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 Système Silurien et les Trilobites de
Bohême. Leipzig, Germany. J.B. Hisrschfeld. 97 pp.
Boeck, C. 1828 (not 1827). Notitser til
Læren 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.