A Three-Dimensional Skeletal Reconstruction of the Stem Amniote Orobates pabsti (Diadectidae): Analyses of Body Mass, Centre of Mass Position, and Joint Mobility
Authors:
Nyakatura et al
Abstract:
Orobates pabsti, a basal diadectid from the lower Permian, is a key fossil for the understanding of early amniote evolution. Quantitative analysis of anatomical information suffers from fragmentation of fossil bones, plastic deformation due to diagenetic processes and fragile preservation within surrounding rock matrix, preventing further biomechanical investigation. Here we describe the steps taken to digitally reconstruct MNG 10181, the holotype specimen of Orobates pabsti, and subsequently use the digital reconstruction to assess body mass, position of the centre of mass in individual segments as well as the whole animal, and study joint mobility in the shoulder and hip joints. The shape of most fossil bone fragments could be recovered from micro-focus computed tomography scans. This also revealed structures that were hitherto hidden within the rock matrix. However, parts of the axial skeleton had to be modelled using relevant isolated bones from the same locality as templates. Based on the digital fossil, mass of MNG 10181 was estimated using a model of body shape that was varied within a plausible range to account for uncertainties of the dimension. In the mean estimate model the specimen had an estimated mass of circa 4 kg. Varying of the mass distribution amongst body segments further revealed that Orobates carried most of its weight on the hind limbs. Mostly unrestricted joint morphology further suggested that MNG 10181 was able to effectively generate propulsion with the pelvic limbs. The digital reconstruction is made available for future biomechanical studies.
Plant architecture and spatial structure of an early Permian woodland buried by flood waters, Sangre de Cristo Formation, New Mexico
Authors:
Rinehart et al
Abstract:
Natural molds of 165 stems were found in life position in a 1 m-thick sandstone bed, lower Permian (Wolfcampian), Sangre de Cristo Formation, northern New Mexico. The sandstone represents a single flood event of a river sourced in the Ancestral Rocky Mountains. Most of the flood-buried plants survived and resumed growth. The stem affinities are uncertain, but they resemble coniferophytic gymnosperms, possibly dicranophylls. Stem diameters (N = 135) vary from 1 to 21 cm, with three strongly overlapping size classes. Modern forest studies predict a monotonically decreasing number (inverse square law) of individuals per size class as diameter increases. This is not seen for fossil stems ≤ 6 cm diameter, reflecting biases against preservation, exposure, and observation of smaller individuals. Stems ≥ 6 cm diameter obey the predicted inverse square law of diameter distribution. Height estimates calculated from diameter-to-height relationships of modern gymnosperms yielded heights varying from ~ 0.9 m to greater than 8 m, mean of ~ 3 m. Mean stand density is approximately 2 stems/m2 (20,000 stems/hectare) for all stems greater than 1 cm diameter. For stems greatre than than 7.5 cm or greater than 10 cm diameter, density is approximately 0.24 stems/m2 (2400 stems/hectare) and 0.14 stems/m2 (1400 stems/hectare). Stem spatial distribution is random (Poisson). Mean all-stem nearest-neighbor distance (NND) averages 36 cm. Mean NND between stems greater than 7.5 cm and greater than than 10 cm diameter is approximately 1.02 m and 1.36 m. NND increases in approximate isometry with stem diameter, indicating conformation to the same spatial packing rules found in extant forests and other fossil forests of varying ages. Nearest-neighbor distance distribution passes statistical testing for normality, but with positive skew, as often seen in extant NND distributions. The size-frequency distribution of the stems is similar to those of Jurassic, early Tertiary, and extant woodlands; the early Permian woodland distribution line has the same slope, but differs in that the overall size range increases over time (Cope's rule). The early Permian woodland is self-thinning; its volume versus density relationship shows a self-thinning exponent between − 1.25 and − 1.5, within the range seen in some extant plant stands (− 1.21 to − 1.7).
New specimen of Cacops woehri indicates differences in the ontogenetic trajectories among cacopine dissorophids.
Authors:
Fröbisch
Abstract:
The Lower Permian Dolese locality has produced numerous exquisitely preserved tetrapod fossils representing members of a lower Permian upland fauna. Therein, at least nine taxa of the clade Dissorophoidea, ranging in size from the large predaceous trematopid Acheloma to the miniaturized amphibamid Doleserpeton, highlight the great taxic and ecological diversity of this anamniote clade. Here we describe a large specimen of the dissorophid Cacops woehri, which was previously only known from the juvenile or subadult holotype skull. Another member of the genus Cacops present at the Dolese locality, Cacops morrisi, is also represented by specimens spanning juvenile, subadult, and adult stages, allowing for a comparison of morphological changes taking place in the late phases of the ontogenetic trajectory of cacopine dissorophids. The new find shows that, in contrast to C. morrisi and C. aspidephorus, C. woehri only undergoes relatively subtle changes in skull morphology in late ontogeny and retains the overall more gracile morphology into adult stages. This includes retention of the rather shallow skull shape as well as a pattern of sculpturing consisting of elongate ridges and grooves and a large occipital flange. This suggests somewhat different functional demands in C. woehri than in other known species of Cacops, possibly associated with a different ecology paralleling the great taxic diversity of dissorophoids at the Dolese locality.
Dimetropus osageorum n. isp. from the Early Permian of Oklahoma (USA): A Trace and its Trackmaker
Authors:
Sacchi et al
Abstract:
A new ichnospecies is named as Dimetropus osageorum n. isp. within the ichnogenus Dimetropus Romer and Price, 1940. The new ichnotaxon comes from the Lower Permian Midco Member of the Wellington Formation, cropping out near Perry, Noble Co. (Oklahoma, USA), and differs from congeneric ichnospecies in the apparent heteropody and in the proportionally shorter digits. The characters of the new ichnotaxon, together with comparative analysis of footprints and of known skeletal remains, suggest referral of the trackmaker to the Caseidae, although edaphosaurid affinities cannot be excluded. Tracks referred to Dimetropus exhibit wide variation, and their respective trackmakers may be ascribed to an accordingly wide range of different zoological taxa among non-therapsid Synapsida and not only to Sphenacodontidae as has been generally believed. At the same time, the process of attributing ichnotaxa, on the basis of well preserved tracks and by comparison with known skeletal remains, is validated.
A new species of the parareptile genus Delorhynchus, based on articulated skeletal remains from Richards Spur, Lower Permian of Oklahoma
Authors:
Reisz et al
Abstract:
Description of a new species of the parareptile genus Delorhynchus is based on a well-preserved partial subadult skeleton, an isolated adult skull, and disarticulated elements recently collected from the Lower Permian Richards Spur locality of Oklahoma, U.S.A. Delorhynchus cifellii, sp. nov., is distinguished from Delorhynchus priscus by the lack of an accessory articulating anterodorsal flange of the maxilla. The hypodigm of Delorhynchus cifellii reveals that Delorhynchus is distinguished from other parareptiles by cranial dermal sculpture consisting of a system of low, smooth tuberosities and a pattern of diffuse shallow, circular dimples. In a phylogenetic analysis of parareptiles, Delorhynchus cifellii is positioned as the sister species of Lanthanosuchoidea. Recognition of Delorhynchus cifellii, sp. nov., and its phylogenetic position among parareptiles highlights the significance of the Richards Spur locality in our understanding of the early evolutionary history of reptiles.
Plicidentine in the Early Permian Parareptile Colobomycter pholeter, and Its Phylogenetic and Functional Significance among Coeval Members of the Clade
Authors:
MacDougall et al
Abstract:
Once thought to be an exclusively anamniote characteristic, plicidentine, a pattern of infolding of dentine, is now known to be found in various amniote clades, including Parareptilia. In the absence of detailed analyses of parareptilian dentition, most parareptiles were assumed to lack plicidentine due to the absence of external indicators, such as plications on the tooth base. The clear presence of this dentinal feature in the largest premaxillary and maxillary teeth of Colobomycter pholeter, led us to the present detailed study within the dentition of this unusual parareptile, and those of coeval members of this clade. Our study reveals that there is large variability in the degree of dentine infolding within C. pholeter dentition, as well as within those of closely related parareptiles. This variability ranges from a lack of plications, to very complex anamniote-like plicidentine. Utilizing computed tomography scans in conjunction with histological sections we also demonstrate the utility of computed tomography scans in conducting non-destructive sampling in the identification of plicidentine. Given the variability of plicidentine in this sample of parareptiles, we hypothesize that one function of parareptilian plicidentine is to increase the surface area for attachment tissues, and we suggest that the use of plicidentine as a character in phylogenetic analyses of parareptiles may be misleading.
