When dead and dying baby harbor seals (Phoca vitulina) began washing up on the beaches of New England (USA) from September to December 2011, it was deemed a tragedy and researchers tried to understand what had killed those 162 seals.
The seals that were still alive when they were first spotted, were suffering from severe pneumonia. Fatal pneumonia as a result of infection with an Influenza virus has been observed previously in seal populations, including outbreaks of Influenza A(H7N7) in 1979 to 1980, Influenza A(H4N5) in 1983, and Influenza A(H4N5) and Influenza A(H3N3) in 1991 to 1992. Such outbreaks are significant not just because of the detriment they pose to animal health but because influenza in mammals can act as a source for human pandemics.
Analysis revealed the presence of Influenza A(H3N8) virus, similar to a virus (A/blue-winged teal/Ohio/926/2002), circulating in North American waterfowl since at least 2002, but with 37 mutations that indicate recent adaption to mammalian hosts. One of these mutations was previously reported in the lethal Influenza A(H5N1) virus.
We know that a separate group Influenza A(H3N8) virus recently adapted itself to horses (see equine Influenza) and then dogs (see canine Influenza). Now, another version has appeared on the scene. What would happen if a dog that is infected with canine Influenza would infect a seal that is already infected with seal Influenza? The seal could become a mixing vessel and a novel potentially lethal virus could emerge.
 Anthony et al: Emergence of fatal avian influenza in New England harbor seals in mBio - 2012. pdf here.