Osteology of the Late Triassic Bipedal Archosaur Poposaurus gracilis (Archosauria: Pseudosuchia) from Western North America.

Poposaurus gracilis is a bipedal pseudosuchian archosaur that has been poorly understood since the discovery of the holotype fragmentary partial postcranial skeleton in 1915. Poposaurus. gracilis is a member of Poposauroidea, an unusually morphologically divergent clade of pseudosuchians containing taxa that are bipedal, quadrupedal, toothed, edentulous, and some individuals with elongated thoracic neural spines (i.e., sails). In 2003, a well preserved, fully articulated, and nearly complete postcranial skeleton of P. gracilis was discovered with some fragmentary cranial elements from the Upper Triassic Chinle Formation of Grand Staircase-Escalante National Monument of southern Utah, USA. The aim of this work is to describe the osteology of this specimen in detail and compare P. gracilis to other closely related pseudosuchian archosaurs. The open neurocentral sutures throughout the majority of the vertebral column, the small size of this individual, and the presence of seven evenly spaced cyclic growth marks in the histologically sectioned femur indicate that this specimen was a skeletally immature juvenile, or subadult when it died. The pes of P. gracilis contains multiple skeletal adaptations and osteological correlates for soft tissue structures that support a hypothesis of digitigrady for this taxon. When coupled with the numerous postcranial characters associated with cursoriality, and the many anatomical traits convergent with theropod dinosaurs, this animal likely occupied a similar ecological niche with contemporaneous theropods during the Late Triassic Period. Anat Rec, 303:874-917, 2020. © 2019 American Association for Anatomy.

Adult-onset lower extremity weakness caused by venous malformation detected by magnetic resonance imaging.

INTRODUCTION: Symptomatic venous malformation (VM) of muscle in adults is rare and usually presents in childhood or adolescence as the individual is growing. We describe an atypical presentation of a malformation affecting the gastrocnemius muscle asymmetrically with onset in adulthood, which created a diagnostic challenge. Electromyography (EMG) and muscle biopsy did not fit clinically and MRI of the gastrocnemius led to the diagnosis. METHODS: The setting for the patient studied was a neuromuscular outpatient clinic. RESULTS: EMG showed decreased insertional activity and motor unit potential recruitment in the right gastrocnemius muscle. Muscle biopsy showed mild neurogenic changes. MRI demonstrated VM in the contralateral gastrocnemius muscle. CONCLUSIONS: This case represents a rare cause of atrophic weakness in adults, but muscle MRI should be considered when other tests are equivocal.

Unidirectional airflow in the lungs of alligators.

The lungs of birds move air in only one direction during both inspiration and expiration through most of the tubular gas-exchanging bronchi (parabronchi), whereas in the lungs of mammals and presumably other vertebrates, air moves tidally into and out of terminal gas-exchange structures, which are cul-de-sacs. Unidirectional flow purportedly depends on bellowslike ventilation by air sacs and may have evolved to meet the high aerobic demands of sustained flight. Here, we show that air flows unidirectionally through parabronchi in the lungs of the American alligator, an amphibious ectotherm without air sacs, which suggests that this pattern dates back to the basal archosaurs of the Triassic and may have been present in their nondinosaur descendants (phytosaurs, aetosaurs, rauisuchians, crocodylomorphs, and pterosaurs) as well as in dinosaurs.