1. Early Life Institute and Department of Geology, Northwest University, Xi'an, 710069, People's Republic of China
2. Yunnan Institute of Geological Sciences, 131 Baita Road, Kunming, People's Republic of China
3. Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK
4. Institute of Vertebrate Palaeontology & Palaeoanthropology, Chinese Academy of Sciences, Beijing, 100044, People's Republic of China

Correspondence to: D-G. Shu¹ Correspondence and requests for materials should be addressed to D-G.S. (e-mail: Email: dgshu@sein.sxgb.com.cn).

Abstract

The first fossil chordates are found in deposits from the Cambrian period (545–490 million years ago), but their earliest record is exceptionally sporadic and is often controversial. Accordingly, it has been difficult to construct a coherent phylogenetic synthesis for the basal chordates. Until now, the available soft-bodied remains have consisted almost entirely of cephalochordate-like animals from Burgess Shale-type faunas. Definite examples of agnathan fish do not occur until the Lower Ordovician (475 Myr BP), with a more questionable record extending into the Cambrian. The discovery of two distinct types of agnathan from the Lower Cambrian Chengjiang fossil-Lagerstätte is, therefore, a very significant extension of their range. One form is lamprey-like, whereas the other is closer to the more primitive hagfish. These finds imply that the first agnathans may have evolved in the earliest Cambrian, with the chordates arising from more primitive deuterostomes in Ediacaran times (latest Neoproterozoic, 555 Myr BP), if not earlier.