The Carboniferous Toxeumorphora dombarense, identified as a late-surviving hyolith, from Peel & Yochelson (1984).

Belongs within: Mollusca.
Contains: Hyolithellida, Circothecida, Orthothecida, Sulcavitida, Hyolithidae, Crispatellidae.

Hyoliths were a group of small shelled animals that mostly lived during the Cambrian and Ordovician (though probable hyoliths remained alive as late as the Permian—Peel & Yochelson 1984). They possessed a bilaterally symmetrical conical shell that was open at one end only and closed by an operculum (Kruse 2002). The relationship of hyoliths to other animals is uncertain—they have most often been treated as molluscs but commonly almost by default. Hyoliths can be divided into two main groups (Kruse 2002): Orthothecimorpha (containing Circothecida and Orthothecida), in which the aperture and conch growth lines are planar, and Hyolithomorpha (containing Sulcavitida and Hyolithida), in which the aperture has a prominent ventral ligula. Hyolithomorphs (at least) also possessed a pair of projecting struts called helens on either side of the operculum; being delicate, these are rarely preserved, so the absence to date of any records of helens in orthothecimorphs does not necessarily indicate their absence. The Middle Cambrian Globorilus globiger was separated from other hyoliths by Fisher (1962) due to its possession of a globular embryonic chamber whereas other hyoliths were supposed to lack a sharp separation between embryonic and younger parts of the shell.

Characteristics (from Kruse 2002): Bilaterally symmetrical conical conch with aperture at one end only, closed by an operculum.

<==Hyolitha [Calyptoptomatida, Hyolithoidea, Hyolithozoes]
    |--Globorilus Syssoiev 1958 [Globorilida, Globorilidae] F62
    |    `--*G. globiger (Saito 1936) [=Hyolithes globiger] F62
    `--Hyolithina F62
         |  i. s.: Pterygothecidae F62
         |           |--Pterygotheca Novak 1891 F62
         |           |    `--*P. barrandei Novak 1891 F62
         |           `--Virgulaxonaria Yin 1937 F62
         |                `--*V. elegans Yin 1937 F62
         |--Orthothecimorpha [Orthothecomorpha] K02
         |    |--Circothecida K02
         |    `--Orthothecida K02
         `--Hyolithomorpha K02
              |  i. s.: Ovalitheca EL11
              |--Sulcavitida K02
              `--Hyolithida [Hyolithina] K02
                   |  i. s.: Hyptiotheca Bengtson in Bengtson et al. 1990 L95
                   |           `--H. karraculum Bengtson in Bengtson et al. 1990 K02
                   |--Hyolithidae K02
                   `--Crispatellidae M02

Hyolitha incertae sedis:
  Cupittheca K02
    |--C. clathrata (Bengtson in Bengtson et al. 1990) K02
    |--C. hemicyclata (Bengtson in Bengtson et al. 1990) K02
    `--C. holocyclata (Bengtson in Bengtson et al. 1990) K02
  ‘Salterella’ planoconvexa Tate 1892 K02
  Conotheca Missarzhevksy in Rozanov et al. 1969 KB09
    |--C. australiensis Bengtson in Bengtson et al. 1990 K02
    `--C. circumflexa Missarzhevksy in Rozanov et al. 1969 KB09
  Parkula bounites Bengtson in Bengtson et al. 1990 K02
  Triplicatella disdoma Conway Morris in Bengtson et al. 1990 K02
  Nganki wumirri Kruse 1990 K02
  Globoritubulus Qian & Zhang 1985 K02
  Eumorpholites bouceki Marek 1967 K02
  Elegantilites tigris Marek 1967 K02
  Insignicornus Sysoyev 1973 K02
  Nevadotheca Malinky 1988 M02
    |--N. arenophilus M02
    |--‘Hyolithus’ socialis M02
    `--‘Hyolithus’ terranovicus Walcott 1891 M02
  Emarites Marek, Malinky & Geyer 1997 M02
  Recilites solitarius (Barrande 1867) M02
  Polylopia Clark 1925 M02
    `--*P. billingsi (Safford 1869) [=Salterella billingsi] F62
  Tetratheca M02
    `--‘Quadrotheca’ clinisepta Syssoiev 1960 [=Costatheca clinisepta] M02
  Ensitheca Duan 1984 M02
  Hyolithellida M90
  Toxeumorphoridae [Toxeumorphorida] PY84
    |--Pseudotoxeuma magnifica Shimanskiy 1963 PY84
    |--Toxeumorphora PY84
    |    |--T. dombarense Shimanskiy 1963 PY84
    |    `--T. langi Shimanskiy 1963 PY84
    `--Macrotheca Waagen 1880 PY84
         |--*M. wynnei Waagen 1880 PY84
         |--M. almgreeni Peel & Yochelson 1984 PY84
         `--M. timorensis Wanner 1941 PY84
  Gompholites striatulus (Barrande 1847) MMB05
  Maxilites Marek 1972 MMB05
    |--M. robustus (Barrande 1867) MMB05
    `--M. snajdri Marek 1972 MMB05
  Slapylites signatulus MMB05
  Tizilites creber MMB05
  Dilytes occultus MMB05
  Leolites MMB05
    |--L. cognatus MMB05
    `--L. paucicostatus MMB05
  Oboedalites MMB05
    |--O. oboediens MMB05
    `--O. peregrinus MMB05
  Chimerolites temperatus MMB05
  Paolites obvius MMB05
  Kygmaeoceras Flower 1954 F62
    `--*K. perplexum Flower 1954 F62
  Pharetrella Hall 1888 F62
    `--*P. tenebrosa Hall 1888 F62
  Phragmotheca Barrande 1867 F62
    `--*P. bohemica Barrande 1867 F62
  Quinquelithes Syssoiev 1958 F62
    `--*Q. pavonaceus Syssoiev 1958 F62

*Type species of generic name indicated


[EL11] Erwin, D. H., M. Laflamme, S. M. Tweedt, E. A. Sperling, D. Pisani & K. J. Peterson. 2011. The Cambrian conundrum: early divergence and later ecological success in the early history of animals. Science 334: 1091–1097.

[F62] Fisher, D. W. 1962. Small conoidal shells of uncertain affinities. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt W. Miscellanea: Conodonts, Conoidal Shells of Uncertain Affinities, Worms, Trace Fossils and Problematica pp. W98–W143. Geological Society of America, and University of Kansas Press.

[KB09] Kouchinsky, A., S. Bengtson, W. Feng, R. Kutygin & A. Val’kov. 2009. The Lower Cambrian fossil anabaritids: affinities, occurrences and systematics. Journal of Systematic Palaeontology 7 (3): 241–298.

[K02] Kruse, P. D. 2002. Biostratigraphic potential of Middle Cambrian hyoliths from the eastern Georgina Basin. Alcheringa 26: 353–398.

[L95] Landing, E. 1995. Upper Placentian–Branchian series of mainland Nova Scotia (middle–upper Lower Cambrian): faunas, paleoenvironments, and stratigraphic revision. Journal of Paleontology 69 (3): 475–495.

[M90] Malinky, J. M. 1990. Cambrian Hyolitha from northeast Canada: reappraisal of the hyolith orders Camerothecida and Diplothecida. Journal of Paleontology 64 (4): 587–595.

[M02] Malinky, J. M. 2002. A revision of Early to Mid Ordovician hyoliths from Sweden. Palaeontology 45: 511–555.

[MMB05] Martí Mus, M., & J. Bergström. 2005. The morphology of hyolithids and its functional implications. Palaeontology 48 (6): 1139–1167.

[PY84] Peel, J. S., & E. L. Yochelson. 1984. Permian Toxeumorphorida from Greenland: an appraisal of the molluscan class Xenoconchia. Lethaia 17: 211–221.

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