was convinced that the longitudinal rod was a notochord and the segments were muscle blocks that he concluded that Pikaia "is a primitive chordate rather than a polychaete. The earliest fish scales are Upper Cambrian, and Pikaia may not be far removed from the ancestral fish." In 1982, he added further description in his Atlas of the Burgess Shale that Pikaia had one or more fins, but did not specify where they were present. Pikaia was not popularly known as a chordate fossil or as an ancient chordate until 1989. That year, Harvard University palaeontologist Stephen Jay Gould wrote in his book Wonderful Life: The Burgess Shale and the Nature of History: "Pikaia 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 Pikaia became generally recognised as a chordate and ancestor of vertebrates. In 1993, Conway Morris came up with another possible chordate feature. He identified structures that looked like gill slits but gave a cautious remark: "[They] 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 normally gill slits in living chordates. He also noticed that Pikaia is similar to Amphioxus in most general aspects, with major difference in its notochord not reaching the anterior end. Not all palaeontologists were convinced of the chordate designation without better analysis. In 2001, Nicholas D. Holland from the Scripps Institution of Oceanography and Junyuan Chen from the Chinese Academy of Sciences criticised the presentation in Wonderful Life, saying that the "reinterpretation [of Pikaia as a chordate] became almost universally accepted after its unqualified and forceful endorsement by Gould"; concluding that "the cephalochordate affinity of Pikaia is at best only weakly indicated by the characters visible in fossils discovered so far." In 2010, an international team of palaeontologists argued that Pikaia has sufficiently invertebrate characters, and that it mostly look like a much younger extinct animal, the Tully monster (Tullimonstrum gregarium), which is still debated as either an invertebrate or a chordate. Another component of Pikaia fossils that constrains the animal to be accepted as a chordate is its distinct invertebrate character; its preservational mode suggests that it had cuticle. The cuticle as a body covering is uncharacteristic of the vertebrates, but is a dominant feature of invertebrates.