Part 10

Vertebrae

The fiftieth vertebra of Conophis vittatus (UMMZ 82642) can be described as follows: The neural spine is elongate, thin and low; the posterior edge is sharply emarginate, and the anterior edge is only slightly emarginate. The zygosphene is thin dorsoventrally; in a ventral or dorsal view the zygosphene has a slightly concave anterior edge, the flat surface of which is oriented ventrolaterally. The centrum is elongate and triangular from below; it is widest at the paradiapophyses and narrowest at the short condylar neck. The condylus is directed posteriorly. The centrum, when viewed laterally, is slightly concave and has prominent subcentral ridges that extend from the median side of the paradiapophysial articular surfaces posteriorly to the neck of the condylus. The paradiapophysial articular surfaces are well developed and have two facets. The diapophysial surface is larger and more spherical than the parapophysial one. The parapophysial process projects beyond the parapophysial articular surface and is nearly even with the lip of the cotyle, which is slightly oval. The neural arch is slightly depressed; its width is somewhat less than the width of the cotyle. The articular surfaces of the postzygapophyses are oval and are directed posterolaterally. There is a strongly developed concave interzygapophysial ridge. A well-developed accessory spine extends laterally beyond the oval articular facets of the pre-zygapophysis and forms a slightly flattened, blunt spine. Excellent drawings of the middle thoracic vertebra of Conophis lineatus dunni from Honduras were published by Auffenberg (1958:6).

Hemipenes

The hemipenes of Conophis are moderately caliculate, having spines covering the surface from the base to near the apex (fig. 9). These spines are largest near the base and are reduced to small papillate projections near the apex. The apex terminates in a small disc having three to five laminae in C. vittatus and one lamina in C. lineatus concolor. The sulcus is bifurcate; the fork is near the base and almost gives the appearance of two sulci on some specimens. Distally the apices are widely separated, and the intervening space gives the hemipenis a slightly bilobed appearance in some species (especially C. vittatus) or a deeply bilobed appearance in others (especially C. lineatus concolor).

The everted hemipenis reaches posteriorly to the eighth subcaudal scale. The sulcus bifurcates at the third subcaudal scale. The situation is similar in situ (Cope, 1895:pl. 28, fig. 2).

There are no apparent hemipenial differences among the species of the genus Conophis. As can be seen in the above description, the hemipenis of C. vittatus is less bilobed and has a more pronounced disc at the apex than the others. The hemipenis of C. lineatus concolor is most bilobed, but has the smallest apical disc. The other species and subspecies vary widely within these extremes.

Food and Feeding

Conophis eats mostly small lizards, especially Cnemidophorus. In Mexico Conophis occurs in semi-arid habitat where Cnemidophorus is common. A specimen each of Conophis vittatus and C. lineatus lineatus were obtained while I was collecting Cnemidophorus. The only record of Conophis having fed on a warm-blooded vertebrate was obtained in the course of this study, when I recovered from the stomach of a Conophis lineatus concolor (CNHM 36299) from Chichen Itza, Yucatan, a heteromyid rodent (Heteromys gaumeri).

Ralph Axtell (personal communication) observed Conophis actively searching for food at dusk. His observations were made near Tehuantepec, Oaxaca, and the snakes were seen to chase lizards of the genus Cnemidophorus. Near Alvarado, Veracruz, in the late afternoon, I watched a Conophis lineatus lineatus follow a lizard into a hole.

Mittleman (1944:122) presents the only discussion of the mode of feeding of a captive specimen of Conophis lineatus ssp. When presented with a Thamnophis slightly smaller than itself, the Conophis struck, and within eight minutes immobilized the Thamnophis. Within one-half hour the Thamnophis was swallowed. Three days later the Conophis ate another Thamnophis, though still distended from its first meal; nine days later it ate a Storeria. In the course of several months, the Conophis ate various toads and hylids and two more Storeria. Apparently members of the genus Conophis do not constrict their prey, but rely upon a combination of loss of blood and action of the venom to completely immobilize their prey.

Ditmars (1931:pls. 26-27) showed three photographs of "Conophis lineatus" (actually Conophis pulcher) ingesting another snake, identified by him as a young Ophis (= Xenodon) colubrinus.

Effect of Poison

The rear fangs of these snakes are large for the size of the snake. Various collectors have been bitten, and several reports of the effect of the poison have been published. The snakes are aggressive and bite constantly while being handled. A field companion, Dale L. Hoyt, was bitten on the forefinger by a specimen of C. l. lineatus and immediately felt a burning sensation. The finger swelled, much as it would if stung by a wasp, but it returned to normal size in about twenty-four hours. Ditmars (1931:legend pl. 27) reported immediate burning pain and a localized swelling, an inch in diameter and half an inch high, which lasted for several hours. Mertens (1952b:83) reported merely that the hand of the gardener at the Instituto Tropical in San Salvador bled strongly for a full hour. Edward H. Taylor was bitten by a specimen of Conophis vittatus (Taylor and Smith, 1939:252); pain and swelling lasted for some time. Taylor (personal communication) is still troubled by damage incurred by that bite, which apparently resulted in mechanical damage to the second joint of the middle finger, for the joint swells when the finger is used or exercised. William E. Duellman (personal communication) was bitten on the hand in July, 1956. There was immediate pain and localized swelling, both of which disappeared several hours later.

TAXONOMIC RELATIONSHIPS AND EVOLUTION

The genus Conophis is known only from the Recent. Except that Conophis belongs to the subfamily xenodontinae and probably is of New World origin, little is known about the relationships of the genus. Auffenberg (1958) described a new genus and species of fossil colubrid snake from the Miocene of Montana as Dryinoides oxyrhachis and compared it with several recent genera. This specimen, of which there is a relatively complete skull and a series of vertebrae, seems most closely to resemble a specimen of Conophis lineatus dunni (UF 7657) from Honduras, with which it was compared in basic osteology. The two genera could be related, for the progenitors of Conophis possibly inhabited much of North America in the Miocene.

Another possibility is that the main stock of the xenodontines reached South America in earliest Tertiary times, and that the formation of the Panamanian and Colombian seaways that separated South America and Central America from the Late Paleocene to the middle of the Pliocene left the Conophis stock isolated in Middle America where members of the genus dispersed through semi-arid habitats.

Turning our attention now to the species within the genus, instead of the genus as a whole, Conophis vittatus is readily set apart from other members of the genus on the basis of the universal presence of seven supralabials. In basic coloration it also differs, having no stripe on the 1st scale-row, or spots on the venter, and a maximum of four broad stripes on the body. The other species appear to be more closely related; these make up the C. lineatus-group. Conophis nevermanni differs so much from the other species that it might be placed in a separate group. Nevertheless, the basic striped pattern, which is masked by the increased melanism of many specimens, indicates that nevermanni is more closely related to the lineatus-group than to vittatus. The lineatus-group, thus, consists of pulcher, nevermanni and the three subspecies of lineatus. In this group the color pattern is characterized by the high frequency of ventral spotting, darkening of part of the supralabials, dark pigmentation on the 1st scale-row, and more than four dark stripes on the body of adults. Conophis lineatus concolor, on which the dark pigmentation on the body apparently is secondarily lost, is an exception.

If differences in color pattern be used as an indication of the relationships between the species and subspecies of the genus Conophis, I would consider C. vittatus the most divergent unit. The subspecies of lineatus closely resemble one another and, as a unit, resemble pulcher from which they differ primarily in the position of the dorsalmost stripes. Conophis nevermanni is more divergent than is pulcher from the species lineatus, but probably is not so far removed from lineatus as is vittatus.

In the light of what has been pointed out immediately above with respect to resemblances of, and differences between, the species, an hypothesis to account for their formation and for their presence in the areas where they are today is the following: Concurrent with climatic fluctuations in the Late Pliocene and Pleistocene, the northernmost population differentiated into the species vittatus, and has subsequently spread north and west from the region of Tehuantepec, Mexico. During the same period nevermanni became isolated in northern Costa Rica.

The species pulcher probably differentiated from the remaining lineatus stock during the Early Pleistocene orogenic upheaval in Guatemala. The pulcher stock was isolated on the Pacific Coastal slopes of Guatemala, while lineatus moved through the subhumid corridor of northern Middle America into Mexico and southward toward Costa Rica (Stuart, 1954a). In the Late Pleistocene and Recent, pulcher moved back across the central Guatemalan highlands occupying its present range in northern Middle America. Primarily because of the formation of unsuitable habitat (wet forest) that presently separates the geographic ranges of populations of lineatus, this species differentiated into three subspecies.

SUMMARY

The genus Conophis Peters, 1860, contains four species. Three are monotypic and the fourth has three subspecies, making a total of six taxa.

The genus is characterized by maxillary teeth of equal size followed by a diastema and two enlarged grooved fangs. The scales are smooth, in 19 rows at mid-body, and 17 nearer the tail. The anal is divided, apical pits are lacking, the head shields are normal for a colubrid, and the hemipenis is bilobed having many large basal spines.

The six taxa are separated primarily on the basis of color pattern, but characters of scutellation, including numbers of dorsals, ventrals, caudals, and places of reduction of the number of dorsal scale-rows, were analyzed.

Snakes of this genus are distributed throughout semi-arid environments from southern Mexico southward into Costa Rica. They feed upon lizards, primarily of the genus Cnemidophorus; in addition they are known to eat small rodents and other snakes.

Conophis is a member of the subfamily Xenodontinae and, as presently understood, has no known living close relatives. A single specimen of Dryinoides from the Miocene of Montana has been compared with this genus. The genus Conophis is thought to have evolved in Middle America. The present distribution and differentiation probably are primarily the result of climatic fluctuations in Middle America, which produced the areas of subhumid environment where Conophis presently lives.

LITERATURE CITED

AUFFENBERG, W.