Palaeontological research can yield an amazing amount of information about the lives of long-dead organisms, as specific as the last meal consumed, the colour of feathers or the precise depth at which a marine organism lived. However, there are some fossils that defy classification, whether because their remains are incomplete, they don’t bear a resemblance to any known form of life or they are just plain weird.

There is a detailed vocabulary used to describe organisms which defy classification and a system of nomenclature to denote confidence limits on probable or speculative affinities, but they are generally grouped together as “problematica”. A handy grab-bag of misfits that have exasperated or eluded scientists, ready for future generations to have a go at. In museums, problematica specimens reside in drawers and cabinets equivalent to the ubiquitous drawer of odds and sods that most people have in the kitchen. You know the one. The one where chopsticks, elastic bands and watch batteries go.

In palaeobiology, fossils are assigned to problematica for a number of different reasons. Sometimes fossil preservation is poor, meaning that identification can’t be resolved. Alternatively, isolated bits of a long-dead body are classified as separate organisms until a complete fossil is found. Lastly, especially with specimens from deep time, fossils bearing no resemblance to any organisms known today are shelved as problematica or perpetually bounced from group to group.

There are some well-known examples of cold case problematica in palaeontology that have been resolved (or come closer to resolution) through re-examination of material or discovery of key fossils. In 2016, Tully Monster was finally given a place in the tree of life, although debate still rages on. Perhaps the best known examples are conodonts, known from microscopic “teeth” elements that had been identified as everything from algae to molluscs. The discovery of fossils with these elements associated with each other led to a jawless eel-like chordate (the major group of animals that includes vertebrates) affinity (Briggs et al 1983).

Interestingly, even if there isn’t consensus around the evolutionary relations and identification of these problematica, they can still be of use in the palaeontological record. Many probematica are useful as index fossils, used to define and delineate boundaries in the geological time scale.



Here’s a not-quite A-Z of palaeontological problematica of some of the better known examples or poorly known organisms. I’ll be honest, sourcing images of these has been problematic (ha) in itself so I’ll describe them using words.

Acritarchs is the name given to microfossils (microproblematica) that truly represents a dumping ground of any number of odd organic tiny structures which aren’t easily recognised as something else. Acritarchs represent some of the earliest evidence of life on Earth. They likely represent biological flotsam and jetsam of organic matter from single celled organisms, algae as well as bits from animals. The etymology of acritarchs comes from the Greek meaning confused origin. Imagine tiny biscuit crumbs in all shapes and sizes.

Amiskwia The famous Burgess Shale, rocks which bear exceptionally preserved fossils from around 500m years ago, offers an amazing insight into the diversity of life at the time including rare soft-bodied fossils and predictably a number of problematica. Two species of Amiskwia are unusual in that the whole animal has been preserved, including what has been interpreted as a brain, yet still defies classification. Molluscan, arrow worm and ribbon worm affinities have been suggested as well as the possibility that it represents an entirely new but now extinct group of animals altogether. Looks like a slug with a moustache and wing flaps.

Cambroclaves These unusual fossils from the Cambrian of China resemble a disc with a striated spike coming out of them (Conway Morris and Chen 1991). Some have been found articulated with each other presumably forming a chainmail-like covering for some kind of as yet unknown organism.

Dinomischus Another organism known from the Burgess Shale as well as from older deposits in China. Two species are described. Resembling a flower with plate petals, a long stem and a body shaped like a cup. Superficially, it resembles extant sponges, crinoids, sea squirts and animals called entoprocts but for the time being it remains unclassifiable.

Gluteus minimus Sharing a name with one of the muscles in the human hip, but more likely a pun on gluteus maximus (but small), these strange bum-shaped fossils from the Upper Devonian of Iowa could be fish teeth. Or brachiopods. Or something else altogether (Davis and Semken 1975).

Libodiscus ascitus With a name that means alien teardrops you know you’re in for a treat. Strange fossils known from a single locality from the Carboniferous and Devonian of Canada. Could have been marine or terrestrial or airborne (Conway Morris et al. 1991). Looks like a teardrop with a cell coat on.

Nannoconus An example of stratigraphically useful fossils although their identification remains problematic. These tiny vase or bell-shaped microfossils resemble the lorica of tintinnids suggesting a possible ciliate relationship and I don’t know what that means either. Nothing to do with Tintin either apparently.

Nectocaris pteryx This weirdo is known from Chinese, Canadian and Australian Cambrian deposits. Known from only one specimen until 2010, when a further 91 specimens were described, the animal resembles an armless cuttlefish with two long large tentacles and even possessed a funnel, like that in modern cephalopods. Others have suggested an arthropod affinity with some striking similarities to modern soft-bodied cephalopods but the debate continues.

“Small shellies” or small shelly fauna. Much like the arcritarchs, small shellies is the name given to a whole host of problematic early “shelled” remains likely representing parts from many different groups of organisms but bundled together for ease of reference. Although difficult to interpret, small shellies may hold the key to understanding the origins of shelled and biomineralised groups of animals. Forms resemble tubes, vases, stacked cups, caps, stars and hooks. Examples like Kimberella and helcionellids have been floated as early molluscs. Or jellyfish. Or something else.

Trilobozoa Trilobozoans are an enigmatic group of animals from the Ediacaran, which includes some of the oldest known multi-cellular organisms. Trilobozoa is a contested group of animals which show tri-radial symmetry which has lead some authorities to link them to cnidarians, the group that includes jellyfish, corals and anemones. Even if their true relationships are unknown there is a multi-layered classification system with a couple of families and numerous ‘species’ described. They look like bread rolls stamped with the Isle of Man triskelion and yeah I know the comparitor is almost as esoteric as the fossils in the first place.

Unifissurinella boulangeri Strange microproblematica from the Eocene of France faintly resembling a calzone pizza but tiny. Named after Bifissurinella, which looks similar but has two of something rather than one. Bifissurinella was problematica but is now referred to as a bryozoan, so perhaps Unifissurinella is too (Poignant 1991).

Westgardia gigantea Known from a single specimen from the Cambrian of California. As the name implies it’s larger than organisms of the same age at a whopping 6cm long, but what it is is currently unknown (Rowland and Carlson 1983). It looks like stone with a kink in it.

The very name problematica highlights how these organisms, like many aspects of biological life defy the human endeavour to nicely label, file and identify the world around us and the world of the past. Long may problem specimens like these irritate palaeontologists, museum curators and Wikipedia editors.

References & further reading



Briggs, D. E. G.; Clarkson, E. N. K. and Aldridge, R. J. 1983. “The conodont animal”. Lethaia. 16 (1): 1–14.

Bronimann, P. 1955. Microfossils incertae sedis from the Upper Jurassic and Lower Cretaceous of Cuba. Micropaleontology, vol. 1, no. 1, pp. 28-51,

Conway Morris, S and Menge, C. 1991. Cambroclaves and Paracarinachitids, early skeletal problematica from the Lower Cambrian of South China. Palaeontology 34(2); 357-397

Conway Morris, S.; Savoy, L. E. and Harris, A. G. 1991. An enigmatic organism from the ‘Exshaw’ Formation (Devonian-Carboniferous), Alberta, Canada. Lethaia, 24: 139-152

Davis, R. A. and Semken Jr., H. A. 1975. Fossils of uncertain affinity from the Upper Devonian of Iowa. Science. 24;187(4173):251-4.

Landing, E. and Bartowski, K. E. 1996. Oldest Shelly Fossils from the Taconic Allochthon and Late Early Cambrian Sea-Levels in Eastern Laurentia. Journal of Paleontology. 70(5): 741-761



Poignant, A. 1991. Unifissurinella, New Genus of Microproblematica from the Upper Eocene of Southwestern France. Micropaleontology, 37(1); 95-97

Rowland, S. M. and Carlson, S. J. 1983. Westgardia gigantea, a New Lower Cambrian Fossil from Eastern California. Journal of Paleontology, 57(6); 1317-1320



J. J. Sepkoski. 2002. A compendium of fossil marine animal genera. Bulletins of American Paleontology 363:1-560

