Fremouw Formation Research Articles

Diminutive temnospondyls from the lower and middle Fremouw Formation (Lower Triassic) of Antarctica

Diminutive temnospondyls from the lower and middle Fremouw Formation (Lower Triassic) of Antarctica

A new lapillopsid from Antarctica and a reappraisal of the phylogenetic relationships of early diverging stereospondyls

ABSTRACT Stereospondyls underwent a global radiation in the Early Triassic, including an abundance of small-bodied taxa, which are otherwise rare throughout the Mesozoic. Lapillopsidae is one such clade and is presently known only from Australia and India. This clade’s phylogenetic position, initially interpreted as micropholid dissorophoids and later as early diverging stereospondyls, remains uncertain. Although the latter interpretation is now widely accepted, lapillopsids’ specific relationship to other Early Triassic clades remains unresolved; in particular, recent work suggested that Lapillopsidae nests within Lydekkerinidae. Here we describe Rhigerpeton isbelli, gen. et sp. nov., based on a partial skull from the lower Fremouw Formation of Antarctica that is diagnosed by a combination of features shared with at least some lapillopsids, such as a longitudinal ridge on the dorsal surface of the tabular, and features not found in lapillopsids but shared with some lydekkerinids, such as the retention of pterygoid denticles and a parachoanal tooth row (as in Lydekkerina, for example). A series of phylogenetic analyses confirm the lapillopsid affinities of R. isbelli but provide conflicting results regarding the polyphyly and/or paraphyly of Lydekkerinidae with respect to lapillopsids. The position of Lapillopsidae within Temnospondyli is highly sensitive to taxon sampling of other predominantly Early Triassic temnospondyls. The occurrence of a lapillopsid in Antarctica brings the documented temnospondyl diversity more in line with historically well-sampled portions of southern Pangea, but robust biogeographic comparisons remain hindered by the inability to resolve many historic Antarctic temnospondyl records to the finer taxonomic scales needed for robust biostratigraphy.

Re-description of the early Triassic diapsid Palacrodon from the lower Fremouw formation of Antarctica.

The rapid radiation and dispersal of crown reptiles following the end-Permian mass extinction characterizes the earliest phase of the Mesozoic. Phylogenetically, this early radiation is difficult to interpret, with polytomies near the crown node, long ghost lineages, and enigmatic origins for crown group clades. Better understanding of poorly known taxa from this time can aid in our understanding of this radiation and Permo-Triassic ecology. Here, we describe an Early Triassic specimen of the diapsid Palacrodon from the Fremouw Formation of Antarctica. While Palacrodon is known throughout the Triassic and exhibits a cosmopolitan geographic range, little is known of its evolutionary relationships. We recover Palacrodon outside of crown reptiles (Sauria) but more crownward than Youngina capensis and other late Permian diapsids. Furthermore, Palacrodon possesses anatomical features that add clarity to the evolution of the stapes within the reptilian lineage, as well as incipient adaptations for arboreality and herbivory during the earliest phases of the Permo-Triassic recovery.

Schroeder Hill, central Transantarctic Mountains, Antarctica: Triassic stratigraphy and Sirius Group glacigenic deposits

AbstractThe geology of the Schroeder Hill region near the head of the Shackleton Glacier, central Transantarctic Mountains, consists of Triassic Fremouw Formation and overlying Falla Formation strata intruded by Jurassic Ferrar Dolerite sills. At ‘Alfie’s Elbow', south-east of Schroeder Hill, upper Fremouw strata are overlain by Upper Cenozoic Sirius Group deposits. These upper Fremouw beds differ from all other examined upper Fremouw strata in the Shackleton Glacier region in being carbonaceous. Quartz-pebble conglomerate characterizes the basal Falla beds, emphasizing a change in provenance. Sirius Group beds occur as a stratigraphic succession draped on modern topography and as structureless sand wedged in modern microtopography. Fremouw beds locally are arched with the fold axis approximately parallel to regional normal faulting related to the uplift and formation of the Transantarctic Mountains.

Upside down: ‘Cryobatrachus’ and the lydekkerinid record from Antarctica

AbstractTemnospondyl amphibians are common in non-marine Triassic assemblages, including in the Fremouw Formation (Lower to Middle Triassic) of Antarctica. Temnospondyls were among the first tetrapods to be collected from Antarctica, but their record from the lower Fremouw Formation has long been tenuous. One taxon, ‘Austrobrachyops jenseni,’ is represented by a type specimen comprising only a partial pterygoid, which is now thought to belong to a dicynodont. A second taxon, ‘Cryobatrachus kitchingi,’ is represented by a type specimen comprising a nearly complete skull, but the specimen is only exposed ventrally, and uncertainty over its ontogenetic maturity and some aspects of its anatomy has led it to be designated as a nomen dubium by previous workers. Here, we redescribe the holotype of ‘C. kitchingi,’ an undertaking that is augmented by tomographic analysis. Most of the original interpretations and reconstructions cannot be substantiated, and some are clearly erroneous. Although originally classified as a lydekkerinid, the purported lydekkerinid characteristics are shown to be unfounded or no longer diagnostic for the family. We instead identify numerous features shared with highly immature capitosaurs, a large-bodied clade documented in the upper Fremouw Formation of Antarctica and elsewhere in the Lower Triassic. Additionally, we describe a newly collected partial skull from the lower Fremouw Formation that represents a relatively mature, small-bodied individual, which we provisionally refer to Lydekkerinidae; this specimen represents the most confident identification of a lydekkerinid from Antarctica to date.

A new bauriamorph therocephalian adds a novel component to the Lower Triassic tetrapod assemblage of the Fremouw Formation (Transantarctic Basin) of Antarctica

ABSTRACT The Fremouw Formation (Transantarctic Basin) of Antarctica preserves an exceptional fossil record of tetrapods from the beginning of the Mesozoic at high paleolatitude. Many of these fossils can be identified to species that also occur in the much richer Lystrosaurus declivis Assemblage Zone of South Africa’s Karoo Basin, but endemic species also occur. A third category of Antarctic fossils includes those that can only be broadly classified or lack sufficient diagnostic features for a synapomorphy-based identification. Therocephalians are a prime example of the last category, with Akidognathidae indet., Baurioidea indet., and cf. Ericiolacerta parva, currently recognized from the lower Fremouw Formation. Here we describe the most complete skull for an Antarctic therocephalian discovered to date. Notictoides absens, gen. et sp. nov., preserves a unique dental formula, a large intranarial portion of the septomaxilla, two bony excrescences along the rostral margin of the lacrimal, and a complete secondary palate formed by the maxilla. These features, in combination with a sagittal crest with a slit-like parietal foramen, a long, low dentary, and reduced upper and lower antecanine tooth count, suggest a relatively derived position for N. absens within baurioids. Indeed, the results of an updated cladistic analysis unite N. absens with the clade including Nothogomphodon, Ordosiodon, and Bauriidae. More broadly, the discovery of a third endemic species in the Lower Triassic rocks of the Fremouw Formation suggests that diversification in the wake of the Permian–Triassic mass extinction was likely more geographically complex than currently appreciated.

Cold capitosaurs and polar plagiosaurs: new temnospondyl records from the upper Fremouw Formation (Middle Triassic) of Antarctica

ABSTRACT The upper Fremouw Formation (Middle Triassic) of Antarctica preserves a diverse record of temnospondyls, with three species currently recognized. To date, all of the described material belongs to a single clade, Capitosauria. Our reanalysis suggests that cursory historical reports suggesting the presence of a benthosuchid (Trematosauria) are in error. Here we report substantial amounts of hemimandibular material of large-bodied temnospondyls from the upper Fremouw Formation. All seven specimens, including the historic material attributed to Trematosauria, exhibit features indicative of capitosaurian affinities. These specimens represent a notable expansion in the physical and conceptual body of temnospondyl material known from the Fremouw Formation, although they cannot be definitively associated with any of the three previously named Antarctic species in the absence of skeletal overlap. In addition, all of the specimens come from large-bodied individuals (i.e., skull lengths exceeding 70 cm), which likely reflects a taphonomic filter created by the high-energy channel lag deposition of the fossiliferous horizon of the upper Fremouw Formation. We also report the first occurrence of a non-capitosaur, an interclavicle belonging to a plagiosaurid. This represents only the third occurrence of Plagiosauridae in southern Pangea during the Triassic, in contrast to a much richer record of this clade in northern parts of the supercontinent and a rich record of the closely related brachyopids in the southern hemisphere. Together with the continued absence of trematosaurs in Antarctica, the plagiosaurid record hints at nuances in the distribution of cosmopolitan clades patterns that are tied to presently unrecognized ecological and physiological differentiators.

Landslides in the Transantarctic Mountains: lower Jurassic and older strata displaced in late Mesozoic to late Cenozoic time

ABSTRACT Eight landslides, seven certain and one possible, have been identified in the central Transantarctic Mountains and one at Carapace Nunatak, south Victoria Land. Four consist of Kirkpatrick Basalt lavas alone, two comprise Kirkpatrick lavas with associated pyroclastic rocks, one consists of Hanson Formation beds and Kirkpatrick lavas, and one involves Fremouw Formation strata. One possible block, of uncertain origin, consists only of Hanson Formation beds. All rocks comprising the displaced blocks, except one, are Early Jurassic in age. The exception is the inferred slide involving the Triassic Fremouw beds. The locations of some landslides are consistent with emplacement on present-day topography, which has been little modified since the middle Miocene, but the time of emplacement of others is either Oligocene to pre-middle Miocene or pre-dates the onset of glaciation in Eocene/Oligocene time. The older landslides reflect fortuitous preservation of an ancient landscape not unlike that of today, one dominated by horizontal beds consisting of resistant dolerite sills and quartz-rich sandstones alternating with intervals of weak fine-grained sedimentary beds, and capped by basalt lavas. The landslides are interpreted to document three stages in landscape evolution: a pre-glaciation semi-arid landscape, an early warm-based glacial environment, and a late cold-based glacial setting.

A new large gomphodont from the Triassic of South Africa and its implications for Gondwanan biostratigraphy

ABSTRACT A partial skull (BP/1/7976) of a very large cynodont from the Middle Triassic Cynognathus Assemblage Zone (Cricodon-Ufudocyclops subzone) of South Africa is described. The specimen represents a new gomphodont taxon, Impidens hancoxi, gen. et sp. nov., diagnosed by five sectorial teeth constituting just over half of the length of the upper postcanine tooth row, and enlarged canine and incisor teeth. BP/1/8123, a skull fragment also from the Cricodon-Ufudocyclops subzone, and AMNH FARB 24421, a partial skull from the upper Fremouw Formation of Antarctica, are also referred to the new species. The presence of this taxon in both the upper Fremouw Formation and Cricodon-Ufudocyclops subzone strengthens evidence of biostratigraphic correlation between these units. Impidens hancoxi, with an inferred skull length of up to 460 mm, was a large-bodied and likely omnivorous gomphodont, and may have played the role of apex predator within the tetrapod fauna of the Cricodon-Ufudocyclops subzone.

First record of the amphibamiform Micropholis stowi from the lower Fremouw Formation (Lower Triassic) of Antarctica

ABSTRACT The fossil record of temnospondyl amphibians in the immediate wake of the Permo-Triassic mass extinction captures extensive taxic and ecological diversity, with most records known from high paleolatitudinal settings. In southern Pangea, the most substantial records come from South Africa and Australia, with a total of over 20 taxa presently recognized. Temnospondyls have also been known from correlated horizons in the lower Fremouw Formation of Antarctica since the late 1960s, but these records are mostly fragmentary, thereby limiting taxonomic resolution to the family level and subsequent biostratigraphic correlations and comparisons between high-latitude basins. Here we report substantial new material of the amphibamiform Micropholis stowi, a relic dissorophoid previously known only from the Katberg Formation (Lystrosaurus declivis Assemblage Zone) of South Africa, from the lower Fremouw Formation. The exceptional preservation of the recently recovered material permits not only confident taxonomic referral but also tentative association of several individuals to the broad-headed morph of the taxon. The recognition of M. stowi in Antarctica represents only the fourth geographic occurrence of a dissorophoid from southern Pangea and supports the hypothesis that high-latitude environments served as refugia for temnospondyls during the mass extinction. In the case of M. stowi, such refugia permitted the persistence of a predominantly Permo-Carboniferous clade, and the Antarctic records discussed here further hint at a poorly sampled cryptic distribution, both of amphibamiforms in southern Pangea and of small-bodied temnospondyls in early Mesozoic deposits.

A Kannemeyeriiform (Synapsida: Dicynodontia) Occipital Plate from the Middle Triassic Upper Fremouw Formation of Antarctica

ABSTRACT A kannemeyeriiform dicynodont is described on the basis of an occipital plate from the upper Fremouw Formation (Middle Triassic) Gordon Valley locality in the Beardmore Glacier region of Antarctica. The Antarctic specimen is comparable in size to Kannemeyeria simocephalus from the well-known Cynognathus Assemblage Zone of the Beaufort Group of South Africa, and represents the largest therapsid currently known from the upper Fremouw Formation. The presence of an occipital condyle with distinct contributions from the exoccipital and the basioccipital; a wide, tri-radiate occipital condyle; and a well-developed tympanic process of the paroccipital, which is situated below the level of the occipital condyle, represent a combination of character states hitherto unknown among Kannemeyeriiformes. Combined with the possible autapomorphic feature of slender, dorsoventrally elongate basal tubera, this may suggest the Antarctic specimen represents a new kannemeyeriiform taxon. This specimen represents the most complete, and only the fourth definitive, dicynodont specimen known from the upper Fremouw Formation, and the contradictory phylogenetic character data from these specimens adds support for the presence of multiple (at least two) kannemeyeriiform taxa within the upper Fremouw tetrapod assemblage. Taken together, these kannemeyeriiform specimens provide additional support for a correlation with the Cynognathus Assemblage Zone, particularly the Trirachodon-Kannemeyeria or Cricodon-Ufudocyclops subzones (= subzones B or C), as well as an Anisian or younger age for the upper Fremouw tetrapod fauna.

A new specimen of Prolacerta broomi from the lower Fremouw Formation (Early Triassic) of Antarctica, its biogeographical implications and a taxonomic revision

Prolacerta broomi is an Early Triassic archosauromorph of particular importance to the early evolution of archosaurs. It is well known from many specimens from South Africa and a few relatively small specimens from Antarctica. Here, a new articulated specimen from the Fremouw Formation of Antarctica is described in detail. It represents the largest specimen of Prolacerta described to date with a nearly fully articulated and complete postcranium in addition to four skull elements. The study of this specimen and the re-evaluation of other Prolacerta specimens from both Antarctica and South Africa reveal several important new insights into its morphology, most notably regarding the premaxilla, manus, and pelvic girdle. Although well-preserved skull material from Antarctica is still lacking for Prolacerta, a detailed comparison of Prolacerta specimens from Antarctica and South Africa corroborates previous findings that there are no characters clearly distinguishing the specimens from these different regions and therefore the Antarctic material is assigned to Prolacerta broomi. The biogeographical implications of these new findings are discussed. Finally, some osteological characters for Prolacerta are revised and an updated diagnosis and phylogenetic analysis are provided.

A novel archosauromorph from Antarctica and an updated review of a high-latitude vertebrate assemblage in the wake of the end-Permian mass extinction

Triassic-aged fossil vertebrates have been sporadically collected from the Fremouw Formation, central Transantarctic Mountains, since their initial discovery in the late 1960s, giving paleontologists insight into high-latitude faunas in the wake of the end-Permian mass extinction event. On a recent expedition (2010–2011), a small reptile skeleton was collected from Graphite Peak, which we present here alongside novel geological data and interpretations taken on site. Antarctanax shackletoni, gen. et sp. nov., is known from a partial postcranial skeleton including cervical and dorsal vertebrae, a humerus, and both pedes. Important morphological information includes well-defined laminae and deep fossae on cervicodorsal vertebrae. The new taxon can be differentiated from previously known Fremouw Formation reptiles (e.g., Prolacerta, Procolophon), as well as those from the Karoo Basin, South Africa (e.g., Mesosuchus, Proterosuchus, Euparkeria). Our inclusion of A. shackletoni in phylogenetic analyses of early amniotes finds it as an archosauriform archosauromorph, increasing known archosauriform diversity in the Early Triassic. The fauna of the lower Fremouw Formation traditionally has been considered to represent a subset of the Lystrosaurus Assemblage Zone of the Karoo Basin, with differences largely a result of pronounced differences in sampling intensity. However, a review of recent changes to the fauna, as well as a reassessment of occurrences based on older literature, indicates that significant discrepancies, including the co-occurrences of taxa known from both earlier and later in time and the presence of endemic forms in Antarctica, exist between the faunas of the Lystrosaurus Assemblage Zone and lower Fremouw Formation.http://zoobank.org/urn:lsid:zoobank.org:pub:B1DAD1A4-7054-454D-89B2-17CAF2865AD4SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Peecook, B. R., R. M. H. Smith, and Christian A. Sidor. 2019. A novel archosauromorph from Antarctica and an updated review of a high-latitude vertebrate assemblage in the wake of the end-Permian mass extinction. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1536664.

Under pressure? Epicormic shoots and traumatic growth zones in high-latitude Triassic trees from East Antarctica.

Investigating the biology of trees that were growing at high latitudes during warmer geological periods is key to understanding the functioning of both past and future forest ecosystems. The aim of this study is to report the first co-occurrence of epicormic shoots and traumatic growth zones in fossil trees from the Triassic of Antarctica and to discuss their biological and environmental implications. Permineralized woods bearing scars of epicormic shoots were collected from the Triassic Fremouw Formation in Gordon Valley, Central Transantarctic Mountains, Antarctica in 2010. Samples from different portions of three specimens were prepared using standard thin section and hydrofluoric (HF) acid peel techniques, and anatomical details were studied in transmitted light. The fossil woods represent the outer part of trunks, with at least 40 growth rings that are 0.2-4.8 mm in width. Anatomical comparisons suggest that they represent a new tree taxon for the Triassic of Antarctica. Numerous small epicormic shoots can be seen crossing the wood almost horizontally and are locally branched. Each specimen also contains several occurrences of traumatic growth zones located in the early wood, in the cells produced either at the very start of the growing season or slightly later. This is the first report of epicormic shoots and traumatic growth zones in the wood of a Triassic tree from Antarctica. Their co-occurrence indicates that these trees from Gordon Valley were subjected to environmental stresses not seen in Triassic trees previously described from this region. This suggests that they had a different biology and/or were growing in a different habitat, which offers a new glimpse into the diversity of high-latitude trees in the Triassic greenhouse climate.

The first occurrence of Cynognathus crateronotus (Cynodontia: Cynognathia) in Tanzania and Zambia, with implications for the age and biostratigraphic correlation of Triassic strata in southern Pangea

ABSTRACTCynognathus crateronotus is a species of large carnivorous cynodont, first named and best known from the Triassic Burgersdorp Formation (Beaufort Group, Karoo Basin) of South Africa. Fossils of the genus have also been reported from the upper Fremouw Formation of Antarctica, the Upper Omingonde Formation of Namibia, and the Río Seco de la Quebrada Formation of Argentina. Without associated cranial material, however, distinguishing the postcrania of Cynognathus from that of the closely related cynognathian, Diademodon tetragonus, has proven difficult. Here we provide a more comprehensive diagnosis for Cynognathus crateronotus and describe two novel occurrences. First, parts of a medium-sized individual were recovered from a scrambled mass of dental and semiarticulated postcranial material from the lower Ntawere Formation of Zambia, a horizon that previously produced fossils of Diademodon and Kannemeyeria. Second, a large individual was collected from a recently discovered locality within the lower part of the Lifua Member of the Manda Beds of Tanzania. A large proportion of the postcranial skeleton, along with some craniodental remains, was found ex situ in a sandy streambed just downstream from a quarry that has produced the dicynodont Dolichuranus, an azendohsaurid archosauromorph, and the avemetatarsalian Teleocrater rhadinus. The widespread occurrence of Cynognathus across southern Pangea demonstrates its utility as a biostratigraphic marker, but recently published radiometric age estimates from Argentina suggest that either the genus persisted for over 10 million years or African strata traditionally interpreted as Middle Triassic are better understood as Late Triassic in age.Citation for this article: Wynd, B. M., B. R. Peecook, M. R. Whitney, and C. A. Sidor. 2018. The first occurrence of Cynognathus crateronotus (Cynodontia: Cynognathia) in Tanzania and Zambia, with implications for the age and biostratigraphic correlation of Triassic strata in southern Pangea; pp. 228–239 in C. A. Sidor and S. J. Nesbitt (eds.), Vertebrate and Climatic Evolution in the Triassic Rift Basins of Tanzania and Zambia. Society of Vertebrate Paleontology Memoir 17. Journal of Vertebrate Paleontology 37(6, Supplement).

New Middle Triassic tetrapods from the upper Fremouw Formation of Antarctica and their depositional setting

ABSTRACTRenewed field work in the Beardmore Glacier region of Antarctica has led to a new collection of tetrapod fossils from the upper member of the Fremouw Formation near Fremouw Peak. This locality records a sedimentary environment remarkably similar to that preserved at Gordon Valley, the only other locality known to preserve Cynognathus Assemblage Zone–equivalent taxa from Antarctica. Fossil bones are generally disarticulated and mixed with logs and reworked mudrock clasts, forming an intraformational channel-lag conglomerate. To date, very few bones of small-bodied taxa have been recovered from the upper Fremouw conglomerates, suggesting that they did not survive the reworking process. We use an apomorphy-based approach to record three previously unrecognized taxa from the upper Fremouw Formation: the dicynodont Angonisaurus, an indeterminate therocephalian therapsid, and an indeterminate crown-group archosaur. Combined with previous data, our work demonstrates that 10 distinct taxa can be recognized from the upper Fremouw, including two endemic temnospondyl species. Our recognition of Angonisaurus in the upper Fremouw Formation provides a new piece of evidence in favor of a correlation with the Cynognathus C subzone (uppermost Burgersdorp Formation) of South Africa and the Lifua Member of the Manda beds of Tanzania.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

A new capitosauroid temnospondyl from the Middle Triassic upper Fremouw Formation of Antarctica

ABSTRACTWe describe a new capitosauroid temnospondyl, Antarctosuchus polyodon, gen. et sp. nov., on the basis of a large and relatively complete skull from the upper Fremouw Formation of Antarctica. The new species is characterized by its possession of numerous, extremely small maxillary, palatine, and ectopterygoid teeth, a dental pattern that suggests specialization on small prey items, possibly invertebrates. The taxon is also characterized by a parachoanal tooth row that extends far posterior to the choana and occipital condyles set close to the midline. A combination of features, including a flat skull and low occiput together with well-developed sensory canals, suggests an aquatic lifestyle. We address the phylogenetic relationships of Antarctosuchus by adding it to a recent cladistic analysis of Capitosauria. The revised data set includes 27 taxa and 53 characters. The results of this analysis place Antarctosuchus within a clade of derived Triassic stereospondyls as the sister taxon to Paracyclotosaurus crookshanki from the Triassic Denwai Formation of India. To date, the upper Fremouw Formation has yielded two endemic temnospondyl species (viz., Kryostega collinsoni and Antarctosuchus polyodon), although indeterminate remains referred to benthosuchids and a cranial fragment assigned to Parotosuchus sp. have also been noted. In contrast to the broadly distributed therapsid taxa recognized from the Middle Triassic of Antarctica (e.g., Cynognathus, Diademodon), the temnospondyl fauna suggests more limited interchange with other coeval southern Pangean basins (e.g., Karoo, Luangwa, Ruhuhu, Waterberg).SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at http://www.tandfonline.com/UJVP.

NEW DIRECTIONS IN VERTEBRATE PALEONTOLOGICAL RESEARCH IN THE TRANSANTARCTIC MOUNTAINS, ANTARCTICA

The emphasis on record setting during the Heroic Age of Antarctic exploration meant that the scientific accomplishments of these expeditions often went overlooked (Larson, 2012). Many people know the story of the ill-fated (and second-place) return of Robert Falcon Scott from the South Pole, but few people are aware that 45 kg of Permian Glossopteris fossils were found with him and his deceased colleagues. Refusal to jettison the material suggests their recognition of its importance for understanding past life on the frozen continent. Since that time, great advances have been made in understanding the ancient life and environments of Antarctica. Here, I review some of these developments in the context of recent vertebrate paleontological research in the Transantarctic Mountains. In 1967 the first terrestrial vertebrate from the central Transantarctic Mountains, a small amphibian jaw, was discovered in Lower Triassic rocks at Graphite Peak (Barrett et al., 1968). Subsequent work has yielded three distinct Mesozoic faunas from the region. Early Triassic vertebrates have been collected at numerous localities in the lower Fremouw Formation around the Beardmore and Shackleton glaciers (Barrett et al., 1968). The Beardmore Glacier region has also produced an early Middle Triassic assemblage at two localities in the upper Fremouw Formation (Hammer et al., 1987; Sidor et al., 2007), and an Early Jurassic assemblage from the Hanson Formation on Mt. Kirkpatrick (Hammer and Hickerson, 1994). Early discoveries from the lower Fremouw Formation (Fig. 1) prompted comparisons to similar faunas from the Karoo Basin of South Africa, and the presence of taxa such as Lystrosaurus provided compelling support for the nascent theory of plate tectonics (Elliot et al., 1970). Antarctic faunas were often considered to represent taxonomic subsets of those found in the Karoo Basin, …

Angonisaurus and Shansiodon, dicynodonts (Therapsida, Anomodontia) from subzone C of the Cynognathus Assemblage Zone (Middle Triassic) of South Africa

ABSTRACT Dicynodonts are the most abundant therapsids from the Beaufort Group (Karoo Basin, South Africa), and they have been used as index fossils to define most of the Beaufort biozones. Although speciose during the Late Permian, dicynodont diversity was greatly reduced by the end-Permian mass extinction. The Cynognathus Assemblage Zone, the uppermost biozone of the Beaufort Group, is traditionally known to host only the dicynodonts Kannemeyeria simocephalus and Kombuisia frerensis. Recent biostratigraphic research in this biozone has revealed the presence of two more poorly known dicynodont genera, Angonisaurus and Shansiodon, which are biostratigraphically constrained to the uppermost Cynognathus Assemblage Zone (subzone C). Although these taxa have been reported from subzone C of the Cynognathus Assemblage Zone previously, we provide the first detailed description of the material in question and justifications for the taxonomic identifications. The presence of Angonisaurus in the Cynognathus subzone C allows a direct correlation between this assemblage and that of the Lifua Member of the Manda beds in Tanzania. A correlation with the Antarctic upper Fremouw Formation also may be possible, but is less certain. The presence of Shansiodon allows a direct correlation with the upper Ermaying Formation of China, but we reject the previously proposed global ‘Shansiodon biochron’ because Shansiodon sensu stricto only occurs in China and South Africa. Biogeographically, Angonisaurus appears to have been widespread but rare in southern Gondwana, and the unusual distribution of Shansiodon mirrors that of Diictodon feliceps in the Permian. Southern African dicynodont assemblages display increased provinciality in the Middle Triassic.

Dordrechtites arcanus sp. nov., an Anatomically Preserved Gymnospermous Reproductive Structure from the Middle Triassic of Antarctica

The genus Dordrechtites is an isolated ovulate structure previously described only from South Africa and Australia as impressions. The discovery of compressed and permineralized specimens of this taxon at the base of Mount Falla (uppermost Fremouw Formation) in the central Transantarctic Mountains extends the geographical and geological distribution of the genus and increases the known floral diversity of the Triassic of Antarctica. The first permineralized species, Dordrechtites arcanus, is described using standard acetate peel techniques and includes internal anatomy of an elongate arm that extends over the top of a central cupule containing two elongate, bilaterally symmetrical, orthotropous ovules. An arc-shaped collateral vascular bundle extends from the arm into the top of the cupule, branches, and then extends around the ovule to about halfway down to the micropylar end. The cupule is parenchymatous and includes transfusion tissue with cells that have pitted walls. The sclerotesta of the ovule is up to 200 μm thick, consisting of an outer layer with longitudinally oriented, thick-walled cells and an inner layer one cell thick of rectangular, thick-walled cells. The micropyle is flared at the attenuated tip of the pyramidal cupule. The four previously described species of Dordrechtites have uncertain affinities, and although the morphology and anatomy of this taxon is now known, the affinities within the gymnosperms are still uncertain.