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digital claws off the ground



     I need to quit lurking for a moment to comment on the recent strand 
     about whether dromaeosaurs did(n't) walk with the digit II claw 
     contacting the ground.  Some discussion went into the matter of what 
     modern ground birds do, and I have some observations here that may be 
     of interest.
          As some of you may know, for several years I have been studying 
     foot skeletons and study skins of ground birds, foot skeletons of 
     dinosaurs, and footprint formation by ratites and other ground birds, 
     in the hope of getting a better idea of how much variation in 
     footprint shape one would expect to see within and across taxa of 
     bipedal dinosaurs.  (I'll be extending this project to crocodilians, 
     and literally finding myself up to my you-know-what in alligators, in 
     a couple years, to complete the phylogenetic bracket around dinosaurs) 
          Several years ago I collected footprints of both species of 
     seriema (Chunga burmeisteri and Cariama cristata), a couple of REALLY 
     COOL South American gruiform ground birds; ecologically they are sort 
     of South America's answer to the secretarybird.  I was amazed to see 
     that both species have a big, rather dromaeosaur-like claw on digit 
     II, and both species walk with this claw carried off the ground.  
     Footprints of both birds (at least the ones I collected) do not have 
     an impression of the claw, or if they do, the claw impresses only when 
     the foot sinks deeply into the substrate.
          Since then I have examined osteological specimens and study skins 
     of both species, and satisfied myself that the birds I worked with 
     were not unusual.  I showed such specimens to Greg Paul and Bob 
     Walters, and I think it blew the minds of said gentlemen.
          I have never read or heard any accounts of what seriemas might be 
     doing with those big claws on digit II.  They aren't nearly as huge, 
     relative to the size of the rest of the foot, as in Deinonychus, say, 
     but it wouldn't surprise me if they played a role in holding or 
     subduing prey.  I'd be more surprised if they weren't used in that 
     fashion.  (Parenthetically, it has been suggested that phorusrhacoids, 
     which are probable seriema relatives, may have used their inner toe 
     claws in attacking prey, but I've never seen a detailed analysis of 
     the functional morphology of their claws.  Such a project, 
     comparing/contrasting with dromaeosaurs and troodonts, might be a fun 
     study of convergent evolution.)
          In any case, seriemas provide a good example of modern birds that 
     hold their digit II claws off the ground while walking, in the manner 
     attributed to dromaeosaurs.
          In other news, I deliver the manuscript of Dinosaurs: Fearfully 
     Great Reptiles, to Indiana University Press this coming Wednesday.  
     We're desperately trying for a Fall (northern hemisphere) 1997 
     publication date.  Now we have to get good slides of some of the color 
     artwork--are you listening, Greg, Brian, et al.?  :)