Artiodus prominens Ivanov and Duffin, 2017
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publication ID |
https://doi.org/ 10.4202/app.00347.2017 |
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persistent identifier |
https://treatment.plazi.org/id/F664303E-FFA9-F530-7D74-0E47D4708C9B |
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treatment provided by |
Felipe |
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scientific name |
Artiodus prominens Ivanov and Duffin |
| status |
sp. nov. |
Artiodus prominens Ivanov and Duffin sp. nov.
Etymology: From Latin prominens , projecting.
Holotype: PM SPU 81-1 , isolated tooth ( Fig. 2A View Fig ).
Type locality: Krasnoufimskie Klyuchiki quarry, town of Krasnoufimsk, Sverdlovsk Region, Middle Urals, Russia.
Type horizon: Divya Formation, Sarginskian Regional Stage, late Artinskian, early Permian.
Material.—14 teeth (PM SPU 81-1–14) and 12 teeth (NHMUK PV P65426, P65427, P65450–59).
Diagnosis. —Multicuspid teeth with pyramidal, flattened labio-lingually, orthodont crown bearing from four to nine triangular cusps: large central, moderate intermediate and small lateral; well-developed lateral carina; strongly developed, prominent labial projection terminating in a large round tubercle and separated from the crown and base surfaces by a depression; distinct ornamentation from straight or recurved cristae of different length; oval or semilunar, elongate, considerably vascularized base with extended lingual part; dense vascular network formed of transverse horizontal, ascending, short secondary and semicircular canals.
Description. —The teeth range in size from 2 to 7 mm mesio-distally. The teeth have a multicuspid, pyramidal crown and a base (or root) which is extended lingually ( Figs. 2D, E View Fig , 3G, I–L View Fig ). The crown is labio-lingually compressed, elongated mesio-distally, slightly inclined lingually ( Fig. 2C View Fig ), and bears distinct cusps, separated from each other by notches, and fused basally ( Figs. 2 View Fig , 3 View Fig ). The central cusp is considerably higher and wider than the moderate intermediate and small lateral cusplets. The height of the cusps decreases mesially and distally away from the central cusp, but some intermediate cusps are slightly higher than surrounding intermediate or lateral ones ( Figs. 2F View Fig , 3A, D, F View Fig ). A number of cusps in the crown varies from four to nine but is usually five or eight.
The crown is either symmetrical, with same number of intermediate and lateral cusps on both mesial and distal sides of the crown (e.g., Figs. 2A View Fig , 3G View Fig ), or asymmetrical. In asymmetrical teeth, the central cusp is distally inclined and flanked by a greater number of mesial cusps than distal ones (e.g., 4 mesial cusps and 3 distal cusps in NHMUK PV P65450; Fig. 3D View Fig ). The cusps are triangular in labial and lingual views, oval in cross section, and a lateral carina or occlusal crest separates the labial from the lingual face of the crown, forming a moderately well-developed cutting edge. The lateral cusps are often incurved ( Fig. 3J View Fig ). In symmetrical teeth, their long axes usually diverge from that of the central cusp ( Fig. 2A, B View Fig ). In asymmetrical teeth, the long axes of the lateral and intermediate cusps are usually sub-parallel to that of the central cusp ( Figs. 2F View Fig , 3A, C, D View Fig ), especially mesially.
The labial side of the teeth bears a strongly developed projection restricted to the lower part of the crown at the base of the central cusp, and continues to the base. This labial projection is separated from the labial face of the teeth by deep grooves on either side, and terminates in a large rounded tubercle sharply separated from the mesial and distal flanks of the crown and base ( Fig. 2B, D View Fig 1 View Fig , F, L). The tubercle is made up mainly of coronal tissues, but the basal part is formed by a thin sliver of base tissue. The two tissues meet at a flat crest which runs circumferentially around the tubercle low down on the tubercle margin ( Fig. 5A, D View Fig ). The boundary between the crown and the base, or the crown/ root junction, is distinct, and marked by a groove on both labial and lingual sides; as described above, the junction can also be traced around the labial projection.
The ornamentation of the crown comprises relatively coarse cristae or vertical ridges of varying length, following trajectories that may be straight, curved or wavy. The labial face of the crown is generally more heavily and densely ornamented than the lingual face, with the longest cristae generally being located toward the central sections of the cusps. In many specimens, the ridges begin just above the crown/ root junction and ascend the crown toward the cusp apices or occlusal crest. In some cases the ridges attain the apices of the central and lateral cusps ( Figs. 2E–G, K, L View Fig , 3 View Fig ), while in many others they terminate approximately two-thirds the way up the crown ( Figs. 2A View Fig 1 View Fig , C, 3B View Fig ). The coarser ridges may bifurcate basally ( Fig. 2A 2, K 2 View Fig ). Short, impersistent cristae are often interspersed between the coarser examples, and may be confined to the upper parts of the crown ( Fig. 2A View Fig ). A very coarse ridge commonly surmounts the crest of the labial projection either in a central position ( Figs. 2F View Fig , 3A, D View Fig ) or rather offset laterally, towards the flanks of the projection ( Fig. 2A 2, K 2 View Fig ). Short ridges also adorn the lateral margins of the labial projection ( Figs. 2A 2 View Fig , D 1 View Fig , F, K 2 View Fig , 3A–F View Fig ). The upper part of the central cusp on the lingual side is frequently smooth ( Fig. 2A View Fig 1 View Fig , C, E, I).
The tooth base is oval or semilunar in outline, elongated mesio-distally, arched, convex on the occlusal side and concave on the basal one ( Figs. 2B, D View Fig 1 View Fig , I, K 2 View Fig , 5D View Fig ). It is lingually offset from the crown underside. The base bears the numerous large and small foramina marking the entrances and exits of the vascular canals which perforate the base. The foramina tend to be more numerous on the labial side, where they are commonly organized into a longitudinal row just beneath the crown/base junction ( Figs. 2F, L View Fig , 3A–F View Fig ). Lingually, a relatively large median foramen may be present on the linguo-basal border beneath the central cusp ( Fig. 3J, K View Fig ). Larger foramina are also present on the mesial and distal flanks of the lingual face of the base, often interspersed with smaller examples ( Figs. 3J, K View Fig , 5B View Fig ). The foramina on both labial and lingual walls of the base enter the base tissues horizontally. A few foramina open onto the basal surface of the base.
Tooth histology: The crown is composed of orthodentine with numerous, strongly branched dentine tubules and a shiny layer of enameloid ( Fig. 4B). The base contains considerably vascularized trabecular dentine but the labial projection comprises compact dentine which lacks canals and dentine tubules. The vascularization system consists of a dense network of internal canals occupying the whole tooth base. The vascularization network comprises transverse horizontal, ascending, secondary and semicircular canals with small ramifications ( Fig. 5C–H View Fig ). The horizontal canals include a wide main canal and narrower moderate canals. They pass across the base from the lingual torus to the labial groove. The ascending canals are vertical or inclined; the main, central is wide and, together with narrower lateral canals occupies and fills the upper part of the base. Two main, vertical ascending canals start their trajectories from the mid basal side of the base and run to the crown/ base junction under the central cusp. Some inclined ascending canals open on the lingual side of the base at the crown/ base junction. The short secondary canals are connected the horizontal canals by means of ascending canals. A narrow circular canal is confined to the labial projection and opens in the grooves forming the flanks of the projection.
Variation and heterodonty: The teeth of the new taxon vary in the height of central cusp, the number of intermediate and lateral cusp pairs, the symmetry of the crown, the degree of cusp inclination, and the development of crown ornamentation. The teeth can be separated into three morphotypes based on the known dentitions of euselachians such as Hamiltonichthys mapesi Maisey, 1989 ( Maisey 1989), Hybodus basanus Egerton, 1845 ( Maisey 1983), Hybodus reticulatus Agassiz, 1837 ( Maisey 1987), and Hybodus brevicostatus Patterson, 1966 ( Patterson 1966).
Morphotype 1 (four teeth): symmetrical teeth with the same number of intermediate and lateral cusplets on both mesial and distal flanks of the crown. The central cusp is very high with a wide base, and is flanked by one pair of intermediate cusps and one pair of lateral ones. The labial projection is relatively wide. The mesial and distal flanks of the crown extend beyond the limits of the base, meaning the crown is wider mesio-distally than the base. The latter projects very strongly in a lingual direction from the crown underside ( Figs. 2A, B, D View Fig 1 View Fig , D 2 View Fig , 3L View Fig ). The height of the crown is up to four times the width of the base. These teeth probably come from a symphyseal or anterior position in the dentition, based on their symmetrical form and similar patterns of heterodonty in the dentitions of relatively high-crowned hybodontid sharks such as H. basanus , H. brevicostatus , and H. reticulatus ( Maisey 1983, 1987; Patterson 1966).
Morphotype 2 (two teeth): comprises smaller teeth in our collection, possessing a slightly asymmetrical crown with a short central cusp, flanked by only one pair of intermediate cusps. The labial projection, although prominent, is narrow, and lingual extension of the base is moderately well developed ( Fig. 2C, E View Fig ). The height of the crown and the width of the base are sub-equal. By reference to the heterodonty shown by relatively well-known high-crowned hybodont dentitions, these teeth are probably antero-laterals or posteriors.
Morphotype 3 (20 teeth):These teeth are characterized by more strongly asymmetrical crown with distally inclined cusps. The central cusp is of moderate size and flanked by two or three intermediate cusps and one lateral cusp pair. The number of mesial intermediate cusps is greater than the number of distal cusps. The labial projection is narrow and very prominent. The lingual extension of the base is relatively short ( Figs. 2F–L View Fig , 3A–K View Fig , 4). Bearing in mind the heterodonty displayed in certain hybodont dentitions, these teeth are probably lateral and postero-lateral teeth.
Although based upon a relatively small number of isolated teeth, the pattern of moderate heterodonty suggested here for Artiodus prominens is an example of simple linear gradient monognathic heterodonty ( Duffin and Ward 1983) in which the following changes take place distally through the dentition of a single jaw ramus: (i) symmetrical symphyseal teeth give way to successively more asymmetrical forms distally; (ii) the central cusp is upright in symphyseal teeth, becoming more distally inclined away from the symphysis; (iii) relative to overall tooth length, the height of the central cusp reduces distally through the dentition; (iv) the number of intermediate cusps increases from one to three pairs; and (v) the labial projection becomes narrower.
The collection of teeth available to use shows no evidence of dignathic, gynandric or ontogenetic heterodonty. A greater number and morphological range of isolated teeth, or fully articulated dentitions of Artiodus are needed for better definition of the types of heterodonty which might be displayed in this taxon.
Stratigraphic and geographic range.—Late Artinskian (early Permian) of the Middle Urals ( Russia).
| PM |
Pratt Museum |
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.