Kinnella laurentiana, Stott & Jin, 2007

Stott, Christopher A. & Jin, Jisuo, 2007, The earliest known Kinnella, an orthide brachiopod from the Upper Ordovician of Manitoulin Island, Ontario, Canada, Acta Palaeontologica Polonica 52 (3), pp. 535-546 : 539-541

publication ID	https://doi.org/ 10.5281/zenodo.13741465
persistent identifier	https://treatment.plazi.org/id/03DDDF58-FFF2-7D5C-4015-B721FBE4F87B
treatment provided by	Felipe
scientific name	Kinnella laurentiana
status	sp. nov.

Treatment

Kinnella laurentiana View in CoL sp. nov.

Figs. 3–5 View Fig View Fig View Fig .

Derivation of the name: After Laurentia, the tectonic plate of North America.

Type material: Holotype, GSC 117899 View Materials ( Fig. 3B View Fig ), and ten figured paratypes, GSC 117898 View Materials (conjoined shell), GSC 117900–117902 View Materials (conjoined shells; Fig. 3C–E View Fig ), GSC 117903–117905 View Materials (ventral valves; Fig. 5A–C View Fig ), GSC 117906–117908 View Materials (dorsal valves; Fig. 5D–F View Fig ).

Type locality: Roadside section 2 km west of Kagawong , Manitoulin Island , Ontario, Canada. Coordinates: 45°54’54.5”N Latitude, 82°16’ 41.7”W Longitude; UTM 0400871 easting, 5085414 northing GoogleMaps .

Type horizon: Lower Kagawong Submember (Gore Bay Biostrome), upper Georgian Bay Formation,Richmondian (mid−Ashgill;upper Katian).

Material.—About 750 silicified specimens, mostly disarticulated valves; all from the Lower Kagawong Submember of the Georgian Bay Formation, Manitoulin Island.

Diagnosis.—Shell small, transversely subelliptical to subquadrate, subequally biconvex with moderately convex dorsal valve; ventral interarea high, apsacline (60–65° with commissual plane) in adult shells, catacline in juveniles; cardinal process swollen anteriorly in larger shells.

Description.—Shell small, transversely subelliptical to subquadrate in outline, strongly and subequally biconvex with ventral valve slightly deeper ( Figs. 3A–E View Fig , 4 View Fig ); average length 3.76 mm (max = 8.1 mm), width 4.8 mm (max = 9.1 mm), and thickness 2.4 mm (max = 5.0 mm). Hinge line straight, about four−fifths of maximum width of shell, with rounded to obtusely angular cardinal extremities. Ventral valve with moderately convex umbo and suberect beak, lacking fold or sulcus; ventral interarea high, strongly apsacline at 60–65° angles with commissural plane; with largely planar surface becoming weakly curved in apical portion ( Fig. 3A 3, B 3, C 3 View Fig , D 2 View Fig ), catacline only in immature shells ( Fig. 3E View Fig 2 View Fig ); delthyrium open, long, narrow, trapezoidal in outline, with two sides nearly parallel in portions near hinge line. Dorsal valve gently sulcate from umbo to anterior margin; dorsal interarea anacline, notably lower than ventral, with open notothyrium. Multicostellae fine, 18–20 per 5 mm at 5 mm arc from apex, increasing in number anteriorly by bifurcation or intercalation; capillae and fine growth lines present; coarser growth lamellae irregularly developed.

Ventral interior: Teeth knobby to wedge−shaped; dental plates strong, extending to level of hinge line or slightly beyond, divergent from each other basolaterally and anteriorly, forming lateral bounding ridges of muscle field ( Fig. 5A View Fig 1 View Fig , A 2, B, C 2 View Fig ). Muscle field subrhomboidal to cordate in outline, occupying 40% length and 28% width of valve, with low myophragm and lateral ridges on floor; anterior bounding ridge present in some specimens. Low median ridge originating from midpoint of anterior margin of muscle field, terminating shortly before anterior margin of valve ( Fig. 5B View Fig ). Crenulations strong around periphery of inner surface in both valves.

Dorsal interior: Hinge sockets open antero−laterally, with well−developed fulcral plates. Cardinal process blade−like, with chevron−crenulated myophore, resting directly on valve floor, with inflated anterior end in some specimens ( Fig. 5D–F View Fig ). Notothyrial cavity simple, lacking notothyrial platform. Low, thick myophragm continuous posteriorly with shaft of cardinal process disappearing towards anterior margin of muscle field. Dorsal adductor muscle field large, subrectangular in outline, extending anteriorly for threefifths length of valve; anterior adductor scars separated by transverse ridge from nearly equal−sized posterior pair ( Fig. 5D View Fig 1 View Fig , D 3 View Fig ); lateral bounding ridges low but well defined.

Discussion.—The new species is assigned to Kinnella on the basis of its small size (rarely exceeding 7 mm in length), fine costellae, high and strongly apsacline ventral interarea, and long, narrow delthyrium with an apical callist. Internally, the crenulated cardinal process merges anteriorly into a thick median septum, and there is no notothyrial platform so that the cardinal process and the median septum are sitting directly on the valve floor. These characters, together with the large, quadrilobate dorsal adductor muscle scars, are typical of Kinnella . Kinnella laurentiana can be distinguished from the widely reported Hirnantian species, K. kielanae , in having a more convex dorsal valve and a less strongly apsacline ventral interarea, which typically approach catacline in the adult shells of the type species ( Lespérance and Sheehan 1976; Williams and Harper 2000). In over one hundred specimens examined, there is a notable range of ontogenetic variation in the tilting angles of the ventral interarea: the immature shells tend to have a nearly catacline ventral interarea, which changes gradually to more typically apsacline in increasingly larger shells (compare Fig. 3A–D View Fig with Fig. 3E View Fig ). A similar ontogenetic variation in the orientation of ventral interarea from catacline to apsacline has also been shown by Lespérance and Sheehan (1976) for K. kielanae from the White Head Formation of Percé, Québec. Another species of Kinnella , K. medlicotti ( Reed, 1915) was recently described by Cocks and Fortey (2002) from Hirnantian strata of Burma. This species is distinguished from K. kielanae only by a slightly more transverse shell outline and a larger ventral interarea and may be conspecific with the type species ( Cocks and Fortey 2002). These authors further suggested that the form of Kinnella known from South China, treated so far as K. kielanae (e.g., Rong 1984), more closely resembles K. medlicotti than K. kielanae as known from Europe; they consequently proposed that use of K. medlicotti be extended to South China. With respect to its length/width ratio, K. laurentiana is more similar to K. medlicotti than to typical K. kielanae (see Cocks and Fortey 2002). K. laurentiana can be distinguished from these other species by its commonly apsacline ventral interarea and the anteriorly inflated cardinal process identified in some specimens. Also, observation of the available material indicates that the dorsal median ridge (myophragm) is lower in K. laurentiana than in the type species, although it is not clear whether or not this has been partly due to the generally coarse silicification of the internal structures.