fur) and guard hairs. Given that the Stage I and II filaments overlap with only

the finest known mammal hairs, and furthermore given differences between modern andCretaceous mammalian faunas, we conducted detailed comparisons to pelages that

represent both the smallest known underhair diameters (30) and contain the widest

taxonomic range of organisms, including numerous marsupials (31). Because the latterwork was based mainly upon guard hairs (typically of slightly larger diameter than

underhairs (31), but more likely to enter in contact with tree resin), measurements weretaken from the narrowest part of each exemplar. Underhair diameters listed for 162

species of mammals (30) yielded a mean value of 59.582.3 m, ranging from 6.8 m to

680 m. Measurements of guard hair diameters for 75 species of Australian mammals(31) yielded a mean value of 48.237.8 m, a minimum of 9.4 m, and a maximum of

168 m. Although these samples clearly display a wide range of diameters, all modern

specimens within the low end of the spectrum were united by two morphological

features. In almost all cases of diameters below 25 m, the medulla (hollow core) of thehair was discontinuous, being subdivided along its length into either a uniserial ladder or

aeriform lattice arrangement (30, 31). This was typically observed in conjunction with

coarse, diamond-shaped cuticular scales arranged with a maximum of two to three scalesfitting within one hair-width and resulting in a jagged margin on the hair when viewed in

longitudinal section (30, 31). Stage I and II filaments differ markedly from this

arrangement. The filaments are hollow, with an outer wall that comprises approximately40% of the total diameter, and is further reduced within apical portions of the filaments.

The hollow nature of the filaments is best illustrated in UALVP 52821, where patchy

translucency and broken edges demonstrate that the filaments have a circular cross-

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section, and that their cores are hollow (Figs. S3, S4A, S11; see also SOM pp. 68,

regarding specimen LSCM analyses and taphonomic considerations). Within areas wherethe filaments are preserved as nearly opaque masses due to darker pigmentation, they

nonetheless preserve faint cross-hatching of very fine light and dark spots (Figs. S4BD).

Within areas where the filaments are translucent, the outer wall clearly does not possess a

jagged margin, which would be clearly observed if cuticular scales were present.

Comparison to fossil mammalian hair

In Canadian amber, there is currently one hair fragment known (TMP 96.9.998).This specimen (Figs. S4E, F) is in the process of being studied and described, but our

preliminary analysis already indicates a number of distinctions between it and the Stage I

and II morphotypes described herein. The hair fragment is significantly wider than any ofthe filaments preserved (approximately 56 m in diameter) and reveals faint indications

of fine, closely-spaced cuticular scales when viewed with dark-field microscopy.

Additional observations suggest that the specimen lacks a broad medullary cavity andthat the medulla is likely discontinuous in either an aeriform lattice or multiserial ladder

pattern, once again in contrast to any of the Stage I and II filaments reported.Additional Mesozoic fossil hair specimens from the Early Cretaceous of France

include two fragments preserved in three dimensions within amber(32). These specimenshave observed diameters that range from 3248 m and from 4978 m, respectively,

and possess cuticular scales that are smoothly undulate with an intermediate spacing (32).

Preservational characteristics of the hair fragments described by these authors are similarto those observed for both hair and the Stage I morphotype filaments from Canadian

amber.

Comparison to fungal and plant remains

In general, the Stage I and II morphotypes reported can be differentiated from plantand fungal remains based upon their comparatively large size, lack of septae, and

preservational characteristics. Most fungal hyphae branch and exhibit a diameter range

from 115 m, but the known range extends from 0.5 m to 1 mm (33). Cell walls inhyphae are generally thin (often 0.2 m or less), with chitin as the main structural

component (34). In amber, this combination of features typically results in filamentous

fungi that are easily observed as mycelia (larger mats of hyphae). These appear vitreous

or white when examined under reflected light (Fig. S4G). Conceivably, groups such asthe Zygomycetes (bread moulds) could produce coenocytic hyphae (those lacking

internal septae) of similar overall morphology to UALVP 52821. However, a subparallel,

non-branching, centimeter-scale series of such hyphae lacking any adventitious septae orterminal sporangia seems highly improbable (35). Furthermore, UALVP 52821 displays

pigmentation and an outer wall thickness that do not match the preservational

characteristics of fungi within this amber deposit.Many of the characteristics that separate Stage I and II morphotypes from fungal

remains also distinguish them from plant remains. The Stage I and II morphotypes exhibit

no evidence of longitudinal subdivision within their hollow cores, and their diameters are

roughly twice to thrice those of xylem cells found in the deposit. Furthermore, xylemcells are typically polygonal in cross-section and when encountered in Canadian amber,

are typically present as adjoined series of cells that form blocky fragments of tissue that

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have been carbonized or perhaps fusainized. Sclerenchyma fibers (commonly referred to

as bast or plant fibers) are the most likely component of woody plants to exhibit thegeneral shape, size, lack of pitting, thickened outer walls, and undivided elongate forms

(36) observed in the amber filaments. Although some sclerenchyma fibers used in textiles

have comparable mean diameters to those observed in Stage I and II filaments, these are

never heavily pigmented, are nearly pentagonal or hexagonal in cross-section withuniformly thick walls, taper at both apices, and exhibit a wide array of apicular

morphologies (36, 37). Furthermore, the plant remains we have recognized in Cretaceous

ambers from western Canada (9), particularly those that breach the surface of theirencapsulating amber nodule, are generally preserved as carbonized remains that preserve

little surface detail at the cellular level.

Comparison to degraded or taphonomically-altered feather remains

An alternate interpretation of the Stage II morphotype we describe is that it

represents a series of degraded feather rachi that have decayed to the point of exposingtheir internal filamentous structure. The morphology of such structures has recently been

explored (38) through biodegradation, using keratin consuming fungi. This has revealedthe underlying structure of the rachis, indicating that filaments that once comprised rachi

bear distinct nodes directly comparable to those of barbules, quite unlike the filamentsrecovered from amber. The inferred Stage II clusters could also be construed as a result

of poorly-preened feathers, in which the barbs have clumped together. Although this

alternative is more difficult to discount, we note that, unlike typical barbs, the filamentsthat comprise the Stage II clusters we describe possess circular cross-sections, in absence

of any indication of a rachis from which they could have originated.

Comparison to pterosaur pycnofibers

Pycnofibers are bushy fibers found in association with pterosaur remains: these havean average diameter between 0.2 and 0.5 mm, and are apparently composed of finer

fibrils of unknown original structure or composition (19). Compared to UALVP 52821,

there is an overlap in the known diameters of the clusters, and they both appear to havesub-centimeter lengths. In the case of pycnofibers, the component fibrils appear to be

much more tightly bound, particularly near the apex of the pycnofiber, which makes their

distinction much more difficult than the loosely-bound Stage II filaments observed in

amber.

Sinosauropteryx prima comparison

In terms of compression fossils, the Stage I morphotype filaments observed inCanadian amber are most comparable to protofeathers from Sinosauropteryx prima. The

integumentary structures ofS. prima display a range of lengths, from ~4 mm to at least

4.0 cm, depending on the specimen and their body position (14, 18). These independentfilaments range in thickness from easily observed 0.2 mm filaments to those that are

considerably smaller than 0.1 mm (14). The filaments are hollow and round in cross-

section (39) and may have been secondary branches of larger structures (14) or isolated

filaments (12). Although the UALVP 52821 specimen does not display filaments withdiameters as large as the maximum reported from S. prima, they are consistent with the

finer filaments found in this specimen, and fall within the range of observed lengths. As

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with the filaments from S. prima, UALVP 52821 filaments are hollow with circular

cross-sections. It must be noted that compression, permineralization, and lack ofdefinition may all have contributed to some degree of distortion of the original

dimensions of filaments associated with S. prima. Compression potentially flattens

otherwise cylindrical filaments, whereas permineralization may increase the apparent

thickness of the outer wall. The lack of definition between individual filaments in S.prima may also yield overestimates of original filament thicknesses.

Sinornithosaurus millenii comparison

The UALVP 52822 clustered filaments described as a Stage II morphotype are most

similar to compression fossils surrounding Sinornithosaurus millenii. In S. millenii,

although there is no direct evidence of a rachis (as with the amber specimens), barbulesare clearly clustered into independent tufts with compressed widths of 13 mm and

lengths of up to 4.5 cm (12, 20). These clustered filaments appear to have been attached

basally, or in one example, inferred to have arisen from a central rachis (12, 20).Although no direct measurements of the filaments that comprise each cluster have been

presented by Xu et al (20) they appear to be of sub-millimeter diameter similar to thefilaments observed in amber. As in the Sinosauropteryx primaprotofeathers, the clusters

found with Sinornithosaurus millenii are likely to have expanded diameters as a result offilament splaying during compression. Their displacement from the body suggests that

the clusters associated with S. millenii were not immediately buried (20), so the main

limitations on the degree of filament splaying would have been the length of time theclusters were allowed to decay, and the rigidity with which the filaments were fixed in

the clusters.

Additional morphological observation techniques

Due to the current rarity of specimens, destructive sampling is not possible with theCanadian amber material (including crack-out studies utilizing scanning electron

microscopy). Synchrotron x-ray microtomography has recently demonstrated great

promise for studying small-scale inclusions within amber. This imaging technique hasdemonstrated unmatched resolution of fine structures (40), yet has been unsuccessful in

the analysis of amber-entombed hair specimens (32) comparable to the Stage I and II

filaments described here, likely as a result of low density contrast. This leaves, beyond

light microscopy, confocal microscopy as the primary source of additional data on theCanadian amber specimens (described below).

Chemical comparison to mammalian hairs

As mammalian hairs constitute the most similar structures in terms of both overall

morphology and preservational characteristics, we sought additional analyses to compare

the chemical composition of the Stage I and II morphotypes to hair. The identification of-keratin or-keratin in the putative protofeathers would provide strong support for our

structural inferences, because these proteins are specific to the integumentary structures

of mammals and reptiles, respectively. The presence of-keratin has been demonstrated

in filaments associated with the non-avian theropod Shuvuiia deserti through the use ofimmunohistochemical responses, measured utilizing -keratin specific antibodies that

were tagged with fluorescent markers and subjected to LSCM (41). Such testing is, at

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present, impossible for specimens such as UALVP 52821 and UALVP 52822 because

they do not provide enough volume for analysis, and furthermore cannot be dissociatedfrom the entombing amber matrix. Moreover, the gymnospermous resin has permeated

filaments during amber polymerization, which is problematic for such analyses because it

is autofluorescent, impermeable, highly insoluble, and contains trace quantities of various

amino acids of botanical origin (42, 43). Finally, Canadian amber is not readily sectionedas it fractures conchoidally. Taken together, these characteristics temper our expectations

for successful immunohistochemical analyses of amber-borne filaments at present, should

additional specimens be located to allow destructive sampling. Fortunately, we caninterrogate this issue non-destructively with confocal microscopic approaches.

Analysis by LSCM and SDCM

Given these caveats, we turned to LSCM and SDCM to assess the composition of

the filaments. Keratin is known to autofluoresce with a predictable emission profile (44).

This makes possible a comparison of fluorescence patterns amongst UALVP 52821,UALVP 52822, and unambiguous feather fragments within the deposit. Ideally,

differences between the excitation and emission profiles of the specimens would permitcomparison between these specimens, as well as a wider range of inclusions within the

deposit, in order to rule out conclusively the alternative origins for the filamentsdiscussed above.

UALVP 52821 was compared to TMP 96.9.997 with both SDCM and LSCM. TMP

96.9.997 is both strongly-pigmented and has completely transparent barbule sections inclose proximity to the slides cover slip. It has a total slide thickness of approximately 2.5

mm, and as one of the thinnest specimens in the feather series is the most likely to

produce a clear excitation response from keratin alone. These specimens were exposed toa wide range of excitation wavelengths (405 nm, 488 nm, and 561 nm UV was not

possible due to the pronounced autofluorescence of amber at these wavelengths). Theresponses of the pigmented keratin, clear keratin, and surrounding amber were contrasted

in TMP 96.9.997 and compared to areas of similar visible response in UALVP 52821.

Analysis of TMP 96.9.997 illustrated the limitations of this approach, asautofluorescence from the amber was strong at all observed excitation wavelengths.

Focusing on keratin within TMP 96.9.997 did not provide an emission profile that was

distinguishable from that of the amber in terms of peak values (Figs. S10AC), but the

intensity produced by keratin provided additional visibility of anatomical details. WhenUALVP 52821 was analyzed, an identical pattern emerged (Figs. S10DF), but the

background interference from the surrounding amber was much greater (because the total

slide thickness in the area sampled was approximately 5 mm). Although these data do notdemonstrate conclusively the presence of keratin within either specimen, LSCM imaging

confirmed the hollow structure of the filaments in UALVP 52821 (Fig. S11).

Furthermore, three-dimensional viewing indicated that the pigmented portion of eachfilament is surrounded by a thin layer that emits with slightly greater intensity than the

surrounding amber. This layer may represent either a reflective surface where the

specimen has pulled away from the amber, or a region of different composition. The

latter appears more likely given the apparent thickness of this feature (35 m wheremeasurable). Similar elevated emission intensities were observed from both keratin in

TMP 96.9.997 and some narrow fractures within the amber of UALVP 52821; thus the

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observations are inconclusive. The pigmented layer within UALVP 52821 is readily

visible and appears to be thin and nearly circular in cross-section. The internal areabounded by the pigmented layer lacks any visible structures, and appears to have been

hollow in life. These observations are strongly supported by instances where the

filaments are cross-cut by either the polished surface of the amber (Fig. S11B), or the

edge of the amber piece itself. Where the filaments are cut cleanly, the hollow coreappears as an oblong shape free of structure. This would be expected if the filaments

possess a nearly circular cross-section, as their orientation within the amber specimen

typically produces oblique sections. Where the filaments breach the surface of the ambernodule, their outlines are rounded and appear circular.

If and when additional representatives of the Stage I and II morphotypes are

recovered from Canadian amber, we plan to pursue chemical analyses to a much greaterextent, particularly once a sufficient archive exists to allow destructive sampling. In the

interim, we are open to suggestions for additional techniques from the community.

Detailed descriptions of individual specimens and consideration of taphonomy and

preservationUALVP 52821 (Stage I morphotype): UALVP 52821 exhibits complex taphonomy:

resin remobilization prior to hardening has sheared off the basal portions of the filaments,and has introduced a series of offsets or micro-faults running through many of them. It

also appears as though minor decay and the escape of trapped gasses have resulted in

fragmentation of the outer wall in many filaments. This has produced a number ofperforations in some of the filaments: these are visible as semicircular incisions of

filament margins that correspond to fragments of the outer wall found floating in the

amber (Figs. S2, S4A). The complete margin of some of these holes is also visible insome places (Fig. S4A inset), providing a clear indication of the thickness of the outer

wall, and confirming the hollow interior of the filaments. Additionally, the filamentsappear to have been arranged in rows at the time of inclusion within the amber mass,

which may reflect either their original arrangement or clumping within the resin (Fig.

S2). Their form of preservation, particularly their patchy translucency, is similar to that ofboth feather remains and a hair fragment recovered from the deposit (Figs. S4E, F). The

alternation of fine light and dark spots that appears to form a cross-hatch pattern on the

surface of some filaments may have a taponomic origin. This pattern is similar to that

observed in insect cuticles that have pulled away from the encapsulating amber within thedeposit, and does not necessarily indicate genuine primary topography.

UALVP 52822 (Stage II morphotype): The clusters of filaments that run parallel to

the longest axis of UALVP 52822 (Fig. 1C) interact with a dark drying line, partlyobscuring the separation between individual filaments at the apex of the cluster. Also, all

clusters breach the exterior surface of the amber nodule, limiting their observed lengths

and any potential to observe basal attachments. The filaments within each clusterconverge basally, regardless of orientation or their preserved lengths. Within the same

amber nodule are a single aphidoid hemipteran, potential insect frass pieces, and a few

partial strands of a spiders web.TMP 96.9.997 and TMP 96.9.1036 (superficially Stage IIb morphotype): TMP

96.9.997 is close to, but does not extensively contact a drying line within the amber. This

has produced a few small areas where dark staining appears to spread outward from

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individual barbules. In TMP 96.9.1036, the contact with a drying line is greater, as is the

areal extent of the darkened surroundings. Exposure and weathering of the latterspecimen explains at least some of the lack of pigmentation in barbules near the apex of

the barb (Fig. S9).

TMP 96.9.553, TMP 94.666.15 and TMP 96.9.546 (pennaceous barbs): In TMP

96.9.553, resin flow and interaction with a drying line has caused barbules on at leastthree of the barbs to draw inward toward the ramus. In TMP 94.666.15, barbules near the

apex and base of the barb are similarly swept inward due to resin flow (Figs. 3I, J). In this

specimen, interaction with the drying line is fairly extensive, and may have caused thedarker color. In TMP 96.9.546, interaction with a drying line has created dark margins

surrounding basal barbules (Fig. 3H), but has had little other effect. A mite that appears

to be a juvenile oribatid (H. Proctor det.) is found in association with TMP 96.9.546, butappears to be within a different flow region in the amber, and not directly associated with

the feather fragment.

TMP 79.16.12 (down feather): The tuft of downy barbules within TMP 79.16.12converges basally (Fig. 3E), but each is truncated at the edge of the amber nodule. Within

the amber nodule are six specimens of the dipteranAdelohelea glabra Borkent, at least 4partial aphidoid hemipteran specimens, and a few isolated strands of spider web.TMP 96.9.334 (coiled barbules): Although the feather portion preserved within the

amber nodule does not appear to encompass any barbs, the presence of specialized

barbules and a broad rachis suggest an advanced Stage IV morphotype for TMP 96.9.334

(Figs. S6, S7). A prominent drying line within the nodule suggests resin flowed towardthe apex of the rachis, sweeping many of the barbules inward toward the rachis, and

causing some of the barbules to tear free and rotate (their nodes show that they face the

opposite direction). Most of these barbules were probably attached to an unpreservedbarb ramus that was basal to the preserved section of feather (as the barb ramus is not

preserved). There is a fragment of what may be barb ramus preserved on the surface ofthe amber nodule (Fig. S7B), but preservation is too poor for identification. Those

barbules that do not terminate on this questionable fragment exit the edge of the amber

piece basally with no indication of attaching to the rachis segment (Fig. S7). The amberslice that entombs the feather is slightly less than 2.25 mm thick, so it is possible that the

window of preservation occurred between barb rami, but this would require a relatively

wide spacing of barb rami. Posterior to the microphysid hemipteran in the amber nodule,

and well removed from rachis, a second set of barbules splays outward in the oppositedirection (Fig. S6B). Unless the rachis has completely folded back on itself outside the

window of preservation (and against the direction of resin flow), this second set of

barbules is difficult to explain as anything other than the remains of a second feather.UALVP 52820 (Stage V, vaned feather fragment): UALVP 52820 is caught within a

large mass of tangled spiders web (Fig. S8). To preserve the web, the amber nodule was

not polished to a thin wafer. As a result, there are numerous drying lines to contend with.Aside from the feather, only a few potential insect frass pellets are found within the

amber nodule.

Additional notes on pigmentation and structure of Canadian amber feather

specimens

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One of the most interesting aspects of the Canadian amber assemblage is the

preservation of pigments within the specimens. Pigmentation has recently been describedfrom a number of non-avian theropods (45, 46) and fossil birds (4649). This work has

hinged upon the identification of melanosomes (pigment bodies within organelles) with

distinctive shapes and arrangements, through the use of scanning electron microscopy

(49). Although preservation is exceptional within amber, examination of the insectassemblage has demonstrated that diagenetic alteration has had a profound effect on the

coloration of the insect remains, and techniques such as melanosome observation are

likely the only way to precisely identify the original colors of the feather specimens.Unfortunately, it is not possible to subject the Canadian amber to the destructive

sampling required to access the melanosomes for SEM examination. This limits the

discussion to pigment intensity and distribution, and comparison with works that havemapped these patterns in modern feathers (24, 25).

UALVP 52821 (Stage I morphotype): The filaments of UALVP 52821 exhibit a

wide range of diffuse (non-localized) pigmentations, ranging from near-transparency toheavily-pigmented, nearly opaque (Fig. S2). Pigmentation along the length of each

filament appears to be relatively consistent, but taphonomic influences complicate thisobservation, and limit any inferences of the original colors. These specimens appear to

have ranged in color from near-white (unpigmented) to near-black (heavily pigmented).No large-scale pigmentation patterns, such as banding created by a series of neighboring

filaments with similar pigmentation can be inferred, although this may be an effect of the

small sample size.UALVP 52822 (Stage II morphotype): Much of the dark coloration in stage II

morphotype specimens (UALVP 52822) is attributable to preserved pigments; however,

it is not possible to observe the distribution of pigments within these structures as theyare nearly opaque (Fig. S5). This, combined with a lack of modern analogues, limits our

interpretation to suggesting tentatively a dark brown or black overall color for thefilament clusters.

TMP 96.9.997 and TMP 96.9.1036 (superficially Stage IIb morphotype): Dark-field

microphotography (Fig. S9) and comparison between the Canadian amber specimens(TMP 96.9.997 and TMP 96.9.1036) and epoxy-embedded modern feathers shows that

the density and distribution of pigments (24, 25) preserved in the fossil material is

consistent with a medium- to dark-brown plumage (Fig. S12). The ramus and proximal

three to four barbule nodes lack or have reduced pigmentation, as do the basal sections ofdistal barbule nodes (Fig. S9B). Within distal barbule nodes, pigment is concentrated in

oblong masses, leaving clear nodes in addition to clear bases within the internodes (Fig.

S9E). Barbules are approximately 6 m in diameter and gradually taper away from theirnodes, which appear to bear three elongate (3 m) prongs (25). This barbule type

conforms to the reduced plumulaceous barbules described within the basal regions of

some contour feathers (17), but the barbs and their barbules are present in a sparse andstrictly aligned pennaceous pattern that does not match well with observed modern

exemplars.

TMP 96.9.553, TMP 94.666.15 and TMP 96.9.546 (pennaceous barbs): In these

specimens, the barbules on both sides of each barb are of pennaceous morphology (17),with ventral plates (blade-like bases) that gradually narrow and become more cylindrical

toward their apices (Figs. 3FK). Barbules range in length from 0.15 mm to 0.35 mm and

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appear to be composed of 10 to 12 distinct nodes. Barbules on these partial feathers

appear to lack differentiation into the smooth proximal and hooked distal series on eitherside of the barb. The barbules do not correspond well to modern reduced pennaceous

morphologies, because barbules on either side of the barb are of relatively even lengths,

comparable shapes, and lack hooklets at their nodes. Within one amber piece containing

16 examples of this morphotype (TMP 96.9.553, Fig. 3F), the individual barbs appear toconverge upon a shared base. These specimens might be identified as a variation on the

open pennaceous (non-interlocking) terminal regions of barbs within contour feathers(17), but this interpretation would require that the bases of individual barbs were drawntogether taphonomically, due to torsion within viscous resin.

Pigmentation is present within two of the three specimens with flattened barbs. In

both of these specimens, the dorsal flange (cylindrical portion) of the basal internode isdarkly pigmented, while the ventral plate bears reduced pigmentation within its ventral

margin (Figs. 3IK). Interrupted pigmentation is apparent within many of the ventral

plates, reflecting segmentation within the base of each barbule (Fig. 3K), as pigmentationis only present within the apical portions of the subsequent internodes. In each of the two

specimens that possess pigmentation, its intensity and distribution are comparable to darkbrown modern feathers (24); however, amber thickness and interactions with drying lines

within the amber preclude more detailed analysis.TMP 79.16.12 (down feather): TMP 79.16.12possesses tufted barbules that lack

pigmentation, with thin, flattened internodes (approximately 8 m in width, 18 m in

breadth, and 170 m in length) ending in moderately inflated nodes (25 m in diameter)with three weak nodal points (Fig. 3E). Individual barbules appear to converge on a short

rachis, although none is apparent within the amber itself. Taken together, these features

suggest an understory position within the plumage, and the overall appearance of thespecimens is similar to that of natal or juvenile down (17). These barbules appear

transparent, and would have been white in life.TMP 96.9.334 (coiled barbules): Pigmentation is diffuse and variable within the

barbules of TMP 96.9.334 (Fig. S6): the overall color would likely have been pale or

white. Interestingly, the basal internodes within each barbule appear to be consistently ofa slightly darker color than their apical equivalents. Structurally, these barbules exhibit a

form of basal coiling that is analogous to that found in some modern birds, such as

sandgrouse, seedsnipes, and grebes. In these modern examples, the coils are used to

sequester water within the plumage. This coiling differs significantly from the curledbarbule bases observed in many taxa (e.g., Fig. S12D), in that the barbules undergo full

rotations, and when exposed to water, they straighten, drawing water in by capillary

action (21). In the modern taxa that exhibit basal coiling, this structure is either used fortransport of water to the nest (in sandgrouse, possibly in seedsnipes) or as a means of

altering the hydrodynamic properties of the bird, in order to facilitate diving (in grebes)

(21, 22, 23). Although neither of these groups exhibit as many basal coils as thoseobserved in TMP 96.6.334, grebes appear to exhibit slightly more coils than the other

taxa. Grebes possess 23 basal coils (23, 24, Figs. S12FG), while sandgrouse possess

1.52 full coils (22), and seedsnipes have less developed basal coiling (21). The basal

coils in TMP 96.9.334 may have served either of the functions known in the modernavifauna, but the high number of coils suggests that they are more likely to have been

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employed in diving behavior, as they would have sequestered a comparatively large

volume of water.UALVP 52820 (Stage V, vaned feather fragment):The preserved feather section of

UALVP 52820 is entombed within a thick piece of amber and crosses multiple drying

lines, making color observations difficult. Transmitted light microphotographs (Fig. S8)

reveal a banded pattern of dark pigmentation within the basal plate and diffuse darkpigmentation within the pennulum, suggesting perhaps a grey or black feather(24).

Although this is only a partial feather, the ramus (barb shaft) is expanded dorsoventrally,

with a distinct dorsal ridge bordered by ledges, a characteristic of rami adapted to formstrong vanes for flight (17). Furthermore, distal series barbules each display a distinct,

narrow pennulum, and a moderately elongate, narrow ventral tooth on the apex of a broad

basal plate. These are adaptations for interlocking with adjacent barbs to form a vane

(17).

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Supplementary figures

Fig. S1

Graph of specimen diameters for filamentous structures (Stage I and II) and barbules in

Canadian amber, compared to other possible sources. Circles indicate mean value,

vertical lines 1 SD, boxes show observed ranges or reported ranges for majority of

specimens (33), and arrows indicate ranges beyond graph area accompanied by maximumvalue.

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Fig. S2

Photomicrographs of Stage I filaments in UALVP 52821. (A) Field of individualfilaments cut obliquely, illustrating distribution of filaments; (B) close-up of boxed area

within A, showing apparent grouping of filaments (arrow) and color variation between

filaments when illuminated from above.

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Fig. S3

Compound microscope images (b.f.) of Stage I filaments in UALVP 52821. (A) Areawhere filaments are truncated by outer surface of amber nodule (pebbled amber surface

in upper-right of figure), arrow indicates one of the faults running through the filaments;

(B) hollow central region of a filament (arrow); see figures S4 and S11 also.

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Fig. S4

Dissecting and compound microscope images of Stage I filaments, fungi, and mammalianhair. (A) Degraded portion of Stage I filament apex in UALVP 52821; vertical arrows

indicate regions where there are holes in the outer wall, angled arrows indicate pieces of

the outer wall floating within the amber; inset shows holes with complete outlines at

double the magnification of A (d.f.); (BD) apparent surface texture of Stage I filament inUALVP 52821, (B) filament adjacent to arrow displays faint cross-hatching pattern of

light and dark areas, (C) filament adjacent to arrow displays clearer cross-hatching,

perhaps as a result of a nearby bend in the filament (d.f.), (D) multiple filaments displayfaint texture where they have pulled away from the surrounding amber (d.f.); (E) TMP

96.9.998, mammalian hair from Canadian amber, with thick cortex and discontinuous

medulla, most likely displaying a multiserial ladder or aeriform lattice pattern adjacent toarrow (b.f.); (F) TMP 96.9.998, showing faint traces of cuticular scales adjacent to

arrows (d.f.); (G) mat of fungal hyphae (white filaments near bottom of image)

contrasted against pair of Stage I filaments (larger, dark filaments near top of image) inUALVP 52821.

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Fig. S5

Compound microscope images (b.f.) of Stage II clusters in UALVP 52822. (A) Distal tipof cluster in Fig. 1C, showing tapered apices of filaments and loose bundling within a

cluster, also with apparent dark, diffuse pigmentation; (B) proximal truncation of cluster

in Fig. 1C, showing tightly adpressed filaments at point where cluster is cross-cut by the

edge of the amber nodule (arrow); (C) loose bundling apparent within other clusters inthe same piece of amber, these clusters are more obliquely oriented within the nodule,

and may show variable pigmentation within filaments (toward upper-left of figure).

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Fig. S6

Compound microscope images of coiled barbules (TMP 96.9.334). (A) Specimenoverview showing coiled barbule bases (predominantly within the lower left of figure)

surrounding thick, flattened rachis (arrow); reddish-brown areas are the result of a

prominent drying line within the amber (b.f.); (B) oblique section through cluster of

coiled barbules surrounding a microphysid hemipteran, with portions of second featherposterior to microphysid (TMP 96.9.334, microphotograph); (C) straight apical barbule

sections exhibiting variable diffuse pigmentation (b.f.); (D, E) close-ups of straight

barbule nodes and internodes, showing flattened internodes that twist slightly along theirlength and exhibit a linear pattern as a result of either ultrastructure or pigment granule

distribution (b.f.).

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Fig. S7

Dissecting microscope images of coiled barbules (TMP 96.9.334). (A) Specimenoverview (opposite to Fig. S6A), showing coiled barbule bases (predominantly within

lower, central part of figure) surrounding thick, flattened rachis (vertical arrows); base of

rachis (lower arrow) recessed with respect to surface of amber piece as a result of

weathering; reddish-brown areas are the result of a prominent drying line within theamber; (B) close-up of rachis base, vertical arrow indicates fragment of possible barb

ramus that is too poorly preserved to permit confident identification, inclined arrows

indicate a few of the many individual barbules that exit the edge of the amber piecewithout making contact with the rachis (this lack of attachment appears to be

characteristic of most of the barbules, although they are crowded basally).

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Fig. S8

Compound microscope images of differentiated barbules with distinct pennulae inUALVP 52820, indicating preservation that is visually identical to Stage I and II

morphotypes. (A) Isolated barb with differentiated barbules and thickened barb shaft

ensnared in spider web (microphotograph) (B) overview of barbules near base of barb,

and surrounding spider web, (b.f.); (C) overview of barbules near distal tip of barb, withclearly defined distal and proximal barbule series (left and right sides of ramus,

respectively), distinguished by the sharp transition between the base and pennulum within

the distal series barbules (arrow), (b.f.); (D) close-up of proximal barbule, showingdistribution of pigmentation, and nodal prongs, (b.f.); (E) close-up of distal barbule,

showing distribution of pigmentation, nodal prongs, and ventral tooth upon basal plate

(arrow) adjacent to abrupt transition into pennulum (b.f.).

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Fig. S9

Compound microscope images of pennaceous barbs with reduced plumulaceous barbules.

(A) Overview of pigmented barb, TMP 96.9.997 (b.f.); (B) close-up of boxed area in A,

showing weak ramus and unpigmented basal barbules, as well as distribution of pigment

within subsequent barbules (b.f.); (C) dark-field image of same feather region, showing

apparent feather color created by pigmentation, as well as distribution of pigmentationwithin barb components; (D) overview of variably pigmented barb with elongate ramus

tip, TMP 96.9.1036, (b.f., micro-panorama compiled using Helicon Focus); (E) close-up

of pigment distribution within basal barbules ofD.

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Fig. S10

SDCM and LSCM data for Stage I morphotype and TMP 96.9.997 emission responsemicrophotographs and emission spectra. (A) Autofluorescence of TMP 96.9.997 when

exposed to laser based excitation at 491 nm (green, filter for emission wavelength

et525/50) and 561 nm (red, filter for emission wavelength et620/60), showing marginally

brighter spots where only keratin is preserved; (B) normalized emission spectrum forsampling points on TMP 96.9.997 when excited at 405 nm, emission from amber (ROI 1)

peaks between 480490 nm, similar, but progressively more muted peaks for

unpigmented keratin (ROI 3) and pigmented regions of barbule (ROI 2); (C) map ofsampling points and emission intensity between 540 and 550 nm TMP 96.9.997; (D)

autofluorescence of UALVP 52821 when exposed to laser based excitation at 491 nm

(green) and 561 nm (red); (E) emission spectrum for sampling points on UALVP 52821when excited at 405 nm, emission from amber (ROI 1) peaks broadly near 540 nm;

similar, but progressively more muted peaks for unpigmented outer wall of filament

when cut obliquely (ROI 2); unpigmented outer wall of filament when cut longitudinally(ROI 4); and pigmented layer (ROI 3); (F) map of sampling points and emission intensity

between 540 and 550 nm in UALVP 52821, arrow indicates rounded outline producedwhere filament breaches surface of amber piece (the pebbled surface at the lower right of

the image, also visible in Fig. S10D).

22


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Fig. S11

LSCM and additional photomicographs of UALVP 52821. (A) Three-dimensional scanof UALVP 52821 at 405 nm excitation (mapping emission intensity between 411 nm and

766 nm); fine white lines correspond to vertical section planes presented in panels to the

left of and below the main figure. Arrow indicates circular cross-section of one filament

apex, directly comparable to B. Brackets delimit filaments cut obliquely, demonstratingouter wall (bright) surrounding thin pigmented layer (dark) and hollow core (comparable

to the surrounding amber), this pattern is also found within longitudinal sections of the

filaments within this piece of amber. (B) Dissecting microscope photomicrograph offilaments in the same region of the amber specimen as A, illustrating appearance of

filaments when sectioned obliquely along polished surface, arrows indicate oblong

internal voids exposed at the section plane.

23


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Fig. S12

Photomicrographs of modern bird feathers for comparison of barbule structure andpigmentation patterns. (A) Plumulaceous barbules from the afterfeather of a pheasant

(b.f.); (B) dark-field image ofA, showing pigment distribution and resulting dull-brown

coloration; (C) close-up of barbules in A, showing pigment concentration near nodes

although somewhat more diffuse, this is comparable to pigmentation in Fig. S8 (b.f.); (D)partially curled barbule bases in the plumulaceous basal barbs within a body contour

feather of a kiwi (Apteryx owenii, RM 5440), for comparison to coiled barbule bases in

Figs. S6 and S7, and also an example of diffuse pigmentation (b.f.); (E) single barb fromwhite belly feather of a grebe (Aechmophorus occidentalis, RAM Z279.78.2), illustrating

coiled barbule bases, predominantly with two basal coils (dissecting microscope); (F)

combined focal-plane image of different barbule from same feather as E, providingoverview of coiling (d.f.); (G) single image of the barbule bases that are partly obscured

in G, due to the orientation of the barbules (d.f.).


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Acknowledgments: We thank the Leuck family and M. Schmidt (donated specimens); M.Caldwell, S. Ogg and M. Srayko (microscopy); E. Koppelhus and H. Proctor(discussions); and J. Gardner, B. Strilisky, A. Howell, and J. Hudon (TMP, RedpathMuseum, and Royal Alberta Museum collections). Research was funded by NaturalSciences and Engineering Research Council of Canada (NSERC) Discovery Grants toB.D.E.C., A.P.W., and P.J.C. and NSERC and Alberta Ingenuity Fund support to R.C.M.
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A Diverse Assemblage of Late Cretaceous Dinosaur and Bird Feathers From Canadian Amber

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