Tiaracrinus Schultze, 1866

Klug, Christian, Baets, Kenneth De, Naglik, Carole June & Waters, Johnny, 2014, A new species of Tiaracrinus from the latest Emsian of Morocco and its phylogeny, Acta Palaeontologica Polonica 59 (1), pp. 135-145 : 140-141

Genus Tiaracrinus Schultze, 1866

Type species: Tiaracrinus quadrifrons Schultze, 1866 , original designation; Stínava near Plumlov , Moravia, Czech Republic, Emsian, Early Devonian .

Species included: Tiaracrinus moravicus Ubaghs and Bouček, 1962 ; Tiaracrinus oehlerti Schlüter, 1881 ; “ Staurosoma rarum ” Barrande, 1887 ; Tiaracrinus quadrifrons Schultze, 1866 ; Tiaracrinus tedraedra Jaekel in Lotz, 1901; Tiaracrinus jeanlemenni sp. nov.; “ Triaracrinus ” sp. (sic!) Kříž, 1992.

Discussion.—Initially described as a crinoid, Tiaracrinus was occasionally attributed to the Rhombifera (Blastozoa) by some early palaeontologists ( Jaekel 1899, 1918; Bath- er 1900). Subsequently it has been consistently assigned to the crinoids (e.g., Frech 1902; Springer 1926; Bassler 1938; Moore et al. 1978; Le Menn 1990; Haude 1993; Hauser 2008). This confusion was probably largely related with its peculiar symmetry, the possible absence of arms and the presence of pores (epispires) on the theca. Here, we briefly discuss these features, their possible implications and problems associated with them:

(i) Symmetry: Tiaracrinus has three basals and four radials, thus determining the tetrameral symmetry of the calyx ( Le Menn 1990). The oral surface is rarely preserved but has been discussed in detail by Le Menn (1990). The calyx shows five different plate numbers per circlet in the calyx. The base shows three plates while the cup is tetrameral. On the oral surface, 13 fields with brachial platelets and eight interoral fields can be seen, which surround the five oral plates ( Le Menn 1990).

(ii) Arms: Tiaracrinus is commonly found without arms and has been described in the Treatise on Invertebrate Paleontology ( Moore et al. 1978: 562) as follows: “Arm facets obscure or absent.Arms and columns unknown”. Later, Haude (1993) assigned limbrachoids from the Middle Devonian of Germany to this genus. He discussed the problems of the systematic position of this genus: “Immerhin ist die Theka so ungewöhnlich gebaut, dass selbst bedeutende Kenner der Pelmatozoen wie Bather (1900: 57) und Jaekel (1918: 99) Tiaracrinus zu den Cystoiden stellten. (An einem Cystoiden wären im übrigen die Limbrachoide wesentlich leichter als [biseriale] versteifte Brachiolen zu interpretieren.)” [Translation: “After all, the theca is constructed in such an unusual way that even important adepts of the pelmatozoans such as Bather (1900: 57) and Jaekel (1918: 99) have assigned Tiaracrinus to the cystoids. (On a cystoid, by the way, the limbrachoids would be much easier to interpret as stiffened [biserial] brachioles.)”]

Le Menn (1990: 163) also discussed this issue: “Le nombre de bras demeure difficile à établir” [Translation: “The number of arms remains difficult to identify”]. While Le Maître (1958a –c) had suggested 18 arms based on 18 ditches on the oral surface, Le Menn (1990) thinks that these ditches were formed by erosion. The latter author discussed the possibilities of five or eight arms, based on the number and arrangement of oral, interoral, and brachial plates. It appears like this question has to stay unanswered until a complete, articulated specimen is found.

(iii) Pores on the calyx: Tiaracrinus displays four fields with epispires ( Fig. 2 ). These epispires have been interpret- ed as representing a plesiomorphic character by Guensburg and Sprinkle (2007: 287): “Crinoid respiratory folds, for instance, are symmetrical internally and externally, whereas rhombiferan internal folds are extended forming interior bulges. Folds of most crinoids occur at triple junctures of plate corners, whereas those of rhombiferans cross plate sides.”

The origin of the type material is unknown according to Hauser (2008), but Le Menn (1987) described similar specimens from the Saint Céneré Formation (Pragian) of the “Tranchée de la voie Sablé”; Massif Armoricain ( France).

Stratigraphic and geographic range.—Species of Tiaracrinus are recorded from: the Emsian of Plumlov (Moravia, Czech Republic), the late Emsian (according to Prokop 1987) of Koňeprusy ( Bohemia, Czech Republic), the Freilingen Formation (Eifelian) of Nollenbach (Eifel, Germany), the Greifensteiner Kalk (near Emsian–Eifelian boundary) of Greifenstein (Lahn-Dill-Kreis, Germany), the Amerboh Group (late Emsian) of the eastern Anti-Atlas ( Morocco), the Kopanina Formation (Ludfordian, Silurian) of Mušlovka quarry ( Bohemia, Czech Republic).

Figures

Fig. 2. Zophocrinid crinoid Tiaracrinus jeanlemenni sp. nov., probably late Polygnathus patulus Conodont Biozone, late Anarcestes lateseptatus Ammonoid Biozone, latest Emsian, Early Devonian, eastern Anti-Atlas Morocco. A. PIMUZ 29739, holotype, “Red cliff” at Hamar Laghdad, Tafilalt. Lateral views (A1, A2), showing the radial channel and the rib-fields; note the ornamentation in the channel near the oral surface in A2. Aboral view (A3), note the small cross section of the trimeral basals and the low rim around it. Oral view (A4), note the ornamentation in the channel near the oral surface. Detail of A3 (A5), note the epispires and the uniform thickness of the ribs. On the top right, the subtle striation is faintly visible between the ribs. Oblique view of the aboral side (A6), showing the epispires. Due to weathering, the ribs obtained a tuberculate ornament (A7). B. PIMUZ 29741, paratype, Jebel Oufatene, Maïder. Aboral view (B1), the rib-fields are less vaulted and the cross section of the calyx less quadrate than in the holotype; the fossil on the top left is a spiriferid. Lateral views (B2, B3), showing the narrow ribs and the smooth surface of the radial channels; in the lateral aspect it looks like the radial channel is tapering towards the oral side of the cup.