Skull Material Research Articles

A new Lower Cretaceous ichthyosaur from Russia reveals skull shape conservatism within Ophthalmosaurinae

AbstractOphthalmosaurinae is a recently recognized clade of derived ichthyosaurs (marine reptiles) ranging from the Bajocian (Middle Jurassic) to the late Albian (late Early Cretaceous). Whereas the Middle–Late Jurassic ophthalmosaurineOphthalmosaurusis often regarded as a hyperspecialized deep diver, very little is known about the anatomy, evolutionary history and ecology of Cretaceous ophthalmosaurines because of the scarcity of the fossils and the lack of well-preserved skull material. Here, we describe the skull of a new basal ophthalmosaurine ichthyosaur,Leninia stellansgen. et sp. nov., from the lower Aptian of western Russia, and compare the ocular characteristics of ophthalmosaurids.Leniniais recovered as a basal ophthalmosaurine; it possesses unique traits such as a star-shaped frontal–parietal suture as well as features previously thought to be unique toOphthalmosaurussuch as a supratemporal–stapes contact. A large sclerotic aperture – significantly larger than in platypterygiine ophthalmosaurids and similar to that of the largest-eyed modern animals (giant and colossal squids) – and reduced dentition appear widespread within ophthalmosaurines. This conservatism suggests ophthalmosaurine ophthalmosaurids occupied similar ecological niche(s) throughout their long evolutionary history.

A new softshelled trionychid turtle of the genus Khunnuchelys from the Upper Cretaceous Bostobe Formation of Kazakhstan

Previously unpublished trionychid turtle material from the Upper Cretaceous (Santonian—lower Campanian) Bostobe Formation from the Baybishe and Baykhozha localities in Kazakhstan is described. The material represents a new species of Khunnuchelys, a large, skull-based clade of Cretaceous Asian trionychids. Concordant with other partial skulls and fragmentary specimens described previously, Khunnuchelys lophorhothon sp. nov. has the unusual features of a beaklike maxilla and a vaulted, expanded triturating surface. In addition, the specimens reveal novel features including a constricted skull roof. Although estimates of the length of the carapace differ depending on estimation method, the skull belonged to a turtle of comparable size to the shell-based species “Trionyx” kansaiensis from the same formation. It is likely that K. lophorhothon and T. lophorhothon kansaiensis are synonymous, but this can be proved only by a find of associated skull and shell material.

The cranial anatomy of the sauropod Turiasaurus riodevensis and implications for its phylogenetic relationships

The skull of Turiasaurus is known from a nearly complete posterior section (e.g. braincase, skull roof, quadrates and left mandible) and fragments of the snout (e.g. portions of premaxilla, maxilla, nasal and lacrimal). Skull material of the holotypic individual was discovered in close association. Comparisons with other sauropods suggest that the Turiasaurus skull most closely resembled those of Jobaria, Camarasaurus and Mamenchisaurus youngi, possessing large spatulate teeth, enlarged and partially retracted external nares, and a broadly rounded muzzle. The list of autapomorphies for Turiasaurus is augmented by the new cranial data, including features such as: (1) a shelf-like projection of bone from the medial surface of the distal end of the maxillary ascending process; and (2) a rounded boss-like area on the lateral surface of the jugal. There are also unusual character states, such as the excavation of the posterior surfaces of the basal tubera (present in Turiasaurus and Losillasaurus) that probably have a wider phylogenetic significance. Phylogenetic analyses, using two different datasets, support the view that Turiasaurus, Losillasaurus and Galveosaurus form a monophyletic Turiasauria clade that lies just outside of Neosauropoda. The addition of the new cranial data slightly strengthens the support for this topology, but the relationships of other taxa (such as Jobaria) become less stable. The Turiasauria might represent a distinct group of non-neosauropods with a wide geographic distribution across Europe and Africa during the Late Jurassic.

Size and Form of the Human Temporomandibular Joint in African-Americans and Caucasians

The aim of this study was to examine contemporary human skull material for possible differences between Caucasians and African-Americans in respect to size and form of the temporomadibular condyles. The material consisted of a total of 129 Caucasian skulls (94 males and 35 females) and 76 African-American skulls (40 males and 36 females). Their mean age at death was 46 years for the Caucasians (range: 19-89 years) and 37 years for the African-Americans (range: 18-70 years). The mediolateral and anteroposterior dimensions of the 410 condyles were measured, and the condylar form was estimated using both anterior and superior views. No statistically significant differences could be found between Caucasians and African-Americans for any of the recorded variables. In conclusion, the present results lend no support for the existence of ethnic differences between the two groups examined in respect of temporomandibular joint size and form. It is likely that other factors such as evolution, overall cranial size, dietary differences, and genetic factors, irrespective of ethnicity, can explain the differences found in different skull samples.

Postcranial morphology and growth of the pachypleurosaur Anarosaurus heterodontus (Sauropterygia) from the Lower Muschelkalk of Winterswijk, The Netherlands

Sauropterygia from the Muschelkalk are only found in lag deposits known as bone beds, and most of the material consists of isolated bones. Alpha taxonomy of Sauropterygia from the Germanic Basin which include Pachypleurosauria is thus based mainly on skull morphology of a few specimens. Articulated or associated postcranial material of pachypleurosaurs, associated with diagnostic skull material, is very rare in the Germanic Basin and currently occurs in larger numbers only in the Lower Muschelkalk of Winterswijk (Gelderland Province, The Netherlands), which continuously produces new material. For the first time, the morphology of several partially articulated skeletons of the pachypleurosaur Anarosaurus heterodontus is described and compared. Some of those specimens have skull material attached; others were identified as pachypleurosaurs on the basis of their long bone histology. The current study revealed that postcranial bones of A. heterodontus feature a diverse morphology reflecting differences during ontogeny. Thus, A. heterodontus specimens could be assigned to size classes (I–III). However, on the basis of morphology, histology, and maximal known size of isolated skulls and humeri, none of these specimens represent fully grown individuals. Growth mark counts of midshaft-femur samples, morphologically assigned to size class III, document that this size class was reached within the first year of life. Size class III continued into the second year of life, and then afterwards skeletal maturity was reached. Thus, a juvenile A. heterodontus grew very fast, which is also indicated by its bone tissue type, composed of a high number of radial vascular canals and a fast-deposited bone matrix. The assignment of isolated bones from Lower to Middle Muschelkalk localities to A. heterodontus is now possible with an extensive amended diagnosis of this taxon. This largely contributes to the understanding of taxonomical diversity and distribution. Morphological comparison of the postcranial skeleton of A. heterodontus with that of the two other valid pachypleurosaurs from the Germanic Basin, Anarosaurus pumilio and Dactylosaurus, supports their close phylogenetic relationship. Furthermore, the skeleton of A. heterodontus has no morphological or histological aquatic adaptation such as pachyostosis or pachyosteosclerosis and thus represents the least degree of aquatic adaptation within Pachypleurosauria.

New material of Alphagaulus pristinus (Mammalia, Rodentia, Mylagaulidae) from the Deep River Formation (Montana, U.S.A.): Implications for ecology, ontogeny, and phylogeny

ABSTRACT The Mylagaulidae are a family of extinct fossorial rodents that are common in the North American Miocene. Alphagaulus pristinus, from the Barstovian of Montana, was previously known only from partial dentaries and isolated teeth, with no well-described skull or postcranial material. Alphagaulus is important to understanding the evolution of burrowing in mylagaulids, because it is within this genus that the most dramatic evolution of fossorial morphology within mylagaulids occurs. The other three species of the genus are all known from partial skulls, rare isolated postcrania for Alphagaulus vetus, and, in the case of Alphagaulus tedfordi, a nearly complete skeleton. We describe new material housed at the University of Washington Burke Museum, including three well-preserved skulls and partial skeletons showing different ontogenetic stages from juveniles to an adult. The description of this new material gives insights into the ontogeny of these burrowing mammals. In particular, it is apparent that the developmental trajectory mimics evolution in the increase of fossorial modifications of the skeleton with time. The description of these specimens also allows reanalysis of the phylogenetic relationships within the Mylagaulidae, confirming that the genus Alphagaulus is paraphyletic. Though the phylogenetic positions of species within the genus are different, our results are more stable than those of previous analyses, allowing greater confidence in the reconstructed relationships among mylagaulid species and genera.

MATERIAL PROPERTIES OF ADULT RAT SKULL

Development of advanced computational rat head models requires accurate material properties of the rat brain, meninges, skull, and other soft tissues. This study investigated adult rat skull material properties, which are very limited in the current literature. A total of 20 skull specimens were harvested from 10 adult rats. High resolution (16 μm) microcomputed tomography scans were performed for each specimen to observe dimensional changes within each specimen and internal porosities through the cross sections. The specimens were tested in three-point bending at loading velocities of 0.02 and 200 mm/s. The elastic modulus, energy absorbed to failure, energy density, and bending stress were calculated using classical beam theory. Results demonstrated that bending velocity (strain rate) had significant effect on elastic modulus and bending stress, but not on energy and energy density. The Young's moduli of rat skull measured in this study were comparable to those measured from the adult human skull.

Degenerative changes of the temporomandibular joint. Relationship to ethnicity, sex and occlusal supporting zones based on a skull material

Objective. The first aim of this study was to examine a contemporary human skull material for possible ethnic differences in respect of degenerative changes in the temporomandibular joints (TMJs). A second aim was to see if there was any correlation between such changes and occlusal support in any of the two groups and, if so, if this correlation was sex-related. Materials and methods: The material consisted of 129 Caucasian skulls and 76 skulls from Afro-Americans. Ninety-four of the Caucasian skulls came from males (73%) and the corresponding figure for the Afro-Americans was 40 (53%). Their mean age at death was 46 years (range: 19–89 years) and 37 years (range: 18–70 years), respectively. Results. Dental status was in general poor and 13% of the Afro-Americans and 26% of the Caucasians were edentulous. Form and surface changes of the TMJs were more common in the present material compared to most previous studies. No differences could be found between the two ethnic groups in respect of degenerative joint changes in the TMJs. In men, no correlation of clinical relevance could be found between severity of joint changes and occlusal support. However, in both Caucasian and Afro-American women, such a correlation was obvious, especially in higher age. Conclusions. The present findings give no evidence for any differences in the prevalence of degenerative changes in the TMJs in Caucasians and Afro-Americans. The strong correlation found between such changes and occlusal support in women but not in men might be explained by hormonal differences.

Palaeolithic dog skulls at the Gravettian Předmostí site, the Czech Republic

Abstract Whether or not the wolf was domesticated during the early Upper Palaeolithic remains a controversial issue. We carried out detailed analyses of the skull material from the Gravettian Předmosti site, Czech Republic, to investigate the issue. Three complete skulls from Předmosti were identified as Palaeolithic dogs, characterized by short skull lengths, short snouts, and wide palates and braincases relative to wolves. One complete skull could be assigned to the group of Pleistocene wolves. Three other skulls could not be assigned to a reference group; these might be remains from hybrids or captive wolves. Modifications by humans of the skull and canine remains from the large canids of Předmosti indicate a specific relationship between humans and large canids.

Development, Validation, and Application of a Parametric Pediatric Head Finite Element Model for Impact Simulations

In this study, a statistical model of cranium geometry for 0- to 3-month-old children was developed by analyzing 11 CT scans using a combination of principal component analysis and multivariate regression analysis. Radial basis function was used to morph the geometry of a baseline child head finite element (FE) model into models with geometries representing a newborn, a 1.5-month-old, and a 3-month-old infant head. These three FE models were used in a parametric study of near-vertex impact conditions to quantify the sensitivity of different material parameters. Finally, model validation was conducted against peak head accelerations in cadaver tests under different impact conditions, and optimization techniques were used to determine the material properties. The results showed that the statistical model of cranium geometry produced realistic cranium size and shape, suture size, and skull/suture thickness, for 0- to 3-month-old children. The three pediatric head models generated by morphing had mesh quality comparable to the baseline model. The elastic modulus of skull had a greater effect on most head impact response measurements than other parameters. Head geometry was a significant factor affecting the maximal principal stress of the skull (p = 0.002) and maximal principal strain of the suture (p = 0.021) after controlling for the skull material. Compared with the newborn head, the 3-month-old head model produced 6.5% higher peak head acceleration, 64.8% higher maximal principal stress, and 66.3% higher strain in the suture. However, in the skull, the 3-month-old model produced 25.7% lower maximal principal stress and 11.5% lower strain than the newborn head. Material properties of the brain had little effects on head acceleration and strain/stress within the skull and suture. Elastic moduli of the skull, suture, dura, and scalp determined using optimization techniques were within reported literature ranges and produced impact response that closely matched those measured in previous cadaver tests. The method developed in this study made it possible to investigate the age effects from geometry changes on pediatric head impact responses. The parametric study demonstrated that it is important to consider the material properties and geometric variations together when estimating pediatric head responses and predicting head injury risks.

Etiopathogenesis of hyperostosis frontalis interna: A mystery still

Hyperostosis frontalis interna is a morphological pattern characterized by single or multiple bony nodules situated on the inner lamina of the frontal bone. It is seldom found in males, but it is a common phenomenon among post-menopausal females in modern societies but relatively rare in antiquity. The etiopathogenesis of the trait is a matter of debate and ranges from genetic predisposition to epigenetic, while endocrine disturbances, aging, and dietary factors are also listed among the causes. We studied the frequency, characteristic features, and etiopathogenesis of the disease in recent cadaveric and dry skull specimens. The frequency of hyperostosis frontalis interna in cadavers and dry skull materials was almost identical, 12.5% and 12.3%, respectively. In cadavers, 87.5% of severe hyperostosis frontalis interna cases were found in females over 65 years-old. Interestingly, in two cadavers we found hyperostotic lesions spreading onto adjacent tissues such as the dura and falx cerebri. We provide some new aspects that may help in better understanding of the etiopathogenesis of hyperostosis frontalis interna. Thereby, we discuss the various etiopathogenesis models found in the literature.

Cranial Anatomy and Phylogenetic Position of the Titanosaurian SauropodBonitasaura salgadoi

Knowledge of titanosaurian cranial anatomy has improved substantially in the last decade because several skulls have come to light or were restudied. The discovery of Bonitasaura salgadoi, a partial titanosaurian skeleton including cranial bones, permitted the definitive recognition of square jaws in a titanosaurian sauropod as well as a peculiar skull morphology that increases the morphological diversity of the group. Here we present a full description and illustration of the skull material of B. salgadoi. Among cranial bones, the lacrimal, quadrate, and dentary exhibit apomorphic differences from those of other titanosaurians. Conversely, the frontal and parietal are more conservative. A phylogenetic analysis recovers B. salgadoi as a member of the Titanosauria, related to mid-sized to large titanosauroids from the Turonian—Campanian of South America, in contrast to a previous hypothesis that suggested a nemegtosaurid affinity. The skull reconstruction presented here shows that the skull of B. salgadoi ...

A revision of enantiornithine (Aves: Ornithothoraces) skull morphology

Enantiornithines are the most speciose avian clade in the Mesozoic, with a fossil record that nearly spans the Cretaceous; however, with less than half of known taxa preserving skull material, our understanding of their cranial morphology remains incomplete. Here we present a comprehensive overview of the current knowledge of enantiornithine skull anatomy and discuss the range of morphologies known for each of the main cranial elements. The typical enantiornithine skull retains numerous ancestral features such as the absence of fusion among bones, the presence of a postorbital bone, a primitive quadrate with a single headed otic process, an unforked dentary, and teeth. The postorbital in at least one taxon is unreduced, suggesting the existence of a complete infratemporal fenestra and thus an unmodified diapsid skull as in confuciusornithids. The rostrum is well known and shows considerable variation, typical of theropods; however, in terms of rostral proportions, enantiornithines are extremely limited within the modern avian spectrum. Although Late Cretaceous skull material is extremely fragmentary, when compared to Early Cretaceous material it reveals a trend towards more specialized morphologies in younger taxa. The foramen magnum in all taxa points caudally, indicating that the ‘flexed’ type skull morphology may not have evolved in this group. Enantiornithine teeth show considerable diversity in numbers, size, morphology and placement, ranging from taxa with large teeth found throughout the jaws to taxa with small, rostrally restricted teeth, to the fully edentulous. Despite limited preservation of skull material, a number of trophic specializations can be deduced from the range of preserved morphologies, further hinting at the morphological and ecological diversity of the Cretaceous Enantiornithes.

Material property influences on the modelling of child brain injuries

Finite element simulations of a human head are often used to enhance our knowledge of injury mechanisms, assist in injury prediction and to develop preventative devices such as helmets and seatbelts. While many adult models have been developed and validated, few child models have been developed due to a lack of material data and experimental studies of which to validate the model. Therefore, many child head injuries are investigated via dimensionally scaled adult head models without the replacement of the adult material properties by the child material properties. This study aims to evaluate whether applying the child material properties to a dimensionally scaled adult head significantly influences the predicted risk of brain injury of a child head due to impact accidents. The adult model of Horgan & Gilchrist (2003) was scaled to the size of a 6-month old child’s head and then this model was compared to the one with child material properties appended. Frontal, lateral and occipital impacts were simulated, and the use of the child material properties was found to decrease the peak von Mises stress in the brain by up to 58.2%. Applying this result to the University Louis Pasteur criterion (Marjoux et al, 2008) yielded a maximum decrease of 90% in the relative risks of severe brain injury. Therefore, when analysing child brain injuries with a scaled adult model, the child material properties should be applied in order to more accurately predict the extent of brain injury. Our further numerical study explored the sensitivity of the skull and brain material properties on head injuries. The results showed that the impact force is mainly affected by the skull material properties and the brain material properties have negligible influence on the impact force. However, the maximum von Mises stress in the brain is mainly affected by the brain material properties.

Three-dimensional reconstruction of cranial defect using active contour model and image registration

In neurosurgery, cranial incisions during craniotomy can be recovered by cranioplasty--a surgical operation using cranial implants to repair skull defects. However, surgeons often encounter difficulties when grafting prefabricated cranial plates into defective areas, since a perfect match to the cranial incision is difficult to achieve. Previous studies using mirroring technique, surface interpolation, or deformed template had limitations in skull reconstruction to match the patient's original appearance. For this study, we utilized low-resolution and high-resolution computed tomography images from the patient to repair skull defects, whilst preserving the original shape. Since the accuracy of skull reconstruction was associated with the partial volume effects in the low-resolution images and the percentage of the skull defect in the high-resolution images, the low-resolution images with intact skull were resampled and thresholded followed by active contour model to suppress partial volume artifacts. The resulting low-resolution images were registered with the high-resolution ones, which exhibited different percentages of cranial defect, to extract the incised cranial part. Finally, mesh smoothing refined the three-dimensional model of the cranial defect. Simulation results indicate that the reconstruction was 93.94% accurate for a 20% skull material removal, and 97.76% accurate for 40% skull material removal. Experimental results demonstrate that the proposed algorithm effectively creates a customized implant, which can readily be used in cranioplasty.

A new taxon of phytosaur (Archosauria: Pseudosuchia) from the Late Triassic (Norian) Sonsela Member (Chinle Formation) in Arizona, and a critical reevaluation of Leptosuchus Case, 1922

Abstract: Leptosuchus Case, 1922 (Reptilia: Phytosauria) from the Late Triassic of the American West is represented by many specimens. Here, I present complete morphological descriptions of the skull material of a new taxon from the Sonsela Member (Chinle Formation) of Petrified Forest National Park, Arizona, with the first rigorous phylogenetic analysis focused on the interrelationships of Leptosuchus. The new taxon is recovered as the sister taxon to Pseudopalatinae. It possesses one unambiguous synapomorphy (the ‘septomaxillae’ form part of the lateral borders of the nares) and shares the presence of a subsidiary opisthotic process with Pseudopalatinae. The new taxon does not fall within the restricted clade Leptosuchus. In my analysis, the previously proposed, but undemonstrated, sister taxon relationship between Angistorhinus and Rutiodon is not supported, Paleorhinus is recovered as paraphyletic, and a subset of taxa traditionally included within Leptosuchus are found to be more closely related to Pseudopalatinae, rendering Leptosuchus paraphyletic. ‘Leptosuchus’adamanensis emerges as sister taxon to Smilosuchus gregorii and is here referred to as Smilosuchus adamanensis nov. comb., and ‘Machaeroprosopus’lithodendrorum is also transferred to Smilosuchus lithodendrorum nov. comb. Documentation of the variation present within Phytosauria, and specifically within Leptosuchus sensu lato, demonstrates higher diversity within Phytosauria than previously appreciated and places the character states previously proposed for Pseudopalatinae into a broader context of shared characters.

Degenerative changes in human temporomandibular joints in relation to occlusal support

Objective. Controversy exists concerning the etiological factors behind degenerative changes in the temporomandibular joints (TMJs). Tooth attrition, occlusal support, food consistency, ageing, gender and genetics are some possible causative factors that have been discussed in the literature. The aim of this study was to examine contemporary human skull material for possible relations between degenerative form and surface changes in the TMJs in relation to occlusal support. Material and methods. The material consisted of 259 human skulls from 170 males and 89 females, with an age range of 18–100 years. Results. Dental status was in general poor, and 22% of skulls were edentulous. Form and surface changes of both the condyles and the temporal components were more common in the present material compared to that in most previous studies. In males, irrespective of age, only weak and clinically insignificant correlations could be found between degenerative TMJ changes and occlusal support. In women, however, the correlations between these variables were in general much stronger, especially at higher ages. Conclusions. The present findings do not lend support to the hypothesis that loss of occlusal support is a causative factor for degenerative changes in the TMJs in male subjects. In women, such a correlation was obvious in the present sample, at least at higher ages. It can be speculated that hormonal factors play a role in the sex difference found.

New Material of North American Side-Necked Turtles (Pleurodira: Bothremydidae)

New cranial and postcranial material of the pleurodire family Bothremydidae, subtribe Bothremydina, from the Gulf Coastal Plain of North America, clarifies the distribution of the genera Bothremys and Chedighaii. New skull material from the Campanian Tar Heel Formation of North Carolina shows the presence of both Bothremys and Chedighaii, based on a maxilla and lower jaw. Additionally, a series of otic chambers and basicrania, while providing important information on morphology, are identified as subtribe Bothremydina, genus and species indeterminate, as the basicranium alone is insufficient to distinguish Bothremys and Chedighaii.An associated skull-shell specimen belonging to the pleurodire subtribe Bothremydina from the Campanian Mooreville Chalk of Alabama, FMNH PR 247, identified in Gaffney et al. (2006) as Chedighaii barberi, is reinterpreted as belonging to the genus Bothremys. A maxilla and jugal fragment found among the material belonging to FMNH PR 247 shows that this specimen has a skull with deep pits on its triturating surface, diagnostic of the genus Bothremys, and in contrast to the flat triturating surface of Chedighaii. Because FMNH PR 247 has an associated partial skull and shell, it was the basis for placing the species “Podocnemis” barberi Schmidt, 1940, the type of which is a shell, in Chedighaii Gaffney et al., 2006. A result of this identification is that the species “Podocnemis” barberi Schmidt, 1940, cannot be assigned to a genus, as the shell morphology of Chedighaii Gaffney et al., 2006, and Bothremys Leidy, 1865, cannot be distinguished at present. A review of the shell material in the subtribe Bothremydina concludes that shells alone are inadequate to reliably distinguish alpha-level taxa in this group at present.It is likely that ALAB PV 2001.2, NCSM 23681, and YPM PU 12951, here referred to Chedighaii sp., belong to a new species of Chedighaii, distinct from Chedighaii hutchisoni, but the material is too incomplete at present to adequately diagnosis it.

Rehabilitation of the worn dentition*

The purpose of this review was to evaluate the literature on the rehabilitation of tooth wear, with some pertinent historical, epidemiological and aetiological aspects of tooth wear provided as background information. In historical skull material, extensive tooth wear, assumed to be the result of coarser diets, was found even in relatively young individuals. Such wear is seldom seen in current populations. Although many of the factors associated with extensive tooth wear in historical material are no longer present or prevalent, new risk factors have emerged. In the young individual, the literature points to a global rise in soft drink consumption as the most significant factor in the development of tooth wear through dental erosion. Among older individuals, lifestyle changes and chronic diseases that are controlled with medications that may, in turn, result in regurgitation and/or dry mouth, are possible reasons amongst others for the widespread clinical impression of an increasing prevalence of tooth wear. The aetiology of tooth wear is multifactorial and the role of bruxism is not known. Clinical controlled trials of restorative and prosthodontic approaches for the range of clinical conditions that wear can give rise to, are limited in number and quality. Equally, the striking lack of evidence regarding the long-term outcomes of treatment methods and materials calls for caution in clinical decision-making. Notwithstanding these observations, clinicians have provided and continue to provide rehabilitative strategies for managing their patients' worn dentitions that range traditionally from extensive prosthodontics to an increasing reliance on adhesive techniques.

Osteoglossomorphs of the marine Lower Eocene of Denmark – with remarks on other Eocene taxa and their importance for palaeobiogeography

Abstract The geological, faunal and palaeoecological conditions of the marine deposits from lowermost Eocene in North Jutland are briefly reviewed as background for the descriptions of six species of osteoglossiform fishes from the Stolle Klint Clay and the overlying Mo-clay (Ølst and Fur Formations respectively). Four of these primitive teleosteans are referred to new genera and species (one based on an almost complete skeleton, three others on skull material, one very incomplete), and the two most fragmentary specimens are referred to Brychaetus sp. and an indeterminate osteoglossiform. The phylogenetic relationships of these fossils are evaluated in the framework of two different models of osteoglossomorph phylogeny provided earlier by Taverne and Hilton. Despite differences in both data bases, methodologies and results given by the two models (the former based on c . 300 characters in an intuitive, qualitative phylogenetic parsimony analysis, the latter on 72 characters in a critical, rigorous, quantitative cladistic analysis) the phylogenetic positions of four of the fossil species are very similar in the two models concerning the relations to the recent forms. The other two species, rather fragmentary, but similar in many ways to the Eocene phareodonts (paraphyletic group), end up very differently in relation to extant forms in the two models. The phylogenetic systematics of all the marine, fossil osteoglossiforms (including Brychaetus, Opsithrissops and Monte Bolca forms) is evaluated as background for interpretation of their (palaeo-)biogeographic significance as marine members of a group, Osteoglossomorpha (of which the recent forms are prime examples of ‘primary division freshwater fishes', and of which the extant osteoglossiforms have a classical ‘Gondwana distribution’. There are 9 marine, Eocene taxa (plus an otolith from the Maastrichtian of USA) and none of the 9 appear more closely-related to any other marine form in either model: they might constitute 9 separate migrations from freshwater into the sea. The phylogenetic results strongly suggest instead, that the extant osteoglossiforms have independently entered freshwater from the sea on two, perhaps even three occasions. This may have happened as late as the Eocene, and phareodonts could be yet another independent invasion of freshwater in the Late Cretaceous. The mormyriforms most likely had an independent invasion into freshwater (in one model even with notopterids as a separate migration from the sea by Mid or Early Cretaceous). Because all the closest outgroups of the Osteoglossomorpha are marine, the group obviously originated in the sea, probably by the Late Jurassic, and it is not impossible that Hiodontiforms in NE Asia and North America underwent another independent freshwater invasion very early in the Cretaceous. What then is wanting? The expected Cretaceous, marine osteoglossomorphs are not found (but note the above otolith).