Charting the Course of Pinniped Evolution: insights from molecular phylogeny and fossil record integration

Pinnipeds (seals, sea lions, walruses, and their fossil relatives) are one of the most successful mammalian clades to live in the oceans. Despite a well-resolved molecular phylogeny and a global fossil record, a complete understanding of their macroevolutionary dynamics remains hampered by a lack of formal analyses that combine these two rich sources of information. We used a meta-analytic approach to infer the most densely sampled pinniped phylogeny to-date (36 recent and 93 fossil taxa) and used phylogenetic paleobiological methods to study their diversification dynamics and biogeographic history. Pinnipeds mostly diversified at constant rates. Walruses however experienced rapid turnover in which extinction rates ultimately exceeded speciation rates from 12-6 Ma, possibly due to changing sea-levels and/or competition with otariids (eared seals). Historical biogeographic analyses including fossil data allowed us to confidently identify the North Pacific and the North Atlantic (plus or minus Paratethys) as the ancestral ranges of Otarioidea (eared seals + walrus) and crown phocids (earless seals), respectively. Yet, despite the novel addition of stem pan-pinniped taxa, the region of origin for Pan-Pinnipedia remained ambiguous. These results suggest further avenues of study in pinnipeds and provide a framework for investigating other groups with substantial extinct and extant diversity.

Spring ligament of the ankle: normal MR anatomy

The plantar calcaneonavicular or spring ligament is visualized inconsistently and incompletely on routine MR images of the foot. This ligament is a vital stabilizer of the longitudinal arch of the foot, providing support for the head of the talus, which rests on the ligament's central portion. Laxity or rupture of the spring ligament permits plantar flexion of the talus. This motion results in valgus alignment of the calcaneus and a flatfoot deformity (pes planovalgus). Laxity or rupture of the spring ligament can develop in cases of chronic dysfunction of the posterior tibial tendon. In rupture of the posterior tibial tendon, surgical management may include plication of the spring ligament in addition to repair or reconstruction of the tendon to stabilize the medial column of the foot. Thus, the status of the spring ligament can be a significant consideration in preoperative planning. This pictorial essay illustrates the normal MR anatomy of the spring ligament, the planes of imaging required for optimal depiction of the ligament, and the neighboring structures with which the ligament can be confused.

The effects of ascorbic acid on the induction of urothelial lesions in mice by 2-acetylaminofluorene

288 BALB/c male mice were allocated to: Group 1-control; Group 2-500 ppm of 2-acetylaminofluorene (2-AAF) in the food, with control water; Group 4-500 ppm of 2-AAF in the food and 250 mg/100 ml of vitamin C in the water; and Group 3-control food and 250 mg% of vitamin C in the water. Major histopathologic changes at the end of 28 days included both inflammation of the lamina propria and hyperplasia of the transitional epithelium of the urinary bladder in mice receiving 2-AAF. The most severe lesions were seen in the mice administered the combination of 2-AAF and vitamin C. It was postulated that either decreased water consumption and concentration of the urine and/or reduction in urinary pH may have contributed to the severity of the lesions.