Anne Kemp

A revision of Australian mesozoic and cenozoic lungfish of the family neoceratodontidae (Osteichthyes:Dipnoi), with a description of four new species

The taxonomy of the predominantly Australian fossil dipnoan genus, Neoceratodus, is revised and the Recent Australian lungfish, Neoceratodus forsteri, and two fossil species, Neoceratodus eyrensis and Neoceratodus nargun, are redefined. Two new species of the related Tertiary genus, Mioceratodus, are described on the basis of tooth plates from central and northern localities in Australia. These are Mioceratodus diaphorus and Mioceratodus poastrus. A new genus, Archaeoceratodus, is erected to include three rare Tertiary species and one Mesozoic species. The Tertiary members of this genus are the type species, Archaeoceratodus djelleh, described originally as Neoceratodus djelleh, and two new species, Archaeoceratodus rowleyi and Archaeoceratodus theganus. The Mesozoic species is Archaeoceratodus avus from Triassic and Cretaceous deposits in southeastern Australia, described originally as Ceratodus avus. All three genera belong in the family Neoceratodontidae.

Skull structure in post-Paleozoic lungfish

ABSTRACT Three dimensional reconstructions of the dermal skulls of Ceratodus sturii, Ptychoceratodus serratus, Asiatoceratodus (Arganodus) atlantis, and Mioceratodus gregoryi are described, and compared with adult skulls of Recent lungfish of the genera Neoceratodus and Protopterus. Inferred patterns of fusion and reduction of the skull bones of Neoceratodus, Mioceratodus, and Protopterus suggest that these form one natural lineage, excluding Ceratodus, Ptychoceratodus, and Asiatoceratodus. The study of skull roofing bones also indicates that Asiatoceratodus atlantis and Ptychoceratodus serratus are related to each other but not close to other Mesozoic and Cenozoic lungfish, and that Ceratodus sturii is a distinct taxon more distantly associated with other derived dipnoans. The dentitions of the different genera provide unifying characters as all are based on initially isolated cusps that fuse in a pattern of radiating ridges to form tooth plates.

Mesozoic continental vertebrates with associated palynostratigraphic dates from the northwestern Ethiopian plateau

The East African Rift separates the northwestern and southeastern Ethiopian high plateaus, which are capped by massive Cenozoic volcanics overlying thick deposits of marine and nonmarine Mesozoic sediments. During geological mapping projects of the 1920s-1930s, a few Mesozoic vertebrate fossils were found on the southeastern plateau. in contrast, beginning in 1976, and then from 1993 to the present, paleontological field work in the Abay (Blue Nile) River gorge along the eastern edge of the northwestern plateau resulted in the discovery of fossil chondrichthyans (Priohybodus, Hybodus, Rhinobatos), osteichthyans (Lepidotes, cf. Pycnodus), dipnoans (Asiatoceratodus), chelonians (Pelomedusidae, Plesiochelyidae, Pleurosternidae), crocodylians (Goniopholis), dinosaurs, (cf. Acrocanthosaurus Hypsilophodontidae), pollen and other microfossils documenting a coastal biota in part, if not entirely, of latest Jurassic (Tithonian) age. These fossils include new biogeographic records for Africa and document biostratigraphic range extensions. The Ethiopian Mesozoic fauna adds to the growing evidence of limited interchange of vertebrates between Africa and Western Europe during the transition from the Jurassic into the Cretaceous.

Four species of Metaceratodus (Osteichthyes: Dipnoi, Family Ceratodontidae) from Australian Mesozoic and Cenozoic deposits

ABSTRACT The ceratodont lungfish Metaceratodus wollastoni is described from new material from central and southern Australia, and three additional species, Metaceratodus ellioti, Metaceratodus bonei, and Metaceratodus palmeri are included in the genus. M. ellioti and M. bonei are new species, and M. palmeri, originally described as Ceratodus palmeri, has been reassigned. The current determinations of species are based on morphological characters. M. wollastoni is found in Lower and Upper Cretaceous deposits in southeast and central Australia. M. ellioti is confined to the Upper Cretaceous of southeast and central Australia. M. bonei is found in the Namba and Etadunna formations in central Australia, late Oligocene to middle Miocene in age, as well as a single record from a possible Pleistocene deposit. M. palmeri comes from strata belonging to the Pliocene and Pleistocene of eastern Australia. At least one species of Metaceratodus also occurs in the Lower Cretaceous Coli-Toro Formation of South America.

Marginal tooth‐bearing bones in the lower jaw of the recent australian lungfish, Neoceratodus forsteri (Osteichthyes, Dipnoi)

Developmental studies of the Recent Australian lungfish, Neoceratodus forsteri, show that this species has two sets of functional tooth‐bearing bones in the lower jaw of young hatchlings. These coincide with an early stage in the life history when the fish is strictly carnivorous. In N. forsteri, a paired tooth‐bearing dentary and an unpaired symphyseal bone and tooth develop slightly later than the permanent vomerine, prearticular, and pterygopalatine tooth plates, which appear at stage 44 of development, and erupt with the permanent dentition between stages 46 and 48, when the hatchling first starts to feed on small aquatic invertebrates. At these stages of development, all of the teeth are long, sharp, and conical and help to retain prey items in the mouth. Disappearance of the transient dentition coincides with complete eruption of the permanent tooth plates and precedes the change to an omnivorous diet. Existence of a transient marginal dentition in this species of lungfish suggests that the presence of an apparently similar marginal dentition in adults of many species of Palaeozoic dipnoans should be considered in phylogenetic analyses of genera within the group, and when analysing the relationships of dipnoans with other primitive animals.

Ultrastructure of developing tooth plates in the australian lungfish, Neoceratodus forsteri (Osteichthyes: Dipnoi)

While the lungfish dentition is partially understood as far as morphology and light microscopic structure is concerned, the ultrastructure is not. Each tooth plate is associated with a dental lamina that develops from the inner layer of endodermal cells that form the oral epithelium. Dentines, bone and cartilage of the jaws differentiate from mesenchyme cells aggregating beneath the oral endothelium. Enamel, in the developing and in the mature form, has similarities to that of other early vertebrates, but unusual characters appear as development proceeds. Ameloblasts are capable of secreting enamel, and, with mononuclear osteoclasts, of remodelling the bone below the tooth plate. The forms of dentine, all based largely on an extracellular matrix of collagen and mineralised with biological apatite, differ from each other and from the underlying bone in the ultrastructure of associated cells and in the mineralised extracellular matrices produced. Cell processes emerging from the odontoblasts and from the osteoblasts vary in length, degree of branching and of anastomoses between the processes, although all of the cell types have large amounts of rough endoplasmic reticulum. Mineralisation of the extracellular matrices varies among the enamel, dentines and bone in the tooth plate. In addition, the development of the hard tissues of the tooth plates indicates that many of the similarities in fine structure of the dentition in lungfish, to tissues in other fish and amphibia, apparent early in development, disappear as the dentition matures.

Amino acid residues in conodont elements

Abstract Thermally unaltered conodont elements, brachiopods, and vertebrates were analyzed with reverse phase high profile liquid chromatography to locate and quantify amino acid remnants of the original organic matrix in the fossils. No consistent similarities in amino acid content were found in conodont taxa, and criteria based on organic residues appear to have no taxonomic significance in the fossils tested from these localities. However, hydroxyproline, an amino acid that is found in the collagen molecules of animals, as well as in the glycoproteins in the cell walls and reproductive tissues of certain plants, is represented in most taxa. The organic matter retained in the impermeable crowns of conodont elements might have been derived originally from a form of collagen. Biochemical analyses, correlated with histochemical tests, demonstrate that organic matter is an integral part of the hyaline tissue of the element crown and not the result of surface contamination. Tests of a range of vertebrate and invertebrate fossil hard tissues produced similar results. The analyses indicate that hyaline tissue in the conodont element crown is not a form of vertebrate enamel, which contains no collagen. Albid tissue, with little or no organic content, is not a form of vertebrate bone or dentine, both based on collagen and low in mineral. Although these results do not help to determine the phylogenetic affinities of conodont animals, they indicate that conodont elements do not contain hard tissues characteristic of vertebrate animals.

Petrodentine in derived Dipnoan tooth plates

Abstract Most lungfish tooth plates, that are arranged in radiating ridges derived from the fusion of separate cusps in young juveniles, are based on a framework of enamel, mantle dentine and bone that encloses a mass of specialized dentines forming the occlusal surface. In most taxa, the specialized dentines are interdenteonal and circumdenteonal dentine, but a few derived genera have petrodentine as well. Petrodentine, as originally defined, describes a specific form of hypermineralized dentine in adult tooth plates of the Recent African lungfish Protopterus. The ontogeny of fossil and Recent lungfish tooth plates demonstrates that petrodentine is derived by continuous enhancement of the hard tissue of the primary core of the initially isolated cusps of the tooth plate, and that interdenteonal dentine with denteons of circumdenteonal dentine is a secondary development in the tooth plate around and below the first formed cusps of the ridges. In dipnoans that lack petrodentine in adults the primary core of the cusps is not enhanced, but is removed by wear. The hard tissues of the dipnoan tooth plate provide useful characters for defining dipnoan taxa, as do the differing arrangements of the tissues in each species. Details of the arrangement of the enclosed specialized dentines are surprisingly variable among genera, and are significant for the structure and function of the tooth plate. Little regularity of structure is discernible in the histology of tooth plates of early dipnoans, but derived genera have more predictable structure. Consistent with other uniquely dipnoan characters, like the composition of the dermal skull, an evolutionary progression is evident within the group in the fine structure of the dentition, and, as with the bones of the dermal skull, little similarity is demonstrable between the dentines of dipnoans and tetrapods.

Australian Triassic lungfish skulls

Skull bones of Gosfordia truncata Wooward, 1891, from the Lower Triassic Hawkesbury Sandstone of New South Wales, Australia, are described for the first time. The skull roofing pattern suggests possible affinities between G. truncata and Paraceratodus germaini. A three-dimensional reconstruction of the skull of Ceratodus formosus Wade, 1935 is included. This reconstruction indicates that this species is not closely related either to the recent Australian lungfish, Neoceratodus forsteri, or to the Triassic Ceratodus (Tellerodus) sturii from Nord Alpen in Austria, and it has no close affinities with G. truncata. A new genus, Ariguna, is therefore proposed to receive Ceratodus formosus Wade, 1935. -from Author

Microstructure of Pharyngeal Tooth Enameloid in the Parrotfish Scarus rivulatus (Pisces:Scaridae)

The microstructure of parrotfish pharyngeal teeth was examined using scanning electron microscopy to infer possible mechanical properties of the dentition with respect to their function. Parrotfish tooth enameloid is formed from fluorapatite crystals grouped into bundles. In the upper and lower pharyngeal jaw, the majority of the crystal bundles are orientated either perpendicularly or vertically to the enameloid surface. The only exception is in the trailing apical enameloid in which the majority of bundles are orientated perpendicularly or horizontally to the trailing surface. A distinct transition occurs through the middle of the apex between the leading and trailing enameloid in teeth of the lower pharyngeal jaw. This transition appears less distinct in the teeth of the upper pharyngeal jaw. Enameloid microstructure indicates that shear forces predominate at the apex of the teeth. In the remainder of the enameloid, the microstructure indicates that wear is predominant, and the shear forces are of less importance.