Phylogeny of Cephalopoda

• Extinct taxa - prolific and diverse; paleontologists are able to identify three distinct fossil clades that are entirely extinct
• Three distinct taxa: Endoceratoidea,

  Actinoceratoidea, and Bactritoidea

  
• Members are entirely extinct and

  information is only based on fossil

  records
• Members are squid-like that have

  external shells called orthocones
• Flourish in Paleozoic era
• Orthoconic shell- straight shells
• Other cephalopods found in the fossil records

  are Nautiloids, Ammonoids, and Belemnites
• Nautiloids

  • early forms were believed to be orthoconic shells later on with rapid diversification, evolved into planispiral shells (coiled in the single plane)
• Nautiloids

  • Shells have nacreous layers and are interconnected internally, having the presence of an internal chamber
• Ammonoids

  • Exhibit generally similar features as nautiloids only differ in the location of siphuncle and the shape of their sutures (undulate)
• Belemnites

  • Considered the ancestors of coleoidea (groups of squid and cuttlefish, and octopus)
• Belemnites

  • Not well represented on the fossil records
• Belemnites

  • Have internal skeleton: reduced in size and often lack calcification
• Superorder Decabrachia : 10-(groups that have

  8 arms and 2 tentacles) – squid and cuttlefish

  • Sepiodea
  • Teuthoidea
• Superorder Octopodiformes: 8- (groups that

  have 8 arms)

  • Vampyromorpha
  • Octopoda
• The position of the siphuncle in ammonoids is

  at the edge of the shell (C: left) and nautiloids

  are in the center of the shell (D: right), with

  simple sutures

  
• Sutures- contact line between the septa

  (chamber walls) and inner shell wall
• BASIC ANATOMY OF BELEMNITE

  • Squid-like
  • Have an internal orthoconic shell divided into three parts: proostracum, phragmocone, and rostrum or guard (bullet-shape, highly resistant part)

  
• • Same with Cladogram A but does not include the three extinct group
  • Ammonoidea- extinct, shelled
  • Nautiloidea – with only one shelled genus (nautilus), slow-moving, deep-water animals

  
• Coleoidea – common includes squid, cuttlefish,

  octopuses, rams, and horned squid (Spirula

  spirula)

  • Considered as a Subclass