Gavin F. Hanke

ANATOMY OF THE EARLY DEVONIAN ACANTHODIAN BROCHOADMONES MILESI BASED ON NEARLY COMPLETE BODY FOSSILS, WITH COMMENTS ON THE EVOLUTION AND DEVELOPMENT OF PAIRED FINS

Abstract New anatomical details are described for the acanthodian Brochoadmones milesi based on nearly complete body fossils from Lochkovian rocks at MOTH, Mackenzie Mountains, Northwest Territories, Canada. The body and caudal peduncle are deep, and a prominent nuchal hump is present before the dorsal fin origin. The caudal fin is correspondingly deep and ventrally, the caudal fin lies close to and is partly joined to the slender anal fin. A delicate pectoral fin trails the flattened pectoral-fin spine where previously known specimens showed only a fin spine resembling a bivalve shell. Seen for the first time in any vertebrate, each of the six pairs of prepelvic spines supports a small, scale-covered finlet. Both prepelvic spines and scale-covered finlets increase in size posteriorly. The series of paired prepelvic finlets originates ventral to the branchial chamber and anteroventral to the pectoral fin, and extends posteriorly as far as the pelvic fins. The scales of the body and fins are thin and flat, without obvious evidence of ossified basal tissue or entry point for vascular tissue. The main lateral-line canal passes dorsal to the branchial chamber and terminates at the trailing edge of the caudal fin web. Lateral-line scales are thicker than body scales and show concentric growth zones. Scales from the dorsal midline of the caudal fin are also thicker, showing few superpositional growth zones in the mesodentine of the crown together with what appears to be cellular basal tissue. The structure and position of the pectoral spine and fin, the extremely thin body scales, the slender anal fin, and the prepelvic finlets are all unique and appear to be autapomorphic features compared to those of other acanthodians. Brochoadmones milesi is derived relative to other fishes traditionally classified in the Climatiiformes. Kathemacanthus rosulentus is removed from the Brochoadmonoidei, leaving only B. milesi in a monotypic suborder.

New species of the acanthodian genus Tetanopsyrus from northern Canada, and comments on related taxa

Abstract Previously, known specimens of the Lochkovian (Lower Devonian) diplacanthid acanthodian genus Tetanopsyrus (all from the MOTH locality in the Northwest Territories, Canada) were thought to belong to a single species, T. lindoei. New specimens from the same locality have shown that two species are present. Tetanopsyrus lindoei is revised and T. breviacanthias, sp. nov. is described, leading to a revised diagnosis of the genus. Both species lack rostral tesserae; instead they have irregularly-shaped, monodontode, rostral scales without basal tissue and with an open pulp cavity. Both species also have enlarged, tuberculated, anterior circumorbital plates. Dorsal spines are shallowly inserted and each is supported by a basal plate that ossified early in ontogeny. The two species are distinguished from each other by the structure of the dorsal spines, the length of the pectoral spines, and the shape of the procoracoids. The revision of Tetanopsyrus has implications also for relationships among acanthodian families. Both Tetanopsyrus (Tetanopsyridae) and Gladiobranchus (Gladiobranchidae) are seen as diplacanthiforms rather than as ischnacanthiforms. Similarities are found in the jaws, circumorbital plates, anterior dorsal spine, dorsal spine basal plates, prepelvic spines, and scapulocoracoids. Other potential relatives of diplacanthids include Uraniacanthus, which has similarities in prepelvic and dorsal spines, and Culmacanthus, whose relationships cannot be settled without further study.

A re-examination of Lupopsyrus pygmaeus Bernacsek & Dineley, 1977 (Pisces, Acanthodii)

ABSTRACT New anatomical details are described for the acanthodian Lupopsyrus pygmaeus Bernacsek & Dineley, 1977, based on newly prepared, nearly complete body fossils from the MOTH locality, Northwest Territories, Canada. New interpretations of previously known structures are provided, while the head, tail, and sensory lines of L. pygmaeus are described for the first time. The pectoral girdle of L. pygmaeus shows no evidence of pinnal and lorical plates as mentioned in the original species description. Instead, the dermal elements of the pectoral region appear to comprise a single pair of prepectoral spines which rest on transversely oriented procoracoids, and large, shallowly inserted, ornamented pectoral fin spines which contact both the procoracoids and scapulocoracoids. The scales of L. pygmaeus lack growth zones and mineralized basal tissue, and superficially resemble scales of thelodonts or monodontode placoid scales of early chondrichthyans, and not the typical scales of acanthodians. However, L. pygmaeus possesses perichondrally-ossified pork-chop shaped scapulocoracoids, a series of hyoidean gill plates, and scale growth that originates near the caudal peduncle; these features suggest a relationship to acanthodians. Prior to this study, both authors conducted separate cladistic analyses which resulted in differing tree positions for L. pygmaeus and its relationships within the Acanthodii. However, both analyses did agree that there is no evidence allying L. pygmaeus to the traditional “climatiid” acanthodians contrary to previous historical classifications.

Partial articulated specimen of the Early Devonian putative chondrichthyan Polymerolepis whitei Karatajūtė-Talimaa, 1968, with an anal fin spine

ABSTRACT Polymerolepis whitei Karatajūtė-Talimaa, 1968 was described based on isolated polyodontode scales recovered from the Ukraine, and originally was thought to be heterostracan (Agnatha). Additional scales with neck canals were described years later, and as a result, P. whitei was reclassified as a bradyodont holocephalan because it had scales similar to those of Listracanthus Newberry & Worthen, 1870. Until now, no articulated body fossils were known, and so the classification of this taxon has remained uncertain and based only on the original authors opinion. New specimens of P. whitei from the Mackenzie Mountains, Northwest Territories, Canada, show articulated scale patches from the head, with the best specimen showing part of an anal fin, caudal peduncle, and caudal fin. This new material confirms that the original account of scale variation was accurate, but also that P whitei possesses an anal fin spine, a feature that, until recently, was thought to be a synapomorphy of acanthodian fishes among Palaeozoic fishes. Several primitive chondrichthyans (Obtusacanthus Hanke & Wilson, 2004; Lupopsyroides Hanke & Wilson, 2004; Kathemacanthus Gagnier & Wilson, 1996; Seretolepis Karatajūtė-Talimaa, 1968a, 1968; Doliodus Traquair, 1893; Antarctilamna Young, 1982, and also problematic taxa such as Gyracanthides Woodward, 1902, and now Polymerolepis Karatajūtė-Talimaa, 1968a, 1968), are known from articulated remains and show a fin-spine complement like that of acanthodian fishes. They also have placoid scales or polyodontode scales that grew by areal rather than superpositional accretion. These taxa blur the distinction that exists in historic literature between acanthodians and early chondrichthyans.

KNERIALEPIS, A NEW GENERIC NAME TO REPLACE KNERIA KARATAJUTE-TALIMAA 1997

Karatajute-Talimaa (1997) described a new putative chondrichthyan (cartilaginous fishes related to and including sharks, rays, and holocephalians) from the Lower Devonian of the Ukraine based on isolated polyodontode scales. The new form was given the name Kneria mashkovae in honor of Professor Rudolf Kner and Dr. Tamara Mashkova. The type locality of the new species is in the Ukraine, Ivane-Zolotoye76 bed 6, Lower Devonian (Lochkovian), Ivane Regional Stage, Ivane formation. This new putative chondrichthyan is known from outcrops on the Dniestr River at Dobrovliany, Ivane-Zolotoye, Zaleshchiki, Pechorna, and Bedrikovtsy. The name Kneria was first used in relation to this new putative chondrichthyan by Karatajute-Talimaa (1992:224) in her discussion of the diversity of Paleozoic chondrichthyan scale morphology. However, the formal diagnosis of K. mashkovae, and the establishment of the putative chondrichthyan genus Kneria, was not completed until 1997. The generic name Kneria is preoccupied by 12 species of East African osteichthyan fishes. The African Kneria species are in the Order Gonorhynchiformes, Suborder Knerioidei, and Family Kneriidae following the classification scheme of Nelson (1994). The genus Kneria and its type species Kneria angolensis were diagnosed by Steindachner (1866; see also Eschmeyer, 1990), and there is no doubt about priority. We here propose the new generic name Knerialepis to replace Kneria of Karatajute-Talimaa (1997); Kneria mashkovae Karatajute-Talimaa, 1997, is the type species of the genus. There are no other known species of Knerialepis. The new generic name retains the patronym that was intended to honor Professor Kner, and reflects the fact that Knerialepis mashkovae was described based on isolated scales. No articulated remains of this putative chondrichthyan have been described to date.