Tupinambis quadrilineatus differs (see Table 2 for scale counts and measurements) from the other species of the genus in the presence of 11–18 femoral pores (15–18 in Tupinambis teguixin, 20–22 in Tupinambis longilineus, 18–26 in Tupinambis palustris), 94–118 scales around the mid-body (94–124 in Tupinambis teguixin, 90–98 in Tupinambis longilineus, 112–119 in Tupinambis palustris), 113–138 dorsal scales (102–126 in Tupinambis teguixin, 110–121 in Tupinambis longilineus, 111–122 in Tupinambis palustris) and the coloration. In Tupinambis quadrilineatus, the upper lateral stripe is well-defined along the flanks, whereas in other species, it is indistinct or absent (Avila-Pires 1995, Colli et al. 1998, Manzani and Abe 2002, Harvey et al. 2012).

The hemipenis of three specimens of Tupinambis quadrilineatus (CHNUFPI 0036, CHNUFPI 0038 and MPEG 30139) were prepared for analysis. The organ is relatively long, robust and slightly bilobed, with a total length of 5.0 cm and a width of 2.0 cm in the distal portion of the body (Figure 1). When inverted, the organ extends as far as the fifteenth subcaudal scale. Sulcus spermaticus bifurcated, deep and centripetal. Edge of the sulcus spermaticus pronounced along its entire length. The point of bifurcation of the lobes extends inwardly towards the central region of the styloid process. A pair of short and prominent lobes (about 16% of the total size of the organ) in the form of styloid process are present on either side of the sulcate and asulcate surface, with a pair of catchment folds (extensions of the lips of the sulcus, in the form of prominent sulcal flaps, with rounded edges) coating the styloid process. The region between the lobes is smooth on both the sulcate and asulcate surfaces. Naked sulcate and asulcate expansion pleat. Between 35 and 38 distal laminae (mean = 36 ± 1, n = 3), arranged in a transverse row on each side, extending from just below the apical folds to the base of the lobes. A lateral sulcus separates the distal laminae from the sulcate and asulcate surfaces. Fifteen to 17 proximal laminae (mean = 16 ±1, n = 3). Basal region smooth on the sulcate surface, and wrinkled on the asulcate surface. Discontinuous laminae and basal papillae absent.

The hemipenial morphology of Tupinambis quadrilineatus is similar to that of other Tupinambinae in the ornamentation of the body, which are bilobed and have lamelae (Cope 1896, Dowling and Duellman 1978, Harvey et al. 2012). As in Salvator merianae, Tupinambis teguixin and Crocodilurus amazonicus (Dowling and Duellman 1978, Harvey et al. 2012), the hemipenis of Tupinambis quadrilineatus lacks the discontinuous distal laminae seen in Ameiva ameiva and Ameivula ocellifera. However, Salvator merianae, formerly considered to be a member of the genus Tupinambis, has a relatively long hemipenis, which lacks the lateral and medial expansion pleats and has more laminae (distal laminae: 56–71 and proximal laminae: 33–40) than other teiids (Harvey et al. 2012). See Table 1 for the differences in the hemipenial morphology of three subfamilies of Teiidae (Harvey et al. 2012). The morphology and ornamentation of the hemipenis play an important role in the diagnosis of species, and have proven to be an excellent indicator of the phylogenetic relationships among taxa (Cope 1896, Böhme 1988, Harvey et al. 2012). Harvey et al. (2012) concluded that the relationships among the genera of Tupinambinae, especially Tupinambis and Salvator, require further study, and that a more detailed analysis of hemipenial morphology, as well as muscles and osteology, may contribute to a more definitive understanding of the systematics of the group.

Based on eight specimens. Snout-vent length 135–260 mm (mean = 234.9 mm); body width 48.4–60.0 mm (mean = 54.0 mm), body height 30.5–44.6 mm (mean = 38.5 mm), head length 51.3–55.9 mm (mean = 53.6 mm), head width 33.9–45.0 mm (mean = 39.7 mm), head height 28.3–36.2 mm (mean = 31.2 mm). See Table 1 for a complete list of the measurements and scale counts recorded in the present study and those available in the literature (Manzani and Abe 1997, Colli et al. 1998, Silveira 2009).

The Tupinambis specimens available in Brazilian collections were examined together with the eight Tupinambis quadrilineatus specimens collected during the present study, in Maranhão and Piauí (Figure 2). The localities reported here represent the northernmost known records of Tupinambis quadrilineatus, and extend the known distribution of the species at least 500 km from the nearest locality, in Balsas, Maranhão (Barreto et al. 2007). This is the northernmost record of the occurrence of the species.

Five Tupinambis quadrilineatus specimens were examined in the collection of the Goeldi Museum. In 1993, specimen MPEG 16817 was collected in Balsas, Maranhão (reported by Barreto et al. 2007), and specimen MPEG 16845 was captured in the municipality of Lagoa Alegre, Piauí. In 2009, three specimens were collected during the Parnaiba Project in Ribeiro Gonçalves (MPEG 30139), and Uruçuí (MPEG 30141), in the state of Piauí, and São Raimundo das Mangabeiras (MPEG 30140), in Maranhão.

The herpetological collection of the Universidade Federal do Piauí provided specimens or records of Tupinambis quadrilineatus from a number of sites in Piauí. Specimen CHNUFPI 0036 (Figure 3A) was collected in 2010 in the Palmares National Forest (05°02'55"S, 42°35'59"W, SAD69), in the municipality of Altos. The vegetation of this area is semi-deciduous tropical forest typical of the Cerrado, an ecotonal region between Cerrado and Amazonia biomes, similar to that found in Lagoa Alegre. Tupinambis quadrilineatus occurs in syntopy with Salvator merianae in this area, as recorded at a number of other sites (Colli et al. 1998, Silveira 2009). Also in 2010, a roadkilled specimen of Tupinambis quadrilineatus (CHNUFPI 0037) was collected in the municipality of Monsenhor Gil (05°39'56"S, 42°35'28"W, SAD69). In May 2011, the third and final Tupinambis quadrilineatus specimen held in the collection (CHNUFPI 0038; Figure 3B–D) was collected in a pitfall trap installed in the vicinity of a small stream within an area dominated by Cerrado savanna (sensu strictu) in the municipality of Guadalupe (05°2'55"S, 42°35'59"W, SAD69). Two other specimens were observed in the municipality of Amarante (06°14'43"S, 42°46'46"W and 06°2'1"S, 43°3'40"W, SAD69) in 2009 and 2011, but specimens were not collected. In this area, the vegetation was dominated by secondary semi-deciduous tropical forest, mixed with patches of Cerrado sensu strictu.

These findings expand the geographic distribution of Tupinambis quadrilineatus is northwards, and encompass the the region between the states of Piauí and Maranhão, which is dominated by Cerrado sensu strictu and/or forested patches of the Cerrado–Amazon ecotone. In this region, Tupinambis quadrilineatus also occurs in syntopy with Salvator merianae, which was previously classified as a member of the genus Tupinambis.