Paradoxides minor
Paradoxidids were some of the largest trilobites
ever. They are relatively common large trilobites in Middle Cambrian
rocks in many parts of the world. About 150 species and subspecies names
are available for Paradoxides (sensu lato), which includes some junior
synonyms (subjective & objective) and some homonyms. Generic-level
taxonomy of paradoxidid trilobites continues to be in a state of confusion,
despite the family treatment by Dean & Rushton (1997). Several
genus-level or subgenus-level names are used by various authors to refer to
groups of Paradoxides-like species that may or may not be
morphologically distinctive (Examples: Paradoxides Brongniart,
1822, Bucephalites Thompson, 1834, Hydrocephalus Barrande, 1846, Phlysacium
Corda in Hawle & Corda, 1847, Phanoptes Corda in Hawle
& Corda, 1847, Plutonia, Hicks, 1871, Plutonides Hicks, 1895,
Eccaparadoxides Šnajdr, 1957, Acadoparadoxides Šnajdr, 1957, Vinicella
Šnajdr, 1957, Eoparadoxides Solovev, 1969, Baltoparadoxides
Šnajdr, 1986, Macrocerca Pillet in Courtessole et al., 1988, Rejkocephalus
Kordule, 1990; some of these are undisputed junior synonyms of other names on
the list).
A nice large specimen of Paradoxides minor is
shown below from the Middle Cambrian of Bohemia. Some workers refer to this
species as Hydrocephalus minor or Paradoxides (Hydrocephalus) minor.
It was first named & described & illustrated by Chris Boeck in 1828 as Trilobites
minor (see Boeck, 1828, pp. 27-30, pl. 2, figs. 12-14).
This species is often placed in the genus or subgenus Hydrocephalus,
named by Joachim Barrande in 1846 for paradoxidid trilobites having noticeably
inflated glabellas in early ontogenetic stages (hydrocephaly is a
condition in some human fetuses or infants involving swelling of the head due
to abnormal fluid buildup). This feature is not apparent in later
holaspids, so many authors consider the use of Hydrocephalus at the
genus level problematic.
Classification: Arthropoda, Trilobita, Polymerida, Paradoxididae
Stratigraphy: upper Jince Formation, Paradoxides gracilis zone, upper Middle
Cambrian
Locality:
Jince area, Stredocesky Region, Bohemia, Czech Republic
Paradoxides
minor (Boeck, 1828) complete
exoskeleton (13.9 cm long), but lacking the librigenae (free cheeks), from the
Jince Formation (Middle Cambrian) of Jince, Bohemia.
Paradoxides
minor (Boeck, 1828) cranidium
attached to thorax (width of cranidium at posterior end of palpebral lobes: 5.1
cm across) from the Jince Formation (Middle Cambrian) of Jince, Bohemia.
Characters of the cephalon/cranidium of paradoxidid
trilobites are often used for defining new species. This is standard
practice for most trilobites if the complete exoskeleton is unknown.
Unfortunately, the paradoxidid head does not have consistently diagnostic
features for species distinctions.
Paradoxides
minor (Boeck, 1828) pygidium
attached to thorax (tail is 1.6 cm across) from the Jince Formation (Middle
Cambrian) of Jince, Bohemia.
Ideally, paradoxidid trilobite species should be
defined based on all characters of the cephalon, thorax, and pygidium.
Typically, only the cranidium is represented in a collection. However, the
pygidium appears to be the most diagnostic sclerite for distinguishing the
numerous species of Paradoxides (sensu lato). Pygidial morphology
does vary somewhat within paradoxidid species, but its overall construction
does seem more taxonomically useful than cranidial characters.
Paradoxides
minor (Boeck, 1828) labrum (hypostome),
or mouthplate (2.6 cm across at its widest) from the Jince Formation (Middle
Cambrian) of Jince, Bohemia.
References cited:
Barrande, J.
1846. Notice Préliminaire sur le Systčme Silurien et les Trilobites de
Bohęme. Leipzig, Germany. J.B. Hisrschfeld. 97 pp.
Boeck, C. 1828 (not 1827). Notitser til
Lćren onm Trilobiterne. Magazin for Naturvidenskaberne 8: 11-44,
pl. 2.
Brongniart, A. & A.-G.
Desmarest. 1822. Histoire Naturelle des Crustacés Fossiles.
Paris. F.-G. Levrault, Libraire. 154 pp. 11 pls.
Courtessole, R., J. Pillet & D. Vizcaino.
1988. Stratigraphie et Paleontologie du Cambrien Moyen Greseux de la
Montagne Noire (Versant Meridional). Carcassonne, France. 55
pp. 8 pls.
Dean, W.T. & A.W.A. Rushton. 1997.
Superfamily Paradoxidoidea. pp. 470-481 in Treatise on
Invertebrate Paleontology, Part O, Arthropoda 1, Trilobita, Revised, volume 1:
Introduction, Order Agnostida, Order Redlichiida. Boulder, Colorado
& Lawrence, Kansas. Geological Society of America & University of
Kansas.
Hawle, I. & A.J.C.
Corda. 1847. Prodrom einer Monographie der Böhmischen Trilobiten.
Prague. J.G. Calve'sche Buchhandlung. 176 pp. 7 pls.
Hicks, H.
1871. Descriptions of new species of fossils from the Longmynd rocks of
St. David’s. Quarterly Journal of the Geological Society of London
27: 399-402, pls. 15-16.
Hicks, H. 1895. On
the genus Plutonides (non Plutonia) from the Cambrian rocks of
St. David’s. Geological Magazine, Series 4 2: 230-231.
Kordule, V.
1990. Rejkocephalus, a new paradoxid genus from the Middle
Cambrian of Bohemia (Trilobita). Vestník
Ústredniho Ústavu Geologického 65: 55-60, 2 pls.
Šnajdr, M.
1957. O novych trilobitech z ceskeho kambria. Vestník Ústredniho Ústavu Geologického 32: 235-244, 2 pls.
Šnajdr, M.
1986. Two new paradoxid trilobites from the Jince Formation (Middle
Cambrian, Czechoslovakia). Vestník Ústredniho Ústavu Geologického
61: 169-174, pls. 1-2.
Solovev, I.A.
1969. Novye vidy Paradoxides (Trilobity) iz goryuchikh slantsev
amginskogo yarusa severnoy Yakutii. Uchenye Zapiski Paleontologiya i
Biostratigrafiya, Nauchno-Issledovatelskiy Insitut Geologii Arktiki 25:
9-20, 5 pls.