Brigham Young University Science Bulletin, Biological Series


The anterior osteological elements of the skull, lower jaw, and wrist along with the anterior myological characters discussed and figured in this report suggest that A. u. parva and C. t. septentrionalis are members of distinct groups which can be differentiated by internal morphologic characters. Although comparisons were restricted to highly geographically separated individuals of the same family, their general body form and structure appear to be similar.

A great number of anatomical structures are shared in common, but the significant differences between them include:

1. General skull appearance. The skull of C. is generally lighter, that is the bones are thinner, than in A. and with a larger portion relatively glabrous on the dorsal surface with little indication of integumentary scutellation. The most notable differences are found in the occipital region of A. where much fusion of elements and exact suturing is difficult to distinguish. In C., the occipital elements are easily distinguished.

2. Skull elements. Those elements of greatest difference and significance are noted in the sections titled descriptions and discussion. The elements include the ectopterygoid, exoccipital, frontal, jugal, os palpebrae, postorbital-postfrontal, premaxilla, and the quadrate.

3. Lower jaw elements. Those elements of greatest difference and significance are noted in the sections titled descriptions and discussion. The elements include the angular, articular, and dentary.

4. Foramina of the skull and lower jaw. The foramina of significant difference between the two genera are noted in the sections titled description and discussion. These include the infratemporal fenestra, mental foramina, nasal foramina, palatine canals, splenial foramina, surangular foramina, and the supralabial foramina.

5. The teeth of the maxilla, dentary, and pterygoid. The teeth are mostly peglike with the first accessory cusp of the dentary appearing on tooth 5 in C. and tooth 6 in A. There are eight peglike teeth on the premaxilla of C. and ten on the premaxilla of A. The greater number is a probable indicator of greater antiquity. In the maxilla a posterior accessory cusp is found on the second tooth of A. and the sixteenth of C. Perhaps the most significant point is that five peglike teeth occur on the pterygoid of C. and none were found on A.

6. The intermedium wrist element. An intermedium was found to be present in the manus of C. communis, C. gularis, C. burti, C. sexlineatus, A. u. parva, A. u. hartwegi, and A. u. sinistra. It is either absent or questionably present in C. t. tigris, C. t. septentrionalis, C. t. gracilis, C. t. canus, C. t. aethiops, C. gularis, C. exsanguis, C. d. deppei, C. d. lineatissisimus, C. h. hyperythrus, C. o. lemniscatus, and A. auberi. It is evident from the above distribution that the presence or absence of the intermedium may not be of paleotelic significance at the generic level, but may be at the specific level. It may also be intraspecifically variable.

7. The musculature. The greatest myological variation appears to be centered around the anterior segment of the ventral musculature. The mylohyoideus complex interdigitates frequently with the geniohyoideus in A. u. parva. Nine separate bundles were found in the species studied. Camp (1923) stated that above the family level in suarians, eight or more bundles was a valid indicator of primitiveness. The other muscles of generic variation include the m. cervicomandibularis, m. constructor colli, m. mandibulohyoideus II, m. omphyoideus, m. styloglossus and the associated basal tongue sheath.

The anatomical differences existing in the sheath associated with the tongue of A. u. parva is of special significance. A basal sheath is connected to the tongue sheath and extends for attachment to cranial and mandibular bones. This establishes a real anatomical basis for the tongue sheath character now used by some to separate these genera. Further exploration of species in these genera should be made to determine the stability of the character. This is particularly true in view of the comments made by Burt (1931b) concerning this structure, which, based on his findings, may be an inadequate character to separate these genera.

It is evident from the findings that specialization has occurred not only intergenerically but intragenerically, and care must be taken to distinguish the two levels of variation. Clearly the presence or absence of the intermedium is of little significance intergenerically, but may be of importance intragenerically. The presence or absence of the pterygoid teeth may also fit this category, but with our present understanding of its paleotelic significance within this family it is impractical to draw a conclusion. Barbour and Noble (1915) and Burt (1931b) concluded from their study of external morphology that Ameiva is a more primitive genus than Cnemid phonis. Our observations of osteological and myological structures which are seemingly of paleotelic significance also support this conclusion.