Lieber, Francis (1798-1872), Author and Professor.

The debate about the origin of the vertebrate dentition has been given fresh fuel by new fossil discoveries and developmental studies of extant animals. Odontodes (teeth or tooth-like structures) can be found in two distinct regions, the 'internal' oropharyngeal cavity and the 'external' skin. A recent hypothesis argues that regularly patterned odontodes is a specific oropharyngeal feature, whereas odontodes in the external skeleton lack this organization. However, this argument relies on the skeletal system of modern chondrichthyans (sharks and their relatives), which differ from other gnathostome (jawed vertebrate) groups in not having dermal bones associated with the odontodes. Their external skeleton is also composed of monoodontode 'placoid scales', whereas the scales of most early fossil gnathostomes are polyodontode, i.e. constructed from several odontodes on a shared bony base. Propagation phase contrast X-ray Synchrotron microtomography (PPC-SRmCT) is used to study the polyodontode scales of the early bony fish Andreolepis hedei. The odontodes constructing a single scale are reconstructed in 3D, and a linear and regular growth mechanism similar to that in a gnathostome dentition is confirmed, together with a second, gap-filling growth mechanism. Acanthodian tooth whorls are described, which show that ossification of the whorl base preceded and probably patterned the development of the dental lamina, in contrast to the condition in sharks where the dental lamina develops early and patterns the dentition. The new findings reveal, for the first time, how polyodontode scales grow in 3D in an extinct bony fish. They show that dentition-like odontode patterning occurs on scales and that the primary patterning unit of a tooth whorl may be the bony base rather than the odontodes it carries. These results contradict the hypothesis that oropharyngeal and external odontode skeletons are fundamentally separate and suggest that the importance of dermal bone interactions to odontode patterning has been underestimated

Testing models of dental development in the earliest bony vertebrates, Andreolepis and Lophosteus

Theories on the development and evolution of teeth have long been biased by the fallacy that chondrichthyans reflect the ancestral condition for jawed vertebrates. However, correctly resolving the nature of the primitive vertebrate dentition is challenged by a dearth of evidence on dental development in primitive osteichthyans. Jaw elements from the Silurian–Devonian stem-osteichthyans Lophosteus and Andreolepis have been described to bear a dentition arranged in longitudinal rows and vertical files, reminiscent of a pattern of successional development. We tested this inference, using synchrotron radiation X-ray tomographic microscopy (SRXTM) to reveal the pattern of skeletal development preserved in the sclerochronology of the mineralized tissues. The tooth-like tubercles represent focal elaborations of dentine within otherwise continuous sheets of the dermal skeleton, present in at least three stacked generations. Thus, the tubercles are not discrete modular teeth and their arrangement into rows and files is a feature of the dermal ornamentation that does not reflect a polarity of development or linear succession. These fossil remains have no bearing on the nature of the dentition in osteichthyans and, indeed, our results raise questions concerning the homologies of these bones and the phylogenetic classification of Andreolepis and Lophosteus

The Waddlia Genome: A Window into Chlamydial Biology

Growing evidence suggests that a novel member of the Chlamydiales order, Waddlia chondrophila, is a potential agent of miscarriage in humans and abortion in ruminants. Due to the lack of genetic tools to manipulate chlamydia, genomic analysis is proving to be the most incisive tool in stimulating investigations into the biology of these obligate intracellular bacteria. 454/Roche and Solexa/Illumina technologies were thus used to sequence and assemble de novo the full genome of the first representative of the Waddliaceae family, W. chondrophila. The bacteria possesses a 2′116′312bp chromosome and a 15′593 bp low-copy number plasmid that might integrate into the bacterial chromosome. The Waddlia genome displays numerous repeated sequences indicating different genome dynamics from classical chlamydia which almost completely lack repetitive elements. Moreover, W. chondrophila exhibits many virulence factors also present in classical chlamydia, including a functional type III secretion system, but also a large complement of specific factors for resistance to host or environmental stresses. Large families of outer membrane proteins were identified indicating that these highly immunogenic proteins are not Chlamydiaceae specific and might have been present in their last common ancestor. Enhanced metabolic capability for the synthesis of nucleotides, amino acids, lipids and other co-factors suggests that the common ancestor of the modern Chlamydiales may have been less dependent on their eukaryotic host. The fine-detailed analysis of biosynthetic pathways brings us closer to possibly developing a synthetic medium to grow W. chondrophila, a critical step in the development of genetic tools. As a whole, the availability of the W. chondrophila genome opens new possibilities in Chlamydiales research, providing new insights into the evolution of members of the order Chlamydiales and the biology of the Waddliaceae

Silurian vertebrate remains from the Oslo Region, Norway, and their implications for regional biostratigraphy

Several vertebrate assemblages are described from the Silurian of the Oslo Region, Norway, based on the review and revision of previous reports of microremains, as well as unpublished material from museum collections. Articulated thelodont specimens from the Rudstangen Fauna, Ringerike Group, are also described here for the first time, revealing a seemingly monogeneric loganelliid assemblage. The oldest assemblage (mid-Llandovery) only contains the thelodont Loganellia cf. aldridgei, while a single sample from upper Llandovery strata produced four Thelodus sp. scales. These scales share features with those from younger Thelodus taxa and give additional support to an early appearance of this genus. The mid-Wenlock faunas consist of thelodonts Loganellia grossi, Loganellia einari and Thelodus laevis. These are joined by the thelodont Paralogania martinssoni, anaspids Rhyncholepis parvula and cf. Pterygolepis nitida, as well as the osteostracans cf. Tyriaspis whitei and Osteostraci gen. et sp. indet. in late Wenlock and earliest Ludlow faunas. These complement the previously described anaspids and osteostracans of the Rudstangen Fauna based on articulated specimens. The faunas of a number of calcarenite samples collectively contain the thelodonts L. grossi, L. einari, P. martinssoni and T. laevis, and are most likely of early Ludlow age. When the vertebrate-producing samples are put in the proposed stratigraphical framework for the Oslo Region that has been refined in recent decades, the faunas fit well into the vertebrate biozonation established for the Silurian, contrary to previous claims. The earliest faunas in the area show similarities to the Llandovery of Britain, whereas thelodonts and anaspids, but not osteostracans, from late Wenlock and early Ludlow are more closely related to Baltic forms. Additional sampling of the area may assist in refining the biostratigraphy and provide insights into Silurian vertebrate distributions in Norway and related regions

Corynebacterium pseudotuberculosis. Pneumonia in a veterinary stuent infected during lobaratory work

We present a case of Corynebacterium pseudotuberculosis pneumonia in a veterinary student, with molecular genetic evidence of acquisition during laboratory work, an observation relevant for laboratory personnel working with C pseudotuberculosis isolates. The patient was clinically cured with 14 months trimethoprim/sulfamethoxazole and rifampicin combination treatment

Escamas de telodontos del Devónico Inferior del Archipiélago Novaya Zemlya, Rusia ártica

Scales of a new thelodont species, Amaltheolepis terranovi sp. nov., are described from the upper Emsian, Lower Devonian Shevchenkinskaya Formation of Novaya Zemlya, Arctic Russia. The new species shows strong resemblance with the Emsian “Verdalen assemblage” from Spitsbergen, supporting an Emsian age for the upper part of the Shevchenkinskaya Formation. This conclusion in the context of the various Amaltheolepis assemblages from Spitsbergen, allows for a more accurate comparison and correlation between assemblages from different regions in the Northern Hemisphere, suggesting that the type species, Amaltheolepis winsnesi from Spitsbergen, is Eifelian in age

Devonian vertebrates from East Greenland: a review of faunal composition and distribution

Blom, Henning, Clack, Jennifer A., Ahlberg, Per E., Friedman, Matt (2007): Devonian vertebrates from East Greenland: a review of faunal composition and distribution. Geodiversitas 29 (1): 119-141, DOI: http://doi.org/10.5281/zenodo.537529