At 00:00 a.m. on December 27, contemporary biology, a subsidiary of the World Authoritative Journal and a subsidiary of the American "Cell" Publishing Group, published online in the form of research newsletters Zhai Dayou, Liu Yu, Hou Xianguang, and Dr. Javier Ortega-Hernández of Cambridge University, Dr. Joanna Wolfe of the Massachusetts Institute of Technology, Engineer Cao Chunjie, senior senior application expert of Carl Zeiss X-ray microscopy, co-completed a research paper entitled "Three-dimensional preserved appendages of a pan-crustacean in the Early Cambrian".
Arthropods are the most diverse animal phylum on Earth from the Cambrian period to date, and pan-crustaceans (collectively referred to as an evolutionary single-lineage group of insects and crustaceans) are the most prosperous group of arthropods. Although scientists have calculated based on DNA molecular clocks that pan-crustaceans have appeared in the Early Cambrian, the relevant fossil evidence has long been limited to larvae preserved in Early Cambrian phosphate fossils and fragments preserved in middle and late Cambrian small carbon fossils, and the key identification characteristics of the adult morphology of early pan-crustaceans and their maturity status have been mystery. Fossils of ercaicunia multinodosa from the Chengjiang biota in Yunnan, China, provide evidence to unravel the mystery.
The multituchocephal villageworm is an arthropod with a pair of crusts and a fishtail-like tail that was discovered and reported in the 1990s. Based on traditional research methods, the academic community's cognition of it is limited to the external morphology of the shell, the back of the trunk and the tail, and due to the covering of the shell and the embedding of the surrounding rock, the details of its appendages have been unknown, so its taxonomy and evolutionary attribution have been suspenseful.
Using three-dimensional X-ray imaging (microCT) with an accuracy of microns, this study observed 20 well-preserved pairs of appendages and their stunning morphological details through the thick shell and surrounding rock.
In addition, this study also reveals for the first time the structure of this class of arthropods surrounded by three pieces of bone. Among the many characteristics of the multi-segment ear material village worm revealed by the cutting-edge technology of micro-CT, the second antennae, the specialized large jaw and the small jaw, and the "upper limb" structure on the appendage hip node are the main identification characteristics of pan-crustaceans, which is the final sound for the identification of multi-section ear wood village insects as the distant ancestors of pan-crustaceans.
This study not only confirms that the procrustaceans originated in the Early Cambrian, but also shows that the specialization of the second antennae and mouth appendages, and the formation of the upper limbs, occurred at the beginning of the separation of the pan-crustaceans from other primitive taxa of arthropods.
Since its discovery by researcher Hou Xianguang in the 1980s, the Chengjiang Biota, a "World Natural Heritage", has produced a large number of exquisite fossils that are amazed by the world, providing one precious material after another for studying the early evolution of many animal phyla and studying the process and mechanism of the "Cambrian explosion".
For a long time, the morphological observation of Chengjiang animal fossils has been mainly limited to the superficial and two-dimensional observation using traditional imaging techniques such as optical microscopy, and the morphological characteristics buried inside fossil specimens have rarely been involved.
Since 2014, researchers represented by Liu Yu, a researcher at the Key Laboratory of Paleontology Research in Yunnan Province, Yunnan University, have innovatively applied the technology of microscopic CT to the study of Chengjiang fossils, revealing a large number of unprecedented and important morphological characteristics, so that the study of Chengjiang animal fossils, especially the study of Chengjiang arthropod fossils, has entered a new stage of revolutionary understanding of morphological information obtained from two-dimensional to three-dimensional.