MARINE FISHES (CHONDRICHTHYES, HOLOCEPHALI, ACTINOPTERYGII) FROM THE UPPER CRETACEOUS (CAMPANIAN) RYBUSHKA FORMATION NEAR BELOE OZERO, SARATOV OBLAST, RUSSIA

A diverse fish paleofauna occurs in the upper Campanian portion of the Rybushka Formation exposed near Saratov city in the Saratov Oblast, Russia. Twenty taxa have been identified, including two holocephalans (Ischyodus bifurcatus and Amylodon karamysh), twelve elasmobranchs (Synechodus sp., Cederstroemia sp., Cretalamna cf. C. borealis, C. cf. C. sarcoportheta, Archaeolamna kopingensis, Eostriatolamia segedini, E. venusta, Pseudocorax laevis, Squalicorax kaupi, Squalicorax morphotype 1, Squalidae indet., and Squatirhina sp.), and six teleosts (Pachyrhizodus sp., Saurocephalus lanciformis, Paralbula casei, Enchodus cf. E. dirus, E. cf. E. gladiolus, and E. petrosus). Many of these taxa are new to the Campanian fish record of Russia, and the assemblage demonstrates that there is significant taxonomic overlap between the Rybushka Formation paleofauna and that of North America

Observations on heterodonty within the dentition of the Atlantic Sharpnose Shark, Rhizoprionodon terraenovae (Richardson, 1836), from the north-central Gulf of Mexico, USA, with implications on the fossil record

The Atlantic Sharpnose Shark, Rhizoprionodon terraenovae (Richardson, 1836), is the most common small coastal requiem shark in the north-central Gulf of Mexico, USA. Despite this fact, little is known about the dental variation within this taxon. To help rectify this shortcoming, we examined 126 male and female R. terraenovae jaws sets across all maturity stages to document the various types of heterodonty occurring in the dentition of this taxon. Quantitative data gathered from a subset of our sample allowed for us to place teeth within the dentition of R. terraenovae into standardized upper and lower parasymphyseal/symphyseal, anterior lateral, and posterior tooth groups. As with all carcharhinid sharks, the dentition of R. terraenovae exhibits monognathic and dignathic heterodonty. We also observed significant ontogenetic heterodonty in the species, as the teeth and dentition progress through five generalized developmental stages as the shark matures. The ontogenetic development of serrations on the teeth appears to be closely related to documented dietary changes as the shark matures. Initial diets are comprised of high percentages of invertebrate prey like shrimp, crabs, and squid, but this transitions through ontogeny to a diet that is more reliant on fishes. We also provide the first documentation of gynandric heterodonty in mature male R. terraenovae, with development of these seasonal teeth likely enabling a male to grasp female sharks during copulation. Our analysis revealed a tremendous amount of variation in the dentition of R. terraenovae, which has direct implications on the taxonomy of fossil Rhizoprionodon. A comparison of the jaws in our sample to those of the extant species of Rhizoprionodon and the morphologically similar Loxodon, Scoliodon, and Sphyrna allowed us to formulate a list of generic-level characteristics to assist with the identification of isolated teeth. When applied to the fossil record, it is shown that some species previously assigned to Rhizoprionodon likely belong to one of the other aforementioned genera. The earliest occurrence of unequivocal Rhizoprionodon teeth in the fossil record are those of the Eocene †R. ganntourensis (Arambourg, 1952), the oldest records of which occur in early Ypresian deposits in Alabama and Mississippi, USA. The early Eocene occurrence of unequivocal fossil Rhizoprionodon teeth in Alabama predates the first occurrence of Negaprion, Galeocerdo, and Carcharhinus teeth in the state, supporting published molecular and morphological phylogenies positing a basal position for Rhizoprionodon within the Carcharhinidae

Late Cretaceous chimaeroids (Chondrichthyes: Holocephali) from Alabama, USA

Tooth plates of three extinct species of callorhynchid holocephalans, Edaphodon mirificus, E. barberi, and Ischyodus bifurcatus have been collected from Upper Cretaceous strata of Alabama. Of the two species of Edaphodon, E. mirificus is represented by isolated tooth plates as well as associated dentitions. Edaphodon barberi was based on a small left mandibular tooth plate, but additional mandibular tooth plates in museum collections show that the diagnostic features seen on the E. barberi holotype are consistently present and therefore useful for species differentiation. Ischyodus bifurcatus is reported for the first time in Alabama and is known from a partial associated dentition and several isolated tooth plates. Most of the fossils are from the upper Santonian to lower Campanian Mooreville Chalk, but two specimens of Edaphodon from a lower Campanian component of the Tombigbee Sand Member of the Eutaw Formation and one from the lower Maastrichtian Ripley Formation represent the first holocephalan records from these lithostratigraphic units in Alabama

Paleocene chimaeroid fishes (Chondrichthyes: Holocephali) from the eastern United States, including two new species of Callorhinchus

Isolated tooth plates collected from Paleocene deposits of Alabama, Arkansas, Illinois, Maryland, Mississippi, New Jersey, South Carolina, Texas, and Virginia represent four genera of chimaeroid fishes. Callorhinchus is reported in the fossil record of North America for the first time and is represented by material from the Danian (early Paleocene) of Mississippi and the Thanetian (late Paleocene) of Maryland and Virginia. Specimens from both locations are identified as new species, the Danian C. phillipsi n. sp. and the Thanetian C. alfordi n. sp. New Paleocene Elasmodus records from North America include two partial mandibulars belonging to E. hunteri from the Thanetian of Maryland, and a nearly complete mandibular from the Danian of New Jersey, tentatively assigned to cf. Elasmodus sp. Two species of Ischyodus are recognized, I. dolloi (Danian and Thanetian) and I. williamsae (Danian), but the two species have not been found in the same lithostratigraphic deposits. Edaphodon mirificus is known from the Danian of New Jersey and Mississippi, and the genus also occurs in the Thanetian of Virginia

New record of an extinct fish, Fisherichthys folmeri Weems (Osteichthyes), from the lower Eocene of Berkeley County, South Carolina, USA

Fisherichthys folmeri Weems 1999 (Sciaenidae?) is an extinct teleostean fish occurring in marine strata of the Gulf and Atlantic coastal plains, USA. We report isolated teeth collected from a lower Eocene (Ypresian) deposit in Berkeley County, South Carolina. Crowns of unworn teeth bear apical papillae surrounding a central depression, but these features are lost as teeth are worn through in vivo usage. The pulp cavity appears to become reduced in size as the tooth matures in the alveolus. Fisherichthys folmeri is thus far only known from Mississippi, South Carolina, and Virginia in strata ranging in age from 50.8 to 55 Ma

New record of an extinct fish, Fisherichthys folmeri Weems (Osteichthyes), from the lower Eocene of Berkeley County, South Carolina, USA

Fisherichthys folmeri Weems 1999 (Sciaenidae?) is an extinct teleostean fish occurring in marine strata of the Gulf and Atlantic coastal plains, USA. We report isolated teeth collected from a lower Eocene (Ypresian) deposit in Berkeley County, South Carolina. Crowns of unworn teeth bear apical papillae surrounding a central depression, but these features are lost as teeth are worn through in vivo usage. The pulp cavity appears to become reduced in size as the tooth matures in the alveolus. Fisherichthys folmeri is thus far only known from Mississippi, South Carolina, and Virginia in strata ranging in age from 50.8 to 55 Ma