Cranial Elements Research Articles

Comparison of prenatal and postnatal ontogeny: cranial allometry in the African striped mouse (Rhabdomys pumilio)

The relationship between prenatal and postnatal ontogenetic allometry is poorly known, and empirical studies documenting prenatal allometry are few, precluding an understanding of changes in growth patterns during life history and their relation to proximal, physiological, and ultimate evolutionary variables. In this study I compare prenatal and postnatal ontogenetic allometry of the cranium in a cleared and stained developmental series of the African striped mouse (Rhabdomys pumilio). Eighteen cranial measurements, reflecting the dimensions of individual elements, were analyzed using bivariate and multivariate estimates of allometry and methods of matrix comparison. Prenatal allometry is characterized in R. pumilio by a relative rapid lengthening of cranial elements, particularly the frontal, parietal, basisphenoid, premaxilla, and palatine, as evidenced by larger bivariate allometric coefficients (>30% increase) and, across all variables measured, a greater proportion of cranial elements growing with a positive allometry than in the postnatal period. Growth dynamics are found to shift for measurements of several elements including the parietal, frontal, and palatine, indicating a nonlinearity of ontogenetic allometry with respect to birth; similar shifts have been found between prenatal and postnatal growth for some regions of the human cranium. Application of common principal component analyses, a generalized extension of principal component analysis, revealed that the prenatal and postnatal matrices shared a highly similar structure, further quantified by high correlations (>0.78) using the random skewers method of matrix comparison. These results indicate a close correspondence between morphology-based variance structures over the course of ontogeny in R. pumilio.

Inferences of diplodocoid (Sauropoda: Dinosauria) feeding behavior from snout shape and microwear analyses.

BackgroundAs gigantic herbivores, sauropod dinosaurs were among the most important members of Mesozoic communities. Understanding their ecology is fundamental to developing a complete picture of Jurassic and Cretaceous food webs. One group of sauropods in particular, Diplodocoidea, has long been a source of debate with regard to what and how they ate. Because of their long lineage duration (Late Jurassic-Late Cretaceous) and cosmopolitan distribution, diplodocoids formed important parts of multiple ecosystems. Additionally, fortuitous preservation of a large proportion of cranial elements makes them an ideal clade in which to examine feeding behavior.Methodology/Principal FindingsHypotheses of various browsing behaviors (selective and nonselective browsing at ground-height, mid-height, or in the upper canopy) were examined using snout shape (square vs. round) and dental microwear. The square snouts, large proportion of pits, and fine subparallel scratches in Apatosaurus, Diplodocus, Nigersaurus, and Rebbachisaurus suggest ground-height nonselective browsing; the narrow snouts of Dicraeosaurus, Suuwassea, and Tornieria and the coarse scratches and gouges on the teeth of Dicraeosaurus suggest mid-height selective browsing in those taxa. Comparison with outgroups (Camarasaurus and Brachiosaurus) reinforces the inferences of ground- and mid-height browsing and the existence of both non-selective and selective browsing behaviors in diplodocoids.Conclusions/SignificanceThese results reaffirm previous work suggesting the presence of diverse feeding strategies in sauropods and provide solid evidence for two different feeding behaviors in Diplodocoidea. These feeding behaviors can subsequently be tied to paleoecology, such that non-selective, ground-height behaviors are restricted to open, savanna-type environments. Selective browsing behaviors are known from multiple sauropod clades and were practiced in multiple environments.

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.

The skull of <em>Postosuchus kirkpatricki</em> (Archosauria: Paracrocodyliformes) from the Upper Triassic of the United States

The skull of Postosuchus kirkpatricki Chatterjee 1985 is known from the holotype and paratype specimens along with disassociated skull elements from several Triassic localities in the southwestern and eastern United States. Recent preparation of the holotype skull allows for more careful examination of the cranial elements and comparison with related taxa. This description indicates that Postosuchus shares several previously unrecognized synapomorphies with crocodylomorphs, including fossae and foramina in the dermatocranium that are not present in other basal pseudosuchians. The sutural arrangements of the skull of Postosuchus presented in this paper differ considerably from previous descriptions, due in part to the reassignment of what was previously considered the prefrontal to the palpebral bone. Also, further preparation of skull elements revealed morphologies that differ from previous descriptions. This new description also indicates a close relationship with Polonosuchus silesiacus Sulej 2005. The only autapomorphic characters of the skull are a distinct, rounded lateral ridge on the maxilla and a foramen present in a large fossa on the anteromedial surface of the maxilla.

A new tool for determining degrees of mineralization in fossil amphibian skeletons: The example of the Late Palaeozoic branchiosaurid Apateon from the Autun Basin, France

Studying ontogenetic features of fossil tetrapods is of major interest for investigating the adaptive strategies of early tetrapods to their palaeoenvironments. To determine the degree of calcification of skeletal elements, biologists have until now relied on X-ray radiographs of organisms or isolated bones, or on thin sections. An X-ray tomographic scan of Apateon, a Carboniferous – Permian branchiosaurid from the Autun Basin, France, reveals distinct density properties related to different mineralized tissues (calcified cartilage versus bone). The rendering of Apateon as a “test individual” provides a 3D map of the degrees of ossification of the axial and cranial elements. The combination of these anatomical observations with histological information from classical thin sections made in limb bones of several other specimens of the same locality allows the detailed determination of their ontogenetic stage. A comparison with the well-known specimens of the Saar-Nahe Basin, Germany, makes it possible to investigate the influence of different palaeoenvironments on ontogenetic features.

The dentary of Suuwassea emilieae (Sauropoda: Diplodocoidea)

Sauropod cranial elements, despite their rarity, contain a significant proportion of the known phylogenetically important character data (see Wilson, 2002; Upchurch et al., 2004). In particular, cr...

A revision of chamaeleonids from the Lower Miocene of the Czech Republic with description of a new species of Chamaeleo (Squamata, Chamaeleonidae)

A revision of Chamaeleo caroliquarti Moody and Roček is presented. The comparisons of the holotypic left dentary with those of specimens subsequently assigned to C. caroliquarti and of the Recent species of Chamaeleo, Furcifer and Calumma is carried out. It is shown that the type dentaries of C. caroliquarti include two different morphotypes with the absence of unique features. Within the Recent chameleons, the exact determination of the individual species merely on the basis of the dentaries is impossible. The holotypic dentary of C. caroliquarti is basically identical with that of C. calyptratus. However, the same morphology of the dentary as present in C. caroliquarti is also present in other species of different genera such as Calumma globifer and Furcifer pardalis. The paratypic dentaries of C. caroliquarti have a different morphology to the holotype and are indistinguishable from that in the Recent C. chamaeleon. On the other hand, a new species of the genus Chamaeleo, C. andrusovi, is described on the basis of isolated cranial elements, which possess clear autapomorphic features. This material comes from the Lower Miocene (Ottnangian) zone MN 4 in the Dolnice locality of the Czech Republic, and it differs from Recent and fossil chameleons in the following combination of characters: (1) its typically developed strongly pustular ornamentation and its distribution on the external surfaces of the skull roofing bones; (2) the frontoparietal suture is digitiform with a well-developed, anteriorly directed mesial spine, and (3) the parietal bone narrows posteriorly at its midlength, it is not bowed dorsally and it does not contribute posteriorly to a dorsal sagittal crest. This new material expands our knowledge of the cranial anatomy of Lower Miocene chameleons.

A NEW SPECIMEN OF NOTHOSAURUS FROM THE LATEST ANISIAN (MIDDLE TRIASSIC) BESANO FORMATION (GRENZBITUMENZONE) OF ITALY

A nearly complete but disarticulated skeleton of a small sized nothosaur is described. The specimen was collected in 2003 from an outcrop of the Besano Formation (Grenzbitumenzone of Swiss authors) of latest Anisian (Middle Triassic) age, in the Monte San Giorgio Area, northern Italy. The osteology of the postcranial skeleton supports the assignment to the genus Nothosaurus , and also excludes its belonging to Nothosaurus giganteus/Paranothosaurus amsleri already known from coeval localities of the Besano Formation in the Swiss part of the Monte San Giorgio area. Despite the lack of most of the skull, which contains diagnostic characters at the species level for Nothosaurus , the few preserved cranial elements suggest similarities with N. juvenilis which skull, and only known part, is also of comparable size. This specimen is particularly significant because it improves the knowledge of the osteology of N. juvenilis and because the second Nothosaurus species, smaller than N. giganteus/P. amsleri , suggests coexistence of sympatric species characterized by size and, probably, trophic differentiation within the genus Nothosaurus in the Monte San Giorgio area as occurred in the coeval Germanic Basin.

Qualitative and Quantitative Diagnosis of Lethal Cranial Neural Tube Defects from the Fetal and Neonatal Human Skeleton, with a Case Study Involving Taphonomically Altered Remains

Cranial neural tube defect, or anencephaly, is the absence of normal brain development because of severe developmental defect in the fetus. While the current incidence of human anencephaly ranges between 1 to 5 per 1000 births, and was higher prior to folic acid supplementation, there is no discussion of anencephaly diagnosis in the forensic literature and only one published example from the archeological record. This article presents both qualitative observations of abnormal cranial elements and an osteometric method to quantitatively determine anencephaly from forensic recovery contexts where taphonomic variables may otherwise mask diagnostic characteristics. Evidence is presented for only the second case of anencephaly diagnosed from a burial context, and the first not involving soft tissue mummification. The initial recognition and accurate prediction of anencephaly is a significant contribution to investigators recovering found human fetal remains.

Quaternary Murid Rodents of Timor Part I: New Material of Coryphomys buehleri Schaub, 1937, and Description of a Second Species of the Genus

Large collections of fragmentary animal bones excavated from archaeological contexts in East Timor between 1968 and 2002 provide new material referable to the recently extinct, gigantic murine genus Coryphomys. We document the upper and lower dentition and palatal anatomy of C. buehleri Schaub, 1937, and identify and name a second species of Coryphomys, based on differences in molar size and morphology and skeletal robusticity. Alternative interpretations of the observed morphological and metric variability (sexual dimorphism, resource-based polymorphism, sample heterochroneity) are each carefully assessed and rejected, and we conclude that the genus comprised two species of approximately similar body size. Preserved cranial elements of both species of Coryphomys feature a high degree of anatomical specialization, including an unusual elaboration of the maxillary sinus complex. Though the specialized anatomy of Coryphomys invites consideration of its phylogenetic relationships, this exercise is hindered by a demonstrable high level of homoplasy (i.e., multiple, independent evolutionary losses and gains) in many of the key craniodental features traditionally surveyed within Murinae, while other features are insufficiently well surveyed for broad-scale analysis. Nevertheless, our comparisons highlight two potentially related lineages among the geographically proximate Murinae—the Philippine Phloeomyini and the Australo-Papuan Hydromyini. The remains of Coryphomys are relatively scarce in all the archaeological samples, but distributional evidence suggests that both species of Coryphomys were found primarily in upland habitats. Late Pleistocene samples document their former presence at lower elevations, possibly reflecting cooler climatic conditions at that time.

A large-scale survey of heterochrony in anuran cranial ossification patterns

Most anurans have a biphasic life cycle, which includes metamorphosis from a tadpole stage to an adult frog. This process involves extensive transformations of the cranial skeleton, which have been of long-standing interest with respect to anuran skeletal evolution and taxonomy. In this study, large-scale patterns of anuran skeletal ossification are assessed by collecting the most comprehensive data set on anuran cranial ossification to date from the literature, including data for 45 anuran and one caudate outgroup species. Ossification sequences were translated into event-pair matrices for explorative phylogenetic analysis and phylogenetically informed parsimony search for heterochrony using the Parsimov algorithm. Rank variability of single bones across species was also analysed. Little phylogenetic signal was retrieved from a parsimony-based phylogenetic analysis of event-pairs, and only a few species that are generally agreed to be closely related are placed close to each other (e.g. some Pipidae and Costata). Parsimov analysis revealed some clade-specific heterochrony in anuran clades of varying inclusiveness. Our results show that relating heterochronic changes in anuran cranial ontogeny to parameters such as direct development or miniaturization is problematic because of the high evolvability of cranial ossification sequences. Rank variation analysis suggests that anuran cranial bones are highly variable in their sequence positioning, possibly because tadpole and adult cranial morphology do not co-evolve. Elements which are lost in some species ossify at the end of the sequence, providing evidence for the notion that failure of anuran cranial elements to ossify is due to processes of paedomorphosis. Die meisten Anura (Froschlurche) zeichnen sich durch einen biphasischen Lebenszyklus aus, während dessen sie eine Metamorphose vom Kaulquappenstadium zum adulten Frosch durchlaufen. Die Metamorphose geht mit weitreichenden Umformungen im kraniellen Skelett einher. Dieses Phänomen stößt seit langem im Rahmen von Fragestellungen mit Bezug auf Skelettevolution und taxonomische Klassifizierung auf Interesse. In der vorliegenden Studie werden anhand der bisher umfassendsten Datenerhebung, basierend auf der Literatur der letzten 50 Jahre, die Reihenfolge der Verknöcherung im Kranialskelett der Anura untersucht. Einbezogen wurden kranielle Verknöcherungs-sequenzen von 45 Vertretern der Anura und einem Vertreter der Caudata (Schwanzlurche). Die Sequenzen wurden als ‘Event-pairs’ kodiert, um eine informelle phylogenetische Analyse nach dem Sparsamkeitsprinzip sowie phylogenetisch basierte Heterochronieanalysen unter Anwendung des Parsimov-Algorithmus durchzuführen. Außerdem wurde die zwischenartliche Variabilität des Verknöcherungszeitpunktes innerhalb der Sequenz für die einzelnen Knochen untersucht. Die phylogenetische Analyse gruppierte einige Arten, welche generell als nahverwandt angesehen werden, z.B. einige Vertreter der Pipiden und Costata. Die Parsimov-Analyse zeigte, daß sich nur wenige Anurengruppen unterschiedlicher Diversität durch Heterochronien ausweisen. Unsere Ergebnisse zeigen, dass eine kausale Verbindung von Heterochronien mit Eigenschaften wie Direktentwicklung problematisch ist. Die Analyse der Verknöcherungsvariabilität weist auf große Variabilität des Verknöcherungs-Zeitpunkt der einzelnen Knochen hin; dies kann möglicherweise durch die relativ unabhängige Evolution von Larval- und Adultschädelmorhpologie erklärt werden. Elemente, die in einigen Arten nicht vorkommen, verknöchern generell am Ende der Sequenz. Dies spricht für die Annahme, daß der Verlust von Schädelknochen bei Anuren auf Pädomorphose zurückzuführen ist.

Description of a new specimen of Ianthasaurus hardestiorum (Eupelycosauria: Edaphosauridae) and a re-evaluation of edaphosaurid phylogeny

Ianthasaurus hardestiorum , a basal edaphosaurid from the Upper Pennsylvanian of Garnett, Kansas, has been described on the basis of two incomplete, juvenile specimens and a series of disarticulated vertebral elements. New skeletal material of this poorly known species includes previously unknown cranial elements, increasing our knowledge of the anatomy and variation in this taxon. The complete ossification of the neural arches and the overall larger size of the vertebrae relative to those previously described indicate that they were part of an adult individual, and marginal tooth morphology resembles more closely that seen in the genus Edaphosaurus . Phylogenetic analysis of edaphosaurid synapsids confirms the hypothesis that Ianthasaurus is a sister-taxon of all other members of the clade. However, the incomplete fossil record of other putative edaphosaurids, such as Lupeosaurus and Glaucosaurus , makes full resolution of their phylogenetic interrelationships difficult to assess.

Skeletogenesis and sequence heterochrony in rodent evolution, with particular emphasis on the African striped mouse, Rhabdomys pumilio (Mammalia)

Data documenting skeletal development in rodents, the most species-rich ‘order’ of mammals, are at present restricted to a few model species, a shortcoming that hinders exploration of the morphological and ecological diversification of the group. In this study we provide the most comprehensive sampling of rodent ossification sequences to date, with the aim of exploring whether heterochrony is ubiquitous in rodent evolution at the onset of skeletal formation. The onset of ossification in 17 cranial elements and 24 postcranial elements was examined for eight muroid and caviomorph rodent species. New data are provided for two non-model species. For one of these, the African striped mouse, Rhabdomys pumilio, sampling was extended by studying 53 autopodial elements and examining intraspecific variation. The Parsimov method of studying sequence heterochrony was used to explore the role that changes in developmental timing play in early skeletal formation. Few heterochronies were found to diagnose the muroid and caviomorph clades, suggesting conserved patterning in skeletal development. Mechanisms leading to the generation of the wide range of morphological diversity encapsulated within Rodentia may be restricted to later periods in development than those studied in this work. Documentation of skeletogenesis in Rhabdomys indicates that intraspecifc variation in ossification sequence pattern is present, though not extensive. Our study suggests that sequence heterochrony is neither pivotal nor prevalent during early skeletal formation in rodents.

Animals and Cotswold-Severn Long Barrows: a Re-examination

In this paper new collaborative research is presented following a re-examination of the faunal remains and architectural evidence from a selected number of Cotswold-Severn long barrow sites. Five different loci of deposition are considered: ‘pre-barrow’ contexts; the chambers; the superstructure of the barrow and the ditches; the forecourt; and blocking material. These spatial locations were chosen following research that has demonstrated that these areas are likely to represent different temporal, as well as spatial, patterns of activity. While the faunal remains are diverse in character, common themes observed at the sites include: the deposition of complete or partial remains of foetal and young animals within chambers; the use of teeth and cranial elements within blocking material; and, within each temporal context, the absence of clear evidence for feasting and the importance of cattle, and the small but constant inclusion of wild mammals. This complexity of practice has the potential to mature our thinking regarding the nature of human–animal relationships within the early Neolithic of Britain and provide a secure foundation of evidence for subsequent interpretations.

Purposeful commingling of adult and child cranial elements from the Chelechol ra Orrak Cemetery, Palau

Continued excavation in 2007 of the early (ca. 2000–3000 calBP) cemetery at Chelechol ra Orrak in Palau, Micronesia revealed the remains of at least six individuals, adding to a minimum number of at least 25 other mostly fragmented individuals recovered in previous years. Of particular interest was the discovery of two isolated adult partial crania one of which, when emptied of sandy matrix, was found to contain a complete child's frontal bone. Here we explore the possibility that the placement of the skulls, particularly the commingling of the adult and child cranial elements, was done purposefully and discuss its significance for early Pacific mortuary behaviours. Copyright © 2009 John Wiley & Sons, Ltd.

Postnatal Ontogeny of the Skull in the Extant North American Turtle Sternotherus odoratus (Cryptodira: Kinosternidae)

There are few published data addressing the types, levels, and patterns of intraspecific variation in gross anatomical structures for nonavian reptiles, especially considering the widespread interest in their morphology and evolutionary history. This study examines variation in both discrete and continuous characters of the postnatal skull for a single population of the kinosternid turtle Sternotherus odoratus. The primary purpose of the study was to elucidate those features that exhibit transformations (and by default those that do not) in the latter two-thirds of postnatal ontogeny—that portion heavily relied upon in phylogenetic analyses of macroanatomical features and most often preserved in the vertebrate fossil record. Data are presented for cranial characters historically used to elucidate phylogenetic relationships in turtles and to assess fossil specimens taxonomically.Results indicate that the number of characters exhibiting postnatal variation, and the levels at which they vary, are surprisingly high considering the conservative nature of both the taxonomic sample and the pool of examined characters. Features associated with the feeding apparatus are among the most variable cranial structures—for both continuous and discrete characters. A relatively large number of discrete transformations occur in structures derived from those cranial elements preformed in cartilage. This concentration demonstrates that developmental trajectories apomorphic for deep nodes in vertebrate phylogenetic history result in relatively late-stage postnatal transformations and high levels of variation in characters informative at much more restricted taxonomic levels. This study provides a baseline of data that future studies examining the ontogenetic and evolutionary history of variation can build upon and it represents a necessary step in understanding the complex system by which variability in developmental modules becomes integrated in the reptile skull.

Giraffidae (Mammalia) de la fin du Néogène de la République de Macédoine (ARYM)

ABSTRACT Giraffidae (Mammalia) from the late Neogene of the Republic of Macedonia (FYROM). Excavations undertaken in several sites of the Republic of Macedonia (FYROM) during the last decades have yielded rich mammalian faunas, including some significant giraffid specimens. An almost complete and uncrushed skull from the upper Miocene of Kirokucuk is the best known specimen of Bohlinia attica; it confirms that this taxon is closely related to Giraffa, even though it is more primitive than the African forms of the latter genus. Helladotherium is represented by cranial and limb-bone remains. The association of these two genera is also found in Bulgaria and at Pikermi in Greece. Cranial elements, including most of a posterior horn, are assigned to a new species of Sivatherium, probably of Pliocene age, and characterized by its huge posterior horns. Its presence implies faunal connections between Southern Europe, Southern Asia and Africa at that time.

Fossil lizards from the locality of Gannat (late Oligocene–early Miocene, France) and a revision of the genus Pseudeumeces (Squamata, Lacertidae)

Pseudeumeces is a distinct lacertid lizard that is known from one species, P. cadurcensis (Filhol). Two species, Ligerosaurus pouiti and “Pseudeumeces” walbeckensis, previously referred to Pseudeumeces, do not belong to this genus. Pseudeumeces cadurcensis is characterized by a heterodont dentition, including large, posterior, crushing teeth on both the maxilla and dentary. Pseudeumeces differs from the Oligocene lacertid lizards Lacerta s.l. filholi and Mediolacerta that have non-expanded, bi- or tricuspid teeth. Dracaenosaurus, an Oligocene lacertid lizard, also possesses crushing, posterior teeth, but its teeth and jaw are much heavier than in those of Pseudeumeces. New specimens from Gannat document cranial elements previously unknown, i.e. frontal and parietal. Pseudeumeces is known with certainty from the early Oligocene (MP25) to the early Miocene (MN1). Notable features of Pseudeumeces (firm lateral contact between the coronoid and the dentary; strongly curved mandibule; tooth morphology and tooth number reduction) corroborate the previous assumption that this lacertid lizard was probably durophagous. Four Oligocene European lacertid lizards form a morphological and chronological series, but the common ancestry of these species has not been definitively proved.

The epipterygoid of crocodyliforms and its significance for the evolution of the orbitotemporal region of eusuchians

ABSTRACT A broad survey of crocodyliform archosaurs and their outgroups was conducted to explore the evolutionary and morphological patterns of the orbitotemporal region, which is a highly apomorphic but poorly understood portion of the head. Data were gathered on the topological similarity and phylogenetic congruence of the epipterygoid, laterosphenoid, and temporal region as a whole, including relevant osteological correlates and such inferred soft tissues as the trigeminal nerves and jaw musculature. Despite the complete suturing of the palatocranial junction, the epipterygoid remained a consistent cranial element throughout crocodyliform evolution, only to be replaced by the topologically analogous, but developmentally neomorphic lateral bridge of the laterosphenoid during the early evolution of eusuchians. These changes led to a unique morphology of the region surrounding the exit of the trigeminal nerve. Mesoeucrocodylian taxa exhibit a diversity of epipterygoid morphologies including waisted (e.g., Araripesuchus), overlapping (e.g., Sarcosuchus), and isolated (e.g., Goniopholis, Leidyosuchus) forms. The isolated form, in which the epipterygoid is uncoupled from the pterygoid and does not to cover the cavum epiptericum laterally, represents a key transition to the extant condition of loss of the epipterygoid. Changes in the epipterygoid coincide with the migration of M. pseudotemporalis superficialis onto the laterosphenoid outside of the dorsotemporal fossa and the topological change in the intermuscular path of the maxillary nerve, both of which are apomorphies found in extant crocodylians. These data reflect a diverse and potentially homoplastic distribution of orbitotemporal morphologies among mesoeucrocodylians and indicate that the epipterygoid was only recently eliminated in crocodyliform evolution.

Gigantism of the Australian Diprotodon Owen 1838 (Marsupialia, Diprotodontoidea) through the Pleistocene

AbstractDiprotodon Owen, 1838 was one of the first fossil mammals described from Australia and has the distinction of being the largest ever marsupial. However, until recently its taxonomy was unclear and knowledge of its continental distribution, palaeoecology and evolution was poorly known. This paper describes cranial elements from an unusually small‐bodied Diprotodon from the Early Pleistocene Nelson Bay Formation, Portland, Australia. It is intermediate in size between the smaller‐bodied Pliocene ancestor, Euryzygoma dunense de Vis 1895 and the larger‐bodied Late Pleistocene D. optatum Owen, 1838. However, it is morphologically inseparable from Late Pleistocene Diprotodon and is here referred to as D. ?optatum. A temporal morphocline most parsimoniously explains the medium body size of the Nelson Bay taxon; thus we provide the first evidence of a transitional form within Diprotodon. The cause(s) of gigantism of the E. dunense–D. ?optatum–D. optatum lineage through the late Cainozoic is unclear but most likely involved the physiological response to changes in the physical and/or biotic environment. Although the size changes within the lineage may have been initially advantageous, they were most likely disadvantageous when the optimum body size was obtained. Our results suggest that Diprotodon was at its largest ever body size during the Late Pleistocene – the time period that coincided with its extinction. Copyright © 2009 John Wiley & Sons, Ltd.