Amy C. Henrici

FIRST WELL-ESTABLISHED TRACK-TRACKMAKER ASSOCIATION OF PALEOZOIC TETRAPODS BASED ON ICHNIOTHERIUM TRACKWAYS AND DIADECTID SKELETONS FROM THE LOWER PERMIAN OF GERMANY

Abstract As a single stratigraphic source and site of high-fidelity vertebrate trackways and superbly preserved skeletons, the Lower Permian Tambach Formation, lowermost unit of the Upper Rotliegend, of the Bromacker locality in the middle part of the Thuringian Forest near Gotha, central Germany, provides a unique opportunity of matching late Paleozoic trackways with their trackmakers. Here the track-trackmaker association is firmly established between two species of the ichnogenus Ichniotherium, Ichniotherium cottae and Ichniotherium sphaerodactylum, and the skeletal fossils of the closely related diadectids Diadectes absitus and Orobates pabsti, respectively. These are the first well-documented species-level identifications of the trackmakers of Paleozoic trackways. The Ichniotherium ichnospecies are principally separated by the relative lengths of the digits of the pes imprint and the degree of overstepping of the pes and manus imprints. Both characters are shown to be clearly due to differences in the number and lengths of phalangeal elements and the number of presacral vertebrae of the diadectid species. The unique methods employed here in establishing the track-trackmaker associations provide not only an innovative data source for studying the evolutionary biology, paleo-biogeography, and locomotor behaviour of the trackmakers, but also a valuable methodology for evaluating taxonomic concepts in vertebrate ichnology.

A NEW DIADECTID (DIADECTOMORPHA), OROBATES PABSTI, FROM THE EARLY PERMIAN OF CENTRAL GERMANY

Abstract A new genus and species of the herbivorous Diadectidae, Orobates pabsti, is described on the basis of several specimens, including two complete, articulated skeletons, a skull with partial postcranium, a partial skull, and a dentigerous jaw fragment. All were collected from the Lower Permian (Wolfcampian) Tambach Formation, lowermost formational unit of the Upper Rotliegend of the Bromacker quarry locality in the midregion of the Thuringian Forest near Gotha, central Germany. A combination of autapomorphic and plesiomorphic character states clearly distinguishes O. pabsti from all other well-known members of Diadectidae and identifies it as the sister taxon to all other diadectids. The description of Orobates pabsti expands further our understanding of the Late Pennsylvanian-Early Permian Diadectidae and records the earliest specialization of tetrapods to high-fiber herbivory. On the basis of paleobiological and paleoenvironmental data only one other Early Permian locality is comparable to the Bro-macker locality, the somewhat younger (Leonardian) fissure fill deposits at Richards Spur, southeastern Oklahoma. This further supports the previously proposed hypothesis, based on similar grounds, that the vertebrates of both localities may have been part of a widespread, terrestrial upland faunal assemblage during the Early Permian.

A new pipoid anuran from the Late Jurassic Morrison Formation at Dinosaur National Monument, Utah

ABSTRACT Rhadinosteus parvus is a small anuran whose diagnosis is based on several partial skeletons and some isolated bones representing metamorphic to newly transformed ontogenetic stages from the Late Jurassic Morrison Formation at the Rainbow Park Microsite, Utah. This frog is a member of the Pipoidea on the basis of an azygous frontoparietal and parasphenoid that lacks lateral alae and is an important addition to the poorly known Jurassic frog fauna. Although other members of the Pipoidea have skeletal specializations for burrowing or swimming, Rhadinosteus possesses an unspecialized skeleton. Presence of ectochordal vertebrae suggest that Rhadinosteus is a member of the Rhinophrynidae, and if so, it is the most primitive member known. Being from the Late Jurassic, Rhadinosteus predates both the previous pipoid, Early Cretaceous, and rhinophrynid, Late Paleocene, records.

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.

Georgenthalia clavinasica, A New Genus and Species of Dissorophoid Temnospondyl from the Early Permian of Germany, and the Relationships of the Family Amphibamidae

Abstract Georgenthalia clavinasica, a new genus and species of amphibamid dissorophoid temnospondyl, is represented by a small, complete, postmetamorphic skull from the Lower Permian Bromacker locality, Germany. It is only the third non-amniote of an assemblage of 12 terrestrial tetrapod taxa known from this locality. It is characterized by a broadly rounded skull with large orbits, a short postorbital length, and a unique keyhole-shaped external naris superficially resembling that of trematopid dissorophoids. New features that help to discriminate between amphibamid species are highlighted. Phylogenetically informative characters present in G. clavinasica include: anterolateral flaring of the lateral margin of frontals; narrow interorbital width; ventral orbital process of the prefrontal contacts palatine; palatine exposed on lateral surface of ventral rim of orbit; large otic notches closely approach the orbits; absence of a supratympanic flange of otic notch; long supratympanic process of squamosal with flange-like process that underlaps the midcentral portion of supratemporal. Several features support a highly terrestrial habitus of G. clavinasica, which is consistent with the interpretation of the fossiliferous beds of the Bromacker quarry as representing an upland terrestrial environment in which limnic conditions were characterized by ephemeral lakes and ponds. A new clade, Olsoniformes, is named for Dissorophidae and Trematopidae (dissorophoids exclusive of Amphibamidae), and new phylogenetic definitions for Amphibamidae, Trematopidae, and Dissorophidae are presented. The small neotenic Micromelerpetontidae, and presumably also the neotenic and larval Branchiosauridae, fall within the newly defined clade Amphibamidae in the current study, and future work should focus on clarifying the nature of this relationship.

A late-surviving basal theropod dinosaur from the latest Triassic of North America

The oldest theropod dinosaurs are known from the Carnian of Argentina and Brazil. However, the evolutionary diversification of this group after its initial radiation but prior to the Triassic–Jurassic boundary is still poorly understood because of a sparse fossil record near that boundary. Here, we report on a new basal theropod, Daemonosaurus chauliodus gen. et sp. nov., from the latest Triassic ‘siltstone member’ of the Chinle Formation of the Coelophysis Quarry at Ghost Ranch, New Mexico. Based on a comprehensive phylogenetic analysis, Daemonosaurus is more closely related to coeval neotheropods (e.g. Coelophysis bauri) than to Herrerasauridae and Eoraptor. The skeletal structure of Daemonosaurus and the recently discovered Tawa bridge a morphological gap between Eoraptor and Herrerasauridae on one hand and neotheropods on the other, providing additional support for the theropod affinities of both Eoraptor and Herrerasauridae and demonstrating that lineages from the initial radiation of Dinosauria persisted until the end of the Triassic. Various features of the skull of Daemonosaurus, including the procumbent dentary and premaxillary teeth and greatly enlarged premaxillary and anterior maxillary teeth, clearly set this taxon apart from coeval neotheropods and demonstrate unexpected disparity in cranial shape among theropod dinosaurs just prior to the end of the Triassic.

HOMOLOGY OF THE ASTRAGALUS AND STRUCTURE AND FUNCTION OF THE TARSUS OF DIADECTIDAE

Abstract Superbly preserved tarsi of a new, undescribed, primitive member of Diadectidae and of Diadectes, the best known member of the family, are described. The major distinction between them is the retention of sutures in the astragalus of the former which clearly indicate an origin from the fusion of three separate ossifications considered homologues of the primitive amphibian tibiale, intermedium, and proximal centrale. Among the Diadectomorpha (includes also Limnoscelidae and Tseajaiidae) only Diadectidae possesses an astragalus, which is considered a synapomorphy of the family within this grouping. Furthermore, the sister-group relationship of the new, undescribed diadectid to the other diadectids demonstrates a transformational, phylogenetic homology of the astragalus via the ontogenetic fusion of the primitive amphibian tarsal bones. The astragalus of diadectids is identical to those of late Paleozoic terrestrial amniotes in structure and relationship to neighboring elements. This, plus the wide acceptance of a close relationship between Diadectomorpha and Amniota, is cited as suggestive of an identical developmental origin of their astragali. In diadectids, including fully mature individuals, an unusual reduction or absence of ossification of some central and distal tarsal bones has resulted in an unique tarsus with large unoccupied areas and a structural pattern in which the only bony link between the tarsus and the digits is via the fourth distal tarsal, producing a crude facsimile of the lacertilian mesotarsal joint. Such a joint would have permitted, as in lacertilians, a wide range of movements which may have served several important functions: 1) maintaining an anteriorly directed pes to maximize the force of its posterior thrust during limb retraction, 2) placement of the pes close to the body midline for greater stride length and more efficient support and greater maneuverability during locomotion.

ELKOBATRACHUS BROCKI, A NEW PELOBATID (AMPHIBIA: ANURA) FROM THE EOCENE ELKO FORMATION OF NEVADA

ABSTRACT Elkobatrachus brocki is a new, small pelobatid anuran that is represented by a small collection of fairly well-preserved and for the most part articulated to closely associated fossils recovered from the middle Eocene Elko Formation near Elko, Nevada. The Elko Formation is divided into three informal members, lower, middle, and upper, and was deposited primarily under warm, temperate conditions in a fluviolacustrine system of a broad, shallow basin extending over a large area of present-day northeastern Nevada. The fossils were preserved in a sandy limestone unit near the base of the middle member, which lies about 100 m above a unit yielding a radiometric date of 46.1 Ma. A phylogenetic analysis suggests that E. brocki is the most primitive pelobatid currently known and differs from all other pelobatids in the following autapomorphies: 1) alary process of premaxilla is broad-based and forms a laterally-deflected, straight blade whose transverse axis is oriented anteroposteriorly; 2) pars acromialis of scapula is triangular with anteriorly directed apex positioned at the level of the dorsal rim of the glenoid fossa; and 3) urostyle length exceeds that of the vertebral column. Elkobatrachus brocki is the oldest known pelobatid that exhibits burrowing specializations in its skeleton. Thus, like extant pelobatids, it very likely could avoid high daytime temperatures and periods of dryness by constructing a burrow in which it estivated. The ability of early Tertiary pelobatids to presumably avoid drought by estivating in burrows is thought to be a preadaptation for hibernation in burrows to survive subfreezing temperatures resulting from global cooling that began in the middle Eocene.

FIRST OCCURRENCE OF XENOPUS (ANURA: PIPIDAE) ON THE ARABIAN PENINSULA: A NEW SPECIES FROM THE UPPER OLIGOCENE OF YEMEN

Abstract A freshwater interbed of the Yemen Volcanic Group in central western Yemen yielded impressions of numerous, articulated, mostly complete frog skeletons. Recent dating of the volcanics and the stratigraphic position of the fossil bearing bed in the sequence support a Late Oligocene age for the frogs. These frogs are described as a new species of Xenopus, a genus that is today mostly confined to subsaharan Africa, and they provide evidence of the former, wider distribution of this genus on the Afro-Arabian Plate. The new species, X. arabiensis, differs from other Xenopus in its long maxilla and maxillary tooth row. It resembles X. muelleri in its dentate, azygous vomer and prominent, cone-shaped, distally-pointed prehallux, but differs from X. muelleri in having an atlantal intercotylar notch and longer distal prehallux bone. Climatic changes during the Neogene probably led to the extinction of Xenopus on the Arabian Peninsula; however, the timing of this event is not certain.

A New Trematopid Amphibian (Temnospondyli: Dissorophoidea) from the Upper Pennsylvanian of Western Pennsylvania: Earliest Record of Terrestrial Vertebrates Responding to a Warmer, Drier Climate

ABSTRACT Fedexia striegeli, a new genus and species of trematopid temnospondyl amphibian, is described on the basis of a single specimen that includes the greater portion of the skull and articulated portions of both mandibles and the atlas-axis complex, The holotype was collected from Upper Pennsylvanian—early Virgilian strata assignable to the lower part of the Casselman Formation of the Conemaugh Group in western Pennsylvania. This is not only the first trematopid to be reported from the State of Pennsylvania, but also, in addition to Actiobates Eaton, 1973, and Anconastes Berman et al., 1987, only the third reported Late Pennsylvanian member of the family that otherwise has a greater Early Permian representation. A cladistic analysis of the Dissorophoidea was performed utilizing primarily cranial characters and only members of Amphibamidae, Trematopidae, and Dissorophidae that are well represented in this field of inquiry. This includes Ecolsonia Vaughn, 1969, whose relationships to the latter two families have been controversial. The resultant cladogram depicts: 1) Fedexia to be nested within a monophyletic Trematopidae as the sister taxon to the terminal dichotomy of Anconastes and Tambachia Sumida et al., 1998; 2) Trematopidae and Dissorophidae as forming monophyletic sister clades; and 3) Ecolsonia, Dissorophus Cope, 1895, and Broiliellus Williston, 1914, as forming an unresolved, terminal trichotomy within the dissorophid clade. Fedexia is representative of a wide variety of Late Pennsylvanian, medium-to-large amphibian and amniote tetrapods that record the earliest occurrence of vertebrates adapted to a terrestrial existence in North America. It is hypothesized that this biotic event was in response to the final stage of a long-term, global climatic trend toward drier conditions during the Pennsylvanian from perhumid to humid during the Early and Middle Pennsylvanian to dry subhumid or semiarid in the latest Virgilian. The lattermost climatic stage, which was also coincident with a marked retreat of the southern polar hemisphere glaciers during the late Paleozoic Ice Age, was followed by a strong and progressive reversal of the climate and an advance of the southern hemisphere glaciers to conditions characteristic of the earlier Pennsylvanian. Climatic changes during the Pennsylvanian are chronicled not only by major changes in rock types and associated lithologies, but also by a shift in the biology of the vertebrates they preserve. Middle Pennsylvanian vertebrates are characterized by large, diverse assemblages of predominantly small, aquatic amphibians and fish preserved in black shales and cannel coals associated with coal-forming and sapropelic fluvial sediments that developed in permanently wet, abandoned river channels. In contrast, the terrestrially adapted vertebrates of the Missourian—Virgilian Pennsylvanian are typically preserved in thin deposits of freshwater limestone or their closely associated paleosols that are interpreted as representing seasonally dry lake deposits. Yet, aquatic amphibians continue to be a major constituent of Late Pennsylvanian vertebrate assemblages.