Icriodus alternatus alternatus Branson and Mehl, 1934

Day, Jed & Over, D. Jeffrey, 2002, Post-extinction survivor fauna from the lowermost Famennian of eastern North America, Acta Palaeontologica Polonica 47 (2), pp. 189-202 : 198

Icriodus alternatus alternatus Branson and Mehl, 1934

Fig. 5D–F .

Icriodus alternatus ; Branson and Mehl 1934: 225–226, pl. 13: 4–6 [fig. 4 = lectotype]; Klapper 1975: 69–70, Icriodus pl. 3: 5, 6.

Icriodus alternatus alternatus Branson and Mehl, 1934 ; Sandberg and Dreesen1984:158–159,pl.2:5,11;seehereforfurthersynonymy.

Remarks.—The P 1 (Pa, I) element of Icriodus alternatus is straight to slightly curved; the middle row of denticles are low, compressed, or poorly developed, and may alternate with or be fused to outer denticles. The basal cavity is expanded to widely flared under the posterior third of element. Icriodus alternatus alternatus is distinguished from I. alternatus helmsi byaP 1 elementinwhichthecuspisalignedwith the medial denticles. Specimens from the upper Hanover Shale possess rounded median denticles fused to the lateral denticles. This morphology is suggestive of I. iowaensis Youngquist and Peterson, 1947 , but the lateral and median denticles are not aligned, as well as the fact that no axial ridge connects the medial denticles.

Figures

Fig. 5. Digital images from scanning electron microscope of conodont P1 (Pa) elements from the Hanover Shale Member of the Java Formation, brachiopod bed approximately 1.4 m above the Frasnian–Famennian boundary at Glade Creek, Bartz Road, Wyoming County, New York. All × 60. A–C. Palmatolepis triangularis Sannemann, 1955. A, B. Lower view and inverse mirror−image of mold of upper surface of P1 (Pa) element, NYSM 15682. C. Inverse mirror−image of mold of upper surface of P1 (Pa) element, NYSM 15683. D–F. Icriodus alternatus alternatus Branson and Mehl, 1934. D, E. Upper and oblique outer views of broken P1 (Pa, I) element showing internal mold of posterior end, NYSM 15684. F. Upper view of P1 (Pa, I) element with missing inner posterior margin, NYSM 15685. G. Icriodus alternatus helmsi Sandberg and Dreesen, 1984, upper view of fractured and covered P1 (Pa, I) element, NYSM 15686 (specimen lost).