Laffonia helvetica Heer, 1877

Laffonia helvetica Heer, 1877

( Figs. 3 View Fig , 4 View Fig ; see also the surface scan data on Sketchfab)

Description

Te specimen exhibits a three-dimensionally preserved fusiform capsule ( Fig. 3A–C View Fig ). It measures round to 108 mm in length, 41 mm in width across the middle of the inferred dorsal surface, and 7 mm in maximum height in the lateral body surface. Te central body is about 67 mm long and 35 mm wide. It tapers distally with the inferred anterior end slightly wider than the posterior. Te anterior end of the body is truncated and not preserved, and the body surface herein is slightly folded inwards ( Figs. 3A View Fig and 4A View Fig ), while the posterior extends outwards forming a long, narrow appendage, i.e. the pedicle ( Figs. 3A, B View Fig and 4B View Fig ). Te preserved part of the pedicle is straight and gradually flattens and fades into the rock without a clear end ( Figs. 3A View Fig , 4B View Fig ). Te width of the distal-most preserved edge of the pedicle is 7 mm and the length of the pedicle is around 40 mm.

Te body surface is ornamented with at least seven distinctive longitudinal ribs ( Figs. 3A, B View Fig , 4A, B View Fig ) that are interrupted at the broken anterior end but continue along the pedicle until its preserved distal-most edge. Tree ribs are evenly distributed on the dorsal surface ( Fig. 3A, D View Fig ), and the distance between the ribs on the middle region is about 11 mm. Tree ribs are arranged densely on the inferred left lateral surface ( Fig. 3B, E View Fig ), with interval distance being 3–4 mm. No longitudinal ribs are identified on the ventral surface, which is largely obscured by the matrix ( Fig. 3C, F View Fig ). Te right lateral surface is only partially exposed at the anterior end of the body, which is apparently compacted into a flat plane ( Fig. 3A View Fig ). Numerous fine oblique lines that are arranged longitudinally are visible between two ribs on the lower middle of the left lateral surface ( Fig. 3B, E View Fig ), but no such lines are observed on the dorsal surface.

A narrow band of about 5 mm wide and at least 45 mm long extends along the right edge of the central body

( Figs. 3A, D View Fig and 4C View Fig ). It is interrupted at the upper lateral side of the pedicle, and the same band continues along the lower lateral side of the pedicle ( Figs. 3A, D View Fig and 4B View Fig ). Te narrow band contains dense transverse striations and exhibits a prominent longitudinal ridge along the midline of the band ( Fig. 4C–E View Fig ). Another such narrow band is also visible at the left edge of the capsule, which extends along the entire length of the pedicle, but it is interrupted at the lower left side of the body and is slightly bent towards the ventral side ( Figs. 3A, B, D, E View Fig and 4B View Fig ). Te narrow bands are here interpreted as flanges. Overall, it is likely that the flange was present in life along the entire lateral body edges.

Phylogenetic results

Te consensus tree places Laffonia in a clade consisting of Crookallia, Vetacapsula , and recent chimaerid egg capsules, and the latter two branches form a sister group

( Fig. 5 View Fig ). Tis group is supported by bootstrap and jackknife values of 60% and 64%, respectively. Recent elasmobranch egg capsules and the fossil capsules Palaeoxyris , Fayolia, Scyliorhinotheca and Rajitheca are resolved as a clade as well, with Palaeoxyris and Fayolia at the most basal position of this clade ( Fig. 5 View Fig ). Tese two clades are placed in a polytomy with rhinochimaerid and callorhinchid egg capsules and Vaillantoonia ( Fig. 5 View Fig ).