Myliobatis sp. 2, Cuvier, 1816

Ebersole, Jun A., Cicimurri, David J. & Stringer, Gary L., 2019, Taxonomy and biostratigraphy of the elasmobranchs and bony fishes (Chondrichthyes and Osteichthyes) of the lower-to-middle Eocene (Ypresian to Bartonian) Claiborne Group in Alabama, USA, inclu, European Journal of Taxonomy 585, pp. 1-274: 130-133

publication ID

https://doi.org/10.5852/ejt.2019.585

publication LSID

lsid:zoobank.org:pub:181B6FBA-ED75-4BB4-84C4-FB512B794749

DOI

http://doi.org/10.5281/zenodo.3664250

persistent identifier

http://treatment.plazi.org/id/18174D41-FF04-FF2B-FD7D-9EE84E960C74

treatment provided by

Plazi

scientific name

Myliobatis sp. 2
status

 

Myliobatis sp. 2 

Figs 47View Fig K–T, 48

Myliobatis toliapicus – Clayton et al. 2013  : fig. 4.g – i.

Ariidae  – Maisch et al. 2016: fig. 3.1–2.

Material examined

UNITED STATES OF AMERICA – Alabama • 287 isolated teeth; Claiborne Group ; ANSP 23427View Materials, MSC 35007, MSC 35008, MSC 35944 (7 specimens), MSC 35945, MSC 37103, MSC 37152, MSC 37290, MSC 37337 (12 specimens), MSC 37560, MSC 37656, MSC 38640, MSC 38790 (6 specimens), MSC 38795View Materials (5 specimens), MSC 38802View Materials (3 specimens), MSC 38804, MSC 38809 (19 specimens), MSC 38818View Materials (8 specimens), MSC 38828View Materials (101 specimens), MSC 38837, MSC 38841 (20 specimens), MSC 38846View Materials (2 specimens), MSC 38849View Materials (2 specimens), MSC 38855View Materials (3 specimens), MSC 38871View Materials (5 specimens), SC 2012.47.220, SC 2012.47.221, SC 2012.47.222 (3 specimens), SC 2012.47.223, SC 2012.47.224 (2 specimens), SC 2012.47.225 (52 specimens), SC 2012.47.226 (10 specimens), SC 2012.47.227 specimens), WSU 12View Materials, WSU 5004View Materials  .

Description

Tooth crown on median teeth wider than long, six-sided, has sharp lateral angles. Upper median teeth have convex crown, straight crown foot. Lower teeth relatively flat, have an undulating crown foot (convex medially, straight laterally). Labial face conspicuously overhangs the root, is weakly concave, may be vertical or slightly lingually inclined. Lingual face is correspondingly convex, may be vertical or slightly inclined. Labial crown face bears a network of fine reticulated ridges on the lower part, grading apically into longitudinal ridges that anastomose and become finer towards the occlusal surface. Ornamentation on lingual face similar, but stronger. Shelf-like and rounded basal transverse ridge at the lingual crown foot. Root polyaulocorhize, on unworn teeth it constitutes one-third to one-half the total tooth height. Labial root face oblique; lingual side of root extends past the crown base.

Upper and lower lateral teeth six-sided, nearly equidimensional, have highly irregular occlusal outline. The labial and lingual faces comparable in shape and ornament to median teeth. Root subdivided into three lobes by two nutritive grooves.

Remarks

This species is represented in our sample by two partial dentitions. MSC 35008View Materials ( Fig. 48View Fig A–F) is the right half of an upper dentition consisting of six incomplete but articulated median teeth, and a single lateral row (articulated with the third through sixth median teeth). Overall, the occlusal surface is convex mesiodistally, and the dentition is convex labiolingually. The two anterior-most median teeth are concave due to their having formed part of the triturating surface.

MSC 35007View Materials ( Fig. 48View Fig G–L) is a partial lower dentition consisting of five sutured median teeth and a single left lateral tooth between the fourth and fifth medians (the second and third medians had become detached but reconnected with B- 76 in ethanol). The sutured median teeth show that the lower dentition was flat mesiodistally and labiolingually. The distal ends of the lateral teeth on both MSC 35007View Materials and MSC 35008View Materials are ablated and it is not entirely clear if other lateral rows were present. However, the fact the distal ends are angular indicates that there was at least one additional row of lateral teeth.

The heavily wrinkled labial and lingual faces of the crown helps to articulate the teeth tightly together, and in oral view the crowns are heavily sutured. The articulation of individual teeth within the dentition is enhanced by the labial crown foot fitting into a lingual furrow of the preceding tooth, as well as overlap of the labial crown foot with the lingual transverse ridge. The labial face of the root also fits tightly against the sloping lingual face of the preceding tooth.

Myliobatis  sp. 2 is easily distinguished from other similar taxa occurring within the Tallahatta/ Lisbon contact zone, the Lisbon Formation, and Gosport Sand. The median teeth of Lisbon Formation Leidybatis  bear an unusual, highly convex area flanked by thinner margins, and the occlusal surface has a thick and tuberculated enameloid covering, both features that are lacking in Myliobatis  . Additionally, the root of Myliobatis  is very high, with an oblique labial face and lamellae that conspicuously extend past the lingual crown foot. This contrasts with the roots of both Leidybatis  and Rhinoptera  , which are typically very low compared to crown thickness, the labial faces are vertical, and the lamellae do not extend past the lingual crown foot. The labial and lingual crown faces on the teeth of Leidybatis  , Aetobatis  , and Rhinoptera  bear vertical wrinkling of differing coarseness, whereas the lower part on Myliobatis  sp. 2 tooth crowns bear reticulated ridges that grade apically into longitudinal ridges. The median teeth of Aetomylaeus  are similar to Myliobatis  sp. 2 but can be differentiated by their pitted labial face and beaded appearance on the lingual face. Additionally, the lateral teeth are wider than long (nearly diamond-shaped) and not nearly as hexagonal as on Myliobatis  sp. 2. Lastly, the lateral angles on Aetomylaeus  teeth are more oblique than on Myliobatis  sp. 2, and the margins of Aetobatus  median teeth are straight.

This morphology was identified as Myliobatis toliapicus  by Clayton et al. (2013), but examination of the larger sample of teeth available to us, in addition to the partial dentitions, leads us to believe that the species is similar, if not conspecific, with M. latidens  as illustrated by Hovestadt & Hovestadt- Euler (2013: pl. 25, figs 12–13). This is based on the labiolingual narrowness of the crown and the highly serrated occlusal outline. However, we refrain from a more specific identification until direct comparisons to the M. latidens  type material can be made.

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the contact of the Tallahatta and Lisbon formations at sites ACon-6 and ACov-11, the basal Lisbon Formation at site ACov-11, the “upper” Lisbon Formation at site ACl-3, the basal Gosport Sand at site ACl-4, and the Gosport Sand at sites ACh-21, ACl-15, and AMo-4. Middle Lutetian to middle Bartonian, zones NP15 to NP17.

Kingdom

Animalia

Phylum

Chordata

Class

Elasmobranchii

Order

Myliobatiformes

Family

Myliobatidae

Genus

Myliobatis

Loc

Myliobatis sp. 2

Ebersole, Jun A., Cicimurri, David J. & Stringer, Gary L. 2019
2019
Loc

Myliobatis toliapicus –

Clayton 2013
2013
Loc

Ariidae

Berg 1958
1958