Portalodus mannoliniae, Potvin-Leduc & Cloutier & Landing & Hernick & Mannolini, 2015

Potvin-Leduc, Daniel, Cloutier, Richard, Landing, Ed, Hernick, Linda Vanaller & Mannolini, Frank, 2015, Givetian (Middle Devonian) sharks from Cairo, New York (USA): Evidence of early cosmopolitanism, Acta Palaeontologica Polonica 60 (1), pp. 183-200 : 186-190

publication ID	https://doi.org/ 10.4202/app.2012.0101
persistent identifier	https://treatment.plazi.org/id/6B2D1521-EF6B-122A-FCED-109CB14F5FD9
treatment provided by	Felipe
scientific name	Portalodus mannoliniae
status	sp. nov.

Treatment

Portalodus mannoliniae sp. nov.

Figs. 3–6 View Fig View Fig View Fig ; SOM 1, 2.

2006 Portalodus bradshawae ; Ginter et al. 2006: 33.

2010 Portalodus bradshawae ; Ginter et al. 2010: 30, fig. 23.

2010 Portalodus sp. nov.; Potvin-Leduc et al. 2010: 148 A.

Etymology: In memory of Sharon M. Mannolini (1968–2003), NYSM, who initiated some of the work at the Cairo locality.

Type material: Holotype NYSM 17715 About NYSM ; paratypes NYSM 17722 About NYSM , 17726 About NYSM , 17736 About NYSM (a juvenile specimen).

Type locality: Cairo quarry, Cairo, Greene County, New York State, USA .

Type horizon: Plattekill Formation, Givetian (Middle Devonian).

Material.— 78 teeth: NYSM 17695–17772 About NYSM , 17959–17964 About NYSM from type locality .

Diagnosis.—Species of Portalodus with cusps smooth on labial and lingual sides. Crown clearly delimited from the tooth base by a collar-like section. Base with at least one, but possibly up to four lingual foramina, with an equal number of labial notches and aboral rostrocaudal grooves. Teeth display a variation in crown and base morphology that is consistent with a monognathic heterodonty. Juvenile teeth smaller (Fig. 5), with cusps more delicate with more pronounced sigmoid shape. Only one lingual foramen present, aboral side almost smooth, without a groove.

Description

General appearance.—The teeth are diplodont, with lingually oriented united cusps. The major and minor cusps are easily distinguished by their asymmetry in size, shape, and orientation; they diverge apically in occlusal and lateral views. Lateral deviation from the base is more pronounced in the major cusp. The cusps are smooth and circular or oval in cross-section. A cutting edge runs along the lateral and mesial edges. The mesial cutting edge is continuous between the cusps. There are no intermediate cusps or crenulations between the cusps. The crown is clearly delimited from the base by a groove. In lateral view, the labial side of the base forms an obtuse angle with the crown; the angle ranges between 122° and 173° (mean = 148°; n = 73). The angle varies with the side of the tooth base, with one part of the tooth base with a slightly more obtuse angle than the other. There is no relation between this angle variation and the major/minor status of the cusps. Part of the base beneath the crown is continuous with it, forming a collar-like section. The base is labially oriented and is devoid of an apical button and basal tubercle. At least one lingual foramen is present.

Two morphotypes were identified based on their size and

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juvenile morphotype adult morphotype linear regression: complete data linear regression: adult linear regression: juvenile shape. The smaller one is interpreted as that of a juvenile Fig. 3 View Fig ) and the larger one is interpreted as adult ( Fig. 4 View Fig ). The proportion of the tooth base, the shape of the crown, and the shape of the cusps also differ between the morphotypes. The ratio of base width to base length is smaller in the juvenile morphotype. The ratio increases linearly with the size of the teeth, without demonstrating different rates of increase between the two morphotypes (Fig. 5). A linear regression for all specimens was significant (F (1, 75) = 1516, p <2.2e- 16), but these regressions were not significantly different when comparing the juvenile and adult morphotypes (ANCOVA: F (3,73) = 525.8, p = 0.1410) (Fig. 5). This increase indicates that growth of the base featured a greater increase in width than in length.

Juvenile morphotype.—The teeth of the juvenile morphotype are similar to the adult morphotype but are much smaller. The width of the base ranges from 0.4 to 2.4 mm and the length of the base ranges from 0.3 to 1.3 mm. The cusps are slender, more compressed laterally, and their sigmoid shape is more pronounced. Distinction between the major and minor cusp is observed but is not as pronounced as in the adult morphotype ( Fig. 3B, C View Fig ). Distinction between the cusps relies mostly on orientation asymmetry. The junction between the crown and the base appears more constricted than in the adult morphotype. The shape of the base is trapezoidal in aboral view. The base widens in the labial direction. The aboral face of the base is smooth. The notch of the labial margin and the basal groove are either absent or barely noticeable. There is a single lingual foramen.

Adult morphotype.— The size of the interpreted adult teeth is variable. The width of the base ranges from 1.2 to 8.8 mm, and the length of the base ranges from 0.9 to 3.7 mm. The cusps tend to be labio-lingually compressed at the base. The relative compression increases as the cusp increases in size. The lingual half of the cusp is more rounded transversally. The cutting edge separates the two sides of the tooth. The cusps are slightly sigmoid in shape, but the minor cusp is straighter. The cusps are either symmetrical ( Fig. 4A, H View Fig ) or show a slight ( Fig. 4B, C View Fig ) to pronounced asymmetry ( Fig. 4D, E View Fig ). The base extends labially; this extension is similar to, or slightly greater than, what is observed in the juvenile morphotype. Its oral surface is covered with low ridges and crevices that begin at the junction of the base and the crown, and radiate from the margin of the base to the crown. The same relief is found on the underside, where it parallels the labio-lingual axis. The base is either round or oval in shape, with its longer axis generally in the medio-lateral axis. In occlusal view, the base may be asymmetrical and extends labially away from the apex of the major cusp. The degree of asymmetry increases with increased deflection of the major cusp ( Fig. 4A–E View Fig ).

The teeth vary in cusp size, orientation, and degree of lateral deflection. This variation is comparable to the monognathic heterodonty found in the Early Devonian Doliodus problematicus ( Miller et al. 2003; Maisey et al. 2009) and Protodus jexi ( Turner and Miller 2008) . The variation in P. mannoliniae sp. nov. teeth is also similar to that described by Johnson (1999) for the Permian xenacanthiform Orthacanthus texensis .

Most teeth have one or two foraminal openings on the lingual margin of the base ( Fig. 4A–C View Fig ), but up to four have been observed ( Fig. 4F View Fig ). The openings on the lingual face are either nearly circular or ovoid and surrounded by a thickened margin that forms a tubercle over the foramen. In rare cases, two superposed openings are present ( Fig. 4H View Fig 2 View Fig , H 3 View Fig ), a condition also observed in the omalodontid Omalodus schultzei ( Hampe et al. 2004) . The number of lingual foramina observed in P. mannoliniae sp. nov. is greater than that noted in P. bradshawae , and appears to be variable and possibly size-related in P. mannoliniae sp. nov. Thus, the number of lingual foramina is not regarded as a diagnostic feature. However, it is interesting that the biggest specimen found at Cairo is about half as large as the largest specimen from Antarctica. Labial notches are present on the labial margin and their number is equal to the number of lingual foramina. The position of the notches varies along the margin; they are usually located in the minor cusp region. Grooves of variable depth that connect a notch to a foramen are often found on the underside of the base, in some cases only weakly developed. The connecting grooves generally parallel the axis of deflection of the major cusp. The number of grooves is equal to the number of foramina.

Two specimens slightly differ from the above-described morphology of the adult morphotype. Specimen NYSM 17758 ( Fig. 4F View Fig ) has a narrow base, as opposed to the broader, rounded base that is more common. Specimen NYSM 17719 ( Fig. 4I View Fig ) shows a secondary cusp that emerges from the mesial side of the major cusp base. A similar feature has been described in Orthacanthus platypternus (specimen SMP-SMU 64308 of Johnson [1987: fig. 3P, R]). Comparable deformed and fused teeth may result from disease, mutation, and trauma ( Johnson 1987; Hampe 1997; Becker et al. 2000), or simple juxtaposition during ontogeny. In this case, trauma or ontogenetic variation is more likely the cause, given that disease and mutation would probably induce more extensive and longer-lasting effects on the whole tooth file rather than on a single tooth ( Becker et al. 2000).

Internal structure.—Both the mature and juvenile morphotypes of Portalodus mannoliniae sp. nov. were investigated by micro-tomodensitometry. Two components were readily identifiable in the teeth: (i) an inner part composing the majority of the tooth, and (ii) an outer layer limited to the crown ( Fig. 6A–C View Fig ). Based on the histology of P. bradshawae ( Hampe and Long 1999) , the internal part of the tooth of P. mannoliniae sp. nov. is identified as trabecular dentine whereas the outer layer would be orthodentine. Hampe and Long (1999) identified in P. bradshawae a third, external layer of enameloid; this layer is not visible in the CT-scan of P. mannoliniae sp. nov. but can be observed in SEM images ( Fig. 6E View Fig 2 View Fig ).

The outer layer of orthodentine is denser and appears darker ( Fig. 6A, B View Fig ). It is present only in the crown, distinguishing it from the base. Hampe and Long (1999) described parallel growth lines in the orthodentine layer in P. bradshawae . One main line is barely distinguishable in the adult morphotype of P. mannoliniae sp. nov. ( Fig. 6A View Fig 2 View Fig ). This line is evident in the SEM pictures ( Fig. 6E View Fig ) and appears to mark a separation between two main layers of orthodentine. The outer layer of the cusp shows the parallel alignment of the dentine tubules ( Fig. 6E View Fig 1 View Fig ).

In Portalodus mannoliniae sp. nov., the cavities of the trabecular dentine are elongated. In the base, they are mostly organized in a lingual to labial direction ( Fig. 6C View Fig ). The cavities become more vertical and wider as they are closer to the crown ( Fig. 6A, B View Fig ), as is the case in P. bradshawae ( Hampe and Long 1999) . One main luminal canal is found within each cusp ( Fig. 6A View Fig 2 View Fig ), but these are accompanied by a network of thinner, vertical cavities ( Fig. 6A View Fig 2 View Fig , D).

Six vascular canals, rather than the four identified by external inspection, cross the base in the labio-lingual axis Fig. 6A, C View Fig ). Two main canals appear to be associated with the median side of each of the cusps. The other four are not symmetrically organized; the left side is irrigated by two small canals, as opposed to a larger single one on the right side ( Fig. 6C View Fig ). The network of cavities is connected to these canals. The basic architecture of the canals is formed by the transverse canals, with the canals extending to the apex of the cusps ( Fig. 6A View Fig 2 View Fig , B 1 View Fig ) and canals connecting the transverse blood canals to the oral surface of the base ( Fig. 6B View Fig 2 View Fig ; see also the video information in SOM).

The cavity network of the trabecular dentine is simpler and the interior of the base appears more porous in the juvenile tooth of Portalodus mannoliniae sp. nov. Otherwise, the organization of the cavities is similar ( Fig. 6G View Fig ). The network formed by the cavities is connected to the single median canal that crosses the base from the lingual to the labial side Fig. 6G View Fig 1 View Fig ). The network of luminae separates into two main canals inside the crown ( Fig. 6F, G View Fig 3 View Fig ) making the cusps more closely connected when compared to the wider separation observed in the base of adult tooth. The cusps are occupied by a single central canal ( Fig. 6H View Fig ), indicating that growth of the tooth was accompanied by addition of canals in the cusp peripheral to the main one. The canal in the cusp connects directly to the median transverse canal ( Fig. 6H View Fig 1 View Fig ). As in the adult morphotype, the median transverse canal is connected by another canal to the oral surface of the base ( Fig. 6H View Fig 2 View Fig ).

Remarks.— Portalodus teeth from the Plattekill Formation identified by Ginter et al. (2010) as P. bradshawae are interpreted herein as those of a new species. This identification is based on the absence of striations on the lingual side of the cusps in P. mannoliniae sp. nov. Variation in the number of cristae is not considered as a valid criterion to distinguish Portalodus species because it is often size-dependent ( Ginter 2004). However, we interpret the cristae by their presence ( P. bradshawae ) or absence ( P. mannoliniae sp. nov.), and regard this character as a valid criterion for specific distinction ( Ginter and Ivanov 1996). While separation between the crown and the tooth base is apparent in P. bradshawae , delimitation is more definite in P. mannoliniae sp. nov. The crown in P. mannoliniae sp. nov. is continuous with a collar-like section of the base that is not seen in described specimens of P. bradshawae ( Long and Young 1995) .

The relative size between the two taxa could support the distinctiveness of the two taxa. In Portalodus bradshawae , the minor cusp is described as at least 33% shorter than the major cusp. Most of the available specimens of P. mannoliniae sp. nov. have either one or both cusps broken. On specimens with fairly well preserved cusps, wear damage was evident, thus indicating that the observed length of the cusp is not representative of its initial length. Consequently, it is not possible to determine if the size relationship described for P. bradshawae holds true for P. mannoliniae sp. nov. However, the few complete teeth of P. mannoliniae sp. nov. either do not present as important a difference between the cusps or have cusps of similar length, both in the juvenile ( Fig. 3A View Fig ) and the adult morphotypes ( Fig. 4A, B, H View Fig ). Teeth showing cusps of similar size could either be symphyseal teeth, or it is possible that P. mannoliniae sp. nov. differs from P. bradshawae by the fact that the minor and the major cusps are of comparable size. None of the specimens, even among the damaged ones, appear to show size discrepancies as important as that seen in specimen AMF 54330 of Long and Young (1995: fig. 7A, D; identified as SN96a [Gavin Young, personal communication 2013]).