Knowledge of the early evolution of fish largely depends on soft-bodied material from the Lower (Series 2) Cambrian period of South China1,2. Owing to the rarity of some of these forms and a general lack of comparative material from other deposits, interpretations of various features remain controversial3,4, as do their wider relationships amongst post-Cambrian early un-skeletonized jawless vertebrates. Here we redescribe Metaspriggina5 on the basis of new material from the Burgess Shale and exceptionally preserved material collected near Marble Canyon, British Columbia6, and three other Cambrian Burgess Shale-type deposits from Laurentia. This primitive fish displays unambiguous vertebrate features: a notochord, a pair of prominent camera-type eyes, paired nasal sacs, possible cranium and arcualia, W-shaped myomeres, and a post-anal tail. A striking feature is the branchial area with an array of bipartite bars. Apart from the anterior-most bar, which appears to be slightly thicker, each is associated with externally located gills, possibly housed in pouches. Phylogenetic analysis places Metaspriggina as a basal vertebrate, apparently close to the Chengjiang taxa Haikouichthys1,2,3,4 and Myllokunmingia1, demonstrating also that this primitive group of fish was cosmopolitan during Lower–Middle Cambrian times (Series 2–3). However, the arrangement of the branchial region in Metaspriggina has wider implications for reconstructing the morphology of the primitive vertebrate. Each bipartite bar is identified as being respectively equivalent to an epibranchial and ceratobranchial. This configuration suggests that a bipartite arrangement is primitive and reinforces the view that the branchial basket of lampreys7 is probably derived. Other features of Metaspriggina, including the external position of the gills and possible absence of a gill opposite the more robust anterior-most bar, are characteristic of gnathostomes8 and so may be primitive within vertebrates.
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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 for assistance with phylogenetic analyses. We also thank M. Collins for technical drawings and reconstructions, and R. Thomas and M. Webster for information on the 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 for support. We thank Parks Canada for granting a collection and research permit to 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 Fund), M. Streng (Uppsala University and the Swedish Research Council), R. Gaines (Pomona College), G. Mangáno (University of Saskatchewan) and a Natural Sciences and Engineering Research Council Discovery Grant (to J.-B.C., #341944). This is Royal Ontario Museum Burgess Shale project number 53.
The authors declare no competing financial interests.
Extended data figures and tables
Extended Data Figure 1 Type material of Metaspriggina walcotti (Simonetta and Insom, 1993) from Walcott’s Quarry (phyllopod bed).
a–i, Specimens are shown with the anterior end to the left. a–f, USNM198612 (lectotype), oblique view. Specimen showing gut (including gut contents, see close up in e) and portion of anterior section; a, part; c–f, counterpart; b, composite stitched images of both part and counterpart at white lines. g–i, USNM198611 (holotype), lateral view. Specimen showing gut (including gut contents, see close up in h); g, part; h, i, counterpart. a–i, Specimens are photographed under dry, direct light (e, h); dry, polarized light (a, d); wet, polarized light (b, c, f); and wet, direct light (g, i) conditions. An, anus; Cc?, possible cranial cartilage; Gu, gut; Li, liver; Na?, possible nasal sacs; No, notochord; My, myomere. Scale bars: 5 mm.
Extended Data Figure 2 Metaspriggina walcotti (Simonetta and Insom, 1993) specimens collected by the Royal Ontario Museum from the Walcott Quarry (greater phyllopod bed).
a–e, All fragmentary specimens are shown in lateral views. a, ROM62962, two specimens in parallel. b, ROM62960. c, ROM57179. d, ROM62965. e, ROM57178. All specimens are photographed under dry, polarized light conditions. He?, possible heart; Gu, gut; Li, liver; My, myomere. Scale bars: 5 mm.
a, TMP (Royal Tyrrell Museum, Drumheller) 2006.36.15, overall view showing approximately 44 individuals (white numbers) including several preserving eyes (blue arrows). Eyes related to particular specimens are indicated next to blue arrows (cyan numbers). b, c, Close up of areas outlined by rectangles in a (tilted 90 degrees clockwise). a–c, Composite images of both parts and counterparts (b, c) and stitched images at white lines (a). Specimens are photographed under dry, polarized light (a, b); and wet, polarized light (c) conditions. Ey, eyes; Li, liver; My, myomere. Scale bars: 4 cm in a; 5 mm in b and c.
a, ROM62948, specimen showing the fusiform posterior tip of the body, flipped 90 degrees to the rest of the body. b, ROM62932, camera lucida drawing showing details of pharyngeal area (see also Fig. 1i). c–f, ROM62933, overall view of oblique specimen (c, see also Fig. 1d, e) and close ups (d, e) of area outlined by rectangle in c. Backscatter scanning electron microscopy (BSE) images (c, e) and energy dispersive spectrometry images (f; except the first frame, which is a BSE image) showing the distribution of elements (from left to right and top to bottom: carbon, oxygen, sodium, magnesium, aluminium, silicon, potassium, titanium, iron) emphasized by whiter zones across one eye (blue rectangle in c). Specimens are photographed under dry, direct light (a); and dry, polarized light (d) conditions. Brv, branchial bars (ventral element); Brd, branchial bars (dorsal element); Bv, blood vessel; Cc?, possible cranial cartilage; Ey, eyes; Ke, keel; My, myomere; Na, nasal sacs; No, notochord; Not, notch. Scale bars: 5 mm in a, b; 2 mm in c; 1 mm in d, e; and 50 μm in f (and following frames).
a, ROM62927, dorso-ventral specimen preserved with eyes. b, c, ROM62951, lateral specimen preserved with eyes and nasal sacs (b, backscatter scanning electron microscopy image of framed area in c). d, ROM62946, lateral specimen preserved with eyes (see also Fig. 1f). e, ROM62957, lateral specimen. Specimens are photographed under dry, polarized light (a, c, d); and wet, polarized light (e) conditions. Es, eosophagus; Ey, eyes; Gu, gut; He?, possible heart; Li, liver; Na, nasal sacs; No, notochord; My, myomere. Scale bars: 5 mm in a, c, d, e; 1 mm in b.
a–d, Specimens from Vermont; e, specimen from Pennsylvania. a–d, USNM 15314a, slab with three specimens preserved laterally (SP 1–3). b, c, Close up of specimen 1 and specimens 2+3, respectively. d, Close up of anterior section of specimen 2 showing preservation of one eye. e, P-Ch-280, lateral specimen originally identified as Emmonsaspis sp. (R. Thomas, personal communication). The specimen was collected and photographed by K. Matt, and is reposited at the North Museum of Natural History and Science, in Lancaster (Pennsylvania). Specimens are photographed under dry, polarized light (a–c); wet, polarized light (d); and dry, direct light (e) conditions. Ey, eyes; He?, possible heart; Li, liver; My, myomere. Scale bars: 10 mm in a–c; 1 mm in d.
Temporal correlations between different stratigraphic occurrences in relation to Chengjiang vertebrates.
Reconstruction created by M. Collins.
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Morris, S., Caron, JB. A primitive fish from the Cambrian of North America. Nature 512, 419–422 (2014). https://doi.org/10.1038/nature13414
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