The genus Anolis includes approximately 300 living species, more than 35 of which occur on the island of Hispaniola (Roughgarden 1995). This systematic diversity is accompanied by ecological diversity allowing as many as six species to coexist by segregating habitat from ground to canopy. The ecological adaptations of anole species are accompanied by morphological features. Species can thus be grouped into ecomorphs (Williams 1983), taking into account both their preferred perches, a reflection of habitat selection, and their body proportions: crown giant, twig dwarf, trunk-crown, trunk, trunk-ground, and bush grass. SMU 74976 falls within the size range of smaller extant species included in the twig dwarf ecomorph. However, while the adaptive significance of anole ecomorphs is clear, the systematic significance of anoles grouped into ecomorphs requires extended phylogenetic analysis (de Queiroz et al. 1998, Poe 1998). With respect to Hispaniolan amber-preserved fossils, de Queiroz et al. (1998) defined a T-clade within the A. chlorocyanus species group based on morphological characters.

The intra- and inter-specific variability of anoles emphasizes a consistent problem in paleontology because samples are often too small to allow evaluation of individual variation. In this case, not only is the sample size small, but SMU 74976 is incomplete with only cranial characters discernible. There are two further complications. The American Museum (AMNH) and Basel (NMBA) specimens of Hispaniolan amber anoles both present postcranial characters, which SMU 74976 does not. Moreover, only SMU 74976 has been CT scanned, providing enhanced resolution of cranial osteological features compared to the other specimens. Nevertheless, this is the sample available for study and it does present a view, however incomplete, of anoles in the Caribbean 15 to 20 million years ago.

Skull measurements, characteristics of the postcranial skeleton, and external morphology allowed Rieppel (1980) to place the NMBA specimen tentatively within the green anole species group, which includes A. chlorocyanus and A. coelestinus, among others (Williams 1965, 1976). De Queiroz et al. (1998), in their study of the American Museum specimen, re-examined the NMBA specimen, recognizing what were considered minor differences between the two. Pterygoid teeth are not present in AMNH DR-SH-1, but two or three are possibly present in the NMBA specimen. Maxillary and dentary tooth counts and positions differ slightly. These differences were attributed to intraspecific variation as seen in other anoles. They concluded that both of the specimens could be tentatively assigned to the A. chlorocyanus species group within the T-clade anoles (de Queiroz et al. 1998). In addition, de Queiroz et al. (1998) considered the diagnosis of Anolis dominicanus, which has as its holotype the NMBA specimen, insufficient to distinguish it from certain extant Anolis species, yet inadequate to synonymize the name.

Direct comparisons among the three anoles in amber considered here are limited because of the condition of each specimen and the techniques used. One characteristic, absence of the splenial, is discernible through CT scanning of SMU 74976, but not observable in the others, to which the technique has not been applied. Absence of the splenial, along with long lateral interclavicular processes in contact with clavicles, define the T-clade anoles (de Queiroz et al. 1998). The pectoral girdle is not preserved in the SMU specimen.

SMU 74976 has two sublabial scales on each side and five loreal rows, as opposed to three sublabials, and three loreal rows in the AMNH specimen (de Queiroz et al. 1998). Both have at least six postmentals and lack gular folds. The AMNH specimen may have postfrontals, but they appear to be lacking in SMU 74976 (however, the relevant area is defleshed and we cannot rule out taphonomic loss). The NMBA specimen appears to lack postfrontals. It also appears to have pterygoid teeth, which are lacking in both the SMU and AMNH specimens.

Morphological characters in anoles, as demonstrated by Poe (1998), for example, are for the most part both variable and homoplastic. While Poe's (1998) phylogenetic analysis of Hispaniolan twig dwarf anoles utilizes more than morphological characters alone, he specifically addresses inherent variability of morphological characters by utilizing frequency, unscaled, and any-instance approaches to phylogenetic analysis. For two relevant skull characters of Poe (character 97, pterygoid-lacrimal contact, and 98, jugal extension) intraspecific variability is considered plesiomorphic.

In all, Poe used 116 characters. Table 1 lists the characters from Poe (1998) that could be scored for SMU 74976. Figure 6 is abstracted from Poe's figure 17 and shows the distribution of characters observed in SMU 74976 along that portion of the cladogram leading to the twig dwarf clade and which Poe specifically discusses. His analyses show monophyly of the Hispaniolan twig dwarf species A. placidus, A. insolitus, and A. sheplani, with the latter two being sister species. The Hispaniolan twig dwarf clade is diagnosed by two unique, unreversed synapomorphies of the parietal, neither of which could be scored in SMU 74976 because of damage to the back of the skull. The sister to the three Hispaniolan twig dwarf species is the Puerto Rican twig dwarf A. occultus. Two characters (103, maxilla extends to ectopterygoid, and 113, loss of splenial) are among the eight synapomorphies supporting the clade. A. darlingtoni and A. solitarius, twig species from Hispaniola and northern South America, and Phenacosaurus heterodermus from South America, are the closest relatives of twig dwarf species. This clade is supported by eleven unambiguous synapomorphies. Four of the characters defining the clade could be scored in SMU 74976. Of those four characters, one shows the derived character state, and three are primitive. Ten characters diagnose the next less inclusive clade, five of which can be scored for SMU 74976, two of those exhibiting the derived character state. The phylogenetic resolution for all the taxa in Poe's cladogram represented by "others" in our Figure 6 is weakly supported and represents deep branches. Poe's demonstration that the derived characters in his cladogram are homoplastic coupled with the mix of primitive and derived characters at relevant basal nodes reveal that SMU 74976 is not a twig dwarf species. Thus, absence of the splenial (character 113) in SMU 74976 is homoplastic with Hispaniolan twig dwarf anoles.

Given the variability seen in modern anoles, uncertainties in observation in the amber-preserved specimens, and differential preservation preventing comparison, we find ourselves in a similar situation to de Queiroz et al. (1998), in that we cannot satisfactorily demonstrate that the three specimens are not members of the same species, nor demonstrate apomorphic characters shared exclusively by all three. They may very well belong to the same species, or their variation may indicate specific diversity; it cannot be determined with certainty at this time. Nevertheless, some speculation is permitted based on characters we can observe and the composition of the modern Hispaniolan fauna. While we can rule out the loss of the splenial in SMU 74976 as an unambiguous synapomorphy with twig dwarf anoles, we cannot rule it out as a synapomorphy with T-clade anoles. If that proves valid, SMU 74976 is more likely to share a close relationship with the AMNH specimen, which exhibits the characteristic T-clade interclavicle morphology. Far less certain, but certainly plausible based on possible identity with the AMNH and NMBA specimens, is inclusion within the A. chlorocyanus species group, as indicated by characters of the caudal vertebrae in the AMNH and NMBA specimens. Morphometric analysis by de Queiroz et al. (1998) includes the AMNH and NMBA specimens within the trunk-crown anole ecomorph. A. chlorocyanus species group anoles are trunk-crown anoles, which inhabit Hispaniola and other Caribbean islands today.