Todd D. Cook

A Freshwater Ichthyofauna from the Late Eocene Birket Qarun Formation, Fayum, Egypt

ABSTRACT A collection of fossil fish teeth and other elements from Eocene deposits on the northshore of Birket Qarun, Fayum Depression, Egypt, is reported. This collection adds significantly to our knowledge, as it consists of material that was screened from the sediments, allowing collection of small teeth that represent taxa not previously reported from the Fayum. Previous collections from these sediments have concentrated on larger remains that generally represent elasmobranchs, which are marine species from deposits lower in the section. Most of this material, collected by screening at the Birket Qarun 2 (BQ-2) locality, represents fully freshwater fishes. It includes the first record of the mormyrid Gymnarchus in the Fayum Depression, which represents the oldest record for this group, known previously only from the late Miocene or younger deposits. Similarly, Mochokidae (Siluriformes) and Hydrocynus (Alestidae) remains from the site are the oldest record of these taxa. Other taxa recovered are the osteichthyans Polypterus (Polypteriformes), Protopterus (Dipnoi), and Parachanna (Channidae), and the chondrichthyans Hypolophodon cf. H. malembeensis (Dasyatoidea incert. fam.), Rhinoptera sherborni (Rhinopteridae), and Coupatezia wousteri (Dasyatoidea incert. fam.). A new ray, Coupatezia attiai, n. sp., Cook, is also described. These fishes confirm the freshwater influence at locality BQ-2 in the Birket Qarun Formation.

A partial skeleton of the Late Cretaceous lamniform shark, Archaeolamna kopingensis, from the Pierre Shale of western Kansas, U.S.A.

ABSTRACT All previous records of the lamniform shark, Archaeolamna kopingensis, are based on isolated teeth. Here we describe a partial skeleton from the Sharon Springs Formation of the Pierre Shale Group of western Kansas, U.S.A. The specimen includes portions of the upper and lower jaws with articulated teeth. The dentition consists of two files of upper and lower anterior teeth that, together with a single file of intrabullar intermediate teeth, are housed in a dental bulla, as well as multiple files of lateral teeth, along with at least two files of lower symphysial teeth and a single file of upper symphysial teeth. The intrabullar intermediate tooth is slightly shorter than the other anterior teeth and has a median cusp with distinctive distal curvature. The dental sequence of A. kopingensis is unique among both extinct and extant lamniforms. Associated with the jaws are fragments of the neurocranium and multiple vertebral centra. A sagittal section through a centrum shows that this shark deposited 18 annual marker bands after its birth and adult size was attained by the 10th band. The robust but penetrating tooth morphology and large jaw circumference suggest that A. kopingensis likely fed upon large prey items.

Cenomanian—Campanian (Late Cretaceous) Mid-Palaeolatitude Sharks of Cretalamna appendiculata Type

The type species of the extinct lamniform genus Cretalamna, C. appendiculata, has been assigned a 50 Ma range (Albian—Ypresian) by a majority of previous authors. Analysis of a partly articulated dentition of a Cretalamna from the Smoky Hill Chalk, Kansas, USA (LACM 128126) and isolated teeth of the genus from Cenomanian to Campanian strata of Western Australia, France, Sweden, and the Western Interior of North America, indicates that the name of the type species, as applied to fossil material over the last 50 years, represents a large species complex. The middle Cenomanian part of the Gearle Siltstone, Western Australia, yielded C. catoxodon sp. nov. and “Cretalamna” gunsoni. The latter, reassigned to the new genus Kenolamna, shares several dental features with the Paleocene Palaeocarcharodon. Early Turonian strata in France produced the type species C. appendiculata, C. deschutteri sp. nov., and C. gertericorum sp. nov. Cretalamna teeth from the late Coniacian part of the Smoky Hill Chalk in Kansas are assigned to C. ewelli sp. nov., whereas LACM 128126, of latest Santonian or earliest Campanian age, is designated as holotype of C. hattini sp. nov. Early Campanian deposits in Sweden yielded C. borealis and C. sarcoportheta sp. nov. A previous reconstruction of the dentition of LACM 128126 includes a posteriorly situated upper lateroposterior tooth, with a distally curved cusp, demonstrably misplaced as a reduced upper “intermediate” tooth. As originally reconstructed, the dentition resembled that of cretoxyrhinids (sensu stricto) and lamnids. Tooth morphology, however, indicates an otodontid affinity for Cretalamna. The root is typically the most diagnostic feature on an isolated Cretalamna tooth. This porous structure is commonly abraded and/or corroded and, consequently, many collected Cretalamna teeth are indeterminable at species level.

A middle Cenomanian euselachian assemblage from the Dunvegan Formation of northwestern Alberta

A euselachian assemblage was recovered from the middle Cenomanian Dunvegan Formation situated in northwestern Alberta. This assemblage is the most northern described within the Western Interior Seaway and provides an important insight into the euselachian faunal diversity of this little-known region of the seaway. Despite its high paleolatitude, the assemblage contains a number of elasmobranch taxa, including Hybodus, Squalicorax, Archaeolamna, Cretodus, Dallasiella, and Cretoxyrhina. The Dunvegan assemblage also contains the first known reports from Canada of the odontaspid shark Johnlongia parvidens, the cretoxyrhinid shark Protolamna carteri, and the ray Pseudohypolophus mcnultyi. This assemblage extends the northern geographical range of all taxa. Preliminary comparisons with other middle Cenomanian Western Interior Seaway assemblages show that the core composition of the Dunvegan assemblage is remarkably similar to that of other time-equivalent assemblages; however, conspicuously absent are species t...

A high latitude euselachian assemblage from the early Turonian of Alberta, Canada

Numerous isolated euselachian teeth were recovered from the early Turonian Kaskapau Formation situated in northwestern Alberta, Canada. This high palaeolatitude assemblage was collected from a sandstone lens along the bank of the Smoky River, and includes 16 species belonging to at least three orders, at least 11 families, and 15 genera. Here we describe Odontaspis watinensis sp. nov. and report the first Canadian occurrence of Polyacrodus sp., Scapanorhynchus sp., and Carcharias aff. C. striatula. The scarcity of benthic taxa in this assemblage supports the previous notion that bottom waters in this region of the Western Interior Seaway experienced enduring anoxic episodes. By comparing the faunal composition of this assemblage with that of middle Cenomanian Canadian assemblages, we show that seven species have a biostratigraphical range that extended across the Cenomanian–Turonian boundary in the northern region of the seaway. Of the taxa described herein, Archaeolamna ex. gr. kopingensis, Cardabiodon aff. C. ricki, Carcharias aff. C. striatula, Odontaspis watinensis, and Johnlongia parvidens have not been reported from deposits of the southernmost region of the seaway and may have been restricted to cooler waters. http://zoobank.org/urn:lsid:zoobank.org:pub:FD671818-2769-484C-B424-F5EF5490A6A9

The first record of the large Cretaceous lamniform shark, Cardabiodon ricki, from North America and a new empirical test for its presumed antitropical distribution

ABSTRACT The first occurrence of the lamniform Cardabiodon ricki is reported from the late Cenomanian of Alberta, Canada. Previously, this taxon was described from Australia and Europe and has been hypothesized in the published literature as having an antitropical distribution. Whereas the occurrence of C. ricki in Alberta seemingly supports this hypothesis, no formal methodology exists to determine if Cardabiodon had an antitropical distribution because sampling for Cenomanian fossil elasmobranchs in the tropics is poor. We offer a novel methodology to test the purported hypothesis of an antitropical distribution for Cardabiodon by examining three paleoecological aspects. We compare the range of sea surface temperatures (SST) and paleolatitudinal ranges of Cardabiodon localities to those of the extant antitropical shark, Lamna nasus, because Cardabiodon should exhibit a similar magnitude of thermal and paleolatitudinal ranges to those of L. nasus. Furthermore, the paleodistribution of Cardabiodon localities should shift with climate change. Cardabiodon is concluded to have an antitropical distribution because (1) the SST range for Cardabiodon was only slightly greater (by 1.7°C) than that recorded for L. nasus; (2) the difference in paleolatitude range for Cardabiodon was 10° latitude less than the modern range for L. nasus; and (3) the paleolatitudes of Cardabiodon localities are positively correlated with global temperature to indicate that, during warm periods, Cardabiodon was found at higher paleolatitudes in both hemispheres, but it was found at warmer, lower latitudes during cooler periods.

A Miocene selachian fauna from Moghra, Egypt

The fossil bearing beds of Moghra, Egypt, have been well known for over 100 years, but the ichthyofaunas have not been examined since the early 1900s. Moghra, on the northern rim of the Qattara Depression, preserves early Miocene (18–17 Ma) fluvio-marine sediments with fossils of wood, invertebrates and vertebrates. The Moghra site is faunally similar to the Libyan Gebel Zelten site, at least in terms of the fossil mammals. The fossil-bearing localities in the Moghra Formation number about 40 and span a distance of about 50 km. There is likely more than one depositional environment represented. The fish previously reported from Moghra include two teleosts, Synodontis (Mochokidae) and Lates (Latidae), as well as the elasmobranchs, Pristis (Pristidae), Myliobatis (Myliobatidae) and Sphyrna (Sphyrnidae). Several more recent expeditions to the Moghra localities recovered abundant selachian remains. This rich assemblage included species from the genera Carcharias (Odontaspididae), Megaselachus (Otodontidae), Cosmopolitodus (Lamnidae), Hemipristis (Hemigaleidae), Galeocerdo and Carcharhinus (Carcharhinidae), Myliobatis (Myliobatidae), Pteromylaeus (Myliobatidae) and Aetobatis (Myliobatidae). With the additional taxa from these collections, we can build a more comprehensive understanding of the Moghra fauna and environment.

Vertebral Morphology, Dentition, Age, Growth, and Ecology of the Large Lamniform Shark Cardabiodon ricki

Cardabiodon ricki and Cardabiodon venator were large lamniform sharks with a patchy but global distribution in the Cenomanian and Turonian. Their teeth are generally rare and skeletal elements are less common. The centra of Cardabiodon ricki can be distinguished from those of other lamniforms by their unique combination of characteristics: medium length, round articulating outline with a very thick corpus calcareum, a corpus calcareum with a laterally flat rim, robust radial lamellae, thick radial lamellae that occur in low density, concentric lamellae absent, small circular or subovate pores concentrated next to each corpus calcareum, and papillose circular ridges on the surface of the corpus calcareum. The large diameter and robustness of the centra of two examined specimens suggest that Cardabiodon was large, had a rigid vertebral column, and was a fast swimmer. The sectioned corpora calcarea show both individuals deposited 13 bands (assumed to represent annual increments) after the birth ring. The identification of the birth ring is supported in the holotype of Cardabiodon ricki as the back-calculated tooth size at age 0 is nearly equal to the size of the smallest known isolated tooth of this species. The birth ring size (5–6.6 mm radial distance [RD]) overlaps with that of Archaeolamna kopingensis (5.4 mm RD) and the range of variation of Cretoxyrhina mantelli (6–11.6 mm RD) from the Smoky Hill Chalk, Niobrara Formation. The revised, reconstructed lower jaw dentition of the holotype of Cardabiodon ricki contains four anterior and 12 lateroposterior files. Total body length is estimated at 5.5 m based on 746 mm lower jaw bite circumference reconstructed from associated teeth of the holotype.

A NEW GENUS AND SPECIES OF FRESHWATER STINGRAY (MYLIOBATIFORMES, DASYATOIDEA) FROM THE LATEST MIDDLE EOCENE OF UTAH, U.S.A.

Abstract Teeth of a new freshwater dasyatoid ray recovered from the latest middle Eocene Brian Head Formation of southern Utah represent the youngest freshwater stingray so far known in the fossil record of North America. The crown morphology of Saltirius utahensis n. gen. n. sp. exhibits strong sexual dimorphism, with the presumed males bearing two prominent margino-labial protuberances and a bifid cusp that produces a saltire-like outline. This unique crown separates this genus and species from any known extinct or extant myliobatiform, but does have some resemblance to the crown of Asterotrygon maloneyi from the lower Eocene Green River Formation of Wyoming. The occurrence of S. utahensis in the Brian Head Formation provides additional evidence for the persistence of warm subtropical temperatures during the late Eocene in southern Utah.

A new genus and species of fossil myliobatoid ray from the Fishburne Formation (lower Eocene/Ypresian) of Berkeley County, South Carolina, USA

Elasmobranch fossils recovered from the Fishburne Formation (lower Eocene/Ypresian) of Berkeley County, South Carolina, USA, include species from four genera of sharks and six genera of rays. Of particular interest was the recovery of multiple isolated teeth from a new genus and species of the cownosed ray family Rhinopteridae, which is the focus of this study. The unique crown morphology separates this genus and species from Rhinoptera. Eorhinoptera grabdai, gen. et sp. nov., is represented by small, bar-shaped teeth in the shape of greatly elongated hexagons. These teeth are the isolated elements of a dental plate. The holotype, with 12 wide root lobes, is the most elongated in the sample being 1 cm long and 1.5 mm wide, indicating an origin in the central region of the plate. Paratypes are less elongated, have 4–8 root lobes and are from more lateral rows. The crown is smooth and has a distinctly convex occlusal surface. Eorhinoptera is only the second genus of cow-nosed ray. Its distinctive crown morphology may have allowed it to exploit different kinds of prey than those favoured by rays that lacked convex tooth crowns.