Pauxillites thaddei, Valent & Corbacho, 2015

Valent, Martin & Corbacho, Joan, 2015, Pauxillites Thaddei A New Lower Ordovician Hyolith From Morocco, Acta Musei Nationalis Pragae Series B 71 (1 - 2), pp. 51-54 : 53

Pauxillites thaddei sp. nov.

Text-fig. 2–3

2013 Pauxillites sp. ; Valent et al., 2013, p. 22, fig. 4A.

H o l o t y p e. GMSB 81381 ( Text-fig. 3b ) part of inner surface of operculum.

P a r a t y p e s. GMSB 81382 ( Text-fig. 3b ), GMSB 81383 and GMSB 81384 ( Text-fig. 3a ) ventral sides of conch.

T y p e l o c a l i t y. Outcrop about 25 km northwest of the town of Zagora, Morocco. The coordinates of the site are N 30º 33.505’ and W 005º 54.316’ .

T y p e h o r i z o n. Upper Fezouata Formation, Floian,

Lower Ordovician.

E t y m o l o g y. After the Czech name Tadeáš (Thaddeus in Latin).

M a t e r i a l. Rock sample with three ventral sides and one incomplete internal surface of operculum.

D i a g n o s i s. Middle-sized hyolithid with strongly rounded ligula, highly rounded dorsum, flat venter and sharply rounded lateral edges. Triclaviculate operculum with long narrow clavicles extending to 4/5 of the operculum diameter. rounded wide ligula. Length of ligula is half of its width. Venter bears fine growth lines. Lateral edges sharply rounded. Based on the operculum, the presumed shape of the complete dorsum was highly rounded. Fragment of dorsum with only fine longitudinal costae; partially visible on the lateral sides of uncovered dorsum. Separate dorsum not found. No other type of ornamentation was ascertained. Type of aperture is not distinguishable.

The size of the triclaviculate operculum clearly corresponds with the nearby ventral side of the conch. The long narrow clavicles are regularly spaced, and reach 4/5 of the operculum diameter. The angle of divergence of the central clavicles is 68°. One elongated bent muscle scar is visible in the area between the clavicles. No muscle scars visible on the conch. No helens were found.

O c c u r r e n c e. This species is known only from the type locality.

D i s c u s s i o n. The newly described species clearly fits the diagnosis of the genus Pauxillites MAREK, 1966 , in the morphology of the conch and triclaviculate operculum. Pauxillites thaddei sp. nov. resembles the subspecies Pauxillites pauxillus meridionalis MAREK, 1983 (Upper Fezouata Formation, Floian, Lower Ordovician; Morocco) in the distribution of clavicles, but differs in having substantially longer clavicles, which extend to 4/5 of the operculum diameter.

D e s c r i p t i o n. Middle-sized hyolithid (about 20 mm long) with straight orthocone conch. Longest specimen 23 mm. Apical angle about 25°. Flat venter with strongly

Figures

Text-fig. 2. Pauxillites thaddei sp. nov., a – reconstruction of ventral side of conch with visible growth-lines and rounded lateral edges; b – reconstruction of inner surface of triclaviculate operculum with muscle scar in the area between clavicles. The dotted line represents the predicted shape of cardinal area.

Text-fig. 3. Pauxillites thaddei sp. nov. a – two complete ventral sides (GMSB 81383 and GMSB 81384) with complete trilobite exoskeleton (Asaphellus sp.). b – complete venter (GMSB 81382) together with part of inner surface of triclaviculate operculum (GMSB 81381). Scale bar 5 mm.