Pikaia - Knowledge

844: 4339: 601: 129: 4369: 4380: 530:, a jawless chordate. It has a small circular mouth that could be used to eat small food particles in a single bite. There are a series of short appendages on either side of the underside of the head just after the mouth, and their exact nature or function is unknown. The pharynx is associated with six pairs of slits with tiny filaments that could be used for respiratory apparatus. In these ways, it differs from the modern lancelets, which have distinct pharyngeal gill slits on either sides of the pharynx and are used for filter feeding. 368: 4088: 4364: 155: 1089:. Realising the fossil to be that of a chordate in the Cambrian rocks, chordates could have originated much earlier than expected, as they commented: "The superb preservation of this Middle Cambrian organism makes it a landmark history of the phylum to which all vertebrates, including man, belong." It is for this knowledge Pikaia as an old chordate that it is often misleadingly and falsely attributed to as an ancestor of all vertebrates, or the oldest fish, or the oldest ancestor of humans. 4346: 4374: 832: 4358: 1065:. It is thought that development of a head structure resulted from a long body shape, a swimming habit, and a mouth at the end that came into contact with the environment first, as the animal swam forward. The search for food required ways of continually testing what lay ahead so it is thought that anatomical structures for seeing, feeling, and smelling developed around the mouth. The information these structures gathered was processed by a swelling of the nerve cord ( 4352: 903:

of the body, with other specimens having up to nine such appendages that could not be parapodia. These external appendages were reinterpreted as gills in a 2024 study. Fins are present as an expansion of the body on the dorsal and ventral sides. They are not present in many specimens indicating that they are delicate membranes and were lost during fossilisation. However, the 2024 study suggested that

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One of the most unusual body parts is a series of appendages just posterior to the tentacles. Walcott had called the appendages parapodia, as a kind of body protrusions that aid locomotion in snails, and mentioned five parapodia in each individual. He was even puzzled by the absence on the major part

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that same year. However, he provided no structural analyses such as using microscopes to confirm the chordate features. The comparative description only earned a "putative" chordate status. The fossil's chordate nature was received sceptically for several decades. Only in 2012, when detailed analysis

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with a distinct pair of tentacles. Due to its small size, only about 1 mm in diameter, the structural details are indistinguishable. Some specimens show a darker central line on the tentacles which may represent a nervous fibre; thus making the tentacles as sensory feelers. A mouth is marked by

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In 1993, Conway Morris came up with another possible chordate feature. He identified structures that looked like gill slits but gave a cautious remark: " may have been present, but are hard to identify with certainty in the compressed material available. The tiny pores on the side of the pharynx are

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The notochord, a flexible rod-like structure that runs along the back of the animal, lengthens and stiffens the body so that it can be flexed from side to side by the muscle blocks for swimming. In the fish and all subsequent vertebrates, the notochord forms the backbone (or vertebral column). The

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The main chordate character is a series of myomeres that extends from the anterior to the posterior region. On average, there are 100 such myomeres in each individual. The muscle segments are not simply "annular shiny lines" as Walcott described, but are in concentric bends in the form of V-shaped

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Whittington and Conway Morris were the first to realise that Walcott's description and classification were not reliable and mostly inaccurate. They compared the body segments as described by Walcott with living animals and found that they were similar to the muscle bundles of chordates such as the

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This interpretation that the chances of evolutionary products are unpredictable is known as evolutionary contingency. Gould, from this statement, is regarded as "the most famous proponent" of the concept. His idea has inspired many research involving evolutionary contingency from palaeontology to

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does not survive in the replay, we are wiped out of future history—all of us, from shark to robin to orangutan... And so, if you wish to ask the question of the age—why do humans exist?—a major part of the answer, touching those aspects of the issue that science can treat at all, must be: because

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fossils show a hollow tubular structure that extends throughout most of the body length, but not the anterior region. It is easily noticeable as a highly light-reflective portion and is known as the dorsal organ. Once described as the notochord, its nature is not yet fully resolved and could be a

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Body elongate, slender, and tapering at each end. It is formed of many segments that are defined by strong annular shiny lines. Head small with two large eyes and two tentacles... Back of the head the first five segments carry short parapodia that appear to be divided into two parts. The enteric

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for the first time. The fossil specimens bears features of notochord and muscle blocks that are fundamental structures of chordates, and not of annelids. In 1977, Conway Morris presented a paper that indicated the possible chordate position, without further explanation. He and Whittington were

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is suggested to have been an active swimming organism that swam close to the seafloor (nektobenthic) using side to side undulations of its flattened posterior for propulsion. The anterior appendages are unlikely to have been used in feeding, and may have had a respiratory function.

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is a vertebrate ancestor, its worm-like appearance notwithstanding, exists in scientific circles. It looks like a worm that has been flattened sideways (lateral compression). The fossils compressed within the Burgess Shale show chordate features such as traces of an elongate

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was an active and free swimmer. It likely swam by throwing its body into a series of S-shaped, zigzag curves, similar to the movement of eels; fish inherited the same swimming movement, but they generally have stiffer backbones. These adaptations may have allowed

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palaeontologist Benjamin Franklin Howell changed the name of the family to Pikaiidae in 1962.) Walcott was aware of the limitation of his classification, as he noted: "I am unable to place it within any of the families of the Polychaeta, owing to the absence of

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a small opening at the anterior end of the gut towards the underside of the head. There are no jaws and teeth. Walcott had mentioned the presence of two large eyes, but no specimens, including Walcott's original collection, show any evidence of eyes.

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has a pair of large, antenna-like tentacles on its head that resembles those of invertebrates such as snails. The attachment of the tentacles makes a two-lobed structure of the head. The tentacles may be comparable to those in the present-day

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Finally, we find among the Burgess Shale fauna one of the earliest-known invertebrate representatives of our own conspicuous corner of the animal kingdom: the chordate phylum... The chordates are represented in the Burgess Shale by the genus

2613:"Soft-Bodied Fossils Are Not Simply Rotten Carcasses - Toward a Holistic Understanding of Exceptional Fossil Preservation: Exceptional Fossil Preservation Is Complex and Involves the Interplay of Numerous Biological and Geological Processes" 1040:

Subsequently, Mallatt and Holland reconsidered Conway Morris and Caron's description, and concluded that many of the newly recognized characters are unique, already-divergent specializations that would not be helpful for establishing

774:, appears to show that cuticle is not necessary for preservation, overruling the taphonomic argument, but the presence of tentacles remains intriguing, and the organism cannot be assigned conclusively, even to the vertebrate 821:

appears a much better solution. Both were initially identified as polychaetes and this line of inference perhaps deserves confrontation with more recent evidence than that available to the authors who proposed these genera.

2009: 647:) as well as fishes, and not to superficial segments of annelids. They pictured that the muscles would be essential for swimming in water in wriggling motions. The enteric canal as observed by Walcott was not an ordinary 1001:

belong to the chordate group of animals from which the vertebrates descended. Molecular studies have refuted earlier hypotheses that lancelets might be the closest living relative to the vertebrates, instead favoring

351:, or a stem-chordate not closely related to any extant lineage. Popularly but falsely attributed as an ancestor of all vertebrates, or the oldest fish, or the oldest ancestor of humans, it is generally viewed as a 1174:

had not existed, the rest of chordate animals might not have evolved, thus completely changing the diversity of life as we know. According to him, contingency is a major factor that drives large-scale evolution

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is the missing and final link in our story of contingency—the direct connection between Burgess decimation and eventual human evolution... Wind the tape of life back to Burgess times, and let it play again. If

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Parry, Luke A.; Smithwick, Fiann; Nordén, Klara K.; Saitta, Evan T.; Lozano-Fernandez, Jesus; Tanner, Alastair R.; Caron, Jean-Bernard; Edgecombe, Gregory D.; Briggs, Derek E. G.; Vinther, Jakob (2018).

332:(segmented blocks of skeletal muscles) span the entire length of the body, and are considered the defining signatures of chordate characters. Its primitive nature is indicated by the body covering, a 1104:

itself was unique as an early chordate or that it was "the actual ancestor of vertebrates;" he presumed that there could be undiscovered fossils that are more closely linked to vertebrate ancestry.

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as a chordate, it became "the most famous early chordate fossil", or "famously known as the earliest described Cambrian chordate". It is estimated to have lived during the latter period of the

605: 1100:, prompted "revised views of evolution, ecology and development," and remarked: "So much for chordate uniqueness marked by slightly later evolution." However, Gould did not believe that 919:

storage organ. The true notochord, along with a nerve cord, is a fine lateral line that runs just beneath the thick dorsal organ. A 2024 study instead found evidence of the gut canal,

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fossils are in the range of 1.5 to 6 centimetres (0.59 to 2.36 in) in length, with an average of 4 centimetres (1.6 in). Having a laterally compressed (taller than wide) and

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The exact phylogenetic position is unclear, though recent studies suggest that it is likely a stem-chordate with crown group traits. Previously proposed affinities include those of

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ct, connective tissue, integument; am, axial musculature; ds, digestive system; nc, dorsal nerve cord; aa, anterior appendages; ?go, possible gonads; ?no, hypothetical notochord.

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Before Pikaia and other Cambrian chordates were fully appreciated, it was generally believed that the first chordates appeared much later, such as in Ordovician (484–443

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Wind back life's tape to the Burgess (first erasing what actually came after), let it play again, and this time a quite different cast may emerge. If the cast lacked

577:, seen as faint vertical lines. The muscles lie on either side of a flexible structure resembling a rod that runs from the tip of the head to the tip of the tail. 1179:) and dictates that evolution has no inevitable destiny or outcome. However, as Gould explained, "The bad news is that we can't possibly perform the experiment." 758:. The cuticle as a body covering is uncharacteristic of the vertebrates, but is a dominant feature of invertebrates. The presence of earlier chordates among the 632:

canal extends from end to end without change in character... This was one of the active, free-swimming annelids that suggest the Nephthydidae of the Polychaeta.

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McCoy, Victoria E.; Wiemann, Jasmina; Lamsdell, James C.; Whalen, Christopher D.; Lidgard, Scott; Mayer, Paul; Petermann, Holger; Briggs, Derek E. G. (2020).

879:. The anatomical examination and interpretation based on 114 fossil specimens confirm the classification as a chordate. According to the new assessment, 733:

is at best only weakly indicated by the characters visible in fossils discovered so far." In 2010, an international team of palaeontologists argued that

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Turner, Susan; Burrow, Carole J.; Schultze, Hans-Peter; Blieck, Alain; Reif, Wolf-Ernst; Rexroad, Carl B.; Bultynck, Pierre; Nowlan, Godfrey S. (2010).

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backbone strengthens the body, supports strut-like limbs, and protects the vital dorsal nerve cord, while at the same time allowing the body to bend.

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fossils that constrains the animal to be accepted as a chordate is its distinct invertebrate character; its preservational mode suggests that it had

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is not an annelid worm. It is a chordate, a member of our own phylum—in fact, the first recorded member of our immediate ancestry." From this remark

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Igawa, Takeshi; Nozawa, Masafumi; Suzuki, Daichi G.; Reimer, James D.; Morov, Arseniy R.; Wang, Yiquan; Henmi, Yasuhisa; Yasui, Kinya (2017-04-25).

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Sallan, Lauren; Giles, Sam; Sansom, Robert S.; Clarke, John T.; Johanson, Zerina; Sansom, Ivan J.; Janvier, Philippe (2017). Zhang, Xi-Guang (ed.).

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of Kangaroo Island in South Australia, had been debated as among the oldest annelids, or at least other invertebrate groups. Polish palaeontologist

5127: 2971:"Chemical signatures of soft tissues distinguish between vertebrates and invertebrates from the Carboniferous Mazon Creek Lagerstätte of Illinois" 5048: 1549: 1522: 4138: 891:(tapering at both ends) body, the exact width and height are variable, and normally its height is twice that of its width throughout it body. 4921: 1069:) – the precursor of the brain. Altogether, these front-end structures formed the distinct part of the vertebrate body known as the head. 4193: 1029:

particularly in having smooth cuticle as well as muscular segmentation, and projections on its backside (ventral chaetae) that look like

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were discovered in 1993. Conway Morris identified the animals as another Cambrian chordate. The fossil specimens are preserved in the

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chevron. The myomeres at the anterior end as simpler in appearance and show circular arrangement. Conway Morris and Caron concluded:

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Not all palaeontologists were convinced of the chordate designation without better analysis. In 2001, Nicholas D. Holland from the

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was not popularly known as a chordate fossil or as an ancient chordate until 1989. That year, Harvard University palaeontologist

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Conway Morris was convinced that the longitudinal rod was a notochord and the segments were muscle blocks that he concluded that

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was probably a slow swimmer, since it lacked the fast-twitch fibers that are associated with rapid swimming in modern chordates.

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does not have hard extracellular (exoskeleton) protection, and the entirely body is essentially soft-bodied. Although primitive,

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has a lancelet-like body, tapering at both ends, laterally flat and lacked a well-defined head. It measures an average of about

336:, which is characteristic of invertebrates and some protochordates. A reinterpretation in 2024 found evidence of the gut canal, 5122: 2882: 1128:, the first chordate, we might not be here—and the world would be no worse... Let us thank our lucky stars for the survival of 407:, Canada. Based on the obvious and regular segmentation of the body, as is the feature of annelids, Walcott classified it as a 805:" in having smooth cuticle as well as muscular segmentation, and projections on its backside (ventral chaetae) that look like 2724: 2697: 2453: 2129: 1836:

Simon, Conway Morris (1977). "Aspects of the Burgess Shale fauna, with particular reference to the non-arthropod component".

1779: 1276: 2867:"Origin and early evolution of the vertebrates: new insights from advances in molecular biology, anatomy, and palaeontology" 2754:

Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences

5102: 4926: 4338: 3596: 3139:"The taphonomy and affinities of the problematic fossil Myoscolex from the Lower Cambrian Emu Bay Shale of South Australia" 5132: 4153: 737:

has sufficiently invertebrate characters, and that it mostly look like a much younger extinct animal, the Tully monster (

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Butterfield, N. J. (1990), "Organic preservation of non-mineralizing organisms and the taphonomy of the Burgess Shale",

3293:"The Phanerozoic aftermath of the Cambrian information revolution: sensory and cognitive complexity in marine faunas" 2565:"The position of arthropods in the animal kingdom: a search for a reliable outgroup for internal arthropod phylogeny" 3194:"The Earliest Annelids: Lower Cambrian Polychaetes from the Sirius Passet Lagerstätte, Peary Land, North Greenland" 1266: 2922:"The 'Tully Monster' is not a vertebrate: characters, convergence and taphonomy in Palaeozoic problematic animals" 478:

The fossils are found only in a restricted series of horizons in the strata exposed on Fossil Ridge, close to the

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Mussini, G.; Smith, M. P.; Vinther, J.; Rahman, I. A.; Murdock, D. J. E.; Harper, D. A. T.; Dunn, F. S. (2024).

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and other Cambrian fauna. In 1979, Whittington and Conway Morris first explained the evolutionary importance of

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inches (3.8 cm) in length. Walcott recorded the longest individuals as 5 cm (2.0 in) in length.

4368: 1774:(R. C. ed.). New York: Geological Society of America and University of Kansas Press. pp. W144–W177. 659:, in several important respects, the conclusion is that it is not a worm but a chordate appears inescapable." 5117: 4931: 3114: 573:

was a compressed, leaf-shaped animal with an expanded tail fin; the flattened body is divided into pairs of

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was reported by Conway Morris and Jean-Bernard Caron, that the chordate position became generally accepted.

4938: 4143: 4114: 2687: 2443: 1449: 1204: 5107: 722: 3652:"The History of Nature and the Nature of History: Stephen Jay Gould on Science, Philosophy, and History" 1646: 600: 128: 4218: 4179: 3868:

Xie, Victoria Cochran; Pu, Jinyue; Metzger, Brian Ph; Thornton, Joseph W.; Dickinson, Bryan C. (2021).

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is simply convergent on the chordates cannot be dismissed, we prefer to build a scenario that regards

4906: 3350:"Developmental and molecular biology of annelid regeneration: a comparative review of recent studies" 2639: 801:

in his formal description in 2003 notes that it "closely resembles the slightly geologically younger

388: 294: 204: 4373: 666:"is a primitive chordate rather than a polychaete. The earliest fish scales are Upper Cambrian, and 4916: 4379: 1594: 541:

as its body covering. Cuticle is a hard protein layer predominantly found in invertebrates such as

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among the Cambrian animals as an epitome of contingent event in the entire evolution of life; if

1113: 1033:'s tentacles. Although chordates normally lack the cuticle, a type of cuticle is present in some 895: 739: 489: 423: 5079: 4988: 4357: 2067: 714:

in most general aspects, with major difference in its notochord not reaching the anterior end.

5053: 4363: 4345: 4128: 1363:"Pikaia gracilens Walcott, a stem-group chordate from the Middle Cambrian of British Columbia" 670:

may not be far removed from the ancestral fish." In 1982, he added further description in his

651:, it runs along with a stiff rod that resembles a notochord. They reported in 1979: "Although 5074: 5066: 3447:"Evolutionary history of the extant amphioxus lineage with shallow-branching diversification" 977:) down either side of the body – all critical features for the evolution of the vertebrates. 352: 247: 3870:"Contingency and chance erase necessity in the experimental evolution of ancestral proteins" 1081:

has received particular attention among the multitude of animal fossils found in the famous

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Simonetta and Insom, from the Burgess Shale (Middle Cambrian), British Columbia, Canada".

1681: 955:. This hypothesis has implications for the evolution of the myomeres, notochord and gills. 907:

was previously interpreted upside down, indicating that the 'dorsal and ventral' sides of

8: 4093: 4054: 441: 431: 306: 3947: 3820: 3612: 3597:"Trends as changes in variance: a new slant on progress and directionality in evolution" 3527: 3462: 3308: 3154: 3045: 2986: 2937: 2348: 2288: 2222: 2025: 1978: 1918: 1872: 1312: 883:

fossils indicate important features that define the animal as a primitive chordate. All

4647: 4495: 4026: 3977: 3904: 3869: 3845: 3805:"Historical contingency and its biophysical basis in glucocorticoid receptor evolution" 3804: 3785: 3679: 3632: 3624: 3549: 3487: 3446: 3427: 3330: 3273: 3223: 3174: 3065: 3057: 3014: 2951: 2902: 2652: 2538: 2498: 2419: 2392: 2368: 2308: 2250: 2184: 2045: 1990: 1938: 1926: 1857:"The significance of the fauna of the Burgess Shale, Middle Cambrian, British Columbia" 1390: 875: 870: 479: 310: 149: 2827: 1880: 5061: 4821: 4769: 4726: 4720: 4683: 4671: 4641: 4296: 4202: 4018: 3969: 3961: 3909: 3891: 3850: 3832: 3777: 3769: 3728: 3720: 3671: 3636: 3577: 3541: 3492: 3474: 3431: 3419: 3377: 3369: 3334: 3322: 3265: 3261: 3215: 3178: 3166: 3106: 3069: 3018: 3006: 2998: 2894: 2886: 2847: 2808: 2769: 2730: 2720: 2693: 2644: 2592: 2584: 2542: 2502: 2490: 2449: 2424: 2360: 2300: 2242: 2234: 2176: 2125: 2087: 2049: 2037: 1982: 1930: 1775: 1750: 1742: 1701: 1500: 1382: 1378: 1326: 1272: 1097: 1017:

The presence of cuticle, one of the principal characters of higher invertebrates, in

920: 685: 396: 356: 337: 279: 36: 3981: 3277: 3227: 3193: 2955: 2906: 2656: 2372: 2312: 2188: 1394: 5026: 4954: 4865: 4848: 4562: 4477: 4030: 4008: 3951: 3899: 3881: 3840: 3824: 3789: 3759: 3710: 3663: 3616: 3553: 3531: 3482: 3466: 3411: 3361: 3312: 3257: 3205: 3158: 3098: 3049: 2990: 2941: 2878: 2839: 2800: 2761: 2634: 2624: 2576: 2534: 2482: 2414: 2404: 2352: 2292: 2254: 2226: 2168: 2117: 2079: 2029: 1974: 1922: 1876: 1732: 1693: 1523:"Pikaia Gracilens Is a Relative of but not the Genetic Ancestor to All Vertebrates" 1492: 1430: 1374: 1316: 359:; it is a close relative of vertebrate ancestors but it is not an ancestor itself. 340:

and myomeres, and suggested that the taxon was previously interpreted upside down.

290: 44: 2156: 1682:"Pikaia gracilens Walcott: Stem Chordate, or Already Specialized in the Cambrian?" 997:, still exists today. With a notochord and paired muscle blocks, the lancelet and 367: 313:. Since its initial discovery, more than a hundred specimens have been recovered. 4834: 4797: 4677: 4628: 4449: 4251: 2714: 1460: 1034: 648: 344: 283: 4351: 3715: 3698: 2828:"Key characters uniting hemichordates and chordates: homologies or homoplasies?" 2765: 2121: 4809: 4787: 4732: 4714: 4665: 4657: 4634: 4592: 4568: 4313: 3470: 3102: 2804: 2787:

Schubert, Michael; Escriva, Hector; Xavier-Neto, José; Laudet, Vincent (2006).

1321: 1296: 1244:, which have a notochord-like structure only at the early stage of their lives. 1176: 770: 3764: 3747: 3620: 3365: 3162: 3053: 2486: 2206: 2109: 2083: 2033: 1496: 1435: 5096: 5011: 4758: 4605: 4580: 4529: 4442: 4324: 4304: 4022: 3965: 3895: 3836: 3773: 3724: 3675: 3545: 3478: 3373: 3326: 3269: 3219: 3170: 3002: 2890: 2851: 2588: 2364: 2304: 2238: 2180: 2091: 2041: 1986: 1934: 1769: 1746: 1686:

Journal of Experimental Zoology Part B: Molecular and Developmental Evolution

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Walcott, a stem-group chordate from the Middle Cambrian of British Columbia

3973: 3913: 3854: 3781: 3732: 3496: 3423: 3381: 3349: 3110: 3010: 2970: 2898: 2866: 2812: 2773: 2648: 2629: 2612: 2580: 2546: 2494: 2428: 2409: 2246: 1754: 1705: 1622: 1573: 1504: 1386: 3210: 2596: 2564: 2393:"The Middle Cambrian fossil Pikaia and the evolution of chordate swimming" 2332: 1737: 1720: 927:

from the specimens, providing more evidence with diagnostic features that

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can be understood from the evolutionary trends. A Cambrian invertebrate,

1007: 952: 948: 853: 566: 550: 61: 40: 3886: 3828: 3317: 3292: 2230: 1942: 1902: 1697: 1037:, indicating that primitive characters are retained in lower chordates. 951:-ward of the chordates with links to the phylogenetically controversial 434:

re-examined the Burgess Shale fauna and noted the anatomical details of

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Studies in History and Philosophy of Biological and Biomedical Sciences

3628: 3061: 2946: 2921: 2157:"False teeth: conodont-vertebrate phylogenetic relationships revisited" 1994: 1962: 1481:"Towards the reconstruction of the bilaterian ancestral pre-MHC region" 1077:

Once thought to be closely related to the ancestor of all vertebrates,

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became generally recognised as a chordate and ancestor of vertebrates.

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10.1002/1521-1878(200102)23:2<142::AID-BIES1021>3.0.CO;2-5

2172: 1812:"Cambrian Geology and Paleontology II: No.5--Middle Cambrian Annelids" 1107: 831: 19:

This article is about the extinct chordate. For the anime series, see

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Contingency and Convergence: Toward a Cosmic Biology of Body and Mind

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Wilt, Fred H.; Killian, Christopher E.; Livingston, Brian T. (2003).

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convinced that the animal was obviously a chordate, as they wrote in

417: 400: 325: 166: 111: 55: 4982: 4171: 4075:. Aberystwyth: Cambrian Printers/The Open University. p. 41-42. 4013: 3996: 2843: 5005: 4792: 4737: 4694: 4489: 4288: 4266: 4228: 4059:

The Crucible of Creation: The Burgess Shale and the Rise of Animals

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Blount, Zachary D.; Lenski, Richard E.; Losos, Jonathan B. (2018).

3667: 1623:"Worm-like creature could be a relative of the earliest vertebrate" 989: 888: 678:

had one or more fins, but did not specify where they were present.

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Conway Morris, Simon (2008). "A Redescription of a Rare Chordate,

1721:"Segment formation in Annelids: patterns, processes and evolution" 4880: 4420: 4410: 4392: 3932:"Contingency and determinism in evolution: Replaying life's tape" 974: 924: 755: 574: 538: 527: 404: 399:

in British Columbia, and described it in 1911. He named it after

376: 333: 329: 298: 116: 91: 48: 20: 3246:"Anatomy and relationships of the Early Cambrian worm Myoscolex" 2786: 2207:"Facts and fancies about early fossil chordates and vertebrates" 747:

which is still debated as either an invertebrate or a chordate.

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Insom, Emilio; Pucci, Antonella; Simonetta, Alberto M. (1995).

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is suggested to have fed on small particles of organic matter.

482:. From the same location, other fish-like animal fossils named 176: 2523:"Development of calcareous skeletal elements in invertebrates" 1268:

Across the Bridge: Understanding the Origin of the Vertebrates

1144:"to save the best for the last," in which he made a statement: 706:

normally gill slits in living chordates. He also noticed that

4699: 3397:"Additional molecular support for the new chordate phylogeny" 813:

In fact, there is little evidence for chordate affinities of

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This article describes a reevaluation of the Pikaia anatomy.

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Wang, Wenjun; Wang, Changliu; Chen, Wei; Ding, Shuo (2021).

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Wonderful Life: The Burgess Shale and the Nature of History

691:

Wonderful Life: The Burgess Shale and the Nature of History

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Hsieh, Shannon; Plotnick, Roy E.; Bush, Andrew M. (2022).

2968: 2609: 2333:"The fossil record and the early evolution of the Metazoa" 2154: 1006:

in this position; other extant and fossil groups, such as

3084:"Genome duplication, extinction and vertebrate evolution" 1771:

Treatise on Invertebrate Paleontology Part W. Miscellanea

1416: 1096:). The establishment of Cambrian chordates, according to 1093: 610:(1911), by Charles Doolittle Walcott, showing fossils of 321: 1900: 3444: 2919: 2789:"Amphioxus and tunicates as evolutionary model systems" 2068:"Cambrian Protochordata, their origin and significance" 2520: 2445:

Brains Through Time: A Natural History of Vertebrates

1574:"Worm-like creature could be humans' oldest ancestor" 588:

to filter particles from the water as it swam along.

4862: 4817: 4784: 4766: 4616: 4538: 4465: 4432: 4320: 4309: 4300: 4293: 4278: 4256: 4239: 4083: 3867: 1550:"An Early Chordate that Lived 513 Million Years Ago" 778:. Its anatomy closely resembles the modern creature 2266: 2264: 2116:, Dordrecht: Springer Netherlands, pp. 13–37, 2065: 1108:

Gould's interpretation and evolutionary contingency

4129:La evolución de las especies: ¿por qué sobrevivió 2719:. Vintage/W.W. Norton & Company. p. 321. 2441: 1725:The International Journal of Developmental Biology 1479:Danchin, Etienne G.J.; Pontarotti, Pierre (2004). 1361:Conway Morris, Simon; Caron, Jean-Bernard (2012). 1360: 3929: 3290: 3191: 2668: 2666: 2471:"Advances in immunological research of amphioxus" 2442:Striedter, Georg F.; Northcutt, R. Glenn (2020). 1901:Conway Morris, Simon; Whittington, H. B. (1979). 1478: 623:Walcott's original summary of the description of 5094: 4113:. Virtual Museum of Canada. 2011. Archived from 4047:Bishop, A., Woolley, A. and Hamilton, W. (1999) 3137:Briggs, Derek E. G.; Nedin, Christopher (1997). 2468: 2261: 411:worm and created a new family Pikaidae for it. ( 3803:Harms, Michael J.; Thornton, Joseph W. (2014). 3081: 3025: 2110:"The Burgess Shale: Different types of animals" 1768:Howell, B. F. (1962). "Worms". In Moore (ed.). 1136:He elaborated the same idea in "An epilogue on 4139:Fossils of the Burgess Shale - Middle Cambrian 4061:. Oxford University Press, New York, New York. 3348:Özpolat, B. Duygu; Bely, Alexandra E. (2016). 2663: 2386: 2384: 2382: 1679: 1423:reveals the origins of the chordate body plan" 1120:to explain the trends of evolutionary changes: 1072: 4187: 4066:Prehistoric Life: the Rise of the Vertebrates 3802: 3354:Current Opinion in Genetics & Development 2562: 2330: 2270: 2108:Hall, Brian K. (1992), Hall, Brian K. (ed.), 1960: 3192:Conway Morris, Simon; Peel, John S. (2008). 3075: 1520: 1025:was described to be structurally similar to 973:, dorsal nerve cord, and blocks of muscles ( 826: 607:Walcott Cambrian Geology and Paleontology II 4071:Sheldon, P., Palmer D., Spicer, B. (2001). 3347: 3136: 3082:Donoghue, P. C. J.; Purnell, M. A. (2005), 3031: 2864: 2379: 2007: 1963:"The Burgess Shale (Middle Cambrian) Fauna" 1854: 1271:. University of Chicago Press. p. 83. 557:. Unlike a typical cuticle, the cuticle of 4194: 4180: 3699:"A case study in evolutionary contingency" 2676:. London: Marshall Publishing Ltd. p66-67. 2475:Developmental & Comparative Immunology 1861:Proceedings of the Geologists' Association 1112:Gould, in his presidential address of the 1048: 959: 127: 4012: 3955: 3903: 3885: 3844: 3763: 3714: 3535: 3486: 3316: 3209: 2945: 2640:1983/c6be6646-a086-4b6f-89e3-29073ee4e8a9 2638: 2628: 2418: 2408: 1736: 1718: 1434: 1320: 1294: 839:based on Conway Morris & Caron (2012) 420:on the body segments back of the fifth." 316:The body structure resembles that of the 1967:Annual Review of Ecology and Systematics 1680:Mallatt, Jon; Holland, Nicholas (2013). 842: 830: 599: 472:Annual Review of Ecology and Systematics 366: 5128:Taxa named by Charles Doolittle Walcott 2825: 2448:. Oxford University Press. p. 70. 2390: 2204: 1809: 1412: 1410: 1408: 1406: 1404: 865:The first comprehensive description of 5095: 3994: 3925: 3923: 3696: 3649: 3565: 3563: 3394: 3239: 3237: 2747: 2685: 2558: 2556: 2516: 2514: 2512: 2326: 2324: 2322: 2200: 2198: 2150: 2148: 2146: 2103: 2101: 2061: 2059: 1956: 1954: 1952: 1767: 1443: 1297:"Cambrian Chordates and Vetulicolians" 835:Previous anatomical reconstruction of 565:shows the essential prerequisites for 4987: 4986: 4201: 4175: 3745: 3594: 3569: 3509: 2712: 2569:Molecular Phylogenetics and Evolution 1896: 1894: 1892: 1890: 1835: 1819:Smithsonian Miscellaneous Collections 1805: 1803: 1801: 1799: 1797: 1795: 1793: 1791: 1675: 1673: 1671: 1669: 1667: 1641: 1639: 1617: 1615: 1356: 1354: 1352: 1350: 1348: 1346: 1344: 1342: 1340: 3243: 2107: 1544: 1542: 1516: 1514: 1474: 1472: 1401: 1290: 1288: 1053:The first sign of head development, 595: 16:Extinct genus of primitive chordates 4151: 3920: 3560: 3234: 2553: 2509: 2319: 2195: 2143: 2098: 2056: 1979:10.1146/annurev.es.10.110179.001551 1949: 1264: 869:was published by Conway Morris and 793:, discovered in 1979 from Cambrian 719:Scripps Institution of Oceanography 13: 4041: 2674:The Atlas of the Prehistoric World 2539:10.1046/j.1432-0436.2003.7104501.x 2114:Evolutionary Developmental Biology 1927:10.1038/scientificamerican0779-122 1903:"The Animals of the Burgess Shale" 1887: 1788: 1664: 1636: 1612: 1337: 14: 5144: 4079: 3091:Trends in Ecology & Evolution 2865:Holland, N. D.; Chen, J. (2001). 2793:Trends in Ecology & Evolution 2008:Butterfield, Nicholas J. (1990). 1647:"Early Vertibrate Relative found" 1539: 1511: 1469: 1466:. Virtual Museum of Canada. 2011. 1285: 320:and it swam perhaps much like an 4378: 4372: 4367: 4362: 4356: 4350: 4344: 4337: 4152:Weisberger, Mindy (2024-06-24). 4086: 3262:10.1111/j.1463-6409.2004.00136.x 2563:Giribet, G.; Ribera, C. (1998). 1379:10.1111/j.1469-185X.2012.00220.x 1161:survived the Burgess decimation. 153: 59: 4073:Fossils and the History of Life 3997:"Stephen Jay Gould (1941–2002)" 3988: 3861: 3796: 3739: 3690: 3643: 3588: 3503: 3438: 3388: 3341: 3284: 3185: 3130: 2962: 2913: 2858: 2819: 2780: 2750:"What are narratives good for?" 2741: 2706: 2679: 2603: 2462: 2435: 2001: 1848: 1829: 1761: 1712: 1595:"Human's oldest ancestor found" 1587: 1231: 1222: 1210:Paleobiota of the Burgess Shale 1057:, is seen in chordates such as 725:criticised the presentation in 533:A major primitive structure of 2686:Powell, Russell (2020-02-04). 1566: 1295:McMenamin, Mark A. S. (2019). 1258: 499: 462:Conway Morris formally placed 1: 5123:Fossil taxa described in 1911 3198:Acta Palaeontologica Polonica 1961:Conway Morris, Simon (1979). 1881:10.1016/S0016-7878(80)80034-4 1719:Balavoine, Guillaume (2014). 1251: 847:Anatomical reconstruction of 136:Anatomical reconstruction of 4939:List of transitional fossils 4111:Burgess Shale Fossil Gallery 3995:Briggs, Derek E. G. (2002). 3395:Delsuc; et al. (2008). 2713:Gould, Stephen Jay (2000) . 1810:Walcott, Charles D. (1911). 1464:Burgess Shale Fossil Gallery 1205:Fossils of the Burgess Shale 939:Whilst the possibility that 362: 7: 5103:Prehistoric chordate genera 4049:Minerals, Rocks and Fossils 3716:10.1016/j.shpsc.2015.12.007 3697:Blount, Zachary D. (2016). 3595:Gould, Stephen Jay (1988). 3570:Gould, Stephen Jay (1989). 3510:Gould, Stephen Jay (1995). 2832:Canadian Journal of Zoology 2766:10.1016/j.shpsc.2015.12.016 2122:10.1007/978-94-015-7926-1_2 1521:SciTechDaily (2012-03-06). 1198: 1166:molecular biology. He used 1073:Evolutionary interpretation 809:'s tentacles. He concluded: 723:Chinese Academy of Sciences 10: 5149: 5133:Cambrian genus extinctions 4219:Timeline of fish evolution 3748:"Evolutionary contingency" 3746:Erwin, Douglas H. (2006). 3471:10.1038/s41598-017-00786-5 3103:10.1016/j.tree.2005.04.008 2826:Ruppert, Edward E (2005). 2805:10.1016/j.tree.2006.01.009 2331:Conway Morris, S. (1993). 2205:Janvier, Philippe (2015). 1855:Whittington, H.B. (1980). 1322:10.3390/geosciences9080354 1182: 1116:on 27 October 1988, cited 721:and Junyuan Chen from the 672:Atlas of the Burgess Shale 18: 4995: 4973: 4947: 4907:Lists of prehistoric fish 4899: 4808: 4757: 4748: 4656: 4615: 4537: 4528: 4464: 4431: 4401: 4391: 4335: 4227: 4209: 3765:10.1016/j.cub.2006.08.076 3621:10.1017/S0022336000059126 3366:10.1016/j.gde.2016.07.010 3163:10.1017/S0022336000038919 3054:10.1017/S0094837300009994 2692:. MIT Press. p. 62. 2487:10.1016/j.dci.2020.103992 2084:10.1080/11250009509356072 2034:10.1017/S0094837300009994 1497:10.1016/j.tig.2004.09.009 1436:10.1016/j.cub.2024.05.026 1419:"A new interpretation of 873:in the May 2012 issue of 827:Comprehensive description 355:chordate alongside other 295:Charles Doolittle Walcott 253: 246: 150:Scientific classification 148: 135: 126: 29: 1215: 911:were actually inverted. 817:. Its relationship with 4965:Vertebrate paleontology 3957:10.1126/science.aam5979 3601:Journal of Paleontology 3143:Journal of Paleontology 2277:Journal of Paleontology 1838:Journal of Paleontology 1651:University of Cambridge 1599:University of Cambridge 1114:Paleontological Society 1049:Development of the head 964:Much debate on whether 960:Evolutionary importance 896:bilaterally symmetrical 740:Tullimonstrum gregarium 575:segmented muscle blocks 490:Smithsonian Institution 454:and the single species 424:University of Cambridge 293:. Described in 1911 by 2630:10.1002/bies.201700167 2581:10.1006/mpev.1998.0494 2410:10.1186/2041-9139-3-12 2273:Metaspriggina walcotti 1163: 1134: 1014:, are more primitive. 957: 862: 840: 824: 634: 620: 460: 380: 282:animal known from the 5113:Burgess Shale animals 5075:Paleobiology Database 3650:Blaser, Kent (1999). 3512:"Of it, not above it" 3211:10.4202/app.2008.0110 2748:Beatty, John (2016). 2072:Bolletino di Zoologia 1738:10.1387/ijdb.140148gb 1146: 1122: 1045:as a basal chordate. 937: 846: 834: 811: 750:Another component of 629: 603: 447: 370: 5118:Transitional fossils 4960:Transitional fossils 4599:Pseudopetalichthyida 4055:Conway Morris, Simon 3576:. pp. 322–323. 3244:Dzik, Jerzy (2004). 2672:Palmer, D., (2000). 2391:Lacalli, T. (2012). 494:Royal Ontario Museum 428:Harry B. Whittington 303:Harry B. Whittington 4094:Paleontology portal 4051:. London: Phillip's 3948:2018Sci...362M5979B 3887:10.7554/eLife.67336 3829:10.1038/nature13410 3821:2014Natur.512..203H 3656:The History Teacher 3613:1988JPal...62..319G 3528:1995Natur.377..681G 3463:2017NatSR...7.1157I 3318:10.1017/pab.2021.46 3309:2022Pbio...48..397H 3155:1997JPal...71...22B 3046:1990Pbio...16..272B 2987:2020Gbio...18..560M 2938:2017Palgy..60..149S 2349:1993Natur.361..219M 2289:2008JPal...82..424M 2231:10.1038/nature14437 2223:2015Natur.520..483J 2026:1990Pbio...16..272B 1919:1979SciAm.241a.122M 1907:Scientific American 1873:1980PrGA...91..127W 1698:10.1002/jez.b.22500 1313:2019Geosc...9..354M 1265:Gee, Henry (2018). 442:Scientific American 432:Simon Conway Morris 307:Simon Conway Morris 5108:Cambrian chordates 4648:Ischnacanthiformes 4496:Cephalaspidomorphi 4064:Norman, D. (1994) 3942:(6415): eaam5979. 3451:Scientific Reports 2947:10.1111/pala.12282 1485:Trends in Genetics 1459:2013-12-24 at the 1367:Biological Reviews 1240:are classified as 876:Biological Reviews 871:Jean-Bernard Caron 863: 841: 688:wrote in his book 621: 480:Yoho National Park 470:in a paper in the 387:was discovered by 381: 357:Cambrian chordates 311:Cambrian explosion 280:primitive chordate 5090: 5089: 5062:Open Tree of Life 4989:Taxon identifiers 4980: 4979: 4895: 4894: 4891: 4890: 4822:Palaeonisciformes 4770:Onychodontiformes 4727:Petalodontiformes 4721:Iniopterygiformes 4684:Phoebodontiformes 4672:Ctenacanthiformes 4642:Diplacanthiformes 4524: 4523: 4297:Myllokunmingiidae 4203:Evolution of fish 4068:, London: Boxtree 3815:(7513): 203–207. 3522:(6551): 681–682. 3416:10.1002/dvg.20450 3250:Zoologica Scripta 2995:10.1111/gbi.12397 2726:978-0-09-927345-5 2699:978-0-262-35660-2 2455:978-0-19-512568-9 2343:(6409): 219–225. 2217:(7548): 483–489. 2173:10.5252/g2010n4a1 2131:978-94-015-7926-1 1781:978-0-8137-3024-0 1554:Discover Magazine 1278:978-0-226-40319-9 1098:Stephen Jay Gould 921:dorsal nerve cord 787:A fossil species 686:Stephen Jay Gould 596:Reinterpretations 464:P. gracilens 456:P. gracilens 397:Stephen formation 338:dorsal nerve cord 301:, and in 1979 by 271: 270: 239:P. gracilens 227: 208: 5140: 5083: 5082: 5070: 5069: 5057: 5056: 5044: 5043: 5031: 5030: 5029: 5016: 5015: 5014: 4984: 4983: 4955:Prehistoric life 4866:Pycnodontiformes 4864: 4849:Acipenseriformes 4819: 4786: 4768: 4755: 4754: 4618: 4563:Brindabellaspida 4540: 4535: 4534: 4478:Pteraspidomorphi 4467: 4434: 4399: 4398: 4383: 4382: 4376: 4371: 4366: 4361: 4360: 4354: 4349: 4348: 4341: 4322: 4311: 4302: 4295: 4280: 4258: 4241: 4196: 4189: 4182: 4173: 4172: 4167: 4165: 4164: 4145:Pikaia gracilens 4125: 4123: 4122: 4105:Pikaia gracilens 4096: 4091: 4090: 4089: 4035: 4034: 4016: 3992: 3986: 3985: 3959: 3927: 3918: 3917: 3907: 3889: 3865: 3859: 3858: 3848: 3800: 3794: 3793: 3767: 3758:(19): R825–826. 3743: 3737: 3736: 3718: 3694: 3688: 3687: 3647: 3641: 3640: 3592: 3586: 3585: 3567: 3558: 3557: 3539: 3537:10.1038/377681a0 3507: 3501: 3500: 3490: 3442: 3436: 3435: 3401: 3392: 3386: 3385: 3345: 3339: 3338: 3320: 3288: 3282: 3281: 3241: 3232: 3231: 3213: 3189: 3183: 3182: 3134: 3128: 3127: 3126: 3125: 3119: 3113:, archived from 3088: 3079: 3073: 3072: 3029: 3023: 3022: 2966: 2960: 2959: 2949: 2917: 2911: 2910: 2862: 2856: 2855: 2823: 2817: 2816: 2784: 2778: 2777: 2745: 2739: 2738: 2710: 2704: 2703: 2683: 2677: 2670: 2661: 2660: 2642: 2632: 2607: 2601: 2600: 2560: 2551: 2550: 2533:(4–5): 237–250. 2518: 2507: 2506: 2466: 2460: 2459: 2439: 2433: 2432: 2422: 2412: 2388: 2377: 2376: 2357:10.1038/361219a0 2328: 2317: 2316: 2297:10.1666/06-130.1 2268: 2259: 2258: 2202: 2193: 2192: 2152: 2141: 2140: 2139: 2138: 2105: 2096: 2095: 2063: 2054: 2053: 2005: 1999: 1998: 1958: 1947: 1946: 1898: 1885: 1884: 1852: 1846: 1845: 1833: 1827: 1826: 1816: 1807: 1786: 1785: 1765: 1759: 1758: 1740: 1731:(6–8): 469–483. 1716: 1710: 1709: 1677: 1662: 1661: 1659: 1658: 1643: 1634: 1633: 1631: 1630: 1619: 1610: 1609: 1607: 1606: 1591: 1585: 1584: 1582: 1581: 1570: 1564: 1563: 1561: 1560: 1546: 1537: 1536: 1534: 1533: 1518: 1509: 1508: 1476: 1467: 1452:Pikaia gracilens 1447: 1441: 1440: 1438: 1414: 1399: 1398: 1358: 1335: 1334: 1324: 1292: 1283: 1282: 1262: 1245: 1235: 1229: 1226: 1035:cephalochordates 1023:Myoscolex ateles 914:The backside of 849:Pikaia gracilens 837:Pikaia gracilens 790:Myoscolex ateles 520: 519: 515: 512: 430:and his student 426:palaeontologist 403:, a mountain in 385:Pikaia gracilens 373:Pikaia gracilens 291:British Columbia 275:Pikaia gracilens 262: 260:Pikaia gracilens 258: 225: 218: 203: 198: 158: 157: 138:Pikaia gracilens 131: 121: 58: 35:Temporal range: 27: 26: 5148: 5147: 5143: 5142: 5141: 5139: 5138: 5137: 5093: 5092: 5091: 5086: 5078: 5073: 5065: 5060: 5052: 5047: 5039: 5034: 5025: 5024: 5019: 5010: 5009: 5004: 4991: 4981: 4976: 4969: 4943: 4887: 4835:Polypteriformes 4804: 4798:Tetrapodomorpha 4744: 4678:Hybodontiformes 4652: 4629:Acanthodiformes 4611: 4520: 4460: 4450:Paraconodontida 4427: 4395: 4387: 4386: 4385: 4377: 4355: 4343: 4333: 4252:Cephalochordate 4223: 4205: 4200: 4162: 4160: 4120: 4118: 4101: 4092: 4087: 4085: 4082: 4044: 4042:Further reading 4039: 4038: 4014:10.1038/417706a 3993: 3989: 3928: 3921: 3866: 3862: 3801: 3797: 3752:Current Biology 3744: 3740: 3695: 3691: 3648: 3644: 3593: 3589: 3568: 3561: 3508: 3504: 3443: 3439: 3410:(11): 592–604. 3399: 3393: 3389: 3346: 3342: 3289: 3285: 3242: 3235: 3190: 3186: 3135: 3131: 3123: 3121: 3117: 3086: 3080: 3076: 3030: 3026: 2967: 2963: 2918: 2914: 2863: 2859: 2844:10.1139/z04-158 2824: 2820: 2785: 2781: 2746: 2742: 2727: 2711: 2707: 2700: 2684: 2680: 2671: 2664: 2608: 2604: 2561: 2554: 2527:Differentiation 2519: 2510: 2467: 2463: 2456: 2440: 2436: 2389: 2380: 2329: 2320: 2269: 2262: 2203: 2196: 2153: 2144: 2136: 2134: 2132: 2106: 2099: 2064: 2057: 2006: 2002: 1959: 1950: 1899: 1888: 1853: 1849: 1844:(Suppl 2): 7–8. 1834: 1830: 1814: 1808: 1789: 1782: 1766: 1762: 1717: 1713: 1678: 1665: 1656: 1654: 1645: 1644: 1637: 1628: 1626: 1621: 1620: 1613: 1604: 1602: 1593: 1592: 1588: 1579: 1577: 1572: 1571: 1567: 1558: 1556: 1548: 1547: 1540: 1531: 1529: 1519: 1512: 1491:(12): 587–591. 1477: 1470: 1461:Wayback Machine 1448: 1444: 1427:Current Biology 1415: 1402: 1359: 1338: 1293: 1286: 1279: 1263: 1259: 1254: 1249: 1248: 1236: 1232: 1227: 1223: 1218: 1201: 1185: 1110: 1075: 1051: 988:lookalike, the 962: 931:is a chordate. 829: 649:digestive tract 598: 517: 513: 510: 508: 502: 389:Charles Walcott 383:The fossils of 379:USNM PAL 57628) 365: 345:cephalochordata 284:Middle Cambrian 278:is an extinct, 267: 264: 256: 255: 242: 224: 216: 202: 196: 152: 122: 120: 119: 114: 109: 104: 99: 94: 89: 84: 79: 74: 69: 64: 53: 52: 41:Middle Cambrian 33: 23: 17: 12: 11: 5: 5146: 5136: 5135: 5130: 5125: 5120: 5115: 5110: 5105: 5088: 5087: 5085: 5084: 5071: 5058: 5045: 5032: 5017: 5001: 4999: 4993: 4992: 4978: 4977: 4974: 4971: 4970: 4968: 4967: 4962: 4957: 4951: 4949: 4945: 4944: 4942: 4941: 4936: 4935: 4934: 4929: 4924: 4919: 4914: 4903: 4901: 4897: 4896: 4893: 4892: 4889: 4888: 4886: 4885: 4884: 4883: 4878: 4873: 4868: 4854: 4853: 4852: 4851: 4840: 4839: 4838: 4837: 4826: 4825: 4814: 4812: 4806: 4805: 4803: 4802: 4801: 4800: 4795: 4790: 4788:Porolepiformes 4777: 4772: 4763: 4761: 4752: 4746: 4745: 4743: 4742: 4741: 4740: 4735: 4733:Symmoriiformes 4729: 4723: 4717: 4715:Eugeneodontida 4705: 4704: 4703: 4702: 4697: 4692: 4686: 4680: 4674: 4666:Elasmobranchii 4662: 4660: 4654: 4653: 4651: 4650: 4644: 4638: 4635:Climatiiformes 4631: 4624: 4622: 4613: 4612: 4610: 4609: 4602: 4595: 4593:Acanthothoraci 4589: 4583: 4577: 4571: 4569:Petalichthyida 4565: 4559: 4553: 4546: 4544: 4532: 4526: 4525: 4522: 4521: 4519: 4518: 4517: 4516: 4510: 4504: 4492: 4486: 4480: 4473: 4471: 4462: 4461: 4459: 4458: 4452: 4446: 4443:Protoconodonta 4438: 4436: 4429: 4428: 4426: 4425: 4424: 4423: 4413: 4407: 4405: 4396: 4389: 4388: 4336: 4334: 4332: 4331: 4330: 4329: 4318: 4314:Myllokunmingia 4291: 4286: 4271: 4270: 4269: 4264: 4249: 4248: 4247: 4233: 4231: 4225: 4224: 4222: 4221: 4216: 4210: 4207: 4206: 4199: 4198: 4191: 4184: 4176: 4170: 4169: 4149: 4141: 4136: 4126: 4098: 4097: 4081: 4080:External links 4078: 4077: 4076: 4069: 4062: 4052: 4043: 4040: 4037: 4036: 3987: 3919: 3860: 3795: 3738: 3689: 3668:10.2307/494379 3662:(3): 411–430. 3642: 3607:(3): 319–329. 3587: 3559: 3502: 3437: 3387: 3340: 3303:(3): 397–419. 3283: 3233: 3204:(1): 137–148. 3184: 3129: 3097:(6): 312–319, 3074: 3040:(3): 272–286, 3024: 2981:(5): 560–565. 2961: 2932:(2): 149–157. 2912: 2877:(2): 142–151. 2857: 2818: 2799:(5): 269–277. 2779: 2740: 2725: 2705: 2698: 2678: 2662: 2623:(1): 1700167. 2602: 2575:(3): 481–488. 2552: 2508: 2461: 2454: 2434: 2378: 2318: 2283:(2): 424–430. 2260: 2194: 2167:(4): 545–594. 2142: 2130: 2097: 2078:(3): 243–252. 2055: 2020:(3): 272–286. 2000: 1948: 1913:(1): 122–135. 1886: 1867:(3): 127–148. 1847: 1828: 1787: 1780: 1760: 1711: 1692:(4): 247–271. 1663: 1635: 1611: 1586: 1565: 1538: 1510: 1468: 1442: 1400: 1373:(2): 480–512. 1336: 1284: 1277: 1256: 1255: 1253: 1250: 1247: 1246: 1230: 1220: 1219: 1217: 1214: 1213: 1212: 1207: 1200: 1197: 1184: 1181: 1177:macroevolution 1142:Wonderful Life 1140:" in his book 1109: 1106: 1074: 1071: 1050: 1047: 961: 958: 857:after Mussini 828: 825: 771:Myllokunmingia 727:Wonderful Life 710:is similar to 597: 594: 569:. When alive, 501: 498: 395:member of the 364: 361: 269: 268: 265: 251: 250: 244: 243: 235: 233: 229: 228: 214: 210: 209: 194: 190: 189: 184: 180: 179: 174: 170: 169: 164: 160: 159: 146: 145: 140:after Mussini 133: 132: 124: 123: 115: 110: 105: 100: 95: 90: 85: 80: 75: 70: 65: 60: 37:Early Cambrian 34: 15: 9: 6: 4: 3: 2: 5145: 5134: 5131: 5129: 5126: 5124: 5121: 5119: 5116: 5114: 5111: 5109: 5106: 5104: 5101: 5100: 5098: 5081: 5076: 5072: 5068: 5063: 5059: 5055: 5050: 5046: 5042: 5037: 5033: 5028: 5022: 5018: 5013: 5007: 5003: 5002: 5000: 4998: 4994: 4990: 4985: 4972: 4966: 4963: 4961: 4958: 4956: 4953: 4952: 4950: 4946: 4940: 4937: 4933: 4930: 4928: 4925: 4923: 4922:cartilaginous 4920: 4918: 4915: 4913: 4910: 4909: 4908: 4905: 4904: 4902: 4898: 4882: 4879: 4877: 4874: 4872: 4869: 4867: 4861: 4860: 4859: 4856: 4855: 4850: 4847: 4846: 4845: 4842: 4841: 4836: 4833: 4832: 4831: 4828: 4827: 4823: 4816: 4815: 4813: 4811: 4807: 4799: 4796: 4794: 4791: 4789: 4783: 4782: 4781: 4778: 4776: 4773: 4771: 4765: 4764: 4762: 4760: 4756: 4753: 4751: 4747: 4739: 4736: 4734: 4730: 4728: 4724: 4722: 4718: 4716: 4712: 4711: 4710: 4707: 4706: 4701: 4698: 4696: 4693: 4691: 4687: 4685: 4681: 4679: 4675: 4673: 4669: 4668: 4667: 4664: 4663: 4661: 4659: 4658:Cartilaginous 4655: 4649: 4645: 4643: 4639: 4636: 4632: 4630: 4626: 4625: 4623: 4621: 4614: 4607: 4606:Stensioellida 4603: 4600: 4596: 4594: 4590: 4588: 4584: 4582: 4581:Ptyctodontida 4578: 4576: 4572: 4570: 4566: 4564: 4560: 4558: 4554: 4552: 4548: 4547: 4545: 4543: 4536: 4533: 4531: 4527: 4515: 4511: 4509: 4505: 4503: 4499: 4498: 4497: 4493: 4491: 4487: 4485: 4481: 4479: 4475: 4474: 4472: 4470: 4463: 4457: 4453: 4451: 4447: 4444: 4440: 4439: 4437: 4430: 4422: 4419: 4418: 4417: 4414: 4412: 4409: 4408: 4406: 4404: 4400: 4397: 4394: 4390: 4384: 4381: 4375: 4370: 4365: 4359: 4353: 4347: 4340: 4327: 4326: 4325:Zhongxiniscus 4319: 4316: 4315: 4307: 4306: 4305:Haikouichthys 4298: 4292: 4290: 4287: 4285: 4284: 4277: 4276: 4275: 4272: 4268: 4265: 4263: 4262: 4255: 4254: 4253: 4250: 4246: 4245: 4238: 4237: 4236:Basal member 4235: 4234: 4232: 4230: 4226: 4220: 4217: 4215: 4212: 4211: 4208: 4204: 4197: 4192: 4190: 4185: 4183: 4178: 4177: 4174: 4159: 4155: 4150: 4148: 4146: 4142: 4140: 4137: 4134: 4132: 4127: 4117:on 2020-11-12 4116: 4112: 4108: 4106: 4100: 4099: 4095: 4084: 4074: 4070: 4067: 4063: 4060: 4056: 4053: 4050: 4046: 4045: 4032: 4028: 4024: 4020: 4015: 4010: 4007:(6890): 706. 4006: 4002: 3998: 3991: 3983: 3979: 3975: 3971: 3967: 3963: 3958: 3953: 3949: 3945: 3941: 3937: 3933: 3926: 3924: 3915: 3911: 3906: 3901: 3897: 3893: 3888: 3883: 3879: 3875: 3871: 3864: 3856: 3852: 3847: 3842: 3838: 3834: 3830: 3826: 3822: 3818: 3814: 3810: 3806: 3799: 3791: 3787: 3783: 3779: 3775: 3771: 3766: 3761: 3757: 3753: 3749: 3742: 3734: 3730: 3726: 3722: 3717: 3712: 3708: 3704: 3700: 3693: 3685: 3681: 3677: 3673: 3669: 3665: 3661: 3657: 3653: 3646: 3638: 3634: 3630: 3626: 3622: 3618: 3614: 3610: 3606: 3602: 3598: 3591: 3583: 3579: 3575: 3574: 3566: 3564: 3555: 3551: 3547: 3543: 3538: 3533: 3529: 3525: 3521: 3517: 3513: 3506: 3498: 3494: 3489: 3484: 3480: 3476: 3472: 3468: 3464: 3460: 3456: 3452: 3448: 3441: 3433: 3429: 3425: 3421: 3417: 3413: 3409: 3405: 3398: 3391: 3383: 3379: 3375: 3371: 3367: 3363: 3359: 3355: 3351: 3344: 3336: 3332: 3328: 3324: 3319: 3314: 3310: 3306: 3302: 3298: 3294: 3287: 3279: 3275: 3271: 3267: 3263: 3259: 3255: 3251: 3247: 3240: 3238: 3229: 3225: 3221: 3217: 3212: 3207: 3203: 3199: 3195: 3188: 3180: 3176: 3172: 3168: 3164: 3160: 3156: 3152: 3148: 3144: 3140: 3133: 3120:on 2008-12-17 3116: 3112: 3108: 3104: 3100: 3096: 3092: 3085: 3078: 3071: 3067: 3063: 3059: 3055: 3051: 3047: 3043: 3039: 3035: 3028: 3020: 3016: 3012: 3008: 3004: 3000: 2996: 2992: 2988: 2984: 2980: 2976: 2972: 2965: 2957: 2953: 2948: 2943: 2939: 2935: 2931: 2927: 2926:Palaeontology 2923: 2916: 2908: 2904: 2900: 2896: 2892: 2888: 2884: 2880: 2876: 2872: 2868: 2861: 2853: 2849: 2845: 2841: 2837: 2833: 2829: 2822: 2814: 2810: 2806: 2802: 2798: 2794: 2790: 2783: 2775: 2771: 2767: 2763: 2759: 2755: 2751: 2744: 2736: 2732: 2728: 2722: 2718: 2717: 2709: 2701: 2695: 2691: 2690: 2682: 2675: 2669: 2667: 2658: 2654: 2650: 2646: 2641: 2636: 2631: 2626: 2622: 2618: 2614: 2606: 2598: 2594: 2590: 2586: 2582: 2578: 2574: 2570: 2566: 2559: 2557: 2548: 2544: 2540: 2536: 2532: 2528: 2524: 2517: 2515: 2513: 2504: 2500: 2496: 2492: 2488: 2484: 2480: 2476: 2472: 2465: 2457: 2451: 2447: 2446: 2438: 2430: 2426: 2421: 2416: 2411: 2406: 2402: 2398: 2394: 2387: 2385: 2383: 2374: 2370: 2366: 2362: 2358: 2354: 2350: 2346: 2342: 2338: 2334: 2327: 2325: 2323: 2314: 2310: 2306: 2302: 2298: 2294: 2290: 2286: 2282: 2278: 2274: 2267: 2265: 2256: 2252: 2248: 2244: 2240: 2236: 2232: 2228: 2224: 2220: 2216: 2212: 2208: 2201: 2199: 2190: 2186: 2182: 2178: 2174: 2170: 2166: 2162: 2161:Geodiversitas 2158: 2151: 2149: 2147: 2133: 2127: 2123: 2119: 2115: 2111: 2104: 2102: 2093: 2089: 2085: 2081: 2077: 2073: 2069: 2062: 2060: 2051: 2047: 2043: 2039: 2035: 2031: 2027: 2023: 2019: 2015: 2011: 2004: 1996: 1992: 1988: 1984: 1980: 1976: 1972: 1968: 1964: 1957: 1955: 1953: 1944: 1940: 1936: 1932: 1928: 1924: 1920: 1916: 1912: 1908: 1904: 1897: 1895: 1893: 1891: 1882: 1878: 1874: 1870: 1866: 1862: 1858: 1851: 1843: 1839: 1832: 1825:(5): 109–144. 1824: 1820: 1813: 1806: 1804: 1802: 1800: 1798: 1796: 1794: 1792: 1783: 1777: 1773: 1772: 1764: 1756: 1752: 1748: 1744: 1739: 1734: 1730: 1726: 1722: 1715: 1707: 1703: 1699: 1695: 1691: 1687: 1683: 1676: 1674: 1672: 1670: 1668: 1652: 1648: 1642: 1640: 1624: 1618: 1616: 1600: 1596: 1590: 1575: 1569: 1555: 1551: 1545: 1543: 1528: 1524: 1517: 1515: 1506: 1502: 1498: 1494: 1490: 1486: 1482: 1475: 1473: 1465: 1462: 1458: 1455: 1453: 1446: 1437: 1432: 1428: 1424: 1422: 1413: 1411: 1409: 1407: 1405: 1396: 1392: 1388: 1384: 1380: 1376: 1372: 1368: 1364: 1357: 1355: 1353: 1351: 1349: 1347: 1345: 1343: 1341: 1332: 1328: 1323: 1318: 1314: 1310: 1306: 1302: 1298: 1291: 1289: 1280: 1274: 1270: 1269: 1261: 1257: 1243: 1242:hemichordates 1239: 1234: 1225: 1221: 1211: 1208: 1206: 1203: 1202: 1196: 1194: 1189: 1180: 1178: 1173: 1169: 1162: 1160: 1155: 1150: 1145: 1143: 1139: 1133: 1131: 1127: 1121: 1119: 1115: 1105: 1103: 1099: 1095: 1090: 1088: 1084: 1083:Burgess Shale 1080: 1070: 1068: 1067:efflorescence 1064: 1063:Branchiostoma 1060: 1056: 1055:cephalization 1046: 1044: 1038: 1036: 1032: 1028: 1024: 1020: 1015: 1013: 1009: 1005: 1000: 996: 995: 994:Branchiostoma 991: 987: 982: 978: 976: 972: 967: 956: 954: 950: 946: 942: 936: 932: 930: 926: 922: 917: 912: 910: 906: 900: 897: 892: 890: 886: 882: 878: 877: 872: 868: 860: 856: 855: 850: 845: 838: 833: 823: 820: 816: 810: 808: 804: 800: 796: 795:Emu Bay shale 792: 791: 785: 783: 782: 781:Branchiostoma 777: 773: 772: 767: 766: 765:Haikouichthys 761: 757: 753: 748: 746: 742: 741: 736: 732: 728: 724: 720: 715: 713: 709: 703: 701: 697: 693: 692: 687: 683: 679: 677: 673: 669: 665: 660: 658: 655:differs from 654: 650: 646: 645: 644:Branchiostoma 640: 633: 628: 626: 619: 618: 613: 609: 608: 602: 593: 591: 587: 582: 578: 576: 572: 568: 564: 560: 556: 552: 548: 544: 540: 536: 531: 529: 524: 506: 497: 495: 491: 487: 486: 485:Metaspriggina 481: 476: 473: 469: 465: 459: 457: 453: 446: 444: 443: 437: 433: 429: 425: 421: 419: 414: 410: 406: 402: 398: 394: 393:Burgess shale 390: 386: 378: 374: 369: 360: 358: 354: 350: 346: 341: 339: 335: 331: 327: 323: 319: 314: 312: 308: 304: 300: 296: 292: 288: 287:Burgess Shale 285: 281: 277: 276: 266:Walcott, 1911 263: 261: 252: 249: 248:Binomial name 245: 241: 240: 234: 231: 230: 226:Walcott, 1911 223: 222: 215: 212: 211: 206: 201: 195: 192: 191: 188: 185: 182: 181: 178: 175: 172: 171: 168: 165: 162: 161: 156: 151: 147: 143: 139: 134: 130: 125: 118: 113: 108: 103: 98: 93: 88: 83: 78: 73: 68: 63: 57: 54:513–505 50: 46: 42: 38: 32: 28: 25: 22: 4996: 4912:spiny sharks 4871:Halecomorphi 4690:Xenacanthida 4575:Phyllolepida 4508:Pituriaspida 4469:Ostracoderms 4403:Cyclostomata 4393:Jawless fish 4342: 4323: 4312: 4303: 4281: 4259: 4243: 4242: 4161:. Retrieved 4157: 4144: 4130: 4119:. Retrieved 4115:the original 4110: 4104: 4072: 4065: 4058: 4048: 4004: 4000: 3990: 3939: 3935: 3877: 3873: 3863: 3812: 3808: 3798: 3755: 3751: 3741: 3706: 3702: 3692: 3659: 3655: 3645: 3604: 3600: 3590: 3572: 3519: 3515: 3505: 3454: 3450: 3440: 3407: 3403: 3390: 3357: 3353: 3343: 3300: 3297:Paleobiology 3296: 3286: 3256:(1): 57–69. 3253: 3249: 3201: 3197: 3187: 3149:(1): 22–32. 3146: 3142: 3132: 3122:, retrieved 3115:the original 3094: 3090: 3077: 3037: 3034:Paleobiology 3033: 3027: 2978: 2974: 2964: 2929: 2925: 2915: 2874: 2870: 2860: 2835: 2831: 2821: 2796: 2792: 2782: 2757: 2753: 2743: 2715: 2708: 2688: 2681: 2673: 2620: 2616: 2605: 2572: 2568: 2530: 2526: 2478: 2474: 2464: 2444: 2437: 2400: 2396: 2340: 2336: 2280: 2276: 2272: 2214: 2210: 2164: 2160: 2135:, retrieved 2113: 2075: 2071: 2017: 2014:Paleobiology 2013: 2003: 1970: 1966: 1910: 1906: 1864: 1860: 1850: 1841: 1837: 1831: 1822: 1818: 1770: 1763: 1728: 1724: 1714: 1689: 1685: 1655:. Retrieved 1653:. 2012-03-06 1650: 1627:. Retrieved 1625:. 2012-03-05 1603:. Retrieved 1601:. 2012-03-06 1598: 1589: 1578:. Retrieved 1576:. 2012-03-05 1568: 1557:. Retrieved 1553: 1530:. Retrieved 1527:SciTechDaily 1526: 1488: 1484: 1463: 1451: 1445: 1426: 1420: 1370: 1366: 1304: 1300: 1267: 1260: 1233: 1224: 1192: 1187: 1186: 1171: 1167: 1164: 1158: 1153: 1148: 1147: 1141: 1137: 1135: 1129: 1125: 1123: 1117: 1111: 1101: 1091: 1086: 1078: 1076: 1066: 1062: 1058: 1052: 1042: 1039: 1030: 1026: 1022: 1018: 1016: 998: 992: 985: 983: 979: 965: 963: 953:yunnanozoans 947:as the most 944: 940: 938: 933: 928: 915: 913: 908: 904: 901: 894:The head is 893: 884: 880: 874: 866: 864: 858: 852: 851:compared to 848: 836: 818: 814: 812: 806: 802: 788: 786: 779: 769: 763: 762:, including 751: 749: 744: 738: 734: 730: 726: 716: 711: 707: 704: 699: 695: 689: 681: 680: 675: 671: 667: 663: 661: 656: 652: 642: 638: 635: 630: 624: 622: 615: 611: 606: 604:Plate 20 of 589: 585: 580: 579: 570: 562: 558: 534: 532: 522: 504: 503: 483: 477: 471: 463: 461: 455: 451: 448: 440: 435: 422: 384: 382: 372: 342: 315: 274: 273: 272: 259: 254: 238: 237: 220: 219: 199: 141: 137: 30: 24: 5021:Wikispecies 4932:lobe-finned 4858:Neopterygii 4844:Chondrostei 4780:Rhipidistia 4759:Lobe-finned 4709:Holocephali 4514:Osteostraci 4416:Hyperoartia 4261:Cathaymyrus 4229:Forerunners 3457:(1): 1157. 3360:: 144–153. 2838:(1): 8–23. 1973:: 327–349. 1301:Geosciences 1238:Acorn worms 1012:graptolites 1008:acorn worms 854:Yunnanozoon 567:vertebrates 551:echinoderms 500:Description 5097:Categories 4917:placoderms 4876:Ginglymodi 4810:Ray-finned 4775:Coelacanth 4620:Acanthodii 4557:Arthrodira 4542:Placoderms 4530:Jawed fish 4502:Galeaspida 4484:Thelodonti 4283:Haikouella 4274:Olfactores 4163:2024-06-25 4121:2012-06-15 3880:: e67336. 3124:2008-11-06 2975:Geobiology 2481:: 103992. 2137:2022-09-23 1657:2022-09-23 1629:2022-09-23 1605:2022-09-23 1580:2022-09-23 1559:2022-09-23 1532:2022-09-23 1307:(8): 354. 1252:References 799:Jerzy Dzik 776:stem group 760:Chengjiang 543:arthropods 466:among the 409:polychaete 371:Fossil of 4975:† extinct 4830:Cladistia 4587:Rhenanida 4551:Antiarchi 4456:Conodonta 4435:Conodonts 4135:(Spanish) 4023:1476-4687 3966:1095-9203 3896:2050-084X 3837:0028-0836 3774:0960-9822 3725:1879-2499 3709:: 82–92. 3676:0018-2745 3637:222252369 3546:0028-0836 3479:2045-2322 3432:205771088 3374:1879-0380 3335:246399509 3327:0094-8373 3270:0300-3256 3220:0567-7920 3179:131851540 3171:0022-3360 3070:133486523 3019:216646333 3003:1472-4669 2891:0265-9247 2871:BioEssays 2852:0008-4301 2760:: 33–40. 2617:BioEssays 2589:1055-7903 2503:230282227 2403:(1): 12. 2365:0028-0836 2305:0022-3360 2239:1476-4687 2181:1280-9659 2092:0373-4137 2050:133486523 2042:0094-8373 1987:0066-4162 1935:0036-8733 1747:1696-3547 1331:2076-3263 1004:tunicates 971:notochord 819:Myoscolex 712:Amphioxus 657:Amphioxus 639:Amphioxus 555:nematodes 468:chordates 418:parapodia 413:Princeton 401:Pika Peak 391:from the 363:Discovery 326:notochord 232:Species: 200:Pikaiidae 173:Kingdom: 167:Eukaryota 144:. 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