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Miller—Some Upper Cambrian and Lower Ordovician Conodonts 9
Fig. 2. Albiconus postcostatus, n. gen. and n.
sp. A-C. Posterior, posterobasal, and lateral views of
holotype from base of House Limestone, Lower Ordovician,
Sevier Lake section of Miller (1969), southern House
Range, Utah; X60, 100, 60; USNM 303279. D. Lateral
view and line drawings showing basal cavity (D ) and
transverse section (D") of paratype from 9m (28 It) above
base of House Limestone, Lower Ordovician, north side
of Sneakover Pass, central House Range, Utah; X60,
USNM 303280.
Hirsutodontus simplex and Clavolummlus
hintzei subzones of the Cordylodus proavus
Zone and in lower Fauna B.
Genus CAMBROOISTODUS, new
Type species. —Oistodus cambricus
Miller, 1969, p. 431.
Description. —Two-element apparatus
composed of erect to reclined simple cone elements.
Characteristic compressed element
robust to moderate in size, asymmetrical due
to lateral bending of cusp; basal cavity very
deep in primitive forms to shallow in more advanced
forms, cusp correspondingly short to
long, varying inversely with depth of basal
cavity; cusp composed of white matter,
strongly compressed laterally, with prominent
anterior and posterior keels; inner side of base
with prominent bulge (caria); upper edge of
posterior adenticulate process meeting
posterior keel at sharp, usually acute, angle.
Less distinctive rounded element symmetrical,
proclined to reclined, oval to round in cross
section; anterior and posterior edges may be
sharp or rounded; basal cavity very deep to
shallow and cusp correspondingly short to
long and composed of white matter; posterior
edge of base forming smooth concave curve.
Evidence of microsculpture lacking on faces of
both elements, even at high magnification.
Discussion. —Two species are referred to
this genus. They were originally described as
Oistodus cambricus Miller, 1969, and O.
inimitus Miller, 1969; however, Lindstrom
(1973) correctly pointed out that these species
should no longer be referred to Oistodus Pander,
and he referred them to Proconodontus
Miller. He also discussed possible synonymies
among 'Proconodontus - notclipeakensis,
carinatus, -P. - cambricus, and -P."
minutus. A better understanding of this group
of species has become possible only after
detailed sampling in many Upper Cambrian
sections where details of the evolution of these
species have been determined. The first two of
the four species are here considered to be
elements of Eoconodontus notclipeakensis,
and the latter two are referred to Cambrooistodus.
E. notclipeakensis is the ancestor
of C. cambricus, which is the ancestor of C.
wit/taus, and all have similar apparatuses.
The rounded elements of all three species are
presently indistinguishable from one another,
and in samples containing more than one of
these species, only the compressed elements
can be identified. The compressed element of
Eoconodontus lacks the posterior process of
Cambrooistodus.
Cambrooistodus differs from Oistodus
Pander by possessing a cusp composed of
white matter rather than hyaline material.
Drepanoistodus LindstrOm and Paroistodus
LindstrOm are Lower Ordovician genera that
may have been derived from Cambrooistodus.
The relationship is uncertain because a
considerable stratigraphic gap separates the
uppermost occurrence of Cambrooistodus
(top of Proconodontus Zone) from the lowermost
occurrence of Drepanoistodus and
Paroistodus (upper Tremadocian). All three
genera have similar apparatuses, but the
details of shape, particularly of the basal cavity,
are very different.
CAMBROOISTODUS CAMBRICUS
(Miller)
Figure 3A, 4E; Plate 1, tigure 9
Oistodus cambricus Miller, 1969, p. 431, text-