TIMOCRINUS GEN. N. (CRINOIDEA, INADUNATA) FROM THE LOWER DEVONIAN OF BOHEMIA
originally published in Casopis
Narodniho Muzea, Rada prirodovedna,
Rudolf J. Prokop1 - Vaclav Petr2
Abstract: New genus of small inadunate crinoids, Timocrinus gen. n., with two new species, T. fidelis sp. n. and T. bellus sp. n., is described from the Lower Devonian (Dalejan = Upper Emsian) Trebotov Limestone of the Barrandian area (Bohemia).
Key words: Crinoidea, Inadunata, Lower Devonian,
Bohemia, Old World Realm, micritic limestones, Timocrinus new genus, new
TIMOCRINUS gen. n.
Type species: Timocrinus fidelis sp. n., Lower Devonian, Dalejan (Upper Emsian), Trebotov Limestone, Bohemia.
Diagnosis: Theca small, round or roundly pentagonal in oral and basal view, with perfect pentamerous symmetry. No anal plates or anal structures present on aboral cup and tegmen. The aboral cup is medium to low bowl-shaped. Cup base more or less convex, with shallow round or oval basal pit. Five small basals (BB), very low, subhorizontal (not visible from side view) or upflaring (visible from the side view). The main portion of the aboral cup is formed of five simple (not compound) radials (RR), with distinctly convex outer sides. Straight upper edge of RR bears very fine crenellae which correspond to crenulated lower edges of orals. Small radial facets at the centre of the summit of RR are situated in shallow but distinct notch and are narrowly rounded, with prominent fulcral ribs and a pair of shallow muscular fossae. Tegmen is low, built of five large triangular orals (OO) from which the ventral cavity of the cup is completely covered. Lateral edges of OO are depressed, forming deep grooves extending from radial facets to the summit of theca. External surface of thecal plates is smooth or weakly vermicular. Arms and column unknown.
Remarks: By its size, shape and organization of the theca the genus Timocrinus gen. n. is similar to Haplocrinites Steininger, 1837 with which it was by some previous authors confused (Ruzicka, 1942). As in members of the genus Haplocrinites, in both known species of the genus Timocrinus the theca has perfect pentamerous symmetry, without any anal structure. On the semipyramidal tegmen of both genera there are also five prominent grooves along the lateral edges of OO, probably for accommodation of well-movable arms in resting position. However, the genus Timocrinus differs from the former one by simple radials, by small radial facets in shallow notches, by lower height of the tegmen (cca only 1/4 or less of the height of the theca), and by lack of a median pore on one of OO. In Haplocrinites there are B, C, and E radials compound, radial facets are larger and notches deeper, height of the tegmen is generally more than 1/2 of the height of the aboral cup, and there is a tiny median pore present on one of OO (i.e. on the posterior oral plate).
Species: Timocrinus fidelis sp. n. and T. bellus sp. n.,
both from the Trebotov Limestone, Dalejan (= Upper Emsian), Barrandian, Bohemia.
(Pl. I., figs. 1-4, Pl.II., fig. 4)
Holotype: Isolated theca inv.n. L 30513 figured on Pl. I., fig. 1.
Type locality: Praha-Holyne.
Type horizon: Lower Devonian, Dalejan (= Upper Emsian), Trebotov
Material: More than 150 isolated thecae and aboral cups.
Description: Aboral cup low bowl-shaped to hemisphaerical (the ratio height:width = 1:1.6 to 1:2), rounded as seen both from above and below. Cup base very low, pentagonal in outline, formed of five small pentagonal BB which are visible laterally only in a few specimens. Basal pit is rounded, shallow. RR strongly convex on their external side, trapezoidal, with straight upper edge. Radial facets are of rounded pentagonal shape, forming only 1/3 or less of the total width of RR. They are in a shallow, distinct notch which is placed in a small, externally protruding elevation of the centre of summit of each radial plate. Sutures between RR are conspicuously depressed.
Tegmen is low, forming 1/4 to 1/6 of the total height of the theca, and built up of five solid trigonal OO. Interoral grooves (in life probably housing arms in resting position) are prominent, channel-shaped, narrowing terminally. Laterally they are bordered with relatively high, slender sharp ridges which do not terminate on the tegmen's summit but on each oral they are bent backwards to the tegmen's basal edge. Brachials, whole arms or columnals 'in situ' are unknown.
Occurrence: Timocrinus fidelis sp. n. represents an important species of the assemblage in the upper layers of micritic, thick-bedded Trebotov Limestone. However, it is abundant only at the typical locality at Praha-Holyne. Isolated thecae and aboral cups have been rarely found also in the section at the roadcut of the highway at Praha-Barrandov, precisely from 2.20 to 1.70 m below the boundary with Middle Devonian (Eifelian) Chotec Limestone.
Dimensions of the holotype (in mm): total height of theca = 2.0,
height of aboral cup = 1.5, max. width of the cup = 2.4.
Timocrinus bellus sp. n.
(Pl. II., figs. 1-3.)
Holotype: Isolated theca inv.n. L 30517, figured on Pl. II, fig. 1.
Type locality: Praha-Holyne.
Type horizon: Lower Devonian, Dalejan (= Upper Emsian), Trebotov Limestone.
Material: More than 80 isolated thecae and aboral cups.
Description: Aboral cup higher and slender than in the type species,
medium bowl-shaped (height:width ratio = 1:1.2 to 1:1.4), pentagonal as seen
both from above and below. Cup base pentalobate in outline, formed of five low
BB, in every case good visible from lateral view. Basal pit very shallow, oval.
RR pentagonal, with straight, finely crenulated upper edge and with less convex
external side than in T. fidelis sp. n. Interradial sutures slender, not
distinctly depressed. Radial facets are almost trapezoidal, in shallow notches.
In contrast to the situation in type species, these facets do not protrude from
the outline of the cup in oral or basal view.
Tegmen is low, forming cca 1/4 to 1/5 of the total height of the theca. Interoral grooves serving as possible insertions of arms in resting position are deep, broadly lancet-shaped in oral view. In this manner the outer surface of OO are formed into a low and broad trihedral pyramid. Brachials, whole arms, as well as columnals 'in situ' are unknown.
Remarks: Skeletal elements very similar to the above described species have been also derived from washings of the stratigraphically older Lodenice and Dvorce-Prokop Limestone (Pragian) and in present also from basal layers of the Chotec Limestone. This material needs further study.
Occurrence: Timocrinus bellus sp. n. is also an important element of the crinoid assemblage of the Trebotov Limestone at Praha-Holyne, however, it is not as abundant as the type species. Except the type locality, it has been also discovered in the quarry "U jezirka" at Praha-Hlubocepy and in the section at the highway-roadcut at Praha-Barrandov, precisely in interval from 7.5 to 0.2 m below the base of the Chotec Limestone (Eifelian).
Dimensions of the holotype (in mm): total height of theca = 1.8, height of the aboral cup = 1.4, max. width of the aboral cup = 2.0.
The authors are indebted for very valuable comments, informations and also
for important portion of material (especially from the section near the
highway-roadcut at Praha-Barrandov) to following colleagues: Radvan Horny, Ivo
Chlupac, Pavel Lukes and Michal Mergl.
MOORE, R. C. et al. (1978): Order Disparida. In: MOORE, R. C. - TEICHERT, C. (Eds.): Treatise on Invertebrate Paleontology, part T, Echinodermata 2, Crinoidea vol. 2: T520-T564. - Geol. Soc. Amer., Boulder, Colorado and Univ. Kansas Press, Lawrence, Kansas.
RUZICKA, B. (1942): Faunisticke seznamy z Barrandienu ze souvrstvi g? (cast II.) a ze dvou lokalit z gy v okoli Prazskem. - Vest. Kral. Ces. Spolec. Nauk., Tr. mat.-prirodoved. (for 1941), XIX, 16 p. Praha.