Barlowodus undetermined
Creators: name: Burrow, Carole Jan
name: Murphy, Michael
name: Turner, Susan
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Thelodontiformes
Barlowodidae
Barlowodus
Barlowodus undetermined

description: BARLOWODUS SP. CF. B. TRIDENS
(FIG. 7 P- S; TABLE 1; SUPPL. 1, FIG. 4)
Referred specimens—one scale from BC II level 430.5’ (131.2 m); one from level 527.25’ (160.7 m); one scale AMF 97874 from BC II level 875’ (266.7 m); this last specimen is missing: Roberts Mountains Formation.
Description and comparison—A scale figured by Parkes (1995, fig. 22.15, 16, captioned as?nikoliviid gen. et sp. indet.; Fig. 7P, Q) is c. 0.4 mm long with a broken posterior crown, which rises quite steeply posteriad. The dorsal crown is elongated and subdivided into three with a raised central section with two high flat-topped ridges with a deep central groove anteriorly that flattens posteriad. Laterally there are expanding lappets,one anteriorly seen to the left, also with a bifurcate dorsal ridge that extends about one-third of the crown, and on the left a series of two broken and one complete ridge that extends about two-thirds of crown length. The posterior points of the lappets tend to be rounded but are also broken. A flattened lateral ridge then extends from the base of the lappets towards the broken posterior tip. The ventral crown is covered with an ultrasculpture of fine parallel striae extending from the anterior crown/neck interface to the posterior tips of the lateral lappets and posterior section of the broken crown. The neck itself is relatively shallow and unornamented. The base is oval, extending about one-quarter of the estimated length of the scale. It is relatively mature with a thick torus surrounding the large central oval pulp opening and with a slight anterior thickening. One small, rounded scale has a strong tripartite crown with deep grooves between the high flat ridges. It is most like the simpler cephalopectoral or trunk of B. tridens (e.g., Märss et al. 2006, text-fig. 65) from the Přidolí Barlow Inlet Formation of Cornwallis Island. The scale from level 527.25’ is tricuspid with clear striated ridges on the sides of the cusps (Fig. 7R, S).
Remarks— Märss et al. (2002, 2006) discovered the thelodont genus Barlowodus in the southern section eastern Cornwallis Island at Read Bay (RBBI and RBBI*), which became the stratotype for the Přidolí Barlow Inlet Formation that is formed from argillaceous carbonate marine rocks. At 59.0 m from only one sample, Märss et al. (2002) identified three taxa, Barlowodus tridens, B. excelsus, and B. floralis, the latter doubtfully. Barlowodus tridens sensu stricto is only known elsewhere from Cornwallis Island. However, scales possibly from this, as well as the other two species of this genus, were recorded from the late Přidolí Barlow Inlet Formation by Märss et al. (2006, pp. 124-126).
The fine microornament on the scale figured by Parkes (1995, fig. 22.15,16; Fig. 7P, Q) is similar to that in other Devonian taxa such as Neoturinia spp., Barlowodus florialis and even Boothialepis thorsteinssoni (Märss et al. 2006, pl. 16). Such fine ridging on the scales might have contributed to drag reduction (e.g., Reif 1985). It is unusual in the Nevadan case being on the ventral surface of the crown; we tentatively refer it to B. sp. cf. tridens. However, it is at a level much higher than the other thelodont scales, in the lower to middle Lochkovian.
description: Published as part of Burrow, Carole Jan, Murphy, Michael & Turner, Susan, 2023, Late Silurian to earliest Devonian vertebrate biostratigraphy of the Birch Creek II section, Roberts Mountains, Nevada, U. S. A., pp. 1-32 in PaleoBios 40 (4) on pages 24-25, DOI: 10.5070/P940454153, http://zenodo.org/record/10913559