Drepanoistodus svendi Rasmussen & Eriksson & Lindskog 2021, sp. nov.
Creators: name: Rasmussen, Jan Audun
name: Eriksson, Mats E.
name: Lindskog, Anders
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Conodonta
Distacodontina
Drepanoistodontidae
Drepanoistodus
Drepanoistodus svendi

description: Drepanoistodus svendi sp. nov.
urn:lsid:zoobank.org:act: 0921F27A-ECF6-498C-8943-4DEB96CFBB38
Fig. 6I–L
Drepanoistodus aff. basiovalis (Sergeeva) - Rasmussen 2001: 73–74, pl. 5 fig. 17.— Mellgren et al. 2012: fig. 5u.
Diagnosis
A Drepanoistodus species characterised by a geniculate element with a recurved cusp and distinct keels on both the cusp and the upper margin of the base. Weakly curved but distinct carinas are developed on both sides of the cusp, especially well developed on the inner side.
Etymology
Named after the Danish palaeontologist and conodont specialist Svend S. Stouge, Natural History Museum of Denmark, University of Copenhagen.
Material examinedFive geniculate elements including three from the Lynna section. Holotype, geniculate element (Fig. 6J–K); LO 12483T.
Type localityRiver bank near the mouth of Lynna River, village of Kolchanovo, St. Petersburg region, Russia (60°00′39″ N, 32°33′49″ E).
Type stratum
Approximately 40 cm below the local top of the Volkhov Formation, sample LY 12-14, ca 20 cm above the base of the Lenodus variabilis Zone sensu Lindskog et al. (2020).
Description
Cusp is recurved (bent weakly downward), with distinct keels developed along the anterior (upper) and posterior (lower) margins. A median, longitudinal, weakly curved carina is developed on both sides of the cusp, most distinct on the inner side of the cusp. Cusp is almost twice as long as the upper margin of the cusp; the mean ratio between the length of the free upper margin and the free cusp (Fig. 3) is ca 0.55 with a standard deviation of 0.13. Basal margin varies from rounded (convex) to almost straight. A distinct keel is developed on the upper margin. Anterior margin is rounded or weakly rounded (convex). Angle A (Fig. 3) between the cusp and upper margin of the base varies considerable with a mean of 24° and standard deviation of 6.9 (Fig. 5B).
Zone. L. Same specimen as I in outer view. M–O. Drepanoistodus viirae sp. nov. M. LO 12484T, holotype, inner view, sample LY12-31, interzone (“uncertain interval”) between the Lenodus variabilis Zone and the Yangtzeplacognathus crassus Zone sensu Lindskog et al. (2020). N. Same specimen as M in outer view. O. LO 12485t, inner view, sample LY 12-31, interzone (“uncertain interval”) between the Lenodus variabilis Zone and the Yangtzeplacognathus crassus Zone sensu Lindskog et al. (2020). P–Q. Drepanoistodus aff. basiovalis (Sergeeva, 1963), LO 12486t, inner and outer view, respectively, sample LY12-9, L. antivariabilis Zone. R –S. Drepanoistodus stougei Rasmussen, 1991, LO 12487t, inner and outer view, respectively, sample LY12-13, L. variabilis Zone. T. Drepanoistodus cf. suberectus (Branson & Mehl, 1933), LO 12488t, inner view, sample LY14-2, Y. crassus Zone. Scale bar = 200 μm (all specimens illustrated at same scale).
Remarks
Drepanoistodus svendi sp. nov. is distinguished from all the other Drepanoistodus species in the present study by the recurved cusp and the curved carina on each side of the cusp. Like D. iommii sp. nov., it is characterised by a clearly longer upper margin of the base compared to the cusp length than in D. basiovalis. The D. svendi sp. nov. population is located in the lower, right quadrangle of the PCA plot, far from any other species of Drepanoistodus, and the biplot vectors representing the recurved cusp and the curved carina point in this direction (Fig. 4). The PERMANOVA test on the first seven PCA axis shows that the probability that the D. basiovalis and D. svendi sp. nov. populations are the same, is exceedingly low (p (same) = 1.00E- 04).
Occurrence
The lower part of the L. variabilis Zone (samples LY12-13, LY12-14). Moreover, D. svendi sp. nov. has been recorded from Steinsodden, Norway, from the top of the B. norrlandicus – D. stougei Zone and the base of the overlying B. medius – H. holodentata Zone, which correlate with the middle part of the L. variabilis Zone (as D. aff. basiovalis sensu Rasmussen 2001), and from the L. pseudoplanus Zone or E. suecicus Zone at the island Osmussaar, Estonia (Mellgren et al. 2012; reported as D. aff. basiovalis).
description: Published as part of Rasmussen, Jan Audun, Eriksson, Mats E. & Lindskog, Anders, 2021, Middle Ordovician Drepanoistodus (Vertebrata, Conodonta) from Baltica, with description of three new species, pp. 106-134 in European Journal of Taxonomy 774 on pages 122-123, DOI: 10.5852/ejt.2021.774.1533, http://zenodo.org/record/5557148