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NovitatesAMERICAN MUSEUM PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET NEW YORK, N.Y. 10024 U.S.A. NUMBER 2718 NOVEMBER 19, 1981 JOHN G. MAISEY Studies on the Paleozoic Selachian Genus Ctenacanthus Agassiz No. 1. Historical Review and Revised Diagnosis of Ctenacanthus, With a List of Referred Taxa AMERICAN MUSEUM Novitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2718, pp. 1-22, figs. 1-21 November 19, 1981 Studies on the Paleozoic Selachian Genus Ctenacanthus Agassiz No. 1. Historical Review and Revised Diagnosis of Ctenacanthus, With a List of Referred Taxa JOHN G. MAISEY1 ABSTRACT Ctenacanthus Agassiz is a genus of elasmo- elasmobranch finspines, whereas others resemble branch, originally recognized by its dorsal fin- hybodontid finspines. The fish described by Dean spines but now known from more complete re- as Ctenacanthus clarkii should be referred to C. mains. However, many other fossils, including compressus. Both C. clarkii and C. compressus isolated spines and complete fish, have been in- finspines are sufficiently like those of C. major cluded in Ctenacanthus, although the spines dif- for these species to remain within the genus. fer from those of the type species, C. major, and Ctenacanthus compressus is the only articulated from other presumably related species. Earlier Paleozoic shark so far described which can be diagnoses of Ctenacanthus are critically reviewed assigned to Ctenacanthus. Ctenacanthus costel- and the significance of previous diagnostic latus finspines are not like those of C. major, but changes is discussed. It is concluded that Cten- instead resemble Sphenacanthus spines. Good- acanthus sensu lato is paraphyletic. Some spines richthys eskdalensis may be closely related to previously assigned to this taxon resemble living Ctenacanthus. INTRODUCTION The genus Ctenacanthus has been used as many paleontologists Ctenacanthus includes a catch-all taxon, rather like the old genus primitive sharks with finspines somewhat Ammonites, and is in need of revision. To like those in Hybodus, and "ctenacanth" 1 Assistant Curator, Department of Vertebrate Paleontology, American Museum of Natural History. Copyright ©) American Museum of Natural History 1981 ISSN 0003-0082 / Price $2.50 2 AMERICAN MUSEUM NOVITATES NO. 2718 B FIG. 1. A-C, Ctenacanthus major Agassiz, type, Bristol City Museum C4152. From Agassiz, 1837, table 4. D-H, C. major Agassiz. From Davis, 1883, plate XLII, BM(NH) P2534. Section (C) faces right, and is taken from (A), which shows the right side. Section (C) is distorted by crushing and is therefore unreliable. Specimen (B) is shown from the left side. Sections (F & G) facing left, and ornament detail (E) are from specimen (D), seen along with (H) from the left side. sharks have often been treated as a mono- Moy-Thomas and Miles (1971), Maisey phyletic group, e.g., Brough (1935), Moy- (1975) and Schaeffer and Williams (1977). Thomas (1936, 1939a, 1939b), Romer (1945), Over the years numerous taxa, based on fin- 1981 MAISEY: CTENACANTHUS 3 spines, have been added to Ctenacanthus. (e.g., fig. IC, F, G), their position on the Some of these spines resemble C. major, the related spine (e.g., fig. 1A) can be plotted. type species, and the present work seeks to Where sections are vertical, either they were restrict Ctenacanthus to include only those drawn at different scales to the spine and species founded on finspines that are similar cannot be plotted accurately (e.g., fig. 3B, to C. major. Over the years since Agassiz D, E, J), or space was unavailable to allow (1837) first described Ctenacanthus fin- the section to be turned (e.g., fig. 6C). In spines, their diagnosis has been tinkered general, original illustrations were faithfully with until almost any Paleozoic phalacan- reproduced, but the orientations and posi- thous shark can satisfy the definition of a tions of sections, and level of posterior clo- "ctenacanth." In the course of my investi- sure (indicated by a small arrow in lateral gations it has become evident not only that views) have been added. Sources of illustra- "ctenacanths" (in the broad context that tions are indicated in the figure captions, all they have become known) are probably para- are reduced, and are not to scale. phyletic, but also that diagnosis of its fin- spines is so amended that it bears little re- REVIEW semblance to the admittedly poor original HISTORICAL description. It is no longer possible to rec- What is Ctenacanthus? oncile the type species, C. major, with ge- neric diagnoses published after 1850. Ctenacanthus is a taxon founded on iso- In recent years the number of phalacan- lated dermal finspines (Agassiz, 1837). thous Paleozoic sharks known from fairly Spines referable to the type species of Cten- complete skeletal remains has grown enor- acanthus, C. major, have never been found mously, although many of these have yet to associated with other remains. However, no- be described. New finds of complete Wod- body has questioned the view that Cten- nika (Schaumberg, 1977) from the German acanthus was a Paleozoic shark, somewhat Kupferschiefer, and many as yet unde- like Hybodus from the Mesozoic, and a few scribed forms from the Carboniferous and fairly complete fossil sharks with finspines Devonian of North America, cannot be eval- have been referred to Ctenacanthus. How- uated critically until the "ctenacanth" prob- ever, only one of these, a specimen of C. lem is re-examined. In the first part of this clarkii (Dean 1909), has a finespine with work I review the literature dealing with similar ornament to C. major, and therefore Ctenacanthus, and attempt to show how corroborates the view that Ctenacanthus successive authors have added progressively was a shark (see below). more confusion. Having trimmed Ctenacan- Agassiz's (1837, p. 10) diagnosis of Cten- thus of all but a central core of species based acanthus spines is as follows: on finspines which closely resemble the type Les Ctenacanthus sont d'immenses rayons species, C. major, I will present a systematic tres-comprimes, 'a base large, mais a cavite plus revision of Ctenacanthus in the second part petite que celle des Oracanthus. La partie de of this work. ces rayons cachee dans les chairs parait avoir ete considerable. Au bord posterieur se voient quelques petites epines. La surface est ornee EXPLANATION OF ILLUSTRATIONS de stries longitudinales, plus rapprochees que The figures in this paper are composites celles des Hybodes, pectinees, c'est-'a-dire cre- made both from specimens and original illus- nelees transversalement et saillantes en forme trations. In the course of preparing these fig- de dents qui alternent d'une serie a I'autre, mais ures it became apparent that there were qui semblent continuer a cause de leur obli- many original discrepancies which needed quite. rectifying or commenting on, and notes are The presence of an intramuscular part is given in the figure legends. characteristic of all elasmobranch dorsal fin- Where sections are shown horizontally spines. It does not appear to be any more 4 AMERICAN MUSEUM NOVITATES NO. 2718 B T., c Im Imm LJ-- 5cm L. 1cm c IIIK L--j~ ~ ~ ~ --- FIG. 2. A-C, Ctenacanthus maximus de Koninck. From de Koninck, 1878, plate 7, IRSNB P1305. Section (B) and ornament detail (C), both facing right, from specimen (A), seen from right side. Level of section not indicated in original, and drawn to a different (but indicated) scale, enabling its approx- imate level to be determined. D-G, C. salopiensis Davis. From Davis, 1883, plate CLIV. Section (G) facing left, was originally based on a restored outline of (D), seen from left side, and its posterior limits were imagined. Section (E), facing left, is incomplete and probably flattened. 1981 MAISEY: CTENACANTHUS 5 n G GC)) cm~~~~~lc B icm~~~~~~ij P~~~H . J -v J? FIG. 3. Ctenacanthus tenuistriatus Agassiz. A-E, from Agassiz, 1837, table 3. (A), Bristol specimen, no catalogue number, now lost. (C), composite from BM(NH) P495, 2225; F-J, from Davis, 1883, plate XLIII, BM(NH) P3109. Levels of sections (B, D, E) facing upward and drawn from (A & C) and (J), drawn from (I), cannot be accurately determined; (J) may be a very oblique section through a fracture shown in (I). Drawing (C) is not a specimen but represents an original composite. Spines (A, C, F, I) are all seen from the right side. 6 AMERICAN MUSEUM NOVITATES NO. 2718 J 2mm R E " L ,4M Ci ~c191, ENO %" N_ .1o ow p E u u v -Q o El. Ii H Icm LCCm-I Q< > T 1981 MAISEY: CTENACANTHUS 7 "considerable" in C. major than in the ma- nament like that of C. major, as his next jority of other elasmobranch finspines. Evi- species, C. brevis, is based on another fin- dently Agassiz was most impressed by the spine which is covered by rows of large, ornamentation pattern as a taxonomic char- rounded, striated tubercles. He never ex- acter. It is difficult to formulate a diagnosis amined the specimen on which C. brevis was based simply on these characteristics, but founded before publication, although he was others appear in the description of C. major aware of its ornamentation. His plate 2, fig- (Agassiz, 1837, p. 11, repeated here in part): ure 2 was copied from a drawing he received Toute sa surface est ornee de gros plis longi- from Buckland. tudinaux, entre lesquels se trouvent des sillons I have examined the large type specimen arrondis et des plis transverses et obliques tres- of C. major (C4152, Bristol City Museum, rapproches, qui forment par leur saillie une England). Unfortunately, much of the Bristol sorte de dentelure sur les cotes de chaque sil- collection was destroyed during the Second lon.