Aturias from the Tertiary of Mexico (1938)

Several representatives of the cephalopod genus Aturia from the Eocene and the Oligocene of Nuevo Leon and Tamaulipas, Mexico, described and illustrated. Also, the morphology and the phylogeny of the genus discussed, and it is concluded that for the present, at least, the recognition of subgenera is not practicable. The Tertiary cephalopod genus Aturia is world-wide in its distribution and it is known from all of the continents, including Australia. The genus has been recorded from a number of localities in North, Central, and South America, but in so far as we have been able to ascertain, no representatives of it have been described or illustrated from Mexico and only one occurrence of it there has so far been reported. Therefore, several specimens from five localities in the states of Nuevo Leon and Tamaulipas, northeastern Mexico, which were kindly sent to us for study by Miss Julia Gardner, seem to merit more than ordinary consideration. Furthermore, these specimens, though not very complete, elucidate certain morphological features of the genus, and from this point of view also they worthy of study. The completion of this investigation has been made possible through financial assistance received from Mr. Frederick O. Thompson of Des Moines, Iowa, to whom we acknowledge our indebtedness. Although stratigraphically the genus Aturia ranges from the Eocene (or uppermost Cretaceous) into the Pliocene, as noted by Olsson (1928), most of the numerous species that have been named are very similar, and it is still a question, how many really distinct species should be recognized. In 1921, von Ihering (p. 76) proposed a subgeneric name Sphenaturia for some forms from southern South America, but as both Schenck (1931) and Spath (1927) have pointed out, von Ihering apparently had an erroneous concept of Aturia aturi (Basterot), the genotype of Aturia (which was originally described from the Miocene of St. Paul de Dax in southwestern France), and the differences between the subgenotype of Sphenaturia and A. aturi do not seem to be of more than specific value. More recently Stenzel (1935) has proposed to recognize three subgenera of Aturia: Aturia s. s., Nilaturia, and Brazaturia. Aturia s. s. is stated to differ from the other subgenera particularly in that its siphonal collars large and its siphuncle is centrodorsan rather than subdorsan in position. Stenzel apparently relied largely on Foord's description of the siphuncle of A. aturi; however, illustrations of topotypes published by Edwards (1849) and particularly of a specimen from Turin published by Spath (1933) seem to indicate that the siphuncle is not centrodorsan but subdorsan as in Nilaturia and Brazaturia. Stenzel states that in Nilaturia the lateral lobes of the sutures rounded and not very deep and the dorsal lobe is deep and wide, but it should be taken into consideration that both of these primitive characters and apparently Stenzel was studying small specimens which might change somewhat as they completed their ontogenetic development.' During the past year we have preSSince these statements were written, Dr. Stenzel has kindly loaned us for study the specimens on which Nilaturia was based, and they do not seem to us to differ materially from typical representatives of Aturia. However, they represent a rather primitive species of the genus. This content downloaded from 157.55.39.191 on Tue, 11 Oct 2016 04:38:02 UTC All use subject to http://about.jstor.org/terms 150 A. K. MILLER AND W. M. FURNISH pared detailed studies of numerous representatives of Aturia from South America and Africa, as well as North America, and although we have made a conscientious effort, we have not been able to use the proposed subgenera. It seems to us that whereas the question of the generic or subgeneric division of the forms that now grouped together under the generic name Aturia is deserving of very careful consideration, it will have to be done with a great deal of caution, and certainly in order to complete the work satisfactorily much more material than has been available to us, including representatives of the subgenotypes, will have to be examined critically. Our studies have gone to show that the individuals undergo considerable change during ontogenetic development (see text fig. 1), and although we believe that we can recognize more or less of a phylogenetic series within the genus, all of the observable differences gradational and can not be used satisfactorily to differentiate sub-