modern optics in exceptionally preserved eyes of early cambrian arthropods from australia

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Modern optics in exceptionally preserved eyes ofEarly Cambrian arthropods from AustraliaMichael S. Y. Lee1,2, James B. Jago1,3, Diego C. Garcıa-Bellido4, Gregory D. Edgecombe5, James G. Gehling1 & John R. Paterson6

Despite the status of the eye as an ‘‘organ of extreme perfection’’1,theory suggests that complex eyes can evolve very rapidly2. The fossilrecord has, until now, been inadequate in providing insight into theearly evolution of eyes during the initial radiation of many animalgroups known as the Cambrian explosion. This is surprisingbecause Cambrian Burgess-Shale-type deposits are replete withexquisitely preserved animals, especially arthropods, that possesseyes3–5. However, with the exception of biomineralized trilobiteeyes, virtually nothing is known about the details of their opticaldesign. Here we report exceptionally preserved fossil eyes from theEarly Cambrian ( 515 million years ago) Emu Bay Shale of SouthAustralia, revealing that some of the earliest arthropods possessedhighly advanced compound eyes, each with over 3,000 large omma-tidial lenses and a specialized ‘bright zone’. These are the oldest non-biomineralized eyes known in such detail, with preservation qualityexceeding that found in the Burgess Shale and Chengjiang deposits.Non-biomineralized eyes of similar complexity are otherwiseunknown until about 85 million years later6,7. The arrangementand size of the lenses indicate that these eyes belonged to an activepredator that was capable of seeing in low light. The eyes are morecomplex than those known from contemporaneous trilobites andare as advanced as those of many living forms. They provide furtherevidence that the Cambrian explosion involved rapid innovation infine-scale anatomy as well as gross morphology, and are consistentwith the concept that the development of advanced vision helped todrive this great evolutionary event8.

The anatomy of many Early and Middle Cambrian (,520–500million years (Myr) ago) organisms is known in considerable detailfrom numerous Burgess-Shale-type deposits worldwide3–5, but the finestructure of these organisms’ eyes is poorly known. Details of the visualsurface are known only from certain Cambrian trilobites and sometiny ‘Orsten’ arthropods9: all of these have compound eyes that aresmall in absolute size and contain few visual units (ommatidia) bearinglenses of uniform size. Yet the evolution of powerful vision has beenproposed as a trigger8,10 for the Cambrian explosion of animals3,5. Wehave recovered exceptionally preserved, large compound eyes (Fig. 1)from the Early Cambrian (Series 2, Stage 4; ,515 Myr ago) Emu BayShale Konservat-Lagerstatte at Buck Quarry, Big Gully, on KangarooIsland in South Australia11–13. The new fossils represent the oldest non-trilobite arthropod eyes that show fine detail of the visual surfaces.

All eyes were found isolated (disarticulated) but they are closely com-parable in morphology and size, which is consistent with their referral toa single taxon of large arthropods (see below). All specimens bear SouthAustralian Museum Palaeontology (SAM P) numbers. The visual sur-faces of three eyes (Fig. 1a–c and Supplementary Fig. 1) are relativelycomplete and form the basis for the descriptions; the remaining four(Supplementary Fig. 2) are similar but do not provide extra information.The fossils are preserved in finely laminated grey mudstone. Scanningelectron microscopy with energy dispersive spectrometry (SEM-EDS)

analysis of the optical surface of specimen P43687 (Supplementary Fig. 3)detected elevated levels of calcium and phosphorus relative to thematrix. This indicates that phosphatization of the primarily chitinous

1South Australian Museum, North Terrace, Adelaide, South Australia 5000, Australia. 2School of Earth and Environmental Sciences, University of Adelaide, South Australia 5005, Australia. 3School ofNatural and Built Environments, University of South Australia, Mawson Lakes, South Australia 5095, Australia. 4Departamento de Paleontologıa, Instituto de Geologıa Economica/Instituto de Geociencias(CSIC-UCM), Jose Antonio Novais 2, Madrid 28040, Spain. 5Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK. 6Division of Earth Sciences, School ofEnvironmental and Rural Science, University of New England, Armidale, New South Wales 2351, Australia.

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Figure 1 | Complex arthropod eyes from the Early Cambrian. a–d, Threefossils of compound eyes from a large arthropod from the Emu Bay Shale, SouthAustralia (a–c), shown in similar hypothesized orientation to the compoundeye of a living predatory arthropod, the robberfly Laphria rufifemorata(d; anterior view of head). All fossil eyes have large central ommatidial lensesforming a light-sensitive bright zone, b, and a sclerotized pedestal, p. Becausethe fossil eyes are largely symmetrical about the horizontal axis, it is not possibleto determine dorsal and ventral surfaces, and thus whether the eyes are left orright. All fossils are oriented as if they are left eyes (medial is to the left of thefigure). In b there is a radial tear (white line) with the top portion of the eyedisplaced downwards to overlie the main part; extensive wrinkling causes somecentral lenses (arrow) to be preserved almost perpendicular to the beddingplane. South Australian Museum numbers are: a, P43629a; b, P43687;c, P43658; d, A29-000885.

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cuticle has occurred in some instances, as in the Orsten biota, the onlyother Cambrian deposit where non-trilobite eyes are exceptionally pre-served9. Phosphatization of organic material is relatively common in theEmu Bay Shale, for example, in Myoscolex14 and Isoxys11. Wrinkling andtearing of the visual surface (for example, Fig. 1b) provide furtherevidence that the cuticle was originally non-biomineralized. Despiteflattening of the overall visual surface, finer features such as ommatidiallenses are preserved in superb detail and three-dimensional relief (Fig. 2and Supplementary Fig. 1).

Each eye comprises a smoothly curved, ovoid visual surface with along axis diameter of about 7–9 mm and a thickly sclerotized pedestalthat is not fully preserved on any specimen. The three most completeeyes are shown in Fig. 1, in the same presumed orientation as similarliving analogues (for example, the robberfly Laphria and krillNematoscelis). The lateral edge of the eye is a smooth arc; the medialedge, which meets the pedestal, seems to be broadly V-shaped. Each ofthe three eyes is preserved in a similar orientation, with the largestlenses near to the centre and smaller lenses on the margin; this suggeststhat each eye was already flattened in this plane during life. The visualsurface contains a dense and highly regular hexagonal array of over3,000 large lenses. The two best-preserved specimens (P43629a andP43687, Fig. 1a, b) share many similarities. The eye surface comprises adense purplish-black (phosphatized) cuticular layer and is convex atthe margins, indicating that the external surface of the eye cuticle isexposed. The corneal or lens surfaces of the ommatidia are darker thanthe intervening spaces. The lenses are recessed in the central region,but some near to the margin are elevated; this variation is probably ataphonomic artefact. The counterpart of P43629a (P43629b) shows amould of the presumed external surface in less detail: the lenses areelevated, there is no dark phosphatized layer and the margins of the eyeare concave. Specimen P43658 (Fig. 1c) is a similar surface to P43629b:the lenses are likewise elevated, there is no dark phosphatized layer andthe margins are concave.

The lenses of the ommatidia exhibit a similar size gradient across allspecimens. The largest lenses, with about 150mm elevational diameter15,are concentrated in the region nearest the pedestal, with size decreasingto half this diameter (,80mm) towards the margins (Fig. 2). Lens sizeis further reduced to about 60mm at the extreme margins but com-pression and oblique orientation make accurate measurement in thisarea difficult. The size gradient is not an artefact of compression ofmarginal lenses for the following reasons: (1) the measurements given

here refer to the longest diameter across each lens—lateral compres-sion of marginal lenses would turn a circle into a progressively narroweroval but it should not reduce the longer diameter; (2) the lenses getprogressively smaller only a short distance from the centre, well beforeany major change in orientation has occurred; and (3) there are deepwrinkles across P43687, causing some central lenses to be preservedalmost perpendicular to the bedding plane (Fig. 1b, arrow), yet thelonger diameter of these lenses is not reduced. Less pronouncedwrinkles occur in other specimens and similarly do not affect thegradient of lens sizes. Interommatidial angles cannot be determinedaccurately owing to compression; however, the lenses of the ommatidiaare preserved horizontally nearest to the pedestal but more obliquelyclose to the margins. This change in orientation happens abruptly, notgradually, indicating that the visual surface was relatively flat near tothe pedestal, with curvature increasing more rapidly near to the margin(that is, the visual surface was not uniformly curved).

The Emu Bay Shale eyes are more elaborate than any knownCambrian visual organ, although comparisons are largely restricted tothe calcitic (and thus optically unusual8) eyes of trilobites. The lenses arenot only very numerous and large, they are also hexagonally arranged ina highly regular six-neighbour arrangement: the densest and most effi-cient packing pattern. In contrast, Early Cambrian eodiscid trilobitessuch as Shizhudiscus and Neocobboldia have fewer than 100 lenses,which are also much smaller (,50mm in diameter) and less regularlyarranged in a less efficient square-grid array16. The extremely regulararrangement of lenses seen here exceeds even that in certain moderntaxa, such as the horseshoe crab Limulus, in which up to one-third oflenses deviate from hexagonal packing17. Eyes with more than 3,000ommatidia and lenses larger than 60mm in diameter are otherwise firstknown from the biomineralized visual organs of early Ordoviciantrilobites, more than 40 million years later (Fig. 3).

The arrangement and size gradient of lenses creates a distinct ‘brightzone’ (also called the acute zone or fovea), where the visual field issampled with higher light sensitivity (due to large ommatidia) andpossibly a higher acuity (due to what seems to be a more parallelorientation of ommatidia). Such visual specializations, characteristicof many modern taxa, are otherwise unknown in the Early Cambrian.The ratio of lens diameters in the bright zone to lens diameters in themargin (,2.5:1) exceeds that found in other Cambrian arthropods(trilobites and cambropachycopids) and is comparable to that in manymodern taxa such as dragonflies, which have ratios of 1.61–2.71:1

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Figure 2 | Cambrian arthropod eye SAM P43629, imaged using a LeicaMZ16FA relief-map stereomicroscope. a, Entire specimen showing thepositions of close-ups in c and f. b, Relief-map three-dimensionalreconstruction of a. c, Close-up of large ommatidial lenses in the bright zone,with white line and numbers referring to the cross-section shown in e. d, Relief-map three-dimensional reconstruction of c. e, Cross-section through four large

lenses indicated by the white line in c; numbers refer to individual lensesrepresented by concavities. f, Close-up of small marginal lenses, with white lineand numbers referring to the cross-section shown in h. g, Relief-map three-dimensional reconstruction of f. h, Cross-section through four small lensesindicated by the white line in f; numbers refer to individual lenses representedby concavities. Further pictures and imaging details are in Supplementary Fig. 2.

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(ref. 18). The ommatidial gradient could have been achieved by twodifferent but non-exclusive developmental processes found in modernarthropods. These are (1) a reduction in insulin/insulin-like growthfactor signalling from the centre to the periphery, which affects cell size19;and (2) the recruitment of a higher number of cells (mainly photorecep-tors) in each central ommatidium20. If these eyes grew in size and omma-tidial number during each instar by recruitment of new peripheralommatidial rows, as occurs in modern non-metamorphosing arthro-pods17, then this too could have caused the older, central ommatidia toconsist of larger cells than the newly developed, marginal ommatidia.

The morphology of the visual surface and analogy to similar eyes inliving arthropods (Fig. 1d) indicate that each eye protruded laterally ordorsolaterally, with the bright zone directed anteriorly or anterodorsally.This bilaterally symmetrical arrangement generates binocular vision(because the left and right bright zones have overlapping visual fields)and also generates wide peripheral fields (because the smaller lenseson the left and right eyes have largely complementary, rather thanoverlapping, visual fields). However, confirmation of this inferencerequires the discovery of articulated remains. Acute forward vision

and lower-resolution peripheral vision are typical of predators thatrequire excellent frontal vision for estimating distance and detectingprey against complex backgrounds; they are also typical of fast-moving organisms in which acute peripheral vision is precluded bya high retinal angular velocity21.

The ommatidial lens facets in the Emu Bay Shale eyes are large(60–150mm, Fig. 3b) but the lenses are not anomalously large giventhe sizes of the eyes; relative sizes are broadly similar to those oftrilobites, living crustaceans and xiphosurans (Supplementary Fig. 4).The association between the size and arrangement of ommatidia andthe level of ambient light has been quantified using the eye parameter‘p’ (ref. 22). Owing to compression of the Emu Bay Shale eyes, p isimpossible to measure. However, p has been evaluated in detail in twotrilobites, Carolinites and Pricyclopyge15, with eyes broadly comparablein both size and shape to the Emu Bay Shale eyes (that is, broadlyconvex with hexagonally close-packed lenses). Carolinites genacinacahas lenses up to 75mm in size, similar to the ,60–80 mm marginallenses of the Emu Bay Shale eyes, and Pricyclopyge binodosa has lensesof up to 180mm, comparable in size to the ,150mm central lenses ofthe Emu Bay Shale eyes. Eyes of broadly equivalent shape and size, withsimilarly sized and packed lenses, could be expected to have similarinterommatidial angles and thus p values. If this extrapolation is valid,the present eyes would have had p values comparable to the rangefound across Carolinites and Pricyclopyge, that is, 2.13–8.31. Suchvalues are typical of taxa living in low-luminance environments22.

True compound eyes with lens-bearing ommatidia are restricted toarthropods23,24. The complexity and large size of the Emu Bay Shale eyesstrongly indicate that they belong to an active arthropod, probably a largepredator. However, a definitive association with any particular taxonmust await articulated remains. In the Emu Bay Shale fauna, the onlysufficiently large arthropods known are the trilobite Redlichia takooensis,the stem-arthropod Anomalocaris and the bivalved arthropod Tuzoia(ref. 11 and citations therein). The eyes are clearly different in shape fromthe seleniform, calcitic eyes of Redlichia and other trilobites. They alsoseem too small to be referable to Anomalocaris. All of the eyes describedhere are 7–9 mm in their longer diameter, suggesting that they camefrom similarly sized adults. The expected eye diameter in adults of bothAnomalocaris species from the Emu Bay Shale is 2–3 times greater thanthis, given the relative sizes of frontal appendages of anomalocarididsfrom the Emu Bay, Burgess and Maotianshan Shales (with specimensfrom the latter deposits having preserved eyes: ref. 25 and citationstherein). The large, unnamed Tuzoia species from the Emu Bay Shalehas stalked compound eyes that are ovoid to round and 6–9 mm indiameter11: very similar to the fossil eyes described here. However, nodetailed structure of the visual surface is preserved in the articulated eyesof Emu Bay Shale or Burgess Shale Tuzoia specimens11,26. Attribution ofthe isolated eyes to Tuzoia would require a taphonomic explanation forwhy disarticulated eyes are more commonly preserved and preserved infiner detail. One possibility is that the fossils reported here are of pre-viously shed corneas. The corneal surfaces of living arthropods detachduring ecdysis and remain loosely connected to the rest of the exuvia;moulted corneas might be more prone to decay and thus more suscep-tible to early diagenetic mineralization (in this case phosphatization)than complete eyes attached to intact organisms.

The evolution of powerful vision is one of the most important cor-relates10 of the Cambrian explosion and has been proposed as a triggerfor this event8. However, although the overall shapes of eyes are knownfor many Cambrian organisms3–5, intricate details of the visual surfaceare known only for trilobites27 and the tiny stem-crustacean cambro-pachycopids, which have bizarre, proportionately huge and mediallyfused compound eyes9. In addition, indistinct ommatidia are preservedin a few Chengjiang fossils, including the non-biomineralized arthro-pods Isoxys and Cindarella28,29. Isoxys inhabited both dim and brightpelagic environments28 whereas Cindarella probably inhabited a brightbenthos29. The specimens described here represent the first microana-tomical evidence confirming the view that highly developed vision in

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Figure 3 | Complexity of the Early Cambrian Emu Bay Shale eyes comparedto eyes in other early Palaeozoic taxa. a, b, Number of ommatidia (a) and lenssize (b) plotted against stratigraphic age for Cambro-Ordovician arthropods;data in Supplementary Table 1. The Emu Bay Shale eyes have many moreommatidia and much larger individual ommatidia than eyes in all otherCambrian taxa. Trilobites are plotted according to eye type: schizochroal eyeshave relatively few, large lenses and are optically unusual compared to typicalcompound eyes27.

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the Early Cambrian was not restricted to trilobites8,10. Furthermore, inpossessing more and larger lenses, plus a distinct bright zone, they aresubstantially more complex than contemporaneous trilobite eyes,which are often assumed to be among the most powerful visual organsof their time27,30. The new fossils reveal that some of the earliest arthropodshad already acquired visual systems similar to those of living forms,underscoring the speed and magnitude of the evolutionary innovationthat occurred during the Cambrian explosion.

Received 6 February 2011; accepted 1 April 2011.

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2. Nilsson, D. E. & Pelger, S. A pessimistic estimate of the time required for an eye toevolve. Proc. R. Soc. Lond. B 256, 53–58 (1994).

3. Briggs, D. E. G., Erwin, D. H. & Collier, F. J. The Fossils of the Burgess Shale(Smithsonian Institution Press, 1994).

4. Hou, X.-G. et al. The Cambrian Fossils of Chengjiang, China: The Flowering of EarlyAnimal Life (Blackwell, 2004).

5. Conway-Morris, S. The Crucible of Creation: The Burgess Shale and the Rise ofAnimals (Oxford Univ. Press, 1998).

6. Ritchie, A. Ainiktozoon loganense Scourfield, a protochordate? from the Silurian ofScotland. Alcheringa 9, 117–142 (1985).

7. van der Brugghen, W., Schram, F. R. & Martill, D. M. The fossil Ainiktozoon is anarthropod. Nature 385, 589–590 (1997).

8. Parker, A. On the origin of optics. Opt. Laser Technol. 43, 323–329 (2011).9. Haug, J. T., Maas, A. & Waloszek, D. Ontogeny of two Cambrian stem crustaceans,

Goticaris longispinosa and Cambropachycope clarksoni. Palaeontographica Abt. A289, 1–43 (2009).

10. Plotnick, R. E., Dornbos, S. Q. & Chen, J.-Y. Information landscapes and sensoryecology of the Cambrian radiation. Paleobiology 36, 303–317 (2010).

11. Garcıa-Bellido, D. C. et al. The bivalved arthropods Tuzoia and Isoxys with soft-partpreservation from the lower Cambrian Emu Bay Shale Lagerstatte (KangarooIsland, Australia). Palaeontology 52, 1221–1241 (2009).

12. Gehling, J. G., Jago, J. B., Paterson, J. R., Garcıa-Bellido, D. C. & Edgecombe, G. D.Thegeological context of the lowerCambrian (Series2)EmuBayShaleLagerstatteand adjacent stratigraphic units, Kangaroo Island, South Australia. Aust. J. EarthSci. 58, 243–257 (2011).

13. Paterson, J. R., Edgecombe, G. D., Garcıa-Bellido, D. C., Jago, J. B. & Gehling, J. G.Nektaspid arthropods from the lower CambrianEmu Bay ShaleLagerstatte, SouthAustralia, with a reassessment of lamellipedian relationships. Palaeontology 53,377–402 (2010).

14. Briggs, D. E. G. & Nedin, C. The taphonomy and affinities of the problematic fossilMyoscolex from the Lower Cambrian Emu Bay Shale of South Australia. J.Paleontol. 71, 22–32 (1997).

15. McCormick, T. & Fortey, R. A. Independent testing of a paleobiological hypothesis:the optical design of two Ordovician pelagic trilobites reveals their relativepaleobathymetry. Paleobiology 24, 235–253 (1998).

16. Zhang, X.-G. & Clarkson, E. N. K. The eyes of Lower Cambrian eodiscid trilobites.Palaeontology 33, 911–932 (1990).

17. Harzsch, S. & Hafner, G. Evolution of eye development in arthropods: Phylogeneticaspects. Arthropod Struct. Dev. 35, 319–340 (2006).

18. Wehner, R. in Comparative Physiology and Evolution of Vision in Invertebrates: C287–616 (Springer, 1981).

19. Oldham, S. et al. The Drosophila insulin/IGF receptor controls growth and size bymodulating PtdInsP3 levels. Development 129, 4103–4109 (2002).

20. Freeman, M. Reiterative use of the EGF receptor triggers differentiation of all celltypes in the Drosophila eye. Cell 87, 651–660 (1996).

21. Land, M. F. & Nilsson, D.-E. Animal Eyes (Oxford Univ. Press, 2002).22. Snyder, A. W. inComparative Physiologyand Evolution of Vision in Invertebrates A (ed.

Autrum, H.) 225–313 (Springer, 1979).23. Warrant, E. & Nilsson, D.-E. Invertebrate Vision (Cambridge Univ. Press, 2006).24. Harzsch, S., Melzer, R. R. & Muller, C. H. G. Mechanisms of eye development and

evolution of the arthropod visual system: The lateral eyes of myriapoda are notmodified insect ommatidia. Org. Divers. Evol. 7, 20–32 (2007).

25. Daley, A. C., Budd, G. E., Caron, J.-B., Edgecombe, G. D. & Collins, D. The BurgessShale anomalocaridid Hurdia and its significance for early euarthropod evolution.Science 323, 1597–1600 (2009).

26. Vannier, J. et al. Tuzoia: morphology and lifestyle of a large bivalved arthropod ofthe Cambrian seas. J. Paleontol. 81, 445–471 (2007).

27. Clarkson, E., Levi-Setti, R. & Horvath, G. The eyes of trilobites: The oldest preservedvisual system. Arthropod Struct. Dev. 35, 247–259 (2006).

28. Schoenemann, B. & Clarkson, E. N. K. Eyes and vision in the Chengjiang arthropodIsoxys indicating adaptation to habitat. Lethaia doi:10.1111/j.1502–3931.2010.00239.x (30 September 2010).

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Supplementary Information is linked to the online version of the paper atwww.nature.com/nature.

Acknowledgements We thank P. and C. Buck for access to and assistance at the fossilsite; N. Schroeder, M. Gemmell, R. Atkinson, M. A. Binnie and numerous others(Supplementary Table 3) for help with excavations and curatorial assistance;A. Netting, P. Hudson and Adelaide Microscopy for imaging; D. Birch and G. Brock forSEM-EDS analysis; A. Baonza and J. F. de Celis for discussions on arthropod eyedevelopment; R. Fortey and A. Parker for comments and the Australian ResearchCouncil (grant LP0774959), South Australian Museum, Spanish Ministry of Science(RYC2007-00090 and grant CGL2009-07073), Beach Energy and Sealink Pty Ltd forfunding.

Author Contributions All authors contributed directly to excavation and interpretationof fossil specimens, analysis and writing the paper. J.B.J., J.R.P. and M.S.Y.L. compiledcomparative eye data, M.S.Y.L. conducted the stereomicroscopy and J.R.P. conductedthe SEM-EDS analyses and digital photography.

Author Information Reprints and permissions information is available atwww.nature.com/reprints. The authors declare no competing financial interests.Readers are welcome to comment on the online version of this article atwww.nature.com/nature. Correspondence and requests for materials should beaddressed to M.S.Y.L. ([email protected]) or J.R.P.([email protected]).

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Supplementary Information: Tables 1-3 SI Table 1. Number and average size of ommatidia for Cambrian and Ordovician arthropods (trilobites, cambropachycopids, and the Emu Bay

Shale eyes), as plotted in Fig. 3 (main text).

Species Clade Age

(Ma) Eye Type*

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Ommatidia Lens

Diameter (average, µm)

Reference (1-30 cited in main text, 31-80 cited below)

Neocobboldia chinlinica Trilobita 520 A 84 20 Zhang & Clarkson 199016, pls 3, 4, text-fig. 8; Gal et al. 200031, fig. 1; Clarkson et al., 200627, fig. 4G, H

Shizhudiscus longquanensis Trilobita 520 A 95 37.5 Zhang & Clarkson 199016, pls 1, 2 Pagetia prolata Trilobita 508 A 32 25 Jell 197532, fig. 2E-H; Jell 197533, pl. 12, figs 1-3 Pagetia ocellata Trilobita 507 A 20 20 Jell 197532, fig. 4C, D Pagetia sinesulcata Trilobita 507 A 59 33 Jell 197532, fig. 2A-D; Jell 197533, pl. 20, figs 1-3, 5 Pagetia thorntonensis Trilobita 506 A 46 35 Jell 197532, fig. 3 Helepagetia argusi Trilobita 502 A 20 45 Jago 197234, pl. 44, figs 4, 6, 9 Paradistazeris hubeiensis Trilobita 501 H 200 36 Peng et al. 200435, pl. 21, fig. 11 “Cedaria” woosteri Trilobita 501 H 45 Hughes et al. 199736, figs 4.2, 5 Catillicephalina

glasgowensis Trilobita 500 H 600 16 Bentley et al. 200937, fig. 9H, I Ctenopyge ceciliae Trilobita 491 H 150 21 Schoenemann et al. 201038, text-figs 2, 3 Sphaerophthalmus alatus Trilobita 491 H 150 30 Clarkson 197339, pl. 95, figs 1, 2 Peltura scarabaeoides Trilobita 491 H 180 40 Clarkson 197339, text-fig. 4c Ctenopyge (Eoctenopyge)

angusta Trilobita 491 H 200 50 Clarkson et al. 200340, pl. 7, figs 4, 5 Sphaerophthalmus humilis Trilobita 491 H 200 50 Clarkson 197339, pl. 94, fig. 6, pl. 95, figs 4-6 Jujuyaspis keideli Trilobita 488 H 1200 60 Aceñolaza et al. 200141, fig. 3 Ogygiocaris? cf. selwyni Trilobita 475 H 3000 62 Whittington 196642, pl. 2, fig. 8

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Toletanaspis borni Trilobita 475 S 110 100 Henry et al. 199243, fig. 2d Oopsites hibernicus Trilobita 474 H 900 100 Fortey 197544, pl. 34, figs 2, 5 Opipeuterella inconnivus Trilobita 474 H 2000 50 Fortey 197445, pl. 14, figs 4, 6, 7 Carolinites genacinaca Trilobita 474 H 4000 75 Fortey 197544, pl. 37, figs 7, 10, 12; McCormick & Fortey 199846 Telephina calandria Trilobita 473 H 900 80 Chatterton et al. 199947, fig. 4.26 Psephosthenapsis glabrior Trilobita 471 H 5000 70 Fortey & Droser 199648, fig. 11.8 Perischoclonus capitalis Trilobita 468 H 200 50 Whittington 196349, pl. 22, fig. 7 Goniotelus kindlei Trilobita 468 H 220 40 Whittington 196349, pl. 14, fig. 9; Whittington 199250, pl. 4, fig. B Kawina torulus Trilobita 468 H 350 60 Whittington 196349, pl. 29, fig. 7 Bathyurellus nitidus Trilobita 468 H 850 50 Whittington 196349, pl. 10, fig. 16 Apatolichas jukesi Trilobita 468 H 3500 30 Whittington 196349, pl. 33, fig. 11; Whittington 199250, pl. 4, fig. A Carolinites rugosus Trilobita 466 H 1300 130 Fortey 197544, pl. 36, figs 1, 7, 17 Retamaspis melendezi Trilobita 465 S 180 180 Hammann 197451, pl. 2, fig. 17b Pricyclopyge binodosa Trilobita 464 H 1200 180 Clarkson 197552, pl. 2, figs 1-3, 5-8; McCormick & Fortey 199846; Bruthansova

200353, pl. 3, figs 9, 12 Asaphus cornutus Trilobita 464 H 3500 80 Clarkson in Whittington et al. 199754, fig. 101.1; Fordyce & Cronin 199355, fig. 6 Ormathops atava Trilobita 463 S 140 90 Henry et al. 199243, fig. 1i Telephina mobergi Trilobita 462 H 150 180 Ahlberg 199556, pl. 3, figs 11, 12 Telephina bicuspis Trilobita 462 H 1100 180 Ahlberg 199556, pl. 1, fig. 9; Bruton & Høyberget 200657, fig. 1-O Crozonaspis struvei Trilobita 462 S 184 270 Clarkson 196858, pl. 1, figs 1-3 Microparia (Quadratapyge)

latilimbata Trilobita 461 H 350 70 Zhou & Zhou 200969, fig. 2A, G Sphaerexochus arenosus Trilobita 458 H 130 70 Chatterton & Ludvigsen 197660, pl. 13, fig. 46 Remopleurides pattersoni Trilobita 458 H 5000 20 Chatterton & Ludvigsen 197660, pl. 22, figs 12, 13 Calyptaulax callirachis Trilobita 458 S 130 220 Chatterton & Ludvigsen 197660, pl. 16, fig. 34 Phacopidella hupei Trilobita 458 S 192 240 Nion & Henry 196661, pl. 24, figs 1a, 1b, 1c, 2a, 2b, 2c. Zeliszkella mytoensis Trilobita 458 S 200 210 Struve 195862, pl. 1, fig. 7d Kloucekia micheli Trilobita 458 S 280 210 Henry 196563, pl. 1, fig. 9 Sphaerexochus pulcher Trilobita 456 H 75 60 Whittington & Evitt 195464, pl. 21, fig. 2 Holia cimelia Trilobita 456 H 170 70 Whittington & Evitt 195464, pl. 19, figs 3, 4; Whittington 199250, pl. 4, figs C, D Eomonorachus intermedius Trilobita 455 S 100 150 Ludvigsen & Chatterton 198265, pl. 2, fig. 13

doi:10.1038/nature10097 SUPPLEMENTARY INFORMATIONRESEARCH


Hispaniaspis (?) sp. indet. Trilobita 453 H 140 80 Fortey 199766, pl. 10, fig. 4 Ovalocephalus ovatus Trilobita 453 H 160 80 Fortey 199766, pl. 9, fig. 8 Telephina convexa Trilobita 453 H 1966 200 Fortey 199766, text-fig. 3; Han 200167, pls 1-4 Calyptaulax brongniartii Trilobita 453 S 225 280 Clarkson & Tripp 198268, figs 4g, 5d; Clarkson et al. 200629, fig. 4A, B Achatella achates Trilobita 452 S 110 230 Ludvigsen & Chatterton 198265, pl. 1, fig. 5 Sagavia chuanxiensis Trilobita 451 H 2000 60 Zhou & Zhou 200769, fig. 2J Flexicalymene cf. quadrata Trilobita 448 H 220 17 Clarkson 197552, pl. 3, figs 9-11 Pseudogygites

latimarginatus Trilobita 447 H 40 Clarkson 197970, pl. 1, fig. 6 Symphysops armata Trilobita 445 H 2500 140 Hammann & Leone 199771, pl. 10, fig. 2 Mucronaspis mucronata Trilobita 445 S 120 210 Cocks & Fortey 199772, pl. 1, fig. 9 Dalmanitina yichangensis Trilobita 445 S 230 360 Zhu & Wu 198373, pl. 5, fig. 1 Goticaris longispinosa Cambropachycopidae 499 H 67 30 Haug et al. 20099, pl. 5, fig. 1 Cambropachycope clarksoni Cambropachycopidae 499 H 149 40 Haug et al. 20099, pl. 11, figs 3, 4 Emu Bay Eye – margin Unknown 515 NA 3100 60 Current paper

Current paper Emu Bay Eye – bright zone Unknown “ “ “ 150 * A = abathochroal, H = holochroal, S = schizochroal.



Species Clade Eye radius

(r) (µm) Log10(√r) Ommatidia

Diameter (d) (µm)

Log10(d) Reference (1-30 cited in main text, 31-80 cited below)

Polyphemus pediculus Crustacea 60 0.89 25 1.40 Nilsson & Oselius 198374, Fig. 1 Leptodora kindtii Crustacea 210 1.16 30 1.48 Wolken & Gallik 196575, Fig. 1 Gennadas sp. Crustacea 300 1.24 15 1.18 Meyer-Rochow & Walsh 197776, p. 89, 91. Thysanopoda tricuspidata Crustacea 550 1.37 28 1.45 Meyer-Rochow & Walsh 197877, p. 61, Fig. 2b Panulirus longipes Crustacea 5000 1.85 80 1.90 Meyer-Rochow 197578, p. 440, 455. Limulus polyphemus Xiphosura 6500 1.91 120 2.08 Fahrenback 196879 p. 279, fig. 1; Miller 195780 p. 426 gives similar ommatidia

diameter of 140 microns Neocobboldia chinlinica Trilobita 120 1.04 22 1.34 Zhang & Clarkson 199016, pl. 4, fig. 1a, b Sphaerophthalmus alatus Trilobita 200 1.15 30 1.48 Clarkson 197339, pl. 95, fig. 1 Perischoclonus capitalis Trilobita 410 1.31 50 1.70 Whittington 196349, pl. 22, figs 2, 4, 6, 7 Apatolichas jukesi Trilobita 1060 1.51 30 1.48 Whittington 199250, pl. 4, fig. A, pl. 96, fig. D Oopsites hibernicus Trilobita 2100 1.66 100 2.00 Fortey 197544, pl. 34, figs 2, 5 Calyptaulax brongniartii Trilobita 2530 1.70 280 2.45 Clarkson & Tripp 198268, fig. 4d, g Telephina convexa Trilobita 3370 1.76 194 2.29 Han 200167, pl. 1 Pricyclopyge binodosa Trilobita 5350 1.86 135 2.13 Clarkson 197552, pl. 2, figs 1, 2 Insects Insecta NA NA NA NA Wehner 198118, p.309; see also Barlow 195281. Emu Bay Shale eye, margin 400 1.80 60 1.78 Current paper Emu Bay Shale eye, bright zone 400 1.80 150 2.18 Current paper

SI Table 2. Eye size and ommatidia size for a range of fossil and living aquatic arthropods. The data were combined with the data for terrestrial

arthropods in Wehner (1981 p. 309) and the combined data are plotted in SI Fig. 4.



Organisation Personnel

Waterhouse Club (South Australian Museum) Carolyn and Trevor Ireland, Don and Margie Heylen, Mary-Lou and Antony Simpson,

Catherine Boros, Margaret Brown, Michael and Heather Clegg, Hank de Wit, Robert

Edwards, Sally Haynes, Robert Finlay-Jones, Suzanne Kent, Diana Laidlaw, Anne Levy,

Jan Lodge, Jan Perry, Bert and Barbara Prowse, Hamish Ramsey, Lyn Pederson, Rob

Searcy, John and Beth Shepherd, Ian Smith, Alun Thomas, Kathleen Cunningham, Diana

Watson, Ian and Mary Wilson

South Australian Museum Staff Natalie Schroeder, Dennis Rice, Mike Gemmell, Mary-Anne Binnie

University of Adelaide Staff Aaron Camens, Trevor Worthy, Jenny Worthy

Other Organisations / Private Paul and Carmen Buck, Ronda Atkinson, Glenn Brock, John Laurie, Pierre Kruse, Allison

Daley, Lars Holmer, John Ellice-Flint, Heather Catchpole, Richard Fortey, Roger Cooper,

Leonie Feutrill

SI Table 3. We thank the above associates and volunteers who have helped with excavations at Buck Quarry.



References for Supplementary Information: Tables

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44. Fortey, R.A. The Ordovician trilobites of Spitsbergen. II. Asaphidae, Nileidae, Raphiophoridae and Telephinidae of the Valhallfonna Formation. Norsk Polarinstitutt Skrifter

162, 1-207 (1975).

45. Fortey, R.A. A new pelagic trilobite from the Ordovician of Spitsbergen, Ireland, and Utah. Palaeontology 17, 111-124 (1974).

46. McCormick, T. & Fortey, R.A. Independent testing of a paleobiological hypothesis: the optical design of two Ordovician pelagic trilobites reveals their relative

paleobathymetry. Paleobiology 24, 235-253 (1998).

47. Chatterton, B.D.E., Edgecombe, G.D., Vaccari, N.E. & Waisfeld, B.G. Ontogenies of some Ordovician Telephinidae from Argentina, and larval patterns in the Proetida

(Trilobita). Journal of Paleontology 73, 219-239 (1999).

48. Fortey, R.A. & Droser, M.L. Trilobites at the base of the Middle Ordovician, western United States. Journal of Paleontology 70, 73-99 (1996).

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50. Whittington, H.B. Trilobites 145 (The Boydell Press, Woodbridge, 1992).

51. Hammann, W. Phacopina und Cheirurina (Trilobita) aus dem Ordovizium von Spanien. Senckenbergiana lethaea 55, 1-151 (1974).

52. Clarkson, E.N.K. The evolution of the eye in trilobites. Fossils and Strata 4, 7-31 (1975).

53. Bruthansová, J. Exuviation of selected Bohemian Ordovician trilobites. Special Papers in Palaeontology 70, 293-308 (2003).

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55. Fordyce, D. & Cronin, T.W. Trilobite vision: a comparison of schizochroal and holochroal eyes with the compound eyes of modern arthropods. Paleobiology 19, 288-303

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(2006).

58. Clarkson, E.N.K. Structure of the eye of Crozonaspis struvei (Trilobita, Dalmanitidae, Zeliszkellinae). Senckenbergiana lethaea 49, 383-393 (1968).

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61. Nion, J. & Henry, J.-L. Phacopidella (Prephacopidella) hupei nov. sp. nouveau Trilobite de l’Ordovicien du Finistere. Bulletin Société géologique de France 8, 884-890

(1966).

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Bretagne, 1962-1963, Nouvelle Série, 199-210 (1965).

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65. Ludvigsen, R. & Chatterton, B.D.E. Ordovician Pterygometopidae (Trilobita) of North America. Canadian Journal of Earth Sciences 19, 2179-2206 (1982).

66. Fortey, R.A. Late Ordovician trilobites from southern Thailand. Palaeontology 40, 397-449 (1997).

67. Han, N.-R. The eyes of Ordovician trilobite Telephina convexa Lu. Acta Palaeontologica Sinica 40, 399-408 (2001).

68. Clarkson, E.N.K. & Tripp, R.P. The Ordovician trilobite Calyptaulax brongniartii (Portlock). Transactions of the Royal Society of Edinburgh: Earth Sciences 72, 287-294

(1982).

69. Zhou, Z.-Y. & Zhou, Z.-Q. The Late Ordovician cyclopygid trilobite Sagavia Koroleva, 1967, from the Pagoda Formation of southwestern Shaanxi, China. Memoirs of the

Association of Australasian Palaeontologists 34, 181-187 (2007).

70. Clarkson, E.N.K. The visual system of trilobites. Palaeontology 22, 1-22 (1979).

71. Hammann, W. & Leone, F. Trilobites of the post-Sardic (Upper Ordovician) sequence of southern Sardinia. Part 1. Beringeria 20, 3-217 (1997).

72. Cocks, L.R.M. & Fortey, R.A. A new Hirnantia fauna from Thailand and the biogeography of the latest Ordovician of South-East Asia. Geobios 20, 117-126 (1997).

73. Zhu, Z.-L. & Wu, H.-J. Late Ashgillian trilobites from Huanghuachang, Yichang County, Hubei Province. in Papers for the Symposium on the Cambrian-Ordovician and

Ordovician-Silurian boundaries, Nanjing, China 112-120 (Nanjing Institute of Geology and Palaeontology, Academia Sinica, 1983).

74. Nilsson, D.-E. & Odselius, R. Regionally different optical systems in the compound eye of the Water-Flea Polyphemus (Cladocera, Crustacea). Proceedings of the Royal

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75. Wolken, J.J. & Gallik, G.J. The compound eye of a crustacean, Leptodora kindtii. Journal of Cell Biology 26, 968-973 (1965).

76. Meyer-Rochow, V.B. & Walsh, S. The eyes of mesopelagic crustaceans: I. Gennadas sp. (Penaeidae). Cell and Tissue Research 184, 87-101 (1977).



77. Meyer-Rochow, V.B. & Walsh, S. The eyes of mesopelagic crustaceans: III. Thysanopoda tricuspidata (Euphausiacea). Cell and Tissue Research 195, 59-79 (1978).

78. Meyer-Rochow, V.B. Larval and adult eye of the Western Rock Lobster (Panulirus longipes). Cell and Tissue Research 162, 439-457 (1975).

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80. Miller, W.H. Morphology of the ommatidia of the compound eye of Limulus. The Journal of Biophysical and Biochemical Cytology 3, 421-428 (1957).

81. Barlow, H.B. The size of ommatidia in apposition eyes. Journal of Experimental Biology 29, 667-674 (1952).



Supplementary Information: Figures 1-4

SI Figure 1. Relief-map images of early Cambrian fossil eye (SAM P43629a) showing three-dimensional preservation of fine surface structure. a, full visual

surface and b, close up of ommatidial lenses (area denoted by white box in a). Images

are rotated from top to bottom. Due to perspective there is no scale; see Main Text Fig.

1 and 2 for scales on planar images.

SUPPLEMENTARY INFORMATIONRESEARCHdoi:10.1038/nature10097


SI Figure 2. Four eye specimens from the Emu Bay Shale, additional to the three shown in Main Text Figure 1. All specimens positioned in the same orientation as

those in Figure 1. a, P45170a, b, P45913a and c, P44368b show most of the full ovoid

visual surface (at least in outline) but only patches of ommatidial lenses, d, P43445a is

a fragment of the visual surface showing well-preserved ommatidial lenses.

Counterparts are present for all specimens, but show little detail.



SI Figure 3. SEM-EDS elemental maps of P43687. Each map shows the relative abundance of each element; the brighter the colour, the more abundant the element. Note that the visual surface of the eye contains high amounts of calcium (Ca) and phosphorus (P), indicating a calcium phosphate composition. The matrix (shown top left) contains elevated concentrations of oxygen (O), aluminium (Al) and silicon (Si), representing the muscovite and other aluminosilicate clay minerals that constitute the fossiliferous mudstones of the Emu Bay Shale.



1.0 1.5 2.0

1.0

1.5

2.0

2.5

Bright Zone

Margin

Eye Size: Log10[!(radius in µm)]

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!"#$%&'(&)*+,-$#"&./$('%&0!-1(-+%("&./$('%&02*+%("&./$('%&0345(/-+%("&./$('%&06(+*7-+%("&./$('%&087-/&%&9"*1-:*%&03-1-',"-&1;5#<=&4<>,&1(<(4(9"*1-:*%&0?:&%,-',"-&19"*1-:*%&0>',*@-',"-&1;5#<=&4<>,&1(<(4(

SI Figure 4. Ommatidial lens size compared to eye size, across fossil and living arthropods. Data in Supp. Table 2; axis scales adopted from Wehner18 (diameter of lens vs square root of eye diameter, both on a log10 scale in microns). Trilobites are plotted separately according to eye type. The Emu Bay Shale eyes are broadly comparable to Cambro-Ordovician trilobites and to living crustaceans and horseshoe crabs.



modern optics in exceptionally preserved eyes of early cambrian arthropods from australia

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