Differentiation of tooth size and shape within the jaw (i.e. heterodonty) is an expected pattern in the majority of Neoselachii sharks. Various forms of heterodonty may be observed within an individual set of jaws, which can be the result of tooth position (monognathic), upper or lower jaw position (dignathic), tooth file or developmental position (ontogeny), or between male and female in sex specific differences (gynandric). Heterodonty patterns result from natural selection as a functional linkage tied to feeding niche for both feeding performance and dietary diversity. However, the types and/or degree of heterodonty present in Devonian sharks such as Cladoselache and Ctenacanthus have not previously been discussed or quantified in the literature. The objective of this study was to analyze a number of associated dentitions from representatives of these two genera, all collected from the Cleveland Shale Member of the Ohio Shale (upper Famennian; Upper Devonian), to test for, and quantify, various types of heterodonty within and across taxonomic lineages of early cladodont sharks. Geometric morphometrics and linear measurements were used to describe tooth shape and resulting axes and measurements were regressed with jaw position, tooth file position, and upper versus lower jaw to test for differentiation associated with various types of heterodonty. Teeth from Cladoselache and Ctenacanthus dentitions that were examined did not show any variation in tooth shape consistent with heterodonty. However, tooth size did vary slightly with jaw position and the presence of symphyseal teeth at the lower jaw symphysis does indicate differentiation between upper and lower jaws. Furthermore, the long period of tooth retention characteristic of these genera create a record of ontogenetic heterodonty within a tooth file observable as an increase in tooth size lingually. Although tooth shape did not significantly co-vary with jaw position in either taxa, significant morphometric differences between the two genera were evident. These findings strengthen the taxonomic validity of the genera and recognized species within these genera and provide further insights into the niche of these Devonian sharks.
PalArch’s Journal of Egyptology/Archaeology of Egypt, 12(2) (2015)
A good number of well-established colleagues, such as Brian Fagan, Kara Cooney and Kent Weeks, have written book reviews of ‘Wonderful Things’ (see http://www.aucpress.com/p-4927-wonderful-things.aspx) and I can only confirm their enthusiasm and opinions. ‘Wonderful Things’ “follows […]
Theropods form a taxonomically and morphologically diverse group of dinosaurs that include extant birds. Inferred relationships between theropod clades are complex and have changed dramatically over the past thirty years with the emergence of cladistic techniques. Here, we present a brief historical perspective of theropod discoveries and classification, as well as an overview on the current systematics of non-avian theropods. The first scientifically recorded theropod remains dating back to the 17th and 18th centuries come from the Middle Jurassic of Oxfordshire and most likely belong to the megalosaurid Megalosaurus. The latter was the first theropod genus to be named in 1824, and subsequent theropod material found before 1850 can all be referred to megalosauroids. In the fifty years from 1856 to 1906, theropod remains were reported from all continents but Antarctica. The clade Theropoda was erected by Othniel Charles Marsh in 1881, and in its current usage corresponds to an intricate ladder-like organization of ‘family’ to ‘superfamily’ level clades. The earliest definitive theropods come from the Carnian of Argentina, and coelophysoids form the first significant theropod radiation from the Late Triassic to their extinction in the Early Jurassic. Most subsequent theropod clades such as ceratosaurs, allosauroids, tyrannosauroids, ornithomimosaurs, therizinosaurs, oviraptorosaurs, dromaeosaurids, and troodontids persisted until the end of the Cretaceous, though the megalosauroid clade did not extend into the Maastrichtian. Current debates are focused on the monophyly of deinonychosaurs, the position of dilophosaurids within coelophysoids, and megaraptorans among neovenatorids. Some recent analyses have suggested a placement of dilophosaurids outside Coelophysoidea, Megaraptora within Tyrannosauroidea, and a paraphyletic Deinonychosauria with troodontids placed more closely to avialans than dromaeosaurids.
Although it is widely believed by archaeologists that the Great Pyramid was built using sleds hauled up ramps, no economically feasible ramp configuration has yet been found which would have permitted the placement of the 44 granite beams weighing up to 75 t and the 2.3 Mm3 of limestone blocks of the pyramid, in a period corresponding to the 27 year reign of Pharaoh Khufu. This paper focuses on engineering considerations: it proposes a simple configuration which is structurally sound and consistent with the archaeological evidence and the principles of ergonomics, mechanics and materials engineering, with a volume of only 6% of that of the pyramid. It demonstrates how the blocks, beams, supporting capstones and pyramidion could have been placed using only the tools found at Giza which date from the 4th Dynasty or earlier, within the constraints imposed by the topography of the Giza Massif.
A diverse vertebrate assemblage was recovered from the Eutaw Formation along a stretch of Luxapalila Creek in Lowndes County, Mississippi. The assemblage is dominated by elasmobranchs but also includes osteichthyans (seven species), archosaurs (one crocodilian, two dinosaurs), and turtles (trionychid and chelonioid). Twenty one elasmobranch taxa were identified (14 selachians and seven batoids), including new species Meristodonoides multiplicatus, Lonchidion cristatum, and Cantioscyllium grandis. Our sample also enabled us to expand the known range of variation for some other poorly diagnosed species. The elasmobranch assemblage consists predominantly of species with presumed benthic habits (14), including the orectolobiform sharks and sclerorhynchid rays, whereas the seven lamniform sharks represent pelagic species. We believe that the sharks and rays inhabited a warm-water, nearshore marine environment.
PalArch’s Journal of Vertebrate Palaeontology, 11(1) (2014)
Perhaps the greatest treasures in paleontology are not individual skeletons of spectacular dinosaurs, but the incredible treasure troves of fossils from the famous “Mother Lode” deposits of fossils known as Lagerstätten. There are about a dozen or so such famous localities around the world, where the fossils have undergone extraordinary preservation. Most preserve the animals in complete articulated state, undisturbed by scavengers and currents, and some even preserve original soft tissue and original colors. These incredible accumulations of fossils tell us so much more than an individual skeleton, because they preserve entire organisms virtually intact, often exhibiting different kinds of behaviors (such as the fish swallowing other fish found in the Green River shales, subject of this book). In addition, they give a nearly unbiased cross-section of nearly all the life in a region at a given time, not filtered by how much hard tissue the organism had that might enhance its chances of preservation. Bit by bit, color-illustrated books of many of these legendary localities, such as the Burgess Shale, the Solnhofen Limestone, and the Messel localities, have been published. […]
PalArch’s Journal of Vertebrate Palaeontology, 10(6) (2013)
I have one vivid memory from my summer vacation between the 2nd and 3rd grade – discovering a ragged and faded copy of All About Strange Beasts of the Past by Roy Chapman Andrews at a neighbor’s garage sale. To me, the most exciting chapter of this elementary-level book was Andrew’s obviously embellished recollection of the discovery of the mired ‘Beast of Baluchistan’ during the famous Central Asiatic Expeditions in the 1920s. The Beast is vividly described as longer than a school bus, nine feet taller than a giraffe, and as heavy as “the great dinosaur Brontosaurus”.
The size of the hornless Oligocene rhinocerotoid Paraceratherium (it has gone by many names) is main reason for its fame and it is not surprising that, along with mega-sharks, mega-dinosaurs, and mega-crocs, there would be a book about mega-rhinos. The back cover of ‘Rhinoceros Giants’ boasts, “The life and times of the largest land animal that ever lived” […]
We present updates for two ancient Egyptian diagonal star tables on coffins A1C and S2Hil. A1C reveals a new triangle decan, H3t s3bw, which brings the total number of triangle decans to 13 and the total number of unique triangle decans to 12 (because of the duplication of nTr D3 pt). We discuss its relevance, why it has likely remained hidden for so long, and why it may have been lost on other star tables. S2Hil is re-examined with new photographs provided by the Roemer- und Pelizaeus-Museum, Hildesheim. We find several striking features of this table that make it unique among the current collection, and also present more information of this table not previously identified.