Tesselacauda kriegerae, Adrain & Karim, 2019

Adrain, Jonathan M. & Karim, Talia S., 2019, Revision of the Early Ordovician (late Tremadocian; Stairsian) cheirurid trilobite Tesselacauda Ross, with species from the Great Basin, western USA, Zootaxa 4661 (2), pp. 201-255 : 215-216

Tesselacauda kriegerae n. sp.

( Plate 13 , Plate 14 , figs 1–16, 19, Plates 15 –18 )

1953 Tesselacauda sp.; Hintze, p. 32.

? 1953 Tesselacauda aff. T. depressa Ross ; Hintze, p. 237, pl. 21, figs 2, 3.

1973 Tesselacauda depressa Ross ; Demeter (partim), p. 48, pl. 1, figs 5, 6, 10, 15 (only; pl. 1, fig. 14 = Pilekiinae gen. nov. 3 sp. nov. B of Adrain et al. [2014, p. 179, fig. 12EE]).

2014 Tesselacauda sp. nov. 2; Adrain et al., p. 179, fig. 12Y, DD.

Material. Holotype, cranidium, SUI 147597 (Pl. 13, figs 10, 12, 13, 18), and assigned specimens SUI 147599, 147601, 147606, 147617, 147618, 147620, and 147622, from Section C 111.6 m, southern House Range, assigned specimens SUI 147595–134173, 147598, 147600, 147603–147605, 147607–147611, 147614–147616, 147623– 147625, 147627, from Section G 26.6 m, and assigned specimens SUI 147602, 147619, 147621, 147626, from Section G 27.0 m, southern Confusion Range, all Fillmore Formation (upper Tremadocian; Stairsian; Bearriverops alsacharovi Zone ), Ibex area, Millard County, western Utah. Assigned specimens SUI 147628, 147633, 147642, 147643, from Section HC6 122.5 m, and SUI 147629–147632, 147634–147641, from Section HC6 124.0 m, Garden City Formation (upper Tremadocian; Stairsian; Bearriverops alsacharovi Zone ), west side of Hillyard Canyon, Franklin Basin, Bear River Range, Franklin County, southeastern Idaho.

Etymology. After Elinor Krieger Coble.

Diagnosis. Dorsal cranidial surfaces with very fine tuberculate sculpture, effaced on glabella in some specimens; posterior projections of intermediate size between T. depressa and T. morrisoni , and of intermediate slope; pygidium with most of dorsal pleural regions effaced, tubercles expressed on at least medial and posterior parts of pygidial axis of large specimens, over entire axis of some specimens; terminal piece small, with length and width subequal.

Description. As with T. morrisoni , a comparison of T. kriegerae and T. depressa is provided. The cranidium of T. kriegerae has the fulcrum set slightly closer to glabella and the posterior projections more strongly downturned giving the appearance that it is overall narrower than T. depressa ; the glabella is broader (tr.) posteriorly and gently tapered anteriorly, with the anterior margin gently anteriorly arched so that overall the glabella appears much less subquadrate, in lateral profile the glabella is held more parallel to horizontal plane with only the front portion (from anterior portion of L3 forward) sloping downward, and LF more strongly inflated; anterior border is shorter (sag.) and more evenly anteriorly arched; the fossulae are deeper; the palpebral lobes are slightly smaller and less steeply angled, with the posterior extension of the palpebral lobe thinner and more posterolaterally directed; the palpebral furrow intersects the axial furrow a little further back along L3; sculpture smooth or with finer tubercles.

Hypostomes of T. kriegerae and T. depressa are very similar, but those of the former are slightly more subquadrate with sagittal length 92.9% (90.8–95.7%) maximum width; the posterior margin of T. kriegerae is more sinuous with a more clearly developed median embayment; middle body less inflated; posterior lobe of middle body more clearly covered with fine granules; anterior wings not as laterally extensive, terminating about level with lateral extent of shoulders, and they are more strongly dorsally flexed; posterior spine pair more robust.

Librigenae of T. kriegerae possess coarse granules on the adaxial portion of border, whereas that portion is smooth and lacks sculpture in those of T. depressa ; sculpture along abaxial portion of the border is coarser; border furrow is broader; overall librigenae are less elongate.

Thoracic segments with much more prominent tubercles on axial ring and distinct row of prominent tubercles on anterior and posterior pleural bands.

Pygidia are narrower (tr.) and dorsoventrally taller, so that pleurae appear longer in posterior view; first pleural segment is directed more posteriorly than in T. depressa , giving anterolateral corner an angular rather than gently rounded appearance; row of tubercles along posterior margin of articulating half-ring more prominent along entire margin (cf. Pl. 16, fig. 2; Pl. 6, fig. 2); first axial segment is slightly longer (sag., exsag.) than T. depressa ; terminal piece is narrower, with width (tr.) and length (sag.) subequal, and on one specimen it is absent (Pl. 16, figs 7, 10; the fourth pair of pleural spines on this specimen are also noticeably smaller than the previous three pairs [see Pl. 16, fig. 13], which is unlike the other recovered T. kriegerae pygidia); sculpture of larger tubercles, which are primarily located on the axis and tips of pleurae, with the occasional tubercle present on the pleurae just adjacent to the axis; doublure taller, especially medially, in anterior view.

Ontogeny. Several juvenile sclerites were recovered from the Garden City Formation at the HC6 section and allow for a more detailed description of the ontogeny of T. kriegerae as follows. The glabella broadens (tr.) posteriorly and gently expands laterally so that it becomes less subrectangular throughout ontogeny; LO–L3 become broader (cf. Pl. 17, fig. 11; Pl. 13, fig. 1); the posterior projections broaden distal to fulcrum and become less strongly downturned from horizontal plane; and a very small nubbin-like genal spine is present on smaller specimens (e.g., Pl. 17, figs 3, 9), it becomes greatly reduced throughout ontogeny. One of the most noticeable ontogenetic changes is the reduction in the prominent tuberculate sculpture present on smaller specimens. The tubercles are coarse, densely spaced, and sometimes elongated (see Pl. 17, figs 11, 12), but they become less dense, much smaller, and less prominent, and totally effaced on some parts of the cranidium of the larger specimens. The pattern of reduction of these prominent tubercles appears to proceed from the posterior portion of the cranidium anteriorly. For example, tubercles cover the fixigenal field on the smallest specimens, but start to become effaced on the posteromedial portion of field (Pl. 17, fig. 2), and eventually the field is nearly free of any larger tubercles (see e.g., Pl. 13, fig. 13); this change also allows for the background sculpture of deep pits on the fixigena to become the dominant sculpture on larger specimens. A similar pattern also appears to be present on the glabella, with a progressive forward reduction in tubercles (cf. Pl. 17, 11; Pl. 14, fig. 1, and Pl. 13, fig. 13). A similar pattern of progressively forward reduction can be seen on the posterior and lateral borders, palpebral lobe, and anterior border; the latter retains a sculpture of much finer granules on the largest specimens.

The smallest hypostome (Pl. 18, fig. 18) has sagittal length 87.0% the maximum width (tr. across the anterior wings) and is relatively slightly wider compared to larger specimens; a sculpture of coarser tubercles (especially on anterior portion of middle body) is present, which becomes finer and more densely spaced; the shoulders become more laterally expanded and rounder; the anterior portion of middle body lengthens; the posterior margin is more transverse, with the median embayment developing later in ontogeny; the anterior spine pair are more posteriorly directed on smallest specimen, and become more laterally directed throughout ontogeny; and the posterior border furrow becomes more effaced, with smallest specimen possessing clear definition between posterior lobe of middle body and posterior border.

The librigena becomes more elongate, with the posterior projection becoming much longer and also thinner; the smallest librigenae possess a region of larger tubercles on the inner portion of the librigenal border, which become reduced throughout ontogeny, with the region covered by much smaller tubercles in larger specimens; the coarse granular sculpture present along the external and ventral margins of the border also become finer throughout ontogeny.

Throughout ontogeny, the pygidium becomes dorsoventrally taller and more inflated, partly due to a lengthening of the pleural region distal to the fulcrum; the axial segments and ring furrows become more transverse and less anteriorly arched; the width of the terminal piece (across its anterior margin) becomes more noticeably smaller than that of the fourth segment; the anterior band of the third pleural segment is just visible on the smallest pygidium (Pl. 18, fig. 28), but is lost during ontogeny and not present on larger specimens.

Discussion. Tesselacauda kriegerae was compared with T. morrisoni in discussion of the latter species. Hintze (1953, p. 237, pl. 21, figs 2, 3) assigned a partial cranidium and a hypostome to “ Tesselacauda aff. T. depressa ”. The given provenance was his locality C-6, which was at 390’ (118.9 m) in his Section C. We have not resampled this horizon, but a collection we made from 380’ (115.8 m), following Hintze’s painted numbers, is from the Pseudoclelandia weymouthae Zone. In all of our sampling, we have not encountered any material of Tesselacauda from this zone or any younger rocks. Tesselacauda kriegerae n. sp. occurs at C 111.6 m and Hintze’s specimens most likely represent this species.

Figures

PLATE 13. Tesselacauda kriegerae n. sp., from Section G 26.6 m and Section C 111.6 m, both Fillmore Formation (upper Tremadocian; Stairsian; Bearriverops alsacharovi Zone), Ibex area, Millard County, western Utah, USA. 1–4. Cranidium, SUI 147595, dorsal, ventral, left lateral, and anterior views, x6 (G 26.6 m). 5, 6, 8. Cranidium, SUI 147596, dorsal, left lateral, and anterior views, x6 (G 26.6 m). 7, 9, 11, 14, 16. Cranidium, SUI 134173, dorsal, left lateral, ventral, anterior, and oblique views, x7.5 (G 26.6 m). 10, 12, 13, 18. Cranidium, holotype, SUI 147597, left lateral, ventral, dorsal, and anterior views, x6 (C 111.6 m). 15, 25, 26. Cranidium, SUI 147598, left lateral, anterior, and dorsal views, x6 (G 26.6 m). 17, 22, 23. Cranidium, SUI 147599, dorsal, anterior, and left lateral views, x8 (C 111.6 m). 19, 20, 24. Cranidium, SUI 147600, anterior, right lateral, and dorsal views, x6 (G 26.6 m). 21. Cranidium, SUI 147601, dorsal view, x6 (C 111.6 m).

PLATE 14. 1–16, 19. Tesselacauda kriegerae n. sp., from Section G 26.6–27.0 m and Section C 111.6 m, both Fillmore Formation (upper Tremadocian; Stairsian; Bearriverops alsacharovi Zone), Ibex area, Millard County, western Utah, USA. 1, 2, 4. Cranidium, SUI 147602, dorsal, right lateral, and anterior views, x17 (G 27.0 m). 3. Right librigena, SUI 147603, external view, x15 (G 26.6 m). 5, 8, 10. Right librigena, SUI 147604, internal, external, and ventrolateral views, x12 (G 26.6 m). 6. Left librigena, SUI 147605, external view, x12 (G 26.6 m). 7. Right librigena, SUI 147606, external view, x15 (C 111.6 m). 9. Left librigena, SUI 147607, external view, x15 (G 26.6 m). 11. Left librigena, SUI 147608, external view, x15 (G 26.6 m). 12, 14, 16. Left librigena, SUI 147609, external, internal, and ventrolateral views, x12 (G 26.6 m). 13, 15. Right librigena, SUI 147610, external and ventrolateral views, x15 (G 26.6 m). 19. Left librigena, SUI 147611, external view, x12 (G 26.6 m). 17, 18, 20. Tesselacauda? flabella Kobayashi, 1955, from Section G 26.6 m, Fillmore Formation (upper Tremadocian; Stairsian; Bearriverops alsacharovi Zone), Ibex area, Millard County, western Utah, USA. 17, 18. Pygidium, SUI 147612, dorsal and left lateral views, x6. 20. Pygidium, SUI 147613, dorsal view, x12.

PLATE 15. Tesselacauda kriegerae n. sp., from Section G 26.6–27.0 m and Section C 111.6 m, both Fillmore Formation (upper Tremadocian; Stairsian; Bearriverops alsacharovi Zone), Ibex area, Millard County, western Utah, USA. 1, 5, 9, 13, 17. Hypostome, SUI 147614, ventral, right lateral, posterior, anterior, and dorsal views, x12 (G 26.6 m). 2, 6, 10, 14, 18. Hypostome, SUI 147615, ventral, right lateral, posterior, anterior, and dorsal views, x15 (G 26.6 m). 3, 7, 11, 15. Hypostome, SUI 147616, ventral, right lateral, posterior, and anterior views, x10 (G 26.6 m). 4, 8, 12, 16. Hypostome, SUI 147617, ventral, left lateral, posterior, and anterior views, x15 (C 111.6 m). 19, 20, 24, 28, 31. Pygidium, SUI 147618, left lateral, dorsal, posterior, ventral, and anterior views, x10 (C 111.6 m). 21, 25, 29. Pygidium, SUI 147619, left lateral, dorsal, and posterior views, x10 (G 27.0 m). 22, 23, 30. Pygidium, SUI 147620, posterior, dorsal, and right lateral views, x12 (C 111.6 m). 26, 27, 34. Pygidium, SUI 147621, right lateral, dorsal, and posterior views, x10 (G 27.0 m). 32, 33, 35. Pygidium, SUI 147622, dorsal, posterior, and left lateral views, x10 (C 111.6 m).

PLATE 16. Tesselacauda kriegerae n. sp., from Section G 26.6–27.0 m, Fillmore Formation (upper Tremadocian; Stairsian; Bearriverops alsacharovi Zone), Ibex area, Millard County, western Utah, USA. 1, 2, 4. Pygidium, SUI 147623, dorsal, right lateral, and posterior views, x15 (G 26.6 m). 3, 5, 6. Pygidium, SUI 134174, dorsal, left lateral, and posterior views, x14 (G 26.6 m). 7, 10, 13, 14, 19. Pygidium, SUI 147624, dorsal, posterior, right lateral, ventral, and anterior views, x14 (G 26.6 m). 8, 9, 12, 15. Pygidium, SUI 147625, left lateral, dorsal, posterior, and ventral views, x12 (G 26.6 m). 11, 16, 17. Pygidium, SUI 147626, dorsal, posterior, and right lateral views, x15 (G 27.0 m). 18, 20, 21. Pygidium, SUI 147627, right lateral dorsal, and posterior views, x15 (G 26.6 m).

PLATE 17. Tesselacauda kriegerae n. sp., from Section HC6 122.5–124.0 m, Garden City Formation (upper Tremadocian; Stairsian; Bearriverops alsacharovi Zone), west side of Hillyard Canyon, Bear River Range, Franklin County, southeastern Idaho, USA. 1, 4, 7. Cranidium, SUI 147628, dorsal, anterior, and left lateral views, x15 (HC6 122.5 m). 2, 5, 8. Cranidium, SUI 147629, dorsal, anterior, and left lateral views, x15 (HC6 124.0 m). 3, 6, 9. Cranidium, SUI 147630, dorsal, anterior, and right lateral views, x20 (HC6 124.0 m). 10, 13, 16. Cranidium, SUI 147631, dorsal, right lateral, and anterior views, x20 (HC6 124.0 m). 11, 12, 14. Cranidium, SUI 147632, dorsal, anterior, and right lateral views, x20 (HC6 124.0 m). 15, 17–20. Hypostome, SUI 147633, ventral, posterior, right lateral, anterior, and dorsal views, x15 (HC6 122.5 m).

PLATE 18. Tesselacauda kriegerae n. sp., from Section HC6 122.5–124.0 m, Garden City Formation (upper Tremadocian; Stairsian; Bearriverops alsacharovi Zone), west side of Hillyard Canyon, Bear River Range, Franklin County, southeastern Idaho, USA. 1. Left librigena, SUI 147634, external view, x20 (HC6 124.0 m). 2. Right librigena, SUI 147635, external view, x20 (HC6 124.0 m). 3, 7, 9. Hypostome, SUI 147636, ventral, left lateral, and posterior views, x12 (HC6 124.0 m). 4, 5, 8, 10. Hypostome, SUI 147637, ventral, left lateral, posterior, and anterior views, x15 (HC6 124.0 m). 6. Right librigena, SUI 147638, external view, x15 (HC6 124.0 m). 11, 12, 14, 16. Hypostome, SUI 147639, posterior, ventral, right lateral, and anterior views, x12 (HC6 124.0 m). 13, 15, 17, 20, 24. Thoracic segment, SUI 147640, dorsal, ventral, anterior, posterior, and right lateral views, x15 (HC6 124.0 m). 18, 19, 21, 22. Hypostome, SUI 147641, ventral, anterior, right lateral, and posterior views, x25 (HC6 124.0 m). 23, 26, 27. Pygidium, SUI 147642, dorsal, posterior, and right lateral views, x15 (HC6 122.5 m). 25, 28, 29. Pygidium, SUI 147643, left lateral, dorsal, and posterior views, x20 (HC6 122.5 m).