Problematica

@book{briggs1986problematica1,
    author = "Briggs, D. E. G. and Conway Morris, S",
    title = "Problematica from the Middle Cambrian Burgess Shale of British Columbia, in Hoffman, A., and Nitecki, M. H., eds., Problematic Fossil Taxa",
    year = "1986",
    publisher = "New York, Oxford University Press, p. 167-183",
    note = "talkorigins\_source = {true}; raw\_reference = {Briggs, D. E. G., and Conway Morris, S., 1986, Problematica from the Middle Cambrian Burgess Shale of British Columbia, in Hoffman, A., and Nitecki, M. H., eds., Problematic Fossil Taxa: New York, Oxford University Press, p. 167-183.}"
}

@book{rozanov1986problematica2,
    author = "Rozanov, A. Y",
    title = "Problematica of the Early Cambrian, in Hoffman, A., and Nitecki, M. H., eds., Problematic Fossil Taxa",
    year = "1986",
    publisher = "New York, Oxford University Press, p. 87-96",
    note = "talkorigins\_source = {true}; raw\_reference = {Rozanov, A. Y., 1986, Problematica of the Early Cambrian, in Hoffman, A., and Nitecki, M. H., eds., Problematic Fossil Taxa: New York, Oxford University Press, p. 87-96.}"
}

@article{awar1987a,
    author = "A.W.A.R.",
    title = "A. Hoffman \& M. H. Nitecki (eds) 1987. Problematic Fossil Taxa. Oxford Monographs on Geology and Geophysics no. 5. xi + 267 pp. Oxford: Clarendon Press. Price £60.00 (hard covers). ISBN 0 19 503992 0.",
    year = "1987",
    journal = "Geological Magazine",
    url = "https://doi.org/10.1017/s0016756800017532",
    doi = "10.1017/s0016756800017532",
    number = "6",
    pages = "600-601",
    volume = "124"
}

@article{angeli1996some,
    author = "Angeli, Nicholas and Stinchcomb, Bruce L. and Eicks, Patricia",
    title = "Some Cambrian Problematica of the Ozark Uplift",
    year = "1996",
    journal = "The Paleontological Society Special Publications",
    url = "https://doi.org/10.1017/s2475262200000113",
    doi = "10.1017/s2475262200000113",
    pages = "9-9",
    volume = "8"
}

@article{waggoner1996phylogenetic,
    author = "Waggoner, Benjamin M.",
    title = "Phylogenetic Hypotheses of the Relationships of Arthropods to Precambrian and Cambrian Problematic Fossil Taxa",
    year = "1996",
    journal = "Systematic Biology",
    url = "https://doi.org/10.1093/sysbio/45.2.190",
    doi = "10.1093/sysbio/45.2.190",
    number = "2",
    pages = "190-222",
    volume = "45"
}

@article{debrenne2001m,
    author = "Debrenne, Françoise",
    title = "M. H. Nitecki, H. Mutvei, and D.V. Nitecki Receptaculitids: A Phylogenetic Debate on a Problematic Fossil Taxon. 1999. Kluwer Academic/Plenum.",
    year = "2001",
    journal = "Journal of Paleontology",
    url = "https://doi.org/10.1017/s002233600001828x",
    doi = "10.1017/s002233600001828x",
    number = "2",
    pages = "472-472",
    volume = "75"
}

Spines referred to the problematic phosphatic Small Shelly Fossil Mongolitubulus Missarzhevsky, 1977 are described from the Lower Cambrian of Greenland. The type species, M. squamifer, is reported from the Henson Gletscher Formation of North Greenland, while M. henrikseni sp. nov. is described from the Bastion Formation of North-East Greenland. Co-occurring small plates with broken spine bases suggest that Mongolitubulus henrikseni may have been a bivalved(?) arthropod with a carapace bearing multiple spines, but it is uncertain if this restoration can be extended to the type species.

@article{skovsted2001the,
    author = "Skovsted, Christian B. and Peel, John S.",
    title = "The problematic fossil Mongolitubulus from the Lower Cambrian of Greenland",
    year = "2001",
    journal = "Bulletin of the Geological Society of Denmark",
    abstract = "Spines referred to the problematic phosphatic Small Shelly Fossil Mongolitubulus Missarzhevsky, 1977 are described from the Lower Cambrian of Greenland. The type species, M. squamifer, is reported from the Henson Gletscher Formation of North Greenland, while M. henrikseni sp. nov. is described from the Bastion Formation of North-East Greenland. Co-occurring small plates with broken spine bases suggest that Mongolitubulus henrikseni may have been a bivalved(?) arthropod with a carapace bearing multiple spines, but it is uncertain if this restoration can be extended to the type species.",
    url = "https://doi.org/10.37570/bgsd-2001-48-07",
    doi = "10.37570/bgsd-2001-48-07",
    pages = "135-147",
    volume = "48"
}

The Early Cambrian problematic fossil Vetustovermis (Glaessner 1979 Alcheringa 3, 21–31) was described as an annelid or arthropod. Anatomical analysis of 17 new specimens from the Lower Cambrian Maotianshan Shale at Anning, Kunming (South China) does not support its affinities with annelids or arthropods. Anatomical features instead resemble other animal groups including modern flatworms, nemertines and molluscs. The presence of a pelagic slug-like form and ventral foot, as well as a head with eyes and tentacles indicates a possible affinity with molluscs, but these characters are not present only in molluscs; some of them are shared with other animal groups, including flatworms and nemertines. For example, a ventral foot-like structure is found in nemertines, ‘turbellarians’, and some polychaete groups. The well differentiated head is seen in separate bilaterian groups, but among molluscs it did not occur before the evolutionary level of the Conchifera. Unlike the ctenia-gills in molluscs, the gills in Vetustovermis are bar-like. All the characters displayed in this 525 million-year old soft-bodied animal fail to demonstrate clear affinity with molluscs or any other known extant or extinct animal groups, but argue for representing an independently evolved animal group, which flourished in Early Cambrian and possibly in Middle Cambrian time.

@article{chen2005an,
    author = "Chen, Jun-yuan and Huang, Di-ying and Bottjer, David J",
    title = "An Early Cambrian problematic fossil: Vetustovermis and its possible affinities",
    year = "2005",
    journal = "Proceedings of the Royal Society B: Biological Sciences",
    abstract = "The Early Cambrian problematic fossil Vetustovermis (Glaessner 1979 Alcheringa 3, 21–31) was described as an annelid or arthropod. Anatomical analysis of 17 new specimens from the Lower Cambrian Maotianshan Shale at Anning, Kunming (South China) does not support its affinities with annelids or arthropods. Anatomical features instead resemble other animal groups including modern flatworms, nemertines and molluscs. The presence of a pelagic slug-like form and ventral foot, as well as a head with eyes and tentacles indicates a possible affinity with molluscs, but these characters are not present only in molluscs; some of them are shared with other animal groups, including flatworms and nemertines. For example, a ventral foot-like structure is found in nemertines, ‘turbellarians’, and some polychaete groups. The well differentiated head is seen in separate bilaterian groups, but among molluscs it did not occur before the evolutionary level of the Conchifera. Unlike the ctenia-gills in molluscs, the gills in Vetustovermis are bar-like. All the characters displayed in this 525 million-year old soft-bodied animal fail to demonstrate clear affinity with molluscs or any other known extant or extinct animal groups, but argue for representing an independently evolved animal group, which flourished in Early Cambrian and possibly in Middle Cambrian time.",
    url = "https://doi.org/10.1098/rspb.2005.3159",
    doi = "10.1098/rspb.2005.3159",
    number = "1576",
    pages = "2003-2007",
    volume = "272"
}

@article{smith2012cambrian,
    author = "Smith, Andrew B",
    title = "Cambrian problematica and the diversification of deuterostomes",
    year = "2012",
    journal = "BMC Biology",
    url = "https://doi.org/10.1186/1741-7007-10-79",
    doi = "10.1186/1741-7007-10-79",
    number = "1",
    volume = "10"
}

The lower-middle Hetang Formation (Cambrian Stage 2–3) deposited in slope-basinal facies in South China is well known for its preservation of the earliest articulated sponge fossils, providing an important taphonomic window into the Cambrian Explosion. However, the Hetang Formation also hosts a number of problematic animal fossils that have not been systematically described. This omission results in an incomplete picture of the Hetang biota and limits its contribution to the understanding of the early evolution of animals. Here we describe a new animal taxon, Cambrowania ovata Tang and Xiao, new genus new species, from the middle Hetang Formation in the Lantian area of southern Anhui Province, South China. Specimens are preserved as carbonaceous compressions, although some are secondarily mineralized. A comprehensive analysis using reflected light microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and micro-CT reveals that the new species is characterized by a spheroidal to fusoidal truss-like structure consisting of rafter-like crossbars, some of which are secondarily baritized and may have been internally hollow. Some specimens have aperture-like structures that are broadly similar to oscula of sponges, whereas others show evidence of a medial split reminiscent of gaping carapaces. While the phylogenetic affinity of Cambrowania ovata Tang and Xiao, n. gen. n. sp. remains problematic, we propose that it may represent carapaces of bivalved arthropods or more likely sponges in early life stages. Along with other problematic metazoan fossils such as hyolithids and sphenothallids, Cambrowania ovata Tang and Xiao, n. gen. n. sp. adds to the diversity of the sponge-dominated Hetang biota in an early Cambrian deepwater slope-basinal environment. UUID: http://zoobank.org/44de9472-7e3f-42d1-9554-7b3434df91d9

@article{tang2019a,
    author = "Tang, Qing and Hu, Jie and Xie, Guwei and Yuan, Xunlai and Wan, Bin and Zhou, Chuanming and Dong, Xu and Cao, Guohua and Lieberman, Bruce S. and Leys, Sally P. and Xiao, Shuhai",
    title = "A problematic animal fossil from the early Cambrian Hetang Formation, South China",
    year = "2019",
    journal = "Journal of Paleontology",
    abstract = "The lower-middle Hetang Formation (Cambrian Stage 2–3) deposited in slope-basinal facies in South China is well known for its preservation of the earliest articulated sponge fossils, providing an important taphonomic window into the Cambrian Explosion. However, the Hetang Formation also hosts a number of problematic animal fossils that have not been systematically described. This omission results in an incomplete picture of the Hetang biota and limits its contribution to the understanding of the early evolution of animals. Here we describe a new animal taxon, Cambrowania ovata Tang and Xiao, new genus new species, from the middle Hetang Formation in the Lantian area of southern Anhui Province, South China. Specimens are preserved as carbonaceous compressions, although some are secondarily mineralized. A comprehensive analysis using reflected light microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and micro-CT reveals that the new species is characterized by a spheroidal to fusoidal truss-like structure consisting of rafter-like crossbars, some of which are secondarily baritized and may have been internally hollow. Some specimens have aperture-like structures that are broadly similar to oscula of sponges, whereas others show evidence of a medial split reminiscent of gaping carapaces. While the phylogenetic affinity of Cambrowania ovata Tang and Xiao, n. gen. n. sp. remains problematic, we propose that it may represent carapaces of bivalved arthropods or more likely sponges in early life stages. Along with other problematic metazoan fossils such as hyolithids and sphenothallids, Cambrowania ovata Tang and Xiao, n. gen. n. sp. adds to the diversity of the sponge-dominated Hetang biota in an early Cambrian deepwater slope-basinal environment. UUID: http://zoobank.org/44de9472-7e3f-42d1-9554-7b3434df91d9",
    url = "https://doi.org/10.1017/jpa.2019.26",
    doi = "10.1017/jpa.2019.26",
    number = "06",
    pages = "1047-1057",
    volume = "93"
}

The Spence Shale of Utah and Idaho preserves a diverse soft-bodied biota from the Cambrian. While the fauna is dominated by arthropods and echinoderms, soft-bodied animals belonging to other groups are known. Here we document Tentalus spencensis gen. et sp. nov. from the High Creek locality of the Spence Shale. The fossil has a crown of short stubby tentacles and appears to have been attached to the sediment through a stalk. The morphology of Tentalus suggests that it is a dinomischiid or deuterostome; however, it cannot be attributed to any of the known species, based on the short and conical tentacles surrounding an oral region, and polyp-like oblong columnar trunk terminating in a stalk, that do not resemble any described species.

@article{kimmig2025a,
    author = "Kimmig, Julien and Nanglu, Karma and Jamison, Paul G.",
    title = "A problematic soft-bodied fossil from the Cambrian (Miaolingian, Wuliuan) of Utah",
    year = "2025",
    journal = "Geological Magazine",
    abstract = "The Spence Shale of Utah and Idaho preserves a diverse soft-bodied biota from the Cambrian. While the fauna is dominated by arthropods and echinoderms, soft-bodied animals belonging to other groups are known. Here we document Tentalus spencensis gen. et sp. nov. from the High Creek locality of the Spence Shale. The fossil has a crown of short stubby tentacles and appears to have been attached to the sediment through a stalk. The morphology of Tentalus suggests that it is a dinomischiid or deuterostome; however, it cannot be attributed to any of the known species, based on the short and conical tentacles surrounding an oral region, and polyp-like oblong columnar trunk terminating in a stalk, that do not resemble any described species.",
    url = "https://doi.org/10.1017/s0016756825100265",
    doi = "10.1017/s0016756825100265",
    volume = "162"
}