Pace Angulation Research Articles

Enigmatic Fossil Footprints from the Sundance Formation (Upper Jurassic) of Bighorn Canyon National Recreation Area, Wyoming

The Sundance Formation (Middle-Upper Jurassic) of Wyoming is well known for pterosaur footprints. Two new partial trackways from the upper Sundance Formation of the Bighorn Canyon National Recreation Area (BICA) of north-central Wyoming are enigmatic. The trackways are preserved in rippled, flaser bedded, glauconitic sand and mud. The deposits were laid down in tidal flats, behind barrier islands, along the mesotidal Sundance Sea. The best-preserved print of the primary trackway possesses four impressions: three shorter digits with negative rotation and an elongate, caudally-oriented mark. The primary trackway has low pace angulation. The combination of morphology and pace angulation matches neither tracks nor body fossils of horseshoe crabs, theropod dinosaurs, pterosaurs, crocodylomorphs, “lacertoids,” or mammaliforms. The secondary trackway, possibly consisting of undertracks, similarly possesses elongate caudal impressions but differs from the former by possessing four subparallel, cranially-oriented digits. These prints also do not closely resemble any of the aforementioned taxa. While the secondary trackway does not lend itself to conclusion, the primary track maker could have been either an injured, pathologic pterosaur or a pterosaurian taxon otherwise unknown from the ichnological record.

China: Panzhihua/Pangang — nanoparticulate TiO 2

Trackways of archosaurs have recently been discovered in sandstones of the Upper Triassic (Norian–Rhaetian) Baoding Formation of Panzhihua City in southern Sichuan Province, China. Based on their overall-morphology, pes imprints are of characteristic chirotheriid shape showing a compact and symmetrical anterior group of digit traces II–IV with the trace of digit III being the longest, and a posterolaterally positioned, long and slender trace of digit V. Imprints of digit I and the manus are not preserved. This could be related to substrate conditions and the relatively shallow impressions, even if peculiarities in the gait such as overstep of the manus by the pes or bipedal movement cannot completely be excluded. Ichnotaxonomically, the imprints are assigned tentatively to cf. Chirotherium. There are some similarities with the type ichnospecies C. barthii from the Middle Triassic that has a global distribution and that was described also from the Guanling Formation (Middle Triassic) of adjacent Guizhou Province. However, the long and slender digit V that lacks a distinct large oval basal pad, the relatively short stride/step length, the low pace angulation, and the slight inward rotation of the imprints toward the midline are different. The peculiar shape of digit V and the lack of digit I in all imprints also preclude an assignment to the common Late Triassic ichnogenus Brachychirotherium or similar ichnotaxa such as Pseudotetrasauropus. An isolated tridactyl footprint on the same surface is different in shape from the chirotheriid ones by the stronger mesaxony and narrower digit divarication. It is considered here as a possible large grallatorid. This is the first occurrence of tetrapod footprints in the Baoding Formation of Sichuan Province and the second record of chirotheriids in the Triassic of China. The Baoding Formation has also yielded a characteristic Upper Triassic flora with cycads, filicopsids, gingkos, and conifers as well as bivalve fossils. The depositional environment can be designated as fluvial-lacustrine with occasional opening to marine areas. Considering biostratigraphic and palaeobiogeographic aspects, the late occurrence of chirotheriids cf. Chirotherium in China supports the view that basal crown-group archosaurs with a distinct tendency toward a functionally tridactyl pes developed and dispersed in parallel to typical tridactyl dinosaurs.

Reclassification of vertebrate trackways from the Permian of Scotland and related forms from Arizona and Germany

The large number of ichnospecies in Permian vertebrate ichnology literature is often a result of a failure to recognize substrate or gait-controlled variations in trackway morphology. Additionally, regional studies were often performed in isolation from studies in other areas. Nomenclatural priority applies to the names first assigned to trackways from the Corncockle and Locharbriggs Sandstone Formations (Permian) of Dumfries and Galloway, Scotland. Only one ichnogenus, Chelichnus, and four ichnospecies are recognized here and all had been identified in the studies of Jardine in 1850 and 1853. Chelichnus represents tetrapod trackways with rounded manus and pes impressions, subequal in size with up to 5 short digits where preservation is complete. The normal trackway pattern shows a pes pace angulation of up to 90° with the manus and pes being impressed close together or possibly with a slight overlap of the manus by the pes. Chelichnus bucklandi shows a pes size of 10 to 25 mm, C. duncani shows a pes size of 25 to 75 mm, C. gigas shows a pes size of 75 to 125 mm, and C. titan displays a pes size exceeding 125 mm in length. This restriction to four ichnospecies is more in accord with the low faunal diversity to be expected from an eolian environment of Late Permian age than was the former taxonomic classification. The Permian ichnofaunas of the Coconino Sandstone of Arizona and the Cornberger Sandstein of Germany are also composed largely of these four ichnospecies.

A new Middle Pennsylvanian (Westphalian) amphibian trackway from the Cross Mountain Formation, East Tennessee Cumberlands

An amphibian trackway collected in minespoil from the Cross Mountain Formation in the Cumberland Mountains of East Tennessee represents the first known Middle Pennsylvanian (Westphalian) amphibian trackway from the southeastern United States. The tracks are impressed onto the upper surface of a bed of fine-grained, cross-laminated sandstone and siltstone, deposited in an upper delta plain environment.The trackway was made by an amphibian with a long glenoacetabular distance and low pace-angulation. The imprints show five digits on the pes and four on the manus. Average measurements for the trackway are: stride, 8.4 cm; pace angulation, 76.1° (manus), 63.1° (pes); track width, 5.5 cm (manus), 6.7 cm (pes); glenoacetabular distance, 16.7 cm. The manus impression averages 2.8 cm long by 3.1 cm wide, and the pes averages 3.8 cm long by 3.1 cm wide. A tail drag is conspicuous along the entire length of the trackway and has a minimum radius of curvature of 9 mm.The trackway is assigned toMatthewichnus caudifern. ichnosp. on the basis of similarities to published material. The trackmaker was probably a temnospondyl labyrinthodont, considering the size of the animal (thus excluding lepospondyls) and the fact that it had a four-digit manus (thus excluding reptiles and anthracosaurian labyrinthodonts).