Antiarch placoderms: pelvic girdles before jaws? No.

Zhu et al. 2012
report that “An antiarch placoderm (Fig. 1) shows that pelvic girdles arose at the root of jawed vertebrates.” They are wrong according to the the large reptile tree (LRT, 1697+ taxa).

Contra Zhu et al. 2012,
jaws were just disappearing, not just appearing, in this taxon. Pelvic fins and their pelvic anchors are known in many more primitive taxa in the LRT.

Taxon exclusion, once again,
rises to the top of paleontological sins (of omission).

Figure 1. Parayunanolepis, an antiarch placoderm and the subject of the Hu et al. paper.

Figure 1. Tiny Parayunanolepis, an antiarch placoderm and the subject of the Zhu et al.2012 paper, shown more than 2x life size.

From the Zhu et all. 2014 abstract:
“To date, it has generally been believed that antiarch placoderms (extinct armoured jawed fishes from the Silurian–Devonian periods) lacked pelvic fins. Parayunnanolepis xitunensis represents the only example of a primitive antiarch with extensive post-thoracic preservation, and its original description has been cited as confirming the primitive lack of pelvic fins in early antiarchs. Here, we present a revised description of Parayunnanolepis and offer the first unambiguous evidence for the presence of pelvic girdles in antiarchs.”

Figure 2. Subset of the LRT focusing on catfish + placoderm clade.

Figure 2. Subset of the LRT focusing on catfish + placoderm clade.

By contrast,
in the LRT tiny  Parayunnanolepis nests with the much larger Bothriolepis, a highly derived placoderm. Several taxa preceding these two have pelvic fins and jaws.

A valid cladogram
is the most important tool in recovering the order of gradually accumulating traits.

Earlier you may remember,
placoderms arose from ordinary fish, not the other way around. The LRT has reordered many tree branches, all due to taxon inclusion. In this fashion the LRT helps recover overlooked hypothetical interrelationships.

References
Zhu M, Yu X-B, Choo B, Wang J-Q and Jia L-T 2012. An antiarch placoderm shows that pelvic girdles arose at the root of jawed vertebrates. Biology Letters Palaeontology 8:453–456.

 

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