Stuart S. Sumida

Lower Permian Terrestrial Paleoenvironments and Vertebrate Paleoecology of the Tambach Basin (Thuringia, Central Germany): The Upland Holy Grail

Abstract The Bromacker section of the Lower Permian, Tambach Formation, in central Germany, yields an important fossil-vertebrate assemblage that was deposited in an upland setting near the center of a small, internally-drained paleo-graben. The fossil-vertebrate assemblage shares many taxa in common with others that are well-documented from North America, but is atypical in the: (1) unusually large abundance of the terrestrial herbivore Diadectes; (2) complete absence of aquatic and semi-aquatic vertebrates; and (3) rarity of medium-to-large carnivorous synapsids. The graben setting and the low-diversity, terrestrial, fossil-vertebrate assemblage together comprise a unique upland paleoecosystem, heretofore undocumented in the Early Permian. The composition of and relative abundances within the assemblage at Bromacker suggest that experiments with “high-fiber” vertebrate herbivores as the dominant or significant basal component of vertebrate food webs had begun by the Early Permian, but only in settings with few or no aquatic and semi-aquatic vertebrates. The combined stratigraphic section at Bromacker consists of portions of two conformable stratigraphic intervals—the Lower and the Upper beds. Depositional events in both were dominated by seasonal-to-subseasonal cycles of flooding in an ephemeral, alluvial-to-lacustrine setting that was hot year-round with annual precipitation similar to that of a wet-and-dry tropical or wetter climate. Excellently preserved, articulated and disarticulated fossil vertebrates indicate subaerial exposure times of short duration and limited reworking. In the case of articulated specimens, death and burial were probably coeval events, most likely caused by floods.

REDESCRIPTION OF SEYMOURIA SANJUANENSIS (SEYMOURIAMORPHA) FROM THE LOWER PERMIAN OF GERMANY BASED ON COMPLETE, MATURE SPECIMENS WITH A DISCUSSION OF PALEOECOLOGY OF THE BROMACKER LOCALITY ASSEMBLAGE

Abstract Two nearly complete, articulated, mature specimens of the amphibian Seymouria are described from the Lower Permian Tambach Formation, lowermost unit of the Upper Rotliegend, of the Bromacker locality in the midregion of the Thuringian Forest near Gotha, central Germany. They are assigned to S. sanjuanensis, known elsewhere only from the Lower Permian deposits of Wolfcampian age in the southwestern United States. This confirms an earlier referral of two immature specimens from the same locality to this species. The new specimens are unusual in being highly ossified and allow for the first time a complete description of the carpus and tarsus of Seymouria. The Bromacker Seymouria specimens are part of an assemblage that is unique among Lower Permian localities in Europe in its taxonomic composition and its depositional environment. The Bromacker vertebrate assemblage includes many taxa found elsewhere only in the Lower Permian of the United States. All are adapted to a highly terrestrial existence, and the herbivore Diadectes and a closely related diadectid yet to be described are the most abundant forms, accounting for over half the articulated specimens encountered. Carnivorous, pelycosaurian-grade synapsid reptiles are exceedingly rare. Fossils at the Bromacker quarry were preserved near the center of a small, internally drained, Early Permian basin, the Tambach Basin. The vertebrates of this extraordinarily rich quarry are commonly excellently preserved, often complete and articulated, and occur almost exclusively in sheet-flood deposits that were almost certainly responsible for their death and burial with little or no transport; only minor attritional processes are evident. Relationships of the paleoenvironments and the biology of the vertebrates of the Bromacker locality based on the stratigraphy, paleontology, sedimentology, and basinal context of the Tambach Formation indicate that the Bromacker assemblage may represent the earliest known and best documented Early Permian example of a truly terrestrial “uplands” ecosystem. It apparently evolved and maintained itself independent of contemporary, water-based food chains that included aquatic and semi-aquatic forms.

Phylogenetic Context for the Origin of Feathers1

SYNOPSIS. A number of hypotheses have been suggested for the origin of birds and feathers. Although distributions of functional complexes have frequently been used to test phylogenetic hypotheses, analysis of the origin of feathers remains hampered by the incomplete fossil record of these unmineralized structures. It is also complicated by approaches that confuse the origins of birds, feathers, and flight without first demonstrating that these relate to the same historical event. Functional speculation regarding the origin of feathers usually focuses on three possible alternatives: (1) flight; (2) thermal insulation; or (3) display. Recent fossil finds of Late Cretaceous feathered dinosaurs in China have demonstrated that feathers appear to have originated in taxa that retained a significant number of primitive nonavian features. Current evidence strongly suggests that birds are theropod dinosaurs, and that the most primitive known feathers are found on nonflying animals. This further suggests that feathers did not evolve as flight structures. Thermoregulatory, display, and biomechanical support functions remain possible explanations for the origin of feathers. As the earliest function of feathers was probably not for aerial locomotion, it may be speculated that the transitional animals represented by the Chinese fossils possessed skin with the tensile properties of reptiles and combined it with the apomorphic characteristics of feathers.

A Phylogenetic Perspective on Locomotory Strategies in Early Amniotes

SYNOPSIS. Past approaches to understanding the evolution of locomotory strategies among Paleozoic amniotes (‘‘primitive reptiles’’ of previous parlance) have been influenced by preservational bias: early occurrences of some amniote taxa were used to polarize the acquisition or development of locomotory structures among the earliest amniotes. Using a phylogeny representing the current consensus in the literature, we investigate the major locomotory strategies that have been posited for Paleozoic amniotes (basal synapsids on one hand and early reptiles on the other) by optimizing the major locomotory styles identified for these taxa onto the consensus tree, in order to present an overview of the pattern of evolution of locomotory strategies inherited and adopted by various amniote lineages.

Comparative anatomy and osteohistology of hyperelongate neural spines in the sphenacodontids Sphenacodon and Dimetrodon (Amniota: Synapsida)

Osteohistological investigations of hyperelongate vertebral spinous processes (neural spines) are presented to elucidate previously unknown aspects of dorsal sail form and function in two, closely related genera of “sail‐backed” synapsids: Sphenacodon and Dimetrodon. Although recent and classic surveys of bone histology in extinct vertebrates have sampled the genus Dimetrodon, new sectioning of Sphenacodon material allows a comparative analysis of these structures among Sphenacodontidae for the first time. Variability within the histological organization of the neural spine is assessed by examining multiple regions along its length, and implications for soft tissue correlates, growth and mechanics are considered here. Both genera exhibit extensive parallel‐fibered and fibrolamellar bone, in addition to lamellar bone. Several features vary along the length of the spine in each species. Muscle scars and extensive Sharpeys fibers are present at the base of the spine; no scars and fewer fibers are manifested ∼55–60 mm above the zygapophyses in mature individuals. The distal cortex of the spine does not exhibit greater vascularity than the proximal region in either genus. However, both genera manifest distinct vascular grooves of variable size along the distal periosteal surface, some of which become incorporated into the distal cortex. The observed histovariability appears to record the transition from the proximal (epaxial muscle embedded) to the distally protruding portion of the spine. These observations and independent pathological evidence support the existence of a short dorsal crest in Sphenacodon and possibly other basal sphenacodontids. Although the thermoregulatory capacity of such a crest remains uncertain, developmental and mechanical features are readily interpretable and are discussed with respect to the origins and early evolution of the dorsal sail in sphenacodontid synapsids. J.Morphol., 2010.

THE BASAL REPTILE THURINGOTHYRIS MAHLENDORFFAE (AMNIOTA: EUREPTILIA) FROM THE LOWER PERMIAN OF GERMANY

Abstract The skeletal anatomy of the Early Permian eureptile Thuringothyris mahlendorffae from the Bromacker Quarry, Germany, is redescribed on the basis of several new specimens. The taxon retains some plesiomorphic characters, such as an ectopterygoid and a tabular, but it also possesses low neural spines and nonswollen neural arches, a combination that is unique for early eureptiles. A phylogenetic analysis places Thuringothyris as the sister taxon of Captorhinidae, excluding any potential “protorothyridid” affinities. Implications of this study are that the swollen neural arches of captorhinids and araeosceloids might have evolved independently, that a downturned rostrum occurred only later in captorhinid evolution, and that the European Permian is important to the understanding of the origin of eureptiles.

An ostodolepid ‘microsaur’ (Lepospondyli) from the Lower Permian Tambach Formation of central Germany

ABSTRACT Tambaroter carrolli is a new genus and species of medium-sized ostodolepid ‘microsaur’ from the Lower Permian Tambach Formation, lowermost formational unit of the Upper Rotliegend, Thuringia, central Germany. Based on a single skull, it is the first ‘microsaur’ to be described from this formation and the first vertebrate fossil known from the Tambach Formation outside of the well-known, nearby Bromacker locality. It possesses typical ostodolepid features, including presence of a recumbent snout, ventral embayment of the cheek, a notch in the posterolateral margin of the tabular, and a well-developed retroarticular process. It can be distinguished from other ostodolepids by proportional characters and bones forming the cheek embayment rim. The presence of Tambaroter in Europe, as the first ostodolepid known from outside of the midcontinent of North America, indicates that the geographic occurrence of this family was more widespread than previously known.

First European Record of a Varanodontine (Synapsida: Varanopidae): Member of a Unique Early Permian Upland Paleoecosystem, Tambach Basin, Central Germany

A new genus and species of varanodontine varanopid, Tambacarnifex unguifalcatus, is described on the basis of the greater portion of the postcranium and a closely associated partial left dentary from the Lower Permian (Wolfcampian) Tambach Formation, the lowermost unit of the Upper Rotliegend, of the Bromacker locality in the midregion of the Thuringian Forest near Gotha, central Germany. Tambacarnifex unguifalcatus can be distinguished from all other varanopids on the basis of unique features of its vertebrae and unguals. A cladistic analysis of Varanopidae resolves T. unguifalcatus as nested within the varanodontines as the sister taxon of Varanops in a terminal dichotomy, which in turn forms the sister clade of the terminal dichotomy Varanodon+Watongia. The position of Aerosaurus is unaltered from previous analyses as the basal taxon of Varanodontinae. Elliotsmithia, which has been assigned alternately to both the varanodontines and the mycterosaurines, is resolved as a member of the latter. Tambacarnifex unguifalcatus is, therefore, the only varanodontine known from outside of North America. Within the Mycterosaurinae clade Mycterosaurus and Mesenosaurus resolve as a terminal dichotomy with Elliotsmithia and Heleosaurus related as successive sister taxa. As in previous analyses, Archaeovenator retains its position as the basal taxon of Varanopidae. Tambacarnifex unguifalcatus was an apex predator in a unique, heretofore undocumented Early Permian paleoecosystem in which the vertebrates were highly terrestrial inhabitants of an upland terrestrial setting, and constituted an early stage in the evolution of the modern terrestrial vertebrate trophic system, with herbivores greatly outnumbering apex predators in diversity, abundance, and biomass.

Healed Fractures in the Neural Spines of an Associated Skeleton of Dimetrodon: Implications for Dorsal Sail Morphology and Function

Abstract Hyperelongate neural spines forming a prominent dorsal “sail” are known in eight genera distributed between two families of pelycosaurian-grade synapsids. Although the function(s) of the sail remain disputed, most researchers assume that resilient soft tissue stretched between the elongate neural spines, extending to the distal tips. Hypotheses to explain the purpose of the sail have included thermoregulation (Romer & Price, 1940; Bramwell & Fellgett, 1973; Haack, 1986; Tracy et al., 1986; Bennett, 1996; Florides et al., 1999) and sexual selection (Tomkins et al., 2010). In this paper, we analyze the natural pathologies found in the neural spines of a very large pelycosaur, Dimetrodon giganhomogenes, as a natural experiment: What would ensue in the event of sail breakage and what does that tell us about sail structure, development, maintenance, and the orientation of the sail? A series of seven associated neural spines from fmnh UC 1134 demonstrate subtle though distinctly abnormal rugosities, a sign most often indicative of a well-healed hard callus of bone fracture. Microstructural examination revealed surprising facts: not only did the abnormal bone areas prove NOT to be fracture hard callus, but the abnormal tissue reflected underlying material failure resulting from slippage between adjacent lamellae of bone. Moreover, the characteristic cranial and caudal orientation of the deep longitudinal grooves contributing to the classic dimetrodont figure-8 spine cross section was rapidly reestablished in vivo by a combination of osteoclastic resorption and additional lamellar deposition of bone to regain the “correct” pre-injury orientation, underscoring the architectural importance of the dumbbell shape in resisting lateral bending. This bone disruption and repair occurred at least five seasons before death, which explains the well-healed external appearance of the lesions. The absence of vascular communicating canals casts doubt on the widely held hypothesis that these grooves contained blood vessels that supplied a thermoregulatory sail. Furthermore, the distal morphology of spines in more complete specimens, including the type fmnh UC 112 and omnh 01727, suggests that the dorsal margin of the sail was located well proximal to the tips of the elongate neural spines. The cross-sectional architecture of the spines suggests a further hypothesis: that the proximal portion of the sail may have also functioned as an energy storage device, facilitating fast locomotion in this top predator.

New Information on the Basal Pelycosaurian-Grade Synapsid Oedaleops

The Early Permian amniote Oedaleops is generally considered to be one of the basalmost pelycosaurian-grade synapsids. Thus it occupies a key position for understanding the phylogenetic relationships of basal synapsids specifically and basal amniote interrelationships more generally. This assessment has until now been based almost exclusively on the remains of a single skull from the Lower Permian Cutler Formation of north-central New Mexico. The identification of additional cranial as well as numerous postcranial elements of at least three additional individuals now permits a more complete understanding of its anatomy and allows the first attempt at a partial body reconstruction of this basal pelycosaurian-grade synapsid. Oedaleops is confirmed as an extremely basal synapsid taxon, but the addition of postcranial data from Oedaleops to data matrices of earlier phylogenetic analyses unexpectedly weakens, as opposed to strengthens, support for the hypotheses of a monophyletic Eothyrididae.