Adding taxa updates the origin of placoderms

Figure 1. Updated (2022) subset of the LRT focusing on placoderms.

Figure 1. Updated (2022) subset of the LRT focusing on placoderms.

Updated June 27, 2022
with a renesting of many placoderms close to galeapsids near the base of the Vertebrata. These developed jaws by convergence with gnathostomes. Ptyctodontida continue to nest with catfish in the LRT (2119 taxa in 2022).

The LRT divides placoderms into three clades;

  1. Arthrodira (open ocean predators like Dunkleosteus, Coccosteus, Fig. 3)
  2. Antiarchi (armored jawless bottom dwellers like DicksonosteusBothriolepis, Fig. 2)
  3. Phyllolepida (tiny-eye taxa like Entelognathus, Cowralepis)

Several traditional placoderms nest elsewhere in the LRT.

  1. Rhenanida – nests with manta rays in the LRT
  2. Wuttagoonaspis – nests with catfish in the LRT
  3. Stensioellida – nests with Guiyu-like lobefins in the LRT
  4. Brindabellspida – nests with the tetrapodomorph Elpistostege in the LRT
  5. Ptyctodontida (chimaera-like taxa like Australoptyctodus, nest with catfish in the LRT)

Several traditional placoderms have not yet been tested in the LRT.

  1. Petalichthyida (includes Diandongpetalichthys)
  2. Acanththoraci (closely related to rhenanids, nesting with manta rays)
  3. Pseudopetalichthyida (similar to rhenanids, nesting with manta rys)

Ptyctodonts, like Austroptyctodus,
(Fig. 2) do not nest with other traditional placoderms in the LRT, but nest closer to Cheirodus. These are the sort of results the LRT recovers only because it tests more taxa.

Carr RK, Johanson Z and Ritchie A 2009. The phyllolepid placoderm Cowralepis mclachlani: Insights into the evolution of feeding mechanisms in jawed vertebrates. Journal of Morphology. 270 (7): 775–804.
Hu Y, Lu J and Young GC 2017. New findings in a 400 million-year-old Devonian placoderm shed light on jaw structure and function in basal gnathostomes. Nature Scientific Reports 7: 7813 DOI:10.1038/s41598-017-07674-y
Miles RS and Young GC 1977. 
Placoderm interrelationships reconsidered in the light of new ptyctodontids from Gogo Western Australia. Linn. Soc. Symp. Series 4: 123-198.
Young GC 1980. A new Early Devonian placoderm from New South Wales, Australia, with a discussion of placoderm phylogeny: Palaeontographica 167A pp. 10–76. 2 pl., 27 fig.
Zhu et al. 2012. An antiarch placoderm shows that pelvic girdles arose at the root of jawed vertebrates. Biology Letters Palaeontology 8:453–456.
Zhu M, Yu X-B, Ahlberg PE, Choo B and 8 others 2013. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature. 502:188–193.
Zhu M et al. 2016. A Silurian maxillate placoderm illuminates jaw evolution. Science 354.6310 (2016): 334-336.


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