Enchodus tineidae, Holloway & Claeson & Sallam & El-Sayed & Kora & Sertich & O’Connor, 2017
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publication ID |
https://doi.org/ 10.4202/app.00331.2016 |
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persistent identifier |
https://treatment.plazi.org/id/03D65037-FFFD-4D11-FF12-F8D26642F806 |
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treatment provided by |
Felipe |
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scientific name |
Enchodus tineidae |
| status |
sp. nov. |
Enchodus tineidae sp. nov.
Figs. 2 View Fig , 3 View Fig . ZooBank LSID: urn:lsid:zoobank.org:pub:2DAEC67C-970D-472A-BE12-BB5EC276FF2E
Etymology: In reference to the type locality near the village of Tineida.
Holotype: MUVP 59 ; a disarticulated, three-dimensionally preserved, partial skull.
Type locality: Northeast of the village of Tineida, Dakhla Oasis, Western Desert, Egypt.
Type horizon: The middle–upper portion of the Duwi Formation, upper Campanian (73 Ma), Upper Cretaceous.
Material. —MUVP 59, right and left dentaries, left anguloarticular, left maxilla, right ectopterygoid, left preopercle, left opercle, and various unidentifiable skull fragments, branchiostegals, and other bone fragments.
Diagnosis. —Extinct enchodontid teleost characterized by the following combination of cranial, jaw, and dental characters: (i) closed mandibular sensory canal, (ii) mandibular symphysis that tapers rostrally, (iii) between six to eight ectopterygoid teeth that are neither curved nor of equal size, (iv) unornamented mandible and preopercular, and (v) opercular ornamentation consisting of radiating ridges.
Description.—Jaws: The dentaries of MUVP 59 are complete ( Figs. 2 View Fig , 3 View Fig ), except for the caudal-most portion of each element. The preserved length of the right dentary is 26.36 cm. The left dentary is broken and displaced in several places, but the combined preserved length of the fragments is roughly equal to that of the right dentary. There is no ornamentation on the lateral surface of the dentary. The dentary exhibits the weathered bases of three rostroventrally projecting dentary prongs and preserves a symphyseal surface with a slot-ridge assembly ( Figs. 2D View Fig , 3B View Fig ). There is no indication, through examination of either the actual specimen or CT scans of the specimen, of an open or partially open mandibular sensory canal. Along its medial aspect, the body of the dentary has a shallow fossa that delimits the caudal margin of the symphysis. At the bifurcation of the dentary into dorsal and ventral rami, there is a sharply incised fossa that continues caudally the length of the dentary and is slightly overhung by the ventral margin of the dorsal ramus that was presumably the site of articulation with the anguloarticular bone. The dorsal margin of the dentary is wide, preserving multiple teeth. The body and ventral ramus of the dentary consists of a thin plate of bone that terminates caudally in a gracile ventral rod.
Two tooth rows are preserved. The lateral row of dentition consists of a margin of small, evenly spaced denticles (2.2 mm in crown height). The medial row comprises eleven massive teeth exhibiting varying crown heights. The rostral-most tooth (d1) has the highest crown at 26.6 mm, with the second tooth (d2) having the lowest crown of the series at 7.9 mm. Caudal to d2, tooth crowns increase in height until position d6, with all succeeding teeth being approximately equal in height. The base of each medial-row tooth is nearly circular in cross-section and associated with a bulbous attachment to the dentary. The crowns of the medial-row teeth are highly rostro-caudally elongate, with convex lateral and medial surfaces. The six rostral-most preserved teeth are recurved. This morphology contrasts with the five caudal-most teeth, which are triangular in profile and have an apex that is centered above the tooth bases. In addition to the eleven preserved medial-row teeth of the right dentary, a gap between d6 and d9 appears to have accommodated two additional teeth that are not preserved. The eleven preserved teeth, in addition to the presumed missing teeth, are distributed across the dentary in an irregular pattern. The eight rostral-most teeth are spaced at regular intervals, whereas the five caudal-most teeth cluster in one triplet and one doublet, with the caudal margin of d9 nearly contacting the rostral margin of d10, the caudal margin of d10 nearly contacting the rostral margin of d11, and the caudal margin of d12 and rostral margin of d 13 in contact with one another ( Figs. 2 View Fig , 3 View Fig ). This arrangement is symmetric on both dentaries, indicating that the distribution is not random. Furthermore, the teeth in each of these clusters are equally sized and well-developed, indicating those teeth are of the same ontogenetic stage, rather than some being mature and others being replacement teeth ( Fink 1981).
The caudal portion of the left anguloarticular ( Fig. 2 View Fig ) is partially preserved, including the quadrate facet. There is a weak ridge along the lateral surface of the anguloarticular, ventral to the quadrate facet, presumably the “ventral bar” of Fielitz (2004). The quadrate facet is defined rostrally by a partially preserved, long coronoid process and caudally by a partially preserved articular process. There is a small retroarticular process, caudal to the quadrate facet. The preserved portion of the maxilla ( Fig. 2 View Fig ) is a straight, mediolaterally flat strip of bone that bears no teeth.
Hyopalatine series: The right ectopterygoid, excluding some of the rostral portion, is preserved ( Figs. 2 View Fig , 3 View Fig ). In cross-section, the ectopterygoid has a V-shaped trough for articulation with the dermopalatine ( Fig. 3D View Fig ). Ventral to this trough, the bases of five teeth are preserved. Similar to the medial-row teeth of the dentary, tooth bases on the ectopterygoid are circular in cross-section. In contrast to the dentary medial-row teeth, the preserved partial crown of the most complete ectopterygoid tooth is circular in cross-section and straight along its height, without any distal curvature. Furthermore, the bases and cylindrical partial tooth crown project at a ventrocaudal angle from the ectopterygoid. The rostral-most preserved ectopterygoid tooth base has the largest diameter at 9.4 mm, with each of the four succeeding teeth exhibiting smaller bases of approximately equal diameters of 7.25 mm. The distance between the bases of E2–E5 and those adjacent to each is approximately equal at 23 mm. The distance between E5– E6 tooth bases is nearly half of the distance between any other two adjacent ectopterygoid teeth at 13.5 mm. Based on the size and spacing of the preserved teeth, an estimated minimum ectopterygoid length of 183.15 mm would be required for the complete element to have possessed nine teeth, if the rostral-most preserved tooth in MUVP 59 represented the original E1 and each of the hypothetical non-preserved caudal teeth were sized and spaced the same as the two caudal-most preserved teeth. That ectopterygoid length would be over sixty-nine percent the length of the dentary, which is morphology inconsistent with known enchodontids. Instead, the rostral-most preserved ectopterygoid tooth in MUVP 59 probably represents E2, with the original E1 and rostral ectopterygoid region not preserved. Such morphology would be consistent with nearly all enchodontids in which six to eight ectopterygoid teeth are present, with the second of the series being the largest SOM 2: character 12 (2)).
Opercular series: The dorsal ramus of the preopercle is preserved ( Fig. 2 View Fig ). Though the ventral extent of the preopercle is incomplete, the preopercle was clearly much longer dorsoventrally than rostrocaudally and appears to have widened ventrally. There is no evidence of dermal ornamentation of the preopercle. The opercle is also partially preserved and also appears to have been longer dorsoventrally than rostrocaudally. The lateral aspect of the opercle is ornamented with rows of ridges that radiate from a central point along the rostral margin of the element to more widespread points along the caudal margin.
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