Kilodaulids

Kilodaulids are a proposed clade of enigmatic marine invertebrates known only from fossil impressions dating to the late Precambrian through the early Paleozoic. The group is defined by a combination of soft-bodied preservation and repetitive dorsal elements, but the exact anatomy is poorly understood due to incomplete fossils. The name kilodaulid reflects historical descriptions of their "cell-like" plates and segmented appearance, though etymology varies by author.

Taxonomy and phylogeny: Kilodaulids occupy a disputed position in the animal family tree. Some workers have recovered them as stem metazoans, others as stem-group annelids or as a separate lineage of early ecdysozoans. The absence of clear diagnostic soft parts makes robust placement difficult, and classifications have shifted with new discoveries and methods.

Morphology: Across specimens, kilodaulids display a slender to rounded body plan with a succession of paired ossicles or plates along the dorsal surface and a tapering posterior. Limb-like appendages are variably preserved. Soft tissues are rarely preserved, leaving many details speculative.

Ecology and life history: Most reconstructions suggest a benthic, slow-moving lifestyle, possibly grazing or filter-feeding microbe-rich substrates. Some models allow a more sessile, encrusting habit on hard substrates.

Distribution and preservation: Kilodaulid fossils have been recovered from several palaeocontinents in rocks ranging from late Precambrian deposits to early Paleozoic formations, with exceptional preservation in Lagerstätten.

Significance: As an enigmatic, poorly preserved group, kilodaulids highlight early experimentation in animal body plans and illustrate ongoing challenges in resolving early metazoan phylogeny.