LETTER Doi:10.1038/Nature13414

Home , Haikouichthys, Jamoytius, Metaspriggina, Pikaia

LETTER doi:10.1038/nature13414

A primitive fish from the Cambrian of North America

Simon Conway Morris1 & Jean-Bernard Caron2,3

Knowledge of the early evolution of fish largely depends on soft- (Extended Data Fig. 4f). Incompleteness precludes a precise estimate of bodied material from the Lower (Series 2) Cambrian period of South size range, but themostcomplete specimens (Fig.1a,b) areabout 60 mm China1,2. Owing to the rarity of some of these forms and a general in length and 8–13 mm in height. Laterally the body is fusiform, widest lack of comparative material from other deposits, interpretations of near the middle, tapering to a fine point posteriorly (Fig. 1a, b and Ex- various features remain controversial3,4, as do their wider relation- tended Data Fig. 4a), whereas in dorsal view the anterior termination is ships amongst post-Cambrian early un-skeletonized jawless verte- rounded (Fig. 1d and Extended Data Fig. 4c–e). The animal was com- brates. Here we redescribe Metaspriggina5 on the basis of new material pressed laterally, as is evident from occasional folding of the body as well from the Burgess Shale and exceptionally preserved material collected as specimensindorso-ventral orientation being conspicuously narrower near Marble Canyon, British Columbia6, and three other Cambrian (Fig. 1a and Extended Data Fig. 5a). Along the anterior ventral margin Burgess Shale-type deposits from Laurentia. This primitive fish dis- there was a keel-like structure (Fig. 1b, g, i, k, l), but no fins have been plays unambiguous vertebrate features: a notochord, a pair of prom- recognized. In the much more abundant specimens of Haikouichthys1,3,4 inent camera-type eyes, paired nasal sacs, possible cranium and arcualia, fins are seldom obvious, suggesting that their absence in Metaspriggina W-shaped myomeres, and a post-anal tail. A striking feature is the might be taphonomic. branchial area with an array of bipartite bars. Apart from the anterior- The diagnostic myomeres are invariably present, but are sometimes most bar, which appears to be slightly thicker, each is associated with highly disorganized especially towards the anterior (Fig. 1b, d, i and externally located gills, possibly housed in pouches. Phylogenetic Extended Data Fig. 1g), suggesting variable levels of decay11. Undisrupted analysis places Metaspriggina as a basal vertebrate, apparently close specimens show open chevrons with the main apices directly anteriorly to the Chengjiang taxa Haikouichthys1–4 and Myllokunmingia1, dem- (Fig. 1h, k and Extended Data Fig. 5c). Dorsally, however, some specimens onstrating also that this primitive group of fish was cosmopolitan show a smaller additional fold with the blunt apex directed posteriorly during Lower–Middle Cambrian times (Series 2–3). However, the (Fig. 1k), while in one specimen (Fig. 1h) another posterior inflection arrangement of the branchial region in Metaspriggina has wider lies towards the ventral side. Overall, therefore, the myomeres have a implications for reconstructing the morphology of the primitive ver- W-shaped configuration. As the body narrows posteriorly the prin- tebrate. Each bipartite bar is identified as being respectively equi- cipal myotomal apices become much more acute (approximately 60u), valent to an epibranchial and ceratobranchial. This configuration and the subsidiary dorsal inflection is probably lost (Extended Data suggests that a bipartite arrangement is primitive and reinforces Figs 1g, i, 4a). The myomeres, totalling at least 40, are considerably more the view that the branchial basket of lampreys7 is probably derived. acute than in Pikaia9 and, in contrast to this chordate, Metaspriggina Other features of Metaspriggina, including the external position of was evidently an effective swimmer15. Parker Slate specimens differ in the gills and possible absence of a gill opposite the more robust anterior- being less slender and having myomeres with a more angular closure most bar, are characteristic of gnathostomes8 and so may be prim- (Extended Data Fig. 6a–d). In dorso-ventral specimens an elongate itive within vertebrates. strand (0.25 mm thick) is identified as the notochord (Fig. 1a–d and Cambrian chordates1–5 are effectively restricted to the Burgess Shale5,9 Extended Data Fig. 1a–d, f). In laterally orientated material the notochord and Chengjiang1–4 Lagersta¨tten, and despite soft-part preservation key lies on the midline, opposite the zone of myotomal closure (Fig. 1h). Occa- structures may be difficult to resolve3,9,10. In addition, differential decay sional narrower strands in the anterior region probably represent parts of various parts of the body may skew interpretation of character states11 of the vascular system (Fig. 1d). and potentially compromise phylogenetic analysis. The head is small and slightly bilobed, with smooth margins and Here we redescribe the poorly known Burgess Shale chordate Meta- possibly a central notch (Fig. 1d and Extended Data Fig. 4c–e). It bears spriggina walcotti5 (Extended Data Fig. 1), on the basis of approximately two prominent eyes (Fig. 1a–d, f, g, i, j, l, m and Extended Data Figs 3, 100 new specimens collected in the Canadian Rockies from several 4b–e, 5a–d, 6d). These appear to have been originally circular (maximum Cambrian Burgess Shale-type deposits. Localities include the Burgess diameter approximately 1.3 mm), but elliptical shapes (Fig. 1d) may re- Shale (Walcott Quarry) in Yoho National Park (Fig. 1g and Extended flect slightly oblique burial. Typically the eye is preserved as a reflective Data Fig. 2), and three sites in Kootenay National Park: Haiduk Peak film, but a well-defined circular area (Fig. 1f) (approximately 0.4 mm) (Extended Data Fig. 3)12 and, most importantly, near Marble Canyon6 appears to be the lens, suggesting a camera-like arrangement. In several (Fig. 1a–f, h–m and Extended Data Figs 4, 5). In addition, Emmonsaspis specimens (Fig. 1c, i, j, l, m and Extended Data Figs 1c, d, 5b), paired (partim) from the Parker Slate Formation13 in Vermont, hitherto ten- circular areas located between the eyes are interpreted as the nasal sacs. tatively identified as a frond-like fossil14, and the Kinzers Formation in The proximity of these structures suggests a single median duct might Pennsylvania (R. Thomas, personal communication), are reinterpreted have connected them. The paired eyes sometimes lie at a steep angle to as Metaspriggina spp. (Extended Data Fig. 6). Despite variations in age the body axis (Extended Data Fig. 5b), suggesting that the head formed (Extended Data Fig. 7 and Supplementary Table 1) and palaeoenviron- a discrete lobe capable of rotation. A median triangular area may repre- mental settings between these occurrences (and by implication tapho- sent cranial cartilage (Fig. 1d and Extended Data Fig. 4c–e), while darker nomic histories) the similarities of anatomy allow reliable reconstructions. dorsal elements might indicate possible arcualia (Fig. 1g). Descriptions are largely based on the more complete ‘Marble Canyon’6 Posterior to the head and ventrally positioned is a large branchial area. fossils (see also Fig. 2). Like other Burgess Shale-type material, fossils are This region is identified on the basis of two sets of bars, seven in total, on preserved as carbonaceous compressions and aluminosilicate minerals each side of the body (Fig. 1d and Extended Data Fig. 4c). In dorso-ventral

1Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK. 2Department of Natural History (Palaeobiology), Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario M5S 2C6, Canada. 3University of Toronto, Department of Ecology and Evolutionary Biology, 25 Willcocks Street, Toronto, Ontario M5S 3B2, Canada.

c b

g j

h i

k l

Figure 1 | Metaspriggina walcotti (Simonetta and Insom, 1993) specimens eyes (framed area in j with the image flipped vertically). k, ROM62954, lateral from Marble Canyon and Walcott’s Quarry collected by the Royal view showing internal organs. l, m, ROM62928, oblique view, and close up Ontario Museum. a–f, h–m, Specimens collected from Marble Canyon. showing eyes in m. a, b, e, h, j–m, Backscatter scanning electron microscopy g, Specimens collected from Walcott’s Quarry. a–m, Complete (a–c) and partial images (e, j), composite images of both parts and counterparts (f–i, k–m) and (d–m) specimens, anterior to the left (except i). a, ROM62935, oblique view. stitched images at white lines (a, b). An, anus; Ar?, possible arcualia; Bc?, b, c, ROM62938, lateral view and close up of the anterior section (framed area possible extra-branchial cartilage; Brv, branchial bars (ventral element); Brd, in c). d, e, ROM62933, oblique view, and close up of gill bars (framed area branchial bars (dorsal element); Brp, branchial bar processes; Bv, blood vessel; in e). Only the position of some gill bars (Brd1 and Brv1 in e) are highlighted by Cc?, possible cranial cartilage; Es, oesophagus; Ey, eyes; Gi, gill filaments; arrows (see also Extended Data Fig. 4c). f, ROM62946, oblique view, pair of Gu, gut; He?, possible heart; Ke, keel; Le, lens; Li, liver; My, myomere; Na, nasal eyes showing presumed lens (see Extended Data Fig. 5d). g, ROM62964, lateral sacs; No, notochord; Not, notch. Scale bars: 5 mm (a, b, g–i, k, l); 2 mm (d); view. h, ROM62924, lateral view, showing W-shaped myomeres and main 1mm(c, e, f, j, m). inflections (thin arrows). i, j, ROM62932, lateral view, and close up showing

Na Figure 2 | Metaspriggina walcotti (Simonetta and Insom, 1993). Diagrammatic anatomical drawing, dorsal and lateral views showing main Ey morphological features (gills and possible blood vessels; arcualia and extra Mo? branchial and cranial cartilages have not been reconstructed). Mo?, possible position of mouth; Ph, pharyngeal area. For other abbreviations, see Fig. 1. Brd Brp view both sets of bars are curved (Fig. 1d), while in lateral aspect the Brv upper series is obliquely inclined ventrally and the lower series is more Ke steeply angled (Fig. 1b, g). Bars may show a series of short extensions (Fig. 1d, e and Extended Data Fig. 4c). In addition, in one specimen No (Fig. 1d, e) the anterior-most dorsal bar appears to be somewhat more robust (0.32 mm in thickness) than the other bars (average 5 0.25 mm, Ph standard deviation 5 0.028). Closely spaced and relatively massive un- equivocal gill filaments seem located distal to the associated bars (Fig. 1d, e), Es except perhaps along the anterior-mostset of bars.No gill openings have been identified, but gills were possibly housed in pouches reminiscent of the arrangement in the related Myllokunmingia1 and Haikouichthys3. He? Faint ventro-lateral structures parallel to the body (Fig. 1d) may represent extra-branchial cartilage. From the roof of the posterior part of the branchial chamber a nar- row strand, sometimes with positive relief, is interpreted as the oesophagus (Fig. 1g, k and Extended Data Fig. 5d, e) and this extends posteriorly Li towards the rest of the gut. An anterior area surrounding the gut trace possiblyrepresentsthe heart(Fig. 1a, b,k and Extended Data Fig. 2e, 6b), followed by a darker area that may be a liver (Fig. 1a, b, g, h, k, l and Ex- tended Data Figs 1a, g, 2b–e, 3b, c, 5a, c, e). Gut content is evident in the posterior section and just before the anus (Fig. 1a and Extended Data Fig. 1e, h). The latter is located on the posterior margin, thus defining a post-anal tail. Gut content is indeterminate, but Metaspriggina may have been microphagous with the short extensions on the gill bars possibly serving an analogous function to gill rakers. Phylogenetic analysis (Fig. 3 and Supplementary Information) indi- Gu cates Metaspriggina to be a stem vertebrate, possibly close to the slightly older Chengjiang taxa Haikouichthys and Myllokunmingia and other-

An wise basal to all other agnathans and gnathostomes. Myllokunmingia is known only from one specimen1, but comparisons to Haikouichthys1–4 show similarities (for example, paired eyes, nasal sacs, lobate head), but also important differences. Although the myomeral configuration is also similar to Haikouichthys1,3,inMetaspriggina the additional ventral chevron (Fig. 1h) and clear dorsal bend define a W-shaped arrangement 16 My directly comparable to fish . The branchial region in Metaspriggina is also more voluminous, potentially consistent with greater respiratory demands. The branchial bars have a markedly different orientation from Haikouichthys, in which not only are they less well-preserved, but in contrast to Metaspriggina the presumed ceratobranchials are parallel to the ventral margin and the upper series of epibranchials lie at a steep angle1,2. The configuration of the branchial bars and associated gills in Meta- spriggina has three wider implications. The first is that this arrangement recalls their frequently invoked ancestral configuration17–19, even though

Figure 3 | Cladogram with backbone constraint for cyclostome a straci monophyly, and using rescaled randaspida consistency indices, showing the TunicataHemichordataCephalochordataPikaia MyllokunmingiaMetasprigginaHaikouichthysCyclostomata EuphaneropsEuconodontaJamoytiusAnaspidaLoganelliaTurinia A AstraspisHeterostraciGaleaspidOsteo Jawed vertebrates position of Metaspriggina as part of basal stem-group soft-bodied vertebrates. The origin and potential loss of key vertebrate Branchial structures is indicated (see basket Supplementary Information for Loss of gill pouches? details). Differentiated mandibular bar

Paired eyes, W-shaped muscles Gill pouches, bipartite branchial bars Proto-mandibular bar? Branchial bars

00 MONTH 2014 | VOL 000 | NATURE | 3 ©2014 Macmillan Publishers Limited. All rights reserved RESEARCH LETTER this is usually regarded as hypothetical19. Primitive serial homology is 6. Caron, J.-B. et al. A new phyllopod bed-like assemblage from the Burgess Shale of the Canadian Rockies. Nature Commun. 5, 3210 (2014). often used as a starting point in discussions on the origin of jaws, although 7. Martin, W. M., Bumm, L. A. & McCauley, D. W. Development of the viscerocranial Metaspriggina is too basal (Fig. 3) to be directly informative in this regard20. skeleton during embryogenesis of the sea lamprey, Petromyzon marinus. Dev. Dyn. The second implication concerns possible links to the branchial config- 238, 3126–3138 (2009). 8. Janvier, P. Early Vertebrates (Oxford Monographs on Geology and Geophysics) Vol. 33 uration in extinct and extant lampreys. An intermediary stage between (Clarendon, 1996). 7 Metaspriggina and the complex branchial basket of living lamprey may 9. Conway Morris, S. & Caron, J.-B. Pikaia gracilens Walcott, a stem-group chordate occur in Euphanerops21 and the possibly synonymous Endeiolepis22. from the Middle Cambrian of British Columbia. Biol. Rev. Camb. Philos. Soc. 87, 22 480–512 (2012). Although their unusual polybranchy may reflect hypoxia , in these 10. Mallatt, J. & Holland, N. Pikaia gracilens Walcott: stem chordate, or already Late Devonian period (Frasnian) agnathans the branchial arches have specialized in the Cambrian? J. Exp. Zool. B Mol. Dev. Evol. 320, 247–271 (2013). fused into single sinuous units and are now associated with an array of 11. Sansom, R. S., Gabbott, S. E. & Purnell, M. A. Atlas of vertebrate decay: a visual and small rods and ‘copular elements’. This may prefigure21 the complex taphonomic guide to fossil interpretation. Palaeontology 56, 457–474 (2013). 7 12. Johnston, K. J., Johnston, P. A. & Powell, W. G. A new Middle Cambrian, Burgess basket of extant lampreys , a configuration that had apparently stabi- Shale-type biota, Bolaspidella Zone, Chancellor Basin, southeastern British lized by the latest Devonian period (Famennian)23. Columbia. Palaeogeogr. Palaeoclimatol. Palaeoecol. 277, 106–126 (2009). Branchial arches of Metaspriggina also show two features reminiscent 13. Webster, M. Systematic revision of the Cambrian trilobite Bathynotus Hall, 1860, 8,24 with documentation of new occurrences in western Laurentia and implications for of gnathostomes. Although considered homologous , the position of intercontinental biostratigraphic correlation. Mem. Assoc. Australasian thegills relativetothebranchial arches differ, being interior inagnathans Palaeontologists 37, 369–406 (2009). but exterior in the gnathostomes and apparently also in Metaspriggina. 14. Conway Morris, S. Ediacaran-like fossils in Cambrian Burgess Shale-type faunas of North America. Palaeontology 36, 593–635 (1993). While differential preservation cannot be ruled out, the anterior-most 15. Lacalli, T. The Middle Cambrian fossil Pikaia and the evolution of chordate branchial arch appears more robust and lacks gills. Correspondingly, swimming. EvoDevo 3, 12 (2012). in gnathostomes the mandibular arch is larger and clearly differen- 16. Van Leeuwen, J. L. A mechanical analysis of myomere shape in fish. J. Exp. Biol. 8 202, 3405–3414 (1999). tiated and only from the second branchial arch (hyoid) are gills borne . 17. Gillis, J. A., Modrell, M. S. & Baker, C. V. H. Developmental evidence for serial Accordingly, if the anterior-most arch in Metaspriggina was to be equated homology of the vertebrate jaw and gill arch skeleton. Nature Commun. 4, 1436 with the mandibular arch then this might suggest that this region was (2013). 18. Kuratani, S. Evolution of the vertebrate jaw from developmental perspectives. Evol. always gill-less. In addition the putative extrabranchial cartilages of this Dev. 14, 76–92 (2012). 8,24 Cambrian fish find a possible parallel in elasmobranchs , although 19. Kuratani, S. Developmental studies of the lamprey and hierarchical evolutionary convergence is perhaps more likely. Finally, both Metaspriggina and steps towards the acquisition of the jaw. J. Anat. 207, 489–499 (2005). 20. Gai, Z.-K., Donoghue, P. C. J., Zhu, M., Janvier, P. & Stampanoni, M. Fossil jawless Haikouichthys are consistent with the earliest vertebrates possessing fish from China foreshadows early jawed vertebrate anatomy. Nature 476, bipartite arches. Apart from a postulated fusion in the lamprey clade, it 324–327 (2011). is suggested that unless homoplasious, this bipartite arrangement may 21. Janvier, P. & Arsenault, M. The anatomy of Euphanerops longaevus Woodward, have persisted crown-ward. If so, then models of jaw articulation such 1900, an anaspid-like jawless vertebrate from the Upper Devonian of Miguasha, 25 Quebec, Canada. Geodiversitas 29, 143–216 (2007). as ‘hinges and caps’ , invaluable in developmental studies, might need 22. Janvier, P., Desbiens, S., Willett, J. A. & Arsenault, M. Lamprey-like gills in a to be treated with caution26 if employed in the context of atavistic home- gnathostome-related Devonian jawless vertebrate. Nature 440, 1183–1185 otic transformations27. (2006). 23. Gess, R. W., Coates, M. I. & Rubidge, B. S. A lamprey from the Devonian period of South Africa. Nature 443, 981–984 (2006). METHODS SUMMARY 24. Mallatt, J. Early vertebrate evolution: pharyngeal structure and the origin of Most specimens from Marble Canyon were collected in situ (Supplementary Table 1). gnathostomes. J. Zool. 204, 169–183 (1984). Specimens were prepared mechanically to remove sediment concealing important 25. Depew, M. J. & Compagnucci, C. Tweaking the hinge and caps: testing a model of the organization of jaws. J. Exp. Zool. B Mol. Dev. Evol. 310, 315–335 (2008). morphological features. Lack of sediment fissility and difficulties of preparation 26. Medeiros, D. M. & Crump, J. G. New perspectives on pharyngeal dorsoventral often make exposure of the fossil (especially at either end) difficult. Specimens were patterning in development and evolution of the vertebrate jaw. Dev. Biol. 371, studied using a range of photographic techniques commonly employed for this type 121–135 (2012). of material9. Pictures of both parts and counterparts were merged in Adobe Photo- 27. Nichols, J. T., Pan, L.-Y., Moens, C. B. & Kimmel, C. B. barx1 represses joints and shopCS6 using the ‘apply image’ function and ‘darken’ blending mode (Fig. 1a, b, promotes cartilage in the craniofacial skeleton. Development 140, 2765–2775 (2013). f–i, k–m and ExtendedDataFigs 1–3,5a,c,d). Scanning electronmicroscopy images were obtained using a JEOL JSM6610-Lv at the University of Toronto (Earth Sciences). Supplementary Information is available in the online version of the paper. Methods regarding phylogenetic analysis can be found in Supplementary Information. Acknowledgements We thank T. Lacalli for comments on an earlier draft of the manuscript, J. Mallatt for an extensive series of critiques, and J. Hoyal-Cuthill and C. Aria Online Content Any additional Methods, Extended Data display items and Source for assistance with phylogenetic analyses. We also thank M. Collins for technical Data are available in the online version of the paper; references unique to these drawings and reconstructions, and R. Thomas and M. Webster for information on the sections appear only in the online paper. Kinzers and Parker formations, respectively. S.C.M. thanks V. Brown for manuscript preparation, and the Department of Earth Sciences and St John’s College, Cambridge Received 21 February; accepted 29 April 2014. for support. We thank Parks Canada for granting a collection and research permit to Published online 11 June 2014. J.-B.C. (YNP-2012-12054). Fieldwork support for the 2012 expedition comes from the Royal Ontario Museum (DMV Research and Acquisition Fund and DNH Fieldwork 1. Shu, D.-G. et al. Lower Cambrian vertebrates from South China. Nature 402, 42–46 Fund), M. Streng (Uppsala University and the Swedish Research Council), R. Gaines (1999). (Pomona College), G. Manga´no (University of Saskatchewan) and a Natural Sciences 2. Shu, D.-G. et al. Head and backbone of the Early Cambrian vertebrate and Engineering Research Council Discovery Grant (to J.-B.C., #341944). This is Royal Haikouichthys. Nature 421, 526–529 (2003). Ontario Museum Burgess Shale project number 53. 3. Hou, X.-G., Aldridge, R. J., Siveter, D. J., Siveter, D. J. & Feng, X.-H. New evidence on Author Contributions J.-B.C. collected fossils, prepared all illustrative material and the anatomy and phylogeny of the earliest vertebrates. Proc. R. Soc. Lond. B 269, conducted phylogenetic analyses. S.C.M. wrote early drafts of paper, and both authors 1865–1869 (2002). discussed results and developed observations and conclusions. 4. Zhang, X.-G. & Hou, X.-G. Evidence for a single median fin-fold and tail in the Lower Cambrian vertebrate, Haikouichthys ercaicunensis. J. Evol. Biol. 17, 1162–1166 Author Information Reprints and permissions information is available at (2004). www.nature.com/reprints. The authors declare no competing financial interests. 5. Conway Morris, S. A redescription of a rare chordate, Metaspriggina walcotti Readers are welcome to comment on the online version of the paper. Correspondence Simonetta and Insom, from the Burgess Shale (Middle Cambrian), British and requests for materials should be addressed to S.C.M. ([email protected]) or Columbia, Canada. J. Paleontol. 82, 424–430 (2008). J.-B.C. ([email protected]).

Extended Data Figure 1 | Type material of Metaspriggina walcotti g–i, USNM198611 (holotype), lateral view. Specimen showing gut (including (Simonetta and Insom, 1993) from Walcott’s Quarry (phyllopod bed). gut contents, see close up in h); g, part; h, i, counterpart. a–i, Specimens are a–i, Specimens are shown with the anterior end to the left. a–f, USNM198612 photographed under dry, direct light (e, h); dry, polarized light (a, d); wet, (lectotype), oblique view. Specimen showing gut (including gut contents, see polarized light (b, c, f); and wet, direct light (g, i) conditions. An, anus; Cc?, close up in e) and portion of anterior section; a, part; c–f, counterpart; possible cranial cartilage; Gu, gut; Li, liver; Na?, possible nasal sacs; No, b, composite stitched images of both part and counterpart at white lines. notochord; My, myomere. Scale bars: 5 mm.

Extended Data Figure 2 | Metaspriggina walcotti (Simonetta and Insom, c, ROM57179. d, ROM62965. e, ROM57178. All specimens are photographed 1993) specimens collected by the Royal Ontario Museum from the Walcott under dry, polarized light conditions. He?, possible heart; Gu, gut; Li, liver; My, Quarry (greater phyllopod bed). a–e, All fragmentary specimens are shown in myomere. Scale bars: 5 mm. lateral views. a, ROM62962, two specimens in parallel. b, ROM62960.

Extended Data Figure 3 | Metaspriggina walcotti (Simonetta and Insom, b, c, Close up of areas outlined by rectangles in a (tilted 90 degrees clockwise). 1993) from Haiduk Cirque. a, TMP (Royal Tyrrell Museum, Drumheller) a–c, Composite images of both parts and counterparts (b, c) and stitched 2006.36.15, overall view showing approximately 44 individuals (white images at white lines (a). Specimens are photographed under dry, polarized numbers) including several preserving eyes (blue arrows). Eyes related to light (a, b); and wet, polarized light (c) conditions. Ey, eyes; Li, liver; My, particular specimens are indicated next to blue arrows (cyan numbers). myomere. Scale bars: 4 cm in a; 5 mm in b and c.

Extended Data Figure 4 | Metaspriggina walcotti (Simonetta and Insom, the distribution of elements (from left to right and top to bottom: carbon, 1993) from Marble Canyon. a, ROM62948, specimen showing the fusiform oxygen, sodium, magnesium, aluminium, silicon, potassium, titanium, iron) posterior tip of the body, flipped 90 degrees to the rest of the body. emphasized by whiter zones across one eye (blue rectangle in c). Specimens b, ROM62932, camera lucida drawing showing details of pharyngeal area are photographed under dry, direct light (a); and dry, polarized light (see also Fig. 1i). c–f, ROM62933, overall view of oblique specimen (c, see also (d) conditions. Brv, branchial bars (ventral element); Brd, branchial bars Fig. 1d, e) and close ups (d, e) of area outlined by rectangle in c. Backscatter (dorsal element); Bv, blood vessel; Cc?, possible cranial cartilage; Ey, eyes; scanning electron microscopy (BSE) images (c, e) and energy dispersive Ke, keel; My, myomere; Na, nasal sacs; No, notochord; Not, notch. Scale bars: spectrometry images (f; except the first frame, which is a BSE image) showing 5mmina, b; 2 mm in c; 1 mm in d, e; and 50 mminf (and following frames).

Extended Data Figure 5 | Metaspriggina walcotti (Simonetta and Insom, e, ROM62957, lateral specimen. Specimens are photographed under dry, 1993) from Marble Canyon. a, ROM62927, dorso-ventral specimen preserved polarized light (a, c, d); and wet, polarized light (e) conditions. Es, eosophagus; with eyes. b, c, ROM62951, lateral specimen preserved with eyes and nasal sacs Ey, eyes; Gu, gut; He?, possible heart; Li, liver; Na, nasal sacs; No, notochord; (b, backscatter scanning electron microscopy image of framed area My, myomere. Scale bars: 5 mm in a, c, d, e; 1 mm in b. in c). d, ROM62946, lateral specimen preserved with eyes (see also Fig. 1f).

Extended Data Figure 6 | Metaspriggina spp. from Vermont and (R. Thomas, personal communication). The specimen was collected and Pennsylvania. a–d, Specimens from Vermont; e, specimen from photographed by K. Matt, and is reposited at the North Museum of Natural Pennsylvania. a–d, USNM 15314a, slab with three specimens preserved History and Science, in Lancaster (Pennsylvania). Specimens are photographed laterally (SP 1–3). b, c, Close up of specimen 1 and specimens 213, respectively. under dry, polarized light (a–c); wet, polarized light (d); and dry, direct light d, Close up of anterior section of specimen 2 showing preservation of one eye. (e) conditions. Ey, eyes; He?, possible heart; Li, liver; My, myomere. Scale bars: e, P-Ch-280, lateral specimen originally identified as Emmonsaspis sp. 10 mm in a–c; 1 mm in d.

Extended Data Figure 7 | Metaspriggina walcotti (Simonetta and Insom, 1993). Temporal correlations between different stratigraphic occurrences in relation to Chengjiang vertebrates.

Extended Data Figure 8 | Metaspriggina walcotti (Simonetta and Insom, 1993). Reconstruction created by M. Collins.