Holmiidae 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 ...

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 lived during the

Lower Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ( ...

(Atdabanian). The Holmiidae is a diverse family of eight genera containing at least 17 species. It includes some of the earliest trilobites of

Baltica Baltica is a paleocontinent that formed in the Paleoproterozoic and now constitutes northwestern Eurasia, or Europe north of the Trans-European Suture Zone and west of the Ural Mountains. The thick core of Baltica, the East European Craton, ...

. Holmiidae occur throughout Baltica (Scandinavia and the eastern seaboard of the Baltic Sea) and Western Laurentia (in the Great Basin of the US and northwestern Canada), and also in Morocco.

Taxonomy

Hupé (1953) defined the Holmiidae as a subfamily (Holmiinae) within the Olenellidae containing ''Holmia'', ''Kjerulfia'' and ''Bondonella''. Harrington et al. (1959) excluded ''Kjerulfia'', while assigning ''Schmidtiellus'' to it. Bergström (1973) included ''Holmia'', '' Elliptocephala'', ''Esmeraldina'', ''Schmidtiellus'' and '' Wanneria''. Repina (1979) assigned ''Holmia'', ''Schmidtiellus'', ''Kjerulfia'', ''Elliptocephala'', ''Bondonella'', ''Andalusiana'' and ''Holmiella'' to the Holmiinae, that together with the

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

Callaviinae comprised the Holmiidae. Palmer and Repina (1993) added ''Holmiella'' but excluded ''Kjerulfia'', they assigned to the Callaviinae. Lieberman, who made cladistic analyses of the Olenellina and the included superfamilies, regards ''Andalusiana'' an advanced " Nevadioidea", ''Callavia'' and ''Bondonella'' as

Judomioidea The Judomioidea are a superfamily of trilobites, a group of extinct marine arthropods. Its species lived during the Lower Cambrian (Atdabanian Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 an ...

, and ''Elliptocephala'' and ''Wanneria'' stemgroup genera closely related to the common ancestor of the Holmiidae and the Biceratopsidae.

Genera

* ''Andalusiana'' Lotze 1958 * ''

Callavia ''Callavia'' is an extinct, monotypic genus of trilobite arthropods. ''C. broegeri'' lived during the late Atdabanian stage, which lasted from 530 to 524 million years ago during the early part of the Cambrian Period in what are today Canada and ...

'' Matthew 1897 * '' Cambropallas'' Geyer 1993 * '' Elliptocephala'' * '' Esmeraldina'' Resser and Howell, 1938 * '' Grandinasus'' Hollingsworth, 2006 * '' Holmia'' Matthew, 1890 synonym ''Baltobergstroemia'' * ''Holmiella'' Fritz, 1972 * '' Iyouella'' Geyer and Palmer 1995 * '' Kjerulfia'' Kiaer, 1917 * '' Montezumaspis'' Hollingsworth, 2006 * '' Palmettaspis'' Fritz, 1995 * Holmia kjerulfi body 01

'' Schmidtiellus'' Moberg ''in'' Moberg and Segerberg, 1906

Relationships within the Holmiidae

The eye ridges in Baltic and Moroccan Holmiidae (''Holmia'', ''Schmidtiellus'') are wide, have a furrow atop the ridges, and the resulting inner band merges with the frontal lobe (L4) of the

glabella The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior to ...

without an axial furrow. This is interpreted as advanced compared with the arrangement of the simple ocular lobes of Laurentian holmiids, which are separated from the L4 by a prominent axial furrow around the glabellar outline.

Description

As with most early trilobites, Holmiidae have an almost flat exoskeleton, that is only thinly calcified, and has crescent-shaped eye ridges. As part of the Olenellina suborder, the Holmiidae lack dorsal sutures in the cephalon. Like all other members of the Olenelloidea superfamily, the eye-ridges spring from the back of the frontal lobe (L4) of the central area of the cephalon (or

). Specifically for the Holmiidae are the following diagnostic characters. The glabella is straight-sided to somewhat constricted and mostly expands forward. The frontal lobe (or L4) is usually broad and rounded. The furrows that separate the lobes are usually curved, moderately incised, and rarely completely cross the midline. The eye ridges of Baltic holmiids are often wide with an ocular furrow, inner band merging with L4 without axial furrow. Laurentian holmiids (''Montezumaspis'', ''Palmetaspis'', ''Grandasinus'', ''Esmeraldina'' and ''Holmiella'') have unfurrowed ocular lobes separated from L4 by axial furrow. The cephalon carries so called genal spines at the corner between the half circle front/side margin and the back margin that is roughly perpendicular to the midline. These spines extend back to at least the fourth thorax segment (T4), counted front to back. The back margin of the cephalon normally carries a node or spine (or intergenal spine), straight behind the point the eye ridge is furthest from the midline or even somewhat further out. Back margin of cephalon inside the intergenal angle transverse or directed posteriorly. The third thorax segment (T3) is not larger than the neighboring segments and does not carry larger spines. Anterior thoracic pleural spines weakly to strongly thornlike except in ''Kjerulfia'' and ''Grandinasus''.

References

{{Taxonbar, from=Q1037930 Olenelloidea Trilobite families Cambrian trilobites Cambrian first appearances Terreneuvian extinctions Fossils of Canada