Kimberella is an extinct genus of marine bilaterian known only from rocks of the Ediacaran period. The slug-like organism fed by scratching the microbial surface on which it dwelt in a manner similar to the gastropods,
Specimens were first found in Australia's Ediacara Hills, but recent research has concentrated on the numerous finds near the White Sea in Russia, which cover an interval of time from . As with many fossils from this time, its evolutionary relationships to other organisms are hotly debated. Paleontologists initially classified Kimberella as a type of cubozoan, but, since 1997, features of its anatomy and its association with scratch marks resembling those made by a radula have been interpreted as signs that it may have been a mollusc. Although some paleontologists dispute its classification as a mollusc, it is generally accepted as being at least a bilaterian. however, the name Kimberia was already in use as a subgenus of Turritella (Gastropoda), according to Dr. N. H. Ludbrook; and a new genus, Kimberella, was proposed by Mary Wade in 1972. in the Ust' Pinega Formation in the White Sea region of northwest Russia, the Kushk Series of central Iran, the Mohyliv Formation in Podolia, Ukraine, and the Kauriyala Formation in the Lesser Himalayan Range region of India. In 2014, Kimberella fossils were found in Brazil, but later studies showed fossils of other Silurian animals. In 2026. Kimberella fossils were reported from the Blueflower Formation of Canada. The White Sea fossils are often associated with the Ediacaran animals Tribrachidium and Dickinsonia, as well as meandering trace fossil trails (possibly made by Kimberella itself), and algae. Beds in the White Sea succession have been dated from 558 to by radiometric dating, using uranium-lead ratios in zircons found in volcanic ash layers that are sandwiched between layers that contain Kimberella fossils. Kimberella fossils are also known from beds both older and younger than this precisely dated range. perhaps by as much as a factor of two. Like many other specimens found in the White Sea, the most common type of symmetry observed appears to be bilateral; with little to no sign of any of the kinds of radial symmetry found in Cnidarians, the group that includes jellyfish, sea anemones and hydras. The Australian fossils were originally described as a type of jellyfish, but this is inconsistent with the bilateral symmetry observed in the fossils. The White Sea fossils and the surrounding sediments also show that Kimberella lived on the surface of the sea-floor. with a minimum length of 2–3 mm. Fedonkin reckons that as it ate, it moved "backwards"; the trail thus created was destroyed by the subsequent grazing activity. Fans of grooves are often found radiating from the "head" end of the organism; these indicate that the organism stayed in one place, and raked the surface of the microbial mat towards it by extension of its head, which bore two "teeth".
The lack of evidence of asexual reproduction suggests that the organisms reproduced sexually. Budding or fission has never been observed.
Classification
thumb|175px|left|[[Kimberichnus teruzzii grazing traces left by Kimberella while it fed]]
All the Kimberella fossils found so far are assigned to one species, K. quadrata. The first specimens were discovered in Australia in 1959. They were originally classified as jellyfish by Martin Glaessner and Mary Wade in 1966,
So far, Kimberella fossils show no sign of a radula, the toothed chitinous "tongue" that is the diagnostic feature of modern molluscs, excluding bivalves. Since radulae are very rarely preserved in fossil molluscs, its absence does not necessarily mean that K. quadrata did not have one. The rocks in the immediate vicinity of Kimberella fossils bear scratch marks that have been compared to those made by the radulae of molluscs as they graze on microbial mats. These traces, named Radulichnus and Kimberichnus, have been interpreted as circumstantial evidence for the presence of a radula. In conjunction with the univalve shell, this has been taken to indicate Kimberella was a mollusc or very closely related to molluscs. In 2001 and 2007, Fedonkin suggested that the feeding mechanism might be a retractable proboscis with hook-like organs at its end. Notably, the scratch marks indicate that the 'teeth' were dragged towards the organism, not pushed away as in molluscs, and that the maximum impact on the sediment was when the mouthpart was furthest from the organism. The direction of grazing is also backwards, as opposed to forwards as in molluscs. It has been argued that the shape of the feeding traces is incompatible with a radula, and that despite the molluscan body form, the lack of a radula places Kimberella well outside the molluscan crown group.
Taken together, sceptics doubt that the available evidence is enough to reliably identify Kimberella as a mollusc or near-mollusc, and suggest that it is presumptuous to call it anything more than a "possible" mollusc, with some authors arguing that there is no clear evidence of Kimberella<nowiki/>'s affinities beyond being an animal.
A possible known relative of Kimberella is Solza margarita from Russia. Some use the grouping "Kimberellomorpha" for those two genera, A few of the Early Cambrian fossils were already known in the mid-19th century, and Charles Darwin saw the apparently sudden appearance and diversification of animals as one of the main objections that could be made against his theory of evolution by natural selection.
The majority of animals more complex than jellyfish and other cnidarians are split into two groups, the protostomes and deuterostomes.