Entomaspididae is a

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

of harpetid

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

s that ranges from the Upper Cambrian to Lower Ordovician of marine strata in China and the United States.

Description

Entomaspidids, as in other harpetid trilobites, have proportionally large, vaulted cephalons, shaped like croissants or bonnets, with the cheeks freed to be modified into long and curved spines in '' Entomaspis'' and '' Hypothetica''. Although the eyes of Entomaspididae are small compared to many other trilobites, the eyes are large when compared to other harpetids bearing eyes. Entomaspidids can be further distinguished from other harpetids by having a continuous border along the rim of the pygidium composed of small, stub-like spines.Suzuki, Yutaro. "Systematic position and palaeoecology of a cavity-dwelling trilobite, Ityophorus undulatus Warburg, 1925, from the Upper Ordovician Boda Limestone, Sweden." Paleontological research 6.1 (2002): 73-83. In overall appearance, the typical Entomaspidid is a near-circular, medallion-like trilobite.

Taxonomy

Entomaspididae is thought to represent the transition between the ancestral

Ptychopariida Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. The earliest species occurred in the second half of the Lower Cambrian, and the last species did not survive the Ordovician–Silurian ...

, and the harpetids. Many researchers question the validity of Entompaspididae as a distinct family, and merge its genera into Harpetidae.Adrain, Jonathan M., and Stephen R. Westrop. "Notchpeakia, a new genus of Upper Cambrian (Sunwaptan)“entomaspidid” trilobites." Journal Information80.6 (2006). Ulrich erected "Entomaspididae" to contain species of '' Entomaspis'' and '' Hypothetica'', from the Latest Cambrian or Earliest Ordovician of Utah.

Distribution

The first entomaspidids appear in the fossil record near the close of the Cambrian period in marine strata of Utah and China. They persist into the Early Ordovician before disappearing from the fossil record.

Recognized taxa

The three genera traditionally placed in Entomaspididae include the type genus, '' Entomaspis'', whose species are found in Utah and Missouri, and '' Hypothetica'', which lived sympatrically with Utah species of ''Entomaspis'', and '' Baikadamaspis'', of Late Cambrian marine strata in China. Many authorities merge ''Hypothetica'' into '' Entomaspis''.

References

{{Taxonbar, from=Q22285129 Harpetida Trilobite families Cambrian first appearances Early Ordovician extinctions