Development and trunk segmentation of early instars of a ptychopariid trilobite from Cambrian Stage 5 of China.
Many three-dimensionally preserved exoskeletons found from the middle Cambrian (Stage 5) Gaotai Formation in Guizhou, southern China, have been assigned to the ptychopariid trilobite Gunnia sp. They represent mainly a series of early instars, exhibiting some delicate structures and morphological variation associated with their trunk segmentation and early development. Morphometric and statistical analyses indicate that the transverse joint appears to occur with the full growth of the third axial ring of the protopygidium, which increases in size much more rapidly than its corresponding protocephalon with growth. The 'one by one' sequential release of thoracic segments from a transitory pygidium does not progress exactly in accordance with the development of the pygidial axis, whose axial rings increase at a relatively faster rate, and an 'immature ring' always appears initially at the rear end of the axis. These new data set up a testable model for revealing trilobite segmentation and provide fresh insights into the development, evolution and taphonomic surroundings associated with the Cambrian trilobites.
1] Key Laboratory for Palaeobiology, Yunnan University, Kunming, Yunnan 650091, China [2] Faculty of Land Resources Engineering, Kunming University of Science and Technology, Kunming, Yunnan 650091, China.
Cen
C
Shen
School of Geosciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK.
Euan N K
EN
Clarkson
Key Laboratory for Palaeobiology, Yunnan University, Kunming, Yunnan 650091, China.
Jie
J
Yang
Key Laboratory for Palaeobiology, Yunnan University, Kunming, Yunnan 650091, China.
Tian
T
Lan
Key Laboratory for Palaeobiology, Yunnan University, Kunming, Yunnan 650091, China.
Jin-bo
JB
Hou
Key Laboratory for Palaeobiology, Yunnan University, Kunming, Yunnan 650091, China.
Xi-guang
XG
Zhang
D000818:Animals; D002681:China; D005580:Fossils; D010163:Paleontology