March 4, 2016
Research Highlight
Hydroids or Hemichordates?
A recent study indicates that some Palaeozoic hydroids identified in the fossil record may actually be hemichordates.
A recent study indicates that some Palaeozoic hydroids identified in the fossil record may actually be hemichordates.
Hydroids are the polyp stage of aquatic invertebrates known as hydrozoan cnidarians. These organisms can be found in a number of environments on Earth today, but their hydroids are rare in the fossil record. Most hydroids from ancient hydrozoan cnidarians lack a biomineralized skeleton, and therefore are often not preserved as fossils. These hydroids can also appear similar to other organisms known as hemichordates, both in terms of their morphology and their ecology.
Putative hydroids from hydrozoan cnidarians have been identified in Palaeozoic rocks, but the new study indicates that these fossils may require reinterpretation.
Previous studies have shown that techniques used to study fossils at very fine scales can help interpret those that would otherwise be problematic to identify. This includes techniques like backscattered electron scanning electron microscopy (BSE-SEM) and energy-dispersive X-ray spectroscopy (EDS). BSE-SEM has been used previously to distinguish between hemichordates and organisms including algae. EDS has been used to study possible Precambrian sponge fossils. The new research demonstrates that these in situ nanoscale analytical techniques can also help distinguish between hydrozoans and hemichordates.
The results suggest that previous interpretations of hydroid fossils need to be tested and refined by characterizing the fossils at the nanoscale.
The research was supported in part by the Exobiology & Evolutionary Biology element of the NASA Astrobiology Program. The study, “The hydroid fossil record and analytical techniques for assessing the affinities of putative hydrozoans and possible hemichordates,” was published in the journal Palaeontology.