Rahman Imran A, Waters Johnny A, Sumrall Colin D, Astolfo Alberto
School of Earth Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
Department of Geology, Appalachian State University, Boone, NC 28608, USA.
Biol Lett. 2015 Oct;11(10). doi: 10.1098/rsbl.2015.0776.
Inferring the development of the earliest echinoderms is critical to uncovering the evolutionary assembly of the phylum-level body plan but has long proven problematic because early ontogenetic stages are rarely preserved as fossils. Here, we use synchrotron tomography to describe a new early post-metamorphic blastoid echinoderm from the Carboniferous (approx. 323 Ma) of China. The resulting three-dimensional reconstruction reveals a U-shaped tubular structure in the fossil interior, which is interpreted as the digestive tract. Comparisons with the developing gut of modern crinoids demonstrate that crinoids are an imperfect analogue for many extinct groups. Furthermore, consideration of our findings in a phylogenetic context allows us to reconstruct the evolution and development of the digestive system in echinoderms more broadly; there was a transition from a straight to a simple curved gut early in the phylum's evolution, but additional loops and coils of the digestive tract (as seen in crinoids) were not acquired until much later.
推断最早的棘皮动物的发育情况对于揭示门级身体结构的进化组装至关重要，但长期以来一直存在问题，因为早期个体发育阶段很少以化石形式保存下来。在这里，我们使用同步加速器断层扫描技术来描述一种来自中国石炭纪（约3.23亿年前）的新的变态后早期芽球棘皮动物。由此产生的三维重建揭示了化石内部的一个U形管状结构，它被解释为消化道。与现代海百合发育中的肠道进行比较表明，海百合对于许多已灭绝的类群来说并不是一个完美的类似物。此外，在系统发育背景下考虑我们的发现，使我们能够更广泛地重建棘皮动物消化系统的进化和发育；在该门的进化早期，消化道从直的转变为简单的弯曲，但消化道的额外环和盘绕（如海百合中所见）直到很久以后才出现。
