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Trilobites - Phylum Arthropoda
Class Trilobita
Subclass Trilobitomorpha
Classification based on: cephalic axial characters
glabella
furrows
suture patterns
caudilization of pygidial segments
Classification of Boardman, et al. 1987:
ORDER POLYMERIDA: (Lower Cambrian - Upper Permian)
small to large
variable pygidium
eyes, facial sutures
more than five thoracic segments usually present in hoaspides
anterior thoracic segment always has articulating half ring
pleural regions of pygidium commonly segmented
ORDER AGNOSTIDA: (Lower Cambrian - Upper Ordovician)
small, no eyes
most lack facial sutures
usually have only two thoracic segments
cephalic axis well separated from anterior border furrow
anterior thoracic segment lacks articulating half ring
pleural regions of pygidium unsegmented
Older classification:
Order Agnostida
small trilobites with subequal cephalon/pygidium
two or three thoracic segments
Range L.C. - U. Ord. Hypagnostus, Peronopsis
Order Redlichiida (Old order name Protoparia)
cephalon large, semicircular
well developed spines
thorax with numerous segments
pygidium diminutive, rudimentary
opisthoparion or anlcylosed sutures
glabellar furrows prominent
eyes elongate and crescentic
Range L.C. - M.C.
Suborder Olenellina: Olenellus, Daquinaspis, Elliptocephalus
Suborder Redlichiina: Redlichia
Suborder Bathynotina: Bathynotus
Order Corynexochida
elongate, sabelliptical
micropygous
semicircular cephalon
well developed genal spine
eyes rigid and elongate
opisthoparion facial suture
thorax with 5-11 segments, spinous terminatious
pygidium with marginal spines, may have smooth border
Range L. C. - U. C.
Olenoides
Order Ptychopariida
more than 3 thoracic segments
opisthoparion sutures, some proparion or marginal
glabella tapers forward
glabellar furrows, where present, are subparallel linear
depressions (this order is a close relative of the Reldichiida
and ancestral to most or all post-C. trilobites exclusive of
Agnostids)
Range L. C. 0 U. Perm.; Shumardia, Ptycoparia, Bumastus, Asaphus,
Entomaspis, Paraharpes, Symphysops, Lonchodomas, Pemphigaspis,
Ameura
Order Phacopida
post C trilobites
derived fro Ptychopariida
proparian sutures, may be gonatoparion or opisthoparion or lacking
forward expanding (Phacopina) or tapering forward glabella
(Calymenina)
varied development of glabellar furrows - not always present
preglabellar field short or lacking
rostral plate may or may not be present
thorax with 8-19 segments
medium to large pygidium (occasionally small)
Range L. Ord. - U. Dev.
Suborder Cheirurina: Ceraurinella, Pliomera, Cybele
Suborder Calyminina: Calymene, Flexicalymene
Suborder Phacopina: Phacops, Dalmanites
Order Lichida
distinctive cephalic and pydidial features
glabella broad, extends to anferior border
pair of lateral glabellar furrows longitudinally elongated
lateral glabellar and occipital lobes tend to fuse with one
another and other parts of the cuanidicum
episthoparion sutures
large pygidia
medium to large cephalon
pygidium pleural segments flattened
three pairs of leaflike spinose pleura
tuberculate dorsal surface
Range L. Ord. - U. Dev. Uralichas
Order Odontopleurida
convex cephalon
glabella expanded at occipital ring, tapers forward
medium or paired spines on lobes
two to three pairs of lateral glabellar lobes
convex genal regions
eye lobes prominent
free checks margined by spines
thorax with 8-10 segments
pleural spines
pygidia short, subtriangular
axis with 2-3 rings
external surface tuberculate to spinose
Range M.C. - U. Dev. Odontopleura
Superclass Crustacea
Class Cirripedia: (Sil - Holocene): Barnacles (Cretaceous - Holocene)
Class Ostracoda: (Cam - Holocene): Ostracods
Superclass Chelicerata
Class Merostomata: (Cam - Holocene): Horseshoe crabs (Sil - Holocene)
Class Arachnida: (Sil - Holocene): Eurypterids (Ord - Permian), spiders, scorpions, ticks,
mites
Superclass Hexapoda
Terrestrial insects (Dev - Holocene)
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