A Silurian placoderm with osteichthyan-like marginal jaw bones.
The gnathostome (jawed vertebrate) crown group comprises two extant clades with contrasting character complements. Notably, Chondrichthyes (cartilaginous fish) lack the large dermal bones that characterize Osteichthyes (bony fish and tetrapods). The polarities of these differences, and the morphology of the last common ancestor of crown gnathostomes, are the subject of continuing debate. Here we describe a three-dimensionally preserved 419-million-year-old placoderm fish from the Silurian of China that represents the first stem gnathostome with dermal marginal jaw bones (premaxilla, maxilla and dentary), features previously restricted to Osteichthyes. A phylogenetic analysis places the new form near the top of the gnathostome stem group but does not fully resolve its relationships to other placoderms. The analysis also assigns all acanthodians to the chondrichthyan stem group. These results suggest that the last common ancestor of Chondrichthyes and Osteichthyes had a macromeric dermal skeleton, and provide a new framework for studying crown gnathostome divergence.
Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China. zhumin@ivpp.ac.cn
Min
M
Zhu
Xiaobo
X
Yu
Per Erik
PE
Ahlberg
Brian
B
Choo
Jing
J
Lu
Tuo
T
Qiao
Qingming
Q
Qu
Wenjin
W
Zhao
Liantao
L
Jia
Henning
H
Blom
You'an
Y
Zhu
D000818:Animals; D002681:China; D005399:Fishes / Q000033:anatomy & histology* / Q000145:classification*; D005580:Fossils; D007568:Jaw / Q000033:anatomy & histology*; D010802:Phylogeny; D013045:Species Specificity