[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

[dinosaur] Hell Creek fossil eggs + fissure and bonebed fauna from UK + early tetrapods





Ben Creisler
bcreisler@gmail.com


Some recent dino-related and non-dino papers:


Frankie D. Jackson & David J. Varricchio
Fossil egg and eggshells from the Upper Cretaceous Hell Creek Formation, Montana. 
Journal of Vertebrate Paleontology (advance online publication)
DOI: 10.1080/02724634.2016.1185432.
http://www.tandfonline.com/doi/full/10.1080/02724634.2016.1185432

Despite over a hundred years of intense paleontological exploration, the terrestrial rocks of the Upper Cretaceous (Maastrichtian) Hell Creek Formation of eastern Montana are remarkable for the absence of fossil eggs. Here, we describe the first fossil egg and additional eggshell fragments from the formation. The two-layered structure of the smooth 1600-µm-thick eggshell of Belonoolithus garbani, oogen. et oosp. nov., permits assignment of the 6 cm × 8 cm egg to Theropoda. Additional theropod eggshells, Dimorphoolithus bennetti, oogen. et oosp. nov., closely resemble Tubercuoolithus choteauensis (incertae sedis) from the Campanian Two Medicine Formation of Montana, differing only in ornamentation. Therefore, we establish Tubercuoolithidae, oofam. nov., to accommodate both eggshell types. Other eggshell types include two varieties of Spheroolithus, as well as Testudoolithus and Krokolithes. Whereas B. garbani and D. bennetti are unique to the Hell Creek Formation, the other three oogenera also occur in the stratigraphically older Two Medicine and Judith River formations of Montana, and the Oldman Formation of southern Alberta, Canada.

=====

David I. Whiteside, Christopher J. Duffin, Pamela G. Gill,John E.A. Marshall, and Michael J. Benton (2016)
The Late Triassic and Early Jurassic fissure faunas from Bristol and South Wales: Stratigraphy and setting. 
Palaeontologia Polonica 67: 257–287
doi: 10.4202/pp.2016.67_257
Free pdf:
http://palaeontologia.pan.pl/PP67/Whiteside.pdf

The famous vertebrate-bearing fissures of the Bristol area in southwest England and in south Wales were traditionally referred to “upland” environmental settings, and assigned an overall time range of some 60 Myr; we reject both of these viewpoints. In terms of the environmental setting, based upon the evidence of palaeogeography, sediments, and fossils, we show that all the Triassic-aged fissures were near-coastal and embedded in karst formed on palaeo-islands in a subtropical archipelago. Further, the dates of these fissure fills in both regions do not span the Carnian to Rhaetian, as commonly supposed, but instead they are probably all Rhaetian. We update information on the Charles Moore Holwell “Microlestes” fissure assemblage and demonstrate that the marine fauna confirms a Rhaetian age. As proposed by previous authors, younger fissure fills around the St. Brides area of South Wales were also formed on an island, but during the Hettangian–Sinemurian. The youngest fissure deposit in the region is Pliensbachian. The age range of the fissures thus shrinks to c. 20 Myr, and the first episode of tetrapod fissure infilling shifts from the time of the Carnian “pluvial” episode, to the early Rhaetian, when western Europe was undergoing major rifting associated with the beginning of the opening of the North Atlantic, and when the Rhaetian sea flooded over landscapes that had long been purely terrestrial and arid. We recognise clear changes in the faunal composition of the terrestrial vertebrate biota from the early Rhaetian, dominated by reptile taxa, with some mammaliamorphs, that then declined rapidly in diversity before the Hettangian. This herpetofauna was followed by three faunal assemblages in the Early Jurassic of St. Brides which became increasingly diverse following the end-Triassic mass extinction; each had prominent mammaliamorphs as well as high numbers, but few species, of rhynchocephalians.  


=======

Ellen M. Meares, Valentina Rossi, Ellen MacDonald, Gareth Coleman, Thomas G. Davies, Caterine Arias-Riesgo, Claudia Hildebrandt, Heather Thiel, Christopher J. Duffin, David I. Whiteside & Michael J. Benton (2016)
The Rhaetian (Late Triassic) vertebrates of Hampstead Farm Quarry, Gloucestershire, UK.
Proceedings of the Geologists' Association (advance online publication)
doi:10.1016/j.pgeola.2016.05.003
http://www.sciencedirect.com/science/article/pii/S0016787816300578


The Rhaetian marine transgression, which occurred across Europe in the latest Triassic, 205.5 Ma, famously deposited one or more bone beds. Attention has generally focused on the basal bone bed alone, but here we explore this bed, and a stratigraphically higher bone bed at the top of the Westbury Formation, and compare the faunas. The Rhaetian at Hampstead Farm Quarry, Chipping Sodbury, Gloucestershire, UK, has produced more than 26,000 identifiable microvertebrate remains, including teeth and scales of chondrichthyan and osteichthyan fishes, as well as vertebrae of sharks, bony fishes, ichthyosaurs, and plesiosaurs. The higher bone bed (‘bed 9’) contains more small specimens than the basal bone bed, and they are also less abraded, suggesting less transport. Both bone beds yield largely the same taxa, but Rhomphaiodon minor and rare Vallisia coppi and Sargodon tomicus are found only in the basal bone bed. Duffinselache is reported only from units above the basal bone bed, but low in the Westbury Formation, and durophagous teeth only from two horizons. Four out of nine chondrichthyan species are common to both bone beds, whereas Rhomphaiodon minor and Ceratodus are absent, and hybodonts in general are rarer, in bed 9. Bed 9 is the richer source of marine reptile remains, including ichthyosaur teeth, jaw fragments, vertebrae, rare plesiosaur teeth and vertebrae, and a few Pachystropheus vertebrae and limb bones. Whereas the basal bone bed represents considerable transport and possible storm bed deposition associated with the onset of the Rhaetian Transgression, bed 9 was deposited under a lower energy regime.


====


Massimo Bernardi, Kenneth D. Angielczyk, Jonathan S. Mitchell and Marcello Ruta (2016)
Phylogenetic stability, tree shape, and character compatibility: a case study using early tetrapods.
Systematic Biology (advance online publication)
doi: 10.1093/sysbio/syw049
http://sysbio.oxfordjournals.org/content/early/2016/06/02/sysbio.syw049.abstract

Phylogenetic tree shape varies as the evolutionary processes affecting a clade change over time. In this study, we examined an empirical phylogeny of fossil tetrapods during several time intervals, and studied how temporal constraints manifested in patterns of tree imbalance and character change. The results indicate that the impact of temporal constraints on tree shape is minimal and highlights the stability through time of the reference tetrapod phylogeny. Unexpected values of imbalance for Mississippian and Pennsylvanian time slices strongly support the hypothesis that the Carboniferous was a period of explosive tetrapod radiation. Several significant diversification shifts take place in the Mississippian and underpin increased terrestrialization among the earliest limbed vertebrates. Character incompatibility is relatively high at the beginning of tetrapod history, but quickly decreases to a relatively stable lower level, relative to a null distribution based on constant rates of character change. This implies that basal tetrapods had high, but declining, rates of homoplasy early in their evolutionary history, although the origin of Lissamphibia is an exception to this trend. The time slice approach is a powerful method of phylogenetic analysis and a useful tool for assessing the impact of combining extinct and extant taxa in phylogenetic analyses of large and speciose clades.


===

J. S. Anderson, J. D. Pardo, H. C. Maddin, M. Szostakiwskyj & A. Tinius (2016)
Is there an exemplar taxon for modelling the evolution of early tetrapod hearing?
Proceedings of the Royal Soceity B 2016 283: 20160027 
DOI: 10.1098/rspb.2016.0027
http://rspb.royalsocietypublishing.org/content/283/1832/20160027

Free pdf:
http://rspb.royalsocietypublishing.org/content/royprsb/283/1832/20160027.full.pdf


Excerpt:

...[W]e assert that the conclusion that 'early tetrapods also may have been able to detect aerial sound before the appearance of the tympanic middle ear', drawn from observations of salamanders and microsaurs is unfounded. Instead, the results of this study provide interesting insights into the strength of the conservation of an auditory apparatus adapted to terrestrial hearing in a group of aquatic salamanders.