Bransonella sp.

Johnson, Gary D. & Thayer, David W., 2009, Early Pennsylvanian xenacanth chondrichthyans from the Swisshelm Mountains, Arizona, USA, Acta Palaeontologica Polonica 54 (4), pp. 649-668 : 665-666

Bransonella sp. “B”

Fig. 18B .

Material.—Single incomplete tooth, UAPL 23512.

Description.—Base longer (am−pl) than wide (l−l; Table 2),

lingual margin bifurcated, but one side of bifurcation and associated anterior/posterior margin missing ( Fig. 18B 1 , B 3 ); asymmetrically−positioned basal tubercle flat to slightly concave, mostly below one principal cusp; apical button subdued with irregular shape, isolated from cusps, with even more subdued lingual extension reaching preserved portion of lingual margin of base; one prominent aboral foramen centrally positioned next to margin of basal tubercle ( Fig. 18B 3 ) plus three smaller foramina; insignificant oral foramina associated with labial margin of apical button, two small foramina on lateral (am/pl) side of lingual extension of base, and one prominent foramen on broken margin of base ( Fig. 18B 1 ) associated with lingual aboral groove ( Fig. 18B 3 ); central foramen may be present. Principal cusps slightly unequal, with distal 1/4 missing in both; both slightly labio−lingually compressed at base and nearly round at distal ends; slightly larger cusp (right side in Fig. 18B 1 ) with longest transverse axis 30° to labial margin, smaller (?posterior) cusp Ṥ 15°; larger cusp with three labial cristae plus one each on lateral and medial margins, smaller cusp with four cristae plus one medial crista (right cusp in Fig. 18B 2 ), most extending onto base, with two on base between cusps (some are too faint to show in Fig. 18B 2 ); lingual cristae absent or faint

( Fig. 18B 1 , Table 2). Intermediate cusp absent. Remarks.—Two anomalies are obvious in UAPL 23512, the offset basal tubercle and lack of an intermediate cusp. The absence of an intermediate cusp is unknown in Bransonella nebraskensis ( Johnson 1984) but its absence sometimes occurs in B. lingulata ( Ivanov and Ginter 1996: 654) . This absence is often associated with posterior teeth in Orthacanthus ( Hampe 1988: fig. 2; 2003: fig. 10d; Johnson 1999) and possibly symphyseal teeth ( Hampe 2003: 206). There is no evidence UAPL 23512 is malformed, despite the position of the basal tubercle; perhaps it is associated with position in the dental arcade, i.e., perhaps posterior, which may also explain the unusual angles between the proximal transverse axes of the cusps relative to the labial margin ( Table 2). The deeply bifurcated (although incomplete) base precludes UAPL 23512 from belonging to B. lingulata . Although matrix obscures a slight concavity in the position of a central foramen, it is almost certainly present, unlike any known Bransonella tooth; tooth size and fragility precluded any opportunity to remove the matrix. But, despite this uncertainty, and given its other features, UAPL 23512 very likely belongs to Bransonella .

Discussion of Bransonella .— Hampe (2003: 226) suggested Bransonella may not be a xenacanthid because of the chevron pattern of the cristae on the labial side, including the base, and the presence of a kidney−shaped basal tubercle and labial foramina on the base of the teeth. The shape of the basal tubercle is too variable ( Fig. 18 , Table 2; Johnson 1984: figs. 1, 3c, 10a) to be of much taxonomic use, although in a majority of Bransonella teeth it probably is lunate (or kidney) shaped ( Ivanov 2005). However, the generally distinct labial rim on the basal tubercle ( Ivanov and Ginter 1996: 652, 656) is unlike that in other xenacanthid genera. This, along with some resemblance of the cristae to Jalodus ( Ginter 1999) , which has a chevron (en echelon) cristae pattern on its three cusps, suggests a close relationship between the Xenacanthida and Phoebodontiformes ( Ginter 1999; Ginter et al. 2002; Ivanov 2005). Hampe (2003: 226) suggested that there is a consistent similarity between the patterns of the cristae between Bransonella and certain nonxenacanthid sharks, which he considered as phoebodontids ( Adamantina ; see also Ivanov 1999). Ivanov and Ginter (1996) and Ivanov (2005) were probably correct in suggesting that Bransonella is a xenacanthid, but probably in a new family ( Ivanov and Ginter 1996: 656), and probably in a new suborder within the Xenacanthida . Hampe and Ivanov (2007a) proposed that Bransonella and Barbclabornia ( Johnson 2003) be placed in a new order, Bransonelliformes . Their primary reason was that both genera possess chevron (inverted “V”−nested) cristae as opposed to all other xenacanthimorphs ( Hampe and Ivanov 2007a) that either possess moreor−less straight (vertical) cristae (as in Triodus ) or no cristae (e.g., Orthacanthus ). They also cite the presence of foramina on the labial margin of the tooth base, but these foramina often appear to be absent in Barbclabornia ( Johnson 2003: figs. 8–11). However, when viewed at higher magnification, a foramen the size of a “microdot” is often observed in these teeth. Hampe and Ivanov (2007a: fig. 1E) indicate one in SMU 64112 ( Johnson 2003: fig. 9M); in the remainder of the illustrated teeth from the same fauna ( Johnson 2003: figs. 8K–N, 9), a labial foramen was confirmed in all but one (SMU 64110), and indeterminate in one (SMU 64108). Near the top of the Texas section, in the Little Moonshine Creek fauna, the 99 measured teeth ( Johnson 1996, 2003: tables 1, 2) were reexamined for the presence of labial foramina; they are present in 69, absent in 24, with six indeterminate. Some had several foramina, and some slightly larger than the “microdot” variety, but still smaller than those shown in illustrations by Johnson (2003: figs. 4–11) except for the very smallest (e.g., Johnson 2003: fig. 10A). The labial foramina are usually on the basal tubercle, but sometimes below one of the cusps. Therefore, although not universal, the presence of labial foramina in Barbclabornia might be considered as a significant character.

Finally, Hampe and Ivanov (2007a) cite the frequent occurrence of a large central lingual foramen leading to a main nutrient canal, which may be a valid character. However, it can also occur in phoebodonts ( Phoebodus gothicus ; Hampe 2000: 358) and in a tooth of uncertain but related affinity ( Johnson 2005b: fig. 1 D, F), and in Diplodoselache parvulus ( Hampe 2003: fig. 6a), Orthacanthus platypternus (Johnson 1999: fig. 13 M). Orthacanthus donnelljohnsi sp. nov. also has a lingual foramen ( Fig. 5A ), but its size is insignificant relative to Hampe and Ivanov’s (2007a) character.

Hampe and Ivanov (2007a) established the priority of Xenacanthiformes Berg, 1940 , over Xenacanthida Glickman, 1964 , ordinal names used interchangeably by various authors; both names are used in this report to reflect usage by various authors.

Bransonella may be the only exclusively marine xenacanth genus. It occurs in marine faunas [ Harlton 1933 ( Zidek 1972, 1973; Suneson and Hemish 1994: 74–82, 103–107); Kozur 1984: 143, pl. 9; Duffin et al. 1996: 238; Ginter et al. 2002: 189; Ivanov 2005] and mixed marine and nonmarine faunas [ Johnson 1984 ( Ossian 1974); Thayer 1985], otherwise not explicitly stated in other references given here, but is associated with other presumably marine chondrichthyans. Bransonella was not present among a variety of marine chondrichthyans described from the Middle Pennsylvanian (upper Moscovian) of central Arizona ( Elliott et al. 2004), suggesting its habitat may have been restricted, perhaps to shallow marine water (Alexander Ivanov, personal communication December 2008).

The nearly cosmopolitan distribution of Bransonella also suggests a marine habitat (Rodrigo Soler−Gijón, personal communication, August 1999). It is known from North America (see B. nebraskensis above), Europe (see B. nebraskensis and B. lingulata above; Bransonella also occurs in Hungary [ Kozur 1984; Hampe and Ivanov 2007a]), Siberia ( Rodina and Ivanov 2002), Iran ( Bransonella ? sp., Devonian, Ginter et al. 2002), South America ( Duffin et al. 1996 reported the presence of? Triodus , but is actually Bransonella : Rodrigo Soler−Gijón, personal communication August 1999; Martha Richter, personal communication, October 2002; and Hampe 2003: 226), and China ( Wang et al. 2004; Wang 2006). Wang (2006: table 3) reported the occurrence of three undescribed (Nian−Zhong Wang, personal communication, April 2007) species from the Tournasian (also Wang et al. 2004), Moscovian− Kasimovian, and Gzhelian.

Figures

Fig. 18. Bransonelliform chondrichthyan teeth of Bransonella, Lower Pennsylvanian, Black Prince Limestone, Swisshelm Mountains, Arizona; A. Bransonella?lingulata, UAPL 23510; lingual−occlusal (A1,?posterior cusp on left) and labial (A2) views. B. Bransonella sp. “B” with broken bifurcated base, UAPL 23512; lingual−occlusal (B1), labial (B2), and aboral (B3) views. C. Bransonella sp. “A”, UAPL 23511; lingual−occlusal (C1, left cusp obscured by matrix; distal portion of right cusp lost after illustration completed), labial (C2), annteromedial or posterolateral (B3), and aboral (B4) views.

Fig. 1. Diplodoselachid chondrichthyan Orthacanthus donnelljohnsi sp. nov., holotype, adult lateral tooth, UAPL 23384, Lower Pennsylvanian, Black Prince Limestone, Swisshelm Mountains, Arizona; lingual−occlusal (A), labial (B), anteromedial (C), and aboral (D) views. Compare with Hampe (2003: fig. 2).

Fig. 3. Diplodoselachid chondrichthyan Orthacanthus donnelljohnsi sp. nov., adult posterolateral tooth (broken intermediate cusp), UAPL 23388, Lower Pennsylvanian, Black Prince Limestone, Swisshelm Mountains, Arizona; lingual (A), lingual−occlusal (B), labial (C), posterior (D), and aboral (E) views.

Fig. 2. Diplodoselachid chondrichthyan Orthacanthus donnelljohnsi sp. nov., adult medial tooth, UAPL 23491, Lower Pennsylvanian, Black Prince Limestone, Swisshelm Mountains, Arizona; lingual−occlusal (A), aboral (B), labial (C), and anterior (D) views.

Fig. 5. Diplodoselachid chondrichthyan Orthacanthus donnelljohnsi sp. nov., adult lateral tooth, UAPL 23383, Lower Pennsylvanian, Black Prince Limestone, Swisshelm Mountains, Arizona; lingual−occlusal (A), aboral (B), and labial (C) views.