The Craniidae are a
family of
brachiopods, commonly known as lamp shells. Although it belongs to a subdivision called the inarticulata which have shells where the mineral content consist of calcium phosphate, the Craniidae have shells that consist of calcium carbonate. Other special characteristics of this family are that no outgrowths are developed to form a hinge between both valves, nor is there any support for the lophophore. As adults, craniids either lived free on the ocean floor or, more commonly, were attached to a hard object with all or part of the
ventral valve. In craniids, a pedicle is not known from any development stage.
They are the only members of the
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
Craniida and the
monotypic suborder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
Craniidina and
superfamily
SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...
Cranioidea; consequently, the latter two
taxa are presently redundant and not used very often. ''
Valdiviathyris'' and ''
Neoancistrocrania'' were sometimes separated in a family Valdiviathyrididae but this has turned out to be unjustified.
Most Craniidae are long
extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
forms known only from
fossils like all other
Craniforma. However, some 20 species of this 470-million-year-old lineage are
surviving
Survival skills are techniques that a person may use in order to sustain life in any type of natural environment or built environment. These techniques are meant to provide basic necessities for human life which include water, food, and shelt ...
today. They include ''
Valdiviathyris quenstedti
''Valdiviathyris quenstedti'' is a small species of brachiopods with a maximum size of about wide.
Distribution Occurrence over time
Specimens attributed to ''V. quenstedti'' from the Upper Eocene have been found near New Zealand.
Recent ...
'' which has remained essentially unchanged for the last 35 million years or so. Although some minimal
evolution would obviously have taken place in the meantime, this was essentially
silent mutations and marginal
adaptations to cooler
habitat. Present-day ''Valdiviathyris'' are all but inseparable from those of the Late
Eocene and the
genus cannot even be divided into
chronospecies. Thus, ''V. quenstedti'' is a true
living fossil and one of the oldest and most long-lived
species known to science.
Gallery
Image:Isocrania costata Sowerby 1823.jpg, '' Isocrania costata'', from the Upper Cretaceous of The Netherlands
Image:EncrustedStroph.JPG, '' Petrocrania'' (small round shells) encrusting an Ordovician strophomenid brachiopod
References
Brachiopod families
Extant Ordovician first appearances
Craniata
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