Notes on a specimen of Diademodon previously referred to Cyclogomphodon

Main articleThe anterior portion of the cranium of a medium-sized cynodont is described. The specimen was previously described briefly by Brink and Kitching (1953 ), who assigned it to the genus Cyclogomphodon Broom, and it was upon this specimen that they based their rediagnosis of that genus. The detailed study of this specimen has revealed that the supposed features which they considered to be generically distinctive for Cyclogomphodon either do not exist or that their validity falls away when this specimen is considered, in an ontogenetic context, as a not yet fully grown individual. It is concluded that this fossil represents a medium-sized, "juvenile", individual of DiademodonNon

An articulated skeleton of a small individual of Diademodon (Therapsida; Cynodontia)

Main articleThis paper records a nearly complete, articulated skeleton of Diademodan in undoubted association with a skull of that animal. Previously, only portions of postcranial skeleton have been found in association with cranial remains of this genus. The skeleton is that of a relatively small (ontogenetically young) individual. Skeletal proportions are tabulated, rib and vertebral differentiation is described and discussed. Diademodon is shown to have had a long tail.Non

Allometric growth in the Diademodontinae (Reptilia; Therapsida); a preliminary report

Main articleThe hypothesis that many, if not all, of the South African and Zambian specimens, which have been regarded as different diademodontine genera and species, actually consitute a taxonomically homogeneous, ontogenetic growth series is tested. The principles of allometric growth were applied to this sample of fossils, which varied considerably in size and shape. The approach which was followed was exclusively morphometric. The results indicate that these specimens do represent various ontogenetic stages of a growth series of only a single species of Diademodon Seeley.Non

Enamel Structure in Primates: A Review of Scanning Electron Microscope Studies

Comparative studies of dental enamel microstructure have involved three main areas of enquiry, with structural features having been investigated in relation to developmental mechanisms, function and/or phylogeny. The phylogenetic, or taxonomic aspect has been emphasized in the majority of studies involving the Order Primates, where efforts have focused upon attempts to recognise structural differences among various hierarchical groups. Studies of primate enamel microstructure by SEM are reviewed here, with emphasis on what has been learned concerning the most suitable preparative techniques that can be employed, and with particular emphasis to the relevance of enamel microstructure in taxonomic analyses of living and fossil primates. No one technique of enamel preparation can be held to be the most suitable for all types of material (e.g., fresh developing, wet mature, dry mature, and fossil enamel) but experience to date allows us to make some recommendations. Two aspects of enamel structure have been shown to possess considerable potential in taxonomic analyses: the enamel prism packing patterns, and the enamel formation rates as documented from prism cross-striation repeat intervals. Although the distribution of enamel prism packing patterns among primates suggests considerable homoplasy of this character, this feature does have considerable taxonomic interest at certain hierarchical levels in Primates. The study of rates of enamel secretion coupled with analyses of enamel thickness has considerable potential in resolving taxonomic and phylogenetic questions

Evidence for salt glands in the Triassic reptile Diademodon (Therapsida; Cynodontia)

Main articleFossilised skulls of Diademodon exhibit rostral depressions which may have housed salt glands. The possible functions of salt glands in this advanced cynodont are examined. Diademodon appears to have been more reptilian than mammalian in its general physiological organisation.the Chairman's Fund of the Anglo American Corporation, the S. L. Sive Memorial Travelling Fellowship, University of the Witwatersrand Medical School, the Medical Referees Fund of the Department of Anatom,. Medical School, and the Bernard Price Institute for Palaeontological Research, University of the Witwatersran

Reptile enamel matrix proteins: Selection, divergence, and functional constraint

The three major enamel matrix proteins (EMPs): amelogenin (AMEL), ameloblastin (AMBN), and enamelin (ENAM), are intrinsically linked to tooth development in tetrapods. However, reptiles and mammals exhibit significant differences in dental patterning and development, potentially affecting how EMPs evolve in each group. In most reptiles, teeth are replaced continuously throughout life, while mammals have reduced replacement to only one or two generations. Reptiles also form structurally simple, aprismatic enamel while mammalian enamel is composed of highly organized hydroxyapatite prisms. These differences, combined with reported low sequence homology in reptiles, led us to predict that reptiles may experience lower selection pressure on their EMPs as compared with mammals. However, we found that like mammals, reptile EMPs are under moderate purifying selection, with some differences evident between AMEL, AMBN, and ENAM. We also demonstrate that sequence homology in reptile EMPs is closely associated with divergence times, with more recently diverged lineages exhibiting high homology, along with strong phylogenetic signal. Lastly, despite sequence divergence, none of the reptile species in our study exhibited mutations consistent with diseases that cause degeneration of enamel (e.g. amelogenesis imperfecta). Despite short tooth retention time and simplicity in enamel structure, reptile EMPs still exhibit purifying selection required to form durable enamel.We calculated the percent identity between amino acid sequences of ameloblastin from various reptile groups. Crocodilians exhibit the highest sequence identity, while identity across squamates was substantially lower. Upon closer examination of the individual squamate clades, however, we found that identity values are actually much higher in snakes, with much of the variation existing between the various lizard infraorders.HIGHLIGHTSReptile enamel matrix proteins are under moderate purifying selection despite polyphyodonty and simple enamel structure.Sequence identity in reptile enamel matrix proteins exhibit correlation with divergence times in spite of differences in substitution rates.Reptile amelogenin operates under a distinct selection regime compared with ameloblastin and enamelin.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150577/1/jezb22857.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150577/2/jezb22857-sup-0001-Supplementary_file.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150577/3/jezb22857-sup-0007-Supplementary_file_S8-DAMBE-Saturation.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150577/4/jezb22857-sup-0002-Supplementary_file_S1-SpeciesTable.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150577/5/jezb22857-sup-0003-Supplementary_file_S2_Alignments.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150577/6/jezb22857-sup-0008-Supplementary_File_S9.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150577/7/jezb22857-sup-0005-Supplementary_file_S6.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150577/8/jezb22857_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150577/9/jezb22857-sup-0009-Supplementary_file_Reptiles.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150577/10/jezb22857-sup-0006-Supplementary_file_S7-DIVERGE.pd

Dental Microwear and Diet of the Plio-Pleistocene Hominin Paranthropus boisei

The Plio-Pleistocene hominin Paranthropus boisei had enormous, flat, thickly enameled cheek teeth, a robust cranium and mandible, and inferred massive, powerful chewing muscles. This specialized morphology, which earned P. boisei the nickname “Nutcracker Man”, suggests that this hominin could have consumed very mechanically challenging foods. It has been recently argued, however, that specialized hominin morphology may indicate adaptations for the consumption of occasional fallback foods rather than preferred resources. Dental microwear offers a potential means by which to test this hypothesis in that it reflects actual use rather than genetic adaptation. High microwear surface texture complexity and anisotropy in extant primates can be associated with the consumption of exceptionally hard and tough foods respectively. Here we present the first quantitative analysis of dental microwear for P. boisei. Seven specimens examined preserved unobscured antemortem molar microwear. These all show relatively low complexity and anisotropy values. This suggests that none of the individuals consumed especially hard or tough foods in the days before they died. The apparent discrepancy between microwear and functional anatomy is consistent with the idea that P. boisei presents a hominin example of Liem's Paradox, wherein a highly derived morphology need not reflect a specialized diet

Enamel thickness variation in the deciduous dentition of extant large-bodied hominoids

Objectives: Enamel thickness features prominently in hominoid evolutionary studies. To date, however, studies of enamel thickness in humans, great apes, and their fossil relatives have focused on the permanent molar row. Comparatively little research effort has been devoted to tissue proportions within deciduous teeth. Here we attempt to fill this gap by documenting enamel thickness variation in the deciduous dentition of extant large‐bodied hominoids. Materials and methods: We used microcomputed tomography to image dental tissues in 80 maxillary and 78 mandibular deciduous premolars of Homo sapiens, Pan troglodytes, Gorilla, and Pongo. Two‐dimensional virtual sections were created from the image volumes to quantify average (AET) and relative (RET) enamel thickness, as well as its distribution across the crown. Results: Our results reveal no significant differences in enamel thickness among the great apes. Unlike the pattern present in permanent molars, Pongo does not stand out as having relatively thicker‐enameled deciduous premolars than P. troglodytes and Gorilla. Humans, on the other hand, possess significantly thicker deciduous premolar enamel in comparison to great apes. Following expectations from masticatory biomechanics, we also find that the “functional” side (protocone, protoconid) of deciduous premolars generally possesses thicker enamel than the “nonfunctional” side. Discussion: Our study lends empirical support to anecdotal observations that patterns of AET and RET observed for permanent molars of large‐bodied apes do not apply to deciduous premolars. By documenting enamel thickness variation in hominoid deciduous teeth, this study provides the comparative context to interpret rates and patterns of wear of deciduous teeth and their utility in life history reconstructions

Human Remains from the Pleistocene-Holocene Transition of Southwest China Suggest a Complex Evolutionary History for East Asians

BACKGROUND: Later Pleistocene human evolution in East Asia remains poorly understood owing to a scarcity of well described, reliably classified and accurately dated fossils. Southwest China has been identified from genetic research as a hotspot of human diversity, containing ancient mtDNA and Y-DNA lineages, and has yielded a number of human remains thought to derive from Pleistocene deposits. We have prepared, reconstructed, described and dated a new partial skull from a consolidated sediment block collected in 1979 from the site of Longlin Cave (Guangxi Province). We also undertook new excavations at Maludong (Yunnan Province) to clarify the stratigraphy and dating of a large sample of mostly undescribed human remains from the site. METHODOLOGY/PRINCIPAL FINDINGS: We undertook a detailed comparison of cranial, including a virtual endocast for the Maludong calotte, mandibular and dental remains from these two localities. Both samples probably derive from the same population, exhibiting an unusual mixture of modern human traits, characters probably plesiomorphic for later Homo, and some unusual features. We dated charcoal with AMS radiocarbon dating and speleothem with the Uranium-series technique and the results show both samples to be from the Pleistocene-Holocene transition: ∼14.3-11.5 ka. CONCLUSIONS/SIGNIFICANCE: Our analysis suggests two plausible explanations for the morphology sampled at Longlin Cave and Maludong. First, it may represent a late-surviving archaic population, perhaps paralleling the situation seen in North Africa as indicated by remains from Dar-es-Soltane and Temara, and maybe also in southern China at Zhirendong. Alternatively, East Asia may have been colonised during multiple waves during the Pleistocene, with the Longlin-Maludong morphology possibly reflecting deep population substructure in Africa prior to modern humans dispersing into Eurasia