THE STRUCTURE AND GROWTH OF THE 

 PLESIOSAURIAN PROPODIAL 



ROY L. MOODIE 



Department of Anatomy, University of Illinois, Chicago 



SIX TEXT FIGURES AND ONE PLATE 



Plesiosaurian propodials^ presenting unusual characters in 

 the presence of grooves, foramina, cavities and canals have been 

 known to paleontologists for some years and they have been 

 commented on by Williston ('03), Lydekker ('89), Kaprijinoff 

 ('82), Smith Woodward ('98) and the writer ('08). 



Since few attempts have yet been made to explain the curi- 

 ous conditions found in the limb bones of plesiosaurs the writer 

 wishes to take this opportunity of offering his views as to the 

 meaning of these structures. The explanation offered below 

 was developed in connection with the study of an immature 

 skeleton of a new plesiosaur described some three years ago 

 (Williston and Moodie '13) in a preliminary way. 



That there may be no misunde^rstanding concerning the use 

 of the word immature, it will be necessary to state that the 

 plesiosaur exliibiting the conditions referred to above simply 

 had not attained its full growth, as is evidenced by the im- 

 mature conditions of the limb bones, in which the articular 



' The terms propoclium, mesopodium and metapodium (which are equivalent 

 to propodial, mesopodial and metapodial) were first used to indicate the sepa- 

 rate portions of the molluscan foot as it occurs in the gastropods and pteropods, 

 where it is divided into three distinct parts. The terms are equivalent to the 

 propterygium, mesopterygium and metapterygium of the fishes. Since in the 

 plesiosaurs there is very little structural difference between the skeletal elements 

 of the fore and hind limb, it being impossible to locate isolated bones except by 

 comparison, and since the bones of these animals are so commonly fovmd dis- 

 associated, paleontologists felt the need of some term to indicate the limb ele- 

 ments without referring to its location on the body, so the terms propodial, 

 mesopodial and metapodial were adopted. Propodial is the more common term, 

 and indicates a limb bone which is either a femur or a humerus. 



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