When the corpses of porpoises began washing up on the beaches of Scotland, and the corpses of baby dolphins off the shores of Virginia in 1997, marine scientists were baffled.  But the evidence was conclusive, and some videotaped evidence sealed the verdict: it was the work of dolphins.

Many people think of dolphins as peaceful, fish eating oceangoing geniuses with a permanent smile.  Now it appears that at the end, instead of waving goodbye and thanking us for all the fish, the dolphins may be preparing to attack.  And really, who could blame them?

Dolphins are apex predators, at the top of their food chain.  And they are also one of the most romanticized animals on the planet.  Therefore many people suspect that they have been killing porpoises and baby dolphins all along, but that we had somehow overlooked it or misinterpreted the signs.

The US Navy took the blame first, and understandably so.  The Navy's "super sonar" plan has been protested ever since it was first announced.  This super sonar ping would expose hidden submarines and underwater features - but it is also a level of magnitude louder than a regular sonar ping.  Loud enough to cause pain to any cetaceans in its path, and even to kill.  When the baby dolphins and porpoises were discovered, the Navy was an obvious culprit.

However, the damage to the corpses was found to be far too focused, rather than the generalized damage you would expect to see from a sonic assault.  Internal injuries were severe, and included broken ribs and spines, ruptured lungs, damaged livers, and massive internal bleeding.  When teeth marks on the bodies were identified as being from dolphins, they moved to the top of the suspect list.

Two new video tapes recently surfaced, showing dolphins violently attacking porpoises.  The Telegraph speculates that previous footage may have been explained away by tourists as being "the mammals at play with their young."  But these dolphins are definitely not playing.

Infanticide is nothing new in the animal world.  When a male lion takes over a new pack, he will systematically kill the cubs which are present.  They represent the genetic legacy of his competitor, and with the cubs out of the picture, the lionesses are freed up to go into heat and bear his own cubs.  

Inter-species murder (defined as killing another animal simply to kill it, not as a method of self defense or hunting for food) is also surprisingly common.  I remember watching a trio of nature documentaries which cover the three-way war which exists in Africa between lions, hyenas, and baboons.  Each group will freely kill members of the other, given half a chance.  

One gruesome theory behind the attacks on the Scottish porpoises is that it serves as, in the words of one researcher, "target practice."  The porpoises are almost exactly the same size as the young dolphins which have been killed, and both acts require the same skill set.

Nature red in tooth and claw, indeed!  Or in this case, "tooth and fluke."