Crab Haul at Wawa
Driving across Canada this summer, I was surprised to encounter this colourfully decorated U-Haul in northern Ontario. It is wonderful to see a corporation using its advertising space to talk about relatively obscure (if very impressive) invertebrates.
Perhaps U-Haul aren’t being entirely accurate when they say that horseshoe crabs “survived” evolution, but I’m sure that the company was trying not to offend the sensibilities of some of the customers who might have ended up driving around with this informative blurb on the side of their vehicle (there are also a few minor inaccuracies in the web explanation that accompanies it, but I still give U-Haul full marks for including this in their Supergraphics series).
Horseshoe crabs (or xiphosurids) did, of course, survive the dinosaurs. Doubly so, since the oldest horseshoe crabs are about twice as old as the oldest dinosaurs (the Ice Ages were just yesterday geologically speaking, so I won’t even try to make that comparison). And horseshoe crabs have evolved, but they have done so slowly. Creatures evolve as much as they need to, in response to selection pressures, and horseshoe crabs have long been superbly adapted to shoreline and nearshore environments. Modern Limulus is not immensely different from Lunataspis and other Ordovician horseshoe crabs, but it is nonetheless different. Those ancient creatures do possess some characters, such as the segmentation between their thorax and telson (tail), that place them closer to the stem-group arthropods than any of their living relatives.
If you want to read more about this subject, Dave Rudkin and I have just published a general review of the evolution of xiphosurids in this new book. I haven’t seen the volume yet, but I am really looking forward to getting a copy!