Early post-metamorphic, Carboniferous blastoid reveals the evolution and development of the digestive system in echinoderms.
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.
School of Earth Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK imran.rahman@bristol.ac.uk.
Imran A
IA
Rahman
Department of Geology, Appalachian State University, Boone, NC 28608, USA.
Johnny A
JA
Waters
Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, USA.
Colin D
CD
Sumrall
Swiss Light Source, Paul Scherrer Institut, Villigen 5232, Switzerland.
Alberto
A
Astolfo
D000818:Animals; D005075:Biological Evolution; D002681:China; D004447:Echinodermata / Q000033:anatomy & histology* / Q000254:growth & development; D005580:Fossils; D041981:Gastrointestinal Tract / Q000033:anatomy & histology / Q000254:growth & development; D010802:Phylogeny
blastoids; development; echinoderms; evolution; synchrotron tomography