Restudy of some plectronocerid nautiloids (Cephalopoda) from the late Cambrian of China; discussion on nautiloid evolution and origin of the siphuncle

ABSTRACT

The sub-class Nautiloidea is divided into two super-orders, Nautilosiphonata and Calciosiphonata, based on different structural types of the connecting rings.

The late Cambrian order Plectronocerida has the calciosiphonate type of connecting ring similar to that in post-Cambrian orthocerids. It is structurally more complex than the nautilosiphonate connecting ring in late Cambrian ellesemerocerid-like nautiloids. The plectronocerid nautiloids, therefore, evolved from the ellesmerocerid-like nautiloids and not vice versa. As indicated by the complex siphuncular structure in plectronocerids, cephalopod evolution began earlier than previously estimated, probably in the early Cambrian. The siphuncle in cephalopods originated from a calcareous septum that became partially non-calcified and formed the connecting ring.

KEYWORDS:

• Late Cambrian
• China
• calciosiphonates
• plectronocerid nautiloids
• ellesmerocerid-like nautiloids
• siphuncular structure
• cephalopod evolution
• origin of siphuncle

Acknowledgments

The author thanks Dr. Xiang Fang, Nanjing Institute of Geology and Palaeontology for valuable contributions, Dr. Steve Mclouglin and Dr. Christian Skovsted, Swedish Museum of Natural History, Stockholm, for improvement of the manuscript, and the two reviewers, Dr. Björn Kröger, Finnish Museum of Natural History, Helsinki University, and an anonymous reviewer for valuable suggestions.

Disclosure Statement

No potential conflict of interest was reported by the author.