THE DINOSAUR TRACHODON ANNECTENS 



By R a. LUCAS 



The skeleton of TracJiodon, or Claosanrns, recently placed on exhi- 

 bition in the U. S. National Museum, is an unusually perfect example 

 of that group of extinct reptiles, the dinosaurs. It was included in 

 the Marsh collection and was one of two nearly complete skeletons 

 obtained by Mr. J. B. Hatcher some years ago on Lance creek, 

 Wyoming. The completeness of the specimen is due to the fact that 

 the animal was either engulfed in quicksand, and so came to his end, 

 or that by some favorable accident, such as a cloudburst or a freshet, 

 the body was otherwise covered with sand immediately after death, 

 and before decomposition had set in. Whatever may have happened, 

 the result was that the bones remained in place, the ribs being 

 attached to their respective vertebrae and the great thigh bones re- 

 maining in their sockets, the legs even having the position they would 

 take in walking. This is shown in pi. lxxii, for in mounting the 

 skeleton the ends of the thigh bones were left as found. Some ex- 

 amples of Trachodon have been obtained in which the impression of 

 the skin was preserved in the surrounding rock, and from these it is 

 known that this animal was covered with small, irregularly six-sided, 

 horny plates, somewhat like those covering portions of the bodies of 

 crocodiles. Unfortunately the wearing away of the rock in which 

 the present specimen was contained had exposed some of the bones, 

 and portions of them had been damaged and the front of the skull 

 weathered away before its discovery in the summer of 1891. The 

 rock containing the bones was then taken up in sections and shipped 

 to Yale University where a large portion of the matrix was removed 

 in order that the bones might be studied. This revealed the presence 

 of long, slender bones, or ossified tendons, that had been embedded 

 in the muscles overlying the backbone in the region of the back and 

 upper part of the tail, and still situated as they were in life. These 

 tendons are not shown in the* specimen as mounted, because in order 

 to display the vertebrae it was necessary to remove the tendons and 

 the underlying rock ; they are, however, present on the right side 

 which is buried in the background. The object of these tendons is 

 to afiford support to the muscles of the back and tail and to strengthen 



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