Placodermi phylogeny

From Palaeos

Gnathostomata
`--o PLACODERMI
   | ?--Stensioella
   | ?--Pseudopetalichthyida
   `==Acanthothoraci (paraphyletic)
      |--Rhenanida
      |--Antiarchi
      `--+--Ptyctodontida
         |--Petalichthyida
         `--Arthrodira
            `--Phyllolepida

Placoderm phylogeny and the interrelations between the different taxa remain highly controversial because of the high degree of parallelism and the difficulty of telling which are the primitive and which the derived traits. The following are several different cladograms and phylogenetic trees that have been proposed for this group.

Most authors consider the antiarchs and arthrodires closely related because they share a single pair of paranuchal plates. Goujet however places them each in distinct clades. Acanthothoracids are usually considered as primitive rhenanids or sister taxa therof (Miles and Young 1977, Long 1995), but Goujet (1984) considers them a basal assemblage of placoderms. Ptyctodontids are sometimes considered the most primitive taxon (Miles and Young 1977, Gardiner 1984, Long 1995), and have a number of features in common with Chondrichthyes (Long 1995), but also share characters with the petalichthyids (Janvier 1996), and are placed by Goujet (1984) in a sister taxon to arthrodires. Phyllolepids have been considered close to arthrodires, and now seem to be included in that clade, with wuttagoonaspids transitional between the two (Long 1995). The poorly known Stensioella and pseudopetalichthyids are considered basal forms by Denison (1978), and primitive, but not the most basal by Gardiner (1984), but their placoderm status is rejected by Janvier (1996). In short, there semes to be little consensus concering many aspects of placoderm phylogeny.

[edit] Phylogenies

Miles and Young 1977:

--+--Ptyctodontida
  `--+--+--+--Pseudopetalichthyida
     |  |  `--+--Acanthothoraci
     |  |     `--Rhenanida
     |  `--+--Petalichthyida
     `--+--Phyllolepida
        `--+--Antiarchi
           `--Arthrodira

Denison 1978:

--+--Stensioellida
  `--+--Pseudopetalichthyida
     `--+--Rhenanida
        `--+--Ptyctodontida
           `--+--Acanthothoraci
              `--+--Petalichthyida
                 `--+--Phyllolepida
                    `--+--Arthrodira
                       `--Antiarchi

Goujet 1984:

--+--o--o--+--Romundina
  |  |  |  |--Brindabellaspis
  |  |  |  `--Palaeacanthaspis
  |  |  `--Antiarchi
  |  `--o--+--Radotina kosorensis
  |     |  |--Radotina tesselata
  |     |  |--Kosoraspis
  |     |  `--Kimapsis
  |     `--Rhenanida
  `--o--"Radotina" prima
     `--+--o--Ptyctodontida
        |  `--Petalichthyida
        `--+--Arthrodira
           `--Phyllolepida

Gardiner 1984

--+--Ptyctodontida
  `--+--+--Gemuendinidae (Rhenanida)
     |  `--Stensioella
     `--+--Pseudopetalichthyida
        `--+--Palaeacanthaspidae
           `--+--Brindabellaspis
              `--+--Petalichthyida
                 `--+--Phyllolepida
                    `--+--Arthrodira
                       `--Antiarchi

Long 1995:

--+--Ptyctodontida
  `--+--Pseudopetalichthyida
     `--+--+--Acanthothoraci
        |  `--Rhenanida
        `--+--Petalichthyida
           `--+--Antiarchi
              `--+--Arthrodira
                 `--Phyllolepida

Janvier 1996 (based on Goujet 1984):

--+--o--o--Romundina
  |  |  `--Antiarchi
  |  |     |--Yunnanolepidoidei
  |  |     `--+--Procondylolepiformes
  |  |        `--+--Sinolepidae
  |  |           `--Euantiarcha
  |  `--o--Radotina kosorensis
  |     `--Rhenanida
  `--o--"Radotina" prima
     `--+--o--Ptyctodontida
        |  `--Petalichthyida
        `--Arthrodira
           |--Actinolepidoidei
           |  |--Actinolepida
           |  `--+--Wuttagoonaspida
           |     `--Phyllolepida
           `--Phlyctaenioidei
              |--Phlyctaenii
              `--+--Brachythoraci
                 `--+--Gemuendaspis
                    `--+--Holonema
                       `--+--Migmatocephalia
                          `--Eubrachythoraci
                             |--Coccosteomorphi
                             `--Pachyosteomorphi

Johanson and Smith 2003, after Goujet 2001

--+--+--Acanthothoraci
  |  `--Rhenanida
  `--+--Antiarchi
     |  |--Yunnanolepidoidei
     |  `--Euantiarcha
     `--+--Ptyctodontida
        `--Arthrodira
           |--Actinolepida
           `--+--Phlyctaenii
              `--Brachythoraci

Mikko's Phylogeny - [After Carroll, 1988 and Goujet, 2001 [from Johanson, 2003] - some problematic taxa excluded, see original page for full tree)

<==o Placodermi (placoderms; panssarihait)
  |?- †Brindabellaspis stensioi Young, 1980 [Brindabellaspida Gardiner, 1993]
  |-- †Stensioella heintzi [Stensioellida: Stensioellidae:; Stensionelliformes]
  `--+-- †Ptyctodontidae [Ptyctodontida; Ptyctodontiformes]
     `--+--o †Paraplesiobatidae [Pseudopetalichthyida; Pseudopetalichthyiformes]
        |  |-- †Paraplesiobatis
        |  `--o †Pseudopetalichtbys [Parapetalichthys)
        |     `-- †P. problematica
        `--+--+-- †Acanthothoraci Stensiö, 1944 [Acanthothoraciformes]
           |  `-- †Rhenanida [Rhenaniformes]
           `--+-- †Macropetalichthyidae [Petalichthyida; Petalichthyiformes]
              `--+-- †Antiarcha [Antiarchiformes; Antiarchi]
                 `--+-- †Phyllolepida [Phyllolepiformes]
                    `-- †Arthrodira Woodward, 1891 

[edit] References

• Carroll, R. L., 1988: Vertebrate paleontology and evolution. W. H. Freeman and company, New York, 1988,
• Johanson, Z., 2003: Placederm branchial and hypobranchial muscles and origin in jawed vertebrates. Journal of Vertebrate Paleontology: Vol. 23, #4, pp. 735-749
• Long, J. A., 1995: The Rise of Fishes: 500 million years of evolution. Johns Hopkins University Press, Baltimore & London, pp. 1-223
• Smith, M. M. & Johanson, Z., 2003: Separate Evolutionary Origins of Teeth from Evidence in Fossil Jawed Vertebrates. Science: Vol. 299, pp. 1235-1236

[edit] Credits

MAK061009, additional material MAK062110, Mikko's tree © Mikko Haaramo 2004, 2005