Early blindsnakes

(Anomalepididae)

Class Reptilia

Order Squamata

Suborder Serpentes

Family Anomalepididae (Early blindsnakes)

Thumbnail description
Small, fossorial snakes with smooth, uniformly sized body scales; highly reduced eyes; small, ventrally placed mouth; rounded snout; and very short tail

Size
3–16 in (7–41 cm)

Number of genera, species
4 genera; 16 species

Habitat
Soil

Conservation status
Not threatened

Distribution
Southern Central America, northern South America, and east-central South America

Evolution and systematics

The family Anomalepididae was first established in 1939 by Edward H. Taylor after he discovered that snakes of the genus Anomalepis exhibit patterns of dentition and scalation that are significantly different from those seen in other blind-snakes. Soon thereafter, anatomical studies revealed that Helminthophis, Liotyphlops, and Typhlophis share many distinctive morphological features with Anomalepis, indicating that these three genera also belong in the family Anomalepididae.

Although morphological evidence strongly suggests that Anomalepididae represents a natural, or monophyletic, group, the interrelationships among the four genera of early blind-snakes and their phylogenetic affinities within Serpentes remain poorly understood. Most recent snake systematists have placed Anomalepididae together with the families Leptotyphlopidae (slender blindsnakes) and Typhlopidae (blindsnakes) in the infraorder Scolecophidia. However, the interrelationships of these three families have been controversial. In general, characters relating to cranial morphology, visceral topography, and scalation patterns suggest that, within Scolecophidia, Anomalepididae is most closely related to Typhlopidae. In contrast, characters associated with the morphology of the hyobranchial apparatus support a close relationship between Leptotyphlopidae and Typhlopidae. Adding further confusion to this issue, a small number of morphological and molecular phylogenetic analyses have concluded that Scolecophidia may be polyphyletic (i.e., that the three families of blindsnakes may not share a close common ancestry).

Unfortunately, the fossil record has offered few clues to help resolve this confusion. No fossils have been discovered yet that can be assigned unequivocally to Anomalepididae (although Suffusio predatrix, from the Paleocene of Texas, has been identified tentatively as an anomalepidid), and the few leptotyphlopid and typhlopid fossils that have been described are known only from very incomplete remains (usually isolated vertebrae). Thus, the evolutionary origin of early blindsnakes and their relationships to other blindsnakes remain enigmatic.

No subfamilies are recognized.

Physical characteristics

Early blindsnakes are among the smallest serpents in the Neotropics. Although five species (Helminthophis flavoterminatus,

Liotyphlops anops, L. beui, L. schubarti, and L. ternetzii) may occasionally reach or exceed 1 ft (31 cm) in total length, most are considerably smaller, reaching adult lengths of only 6–10 in (15–25 cm) and adult weights of less than 0.1 oz (2.8 g). In addition to being short in length, these fossorial snakes are also quite slender, having maximum body widths of only 0.04–10.2 inches (1–5 mm) and aspect ratios (total length divided by body width) ranging from 32 to as high as 86.

Like other blindsnakes (Leptotyphlopidae and Typhlopidae), early blindsnakes have small, ventrally placed mouths; highly reduced eyes that are barely (if at all) visible beneath the overlying head scales; and cylindrical bodies covered with smooth, circular, and uniformly sized scales (they lack the enlarged belly scales present in most other forms of snakes). However, anomalepidids can be distinguished from other sympatric blindsnakes by the presence of two (or rarely three) anal shields (Leptotyphlops has only one and Typhlops has three to five) and teeth on both the upper and lower jaws (Leptotyphlops lacks upper teeth and Typhlops lacks lower teeth). In addition, most anomalepidids have more than 20 rows of scales encircling the body, whereas all New World Leptotyphlops have 14 and all mainland Neotropical Typhlops have 20 or fewer. Finally, most members of the family are characterized by a distinctive color pattern in which the body is uniformly dark in color (black or dark brown), but the head and often at least parts of the tail are light in color (white, yellow, or pink). The four species of Anomalepis stand as exceptions to this generalization, however, being uniformly brown or reddish brown in coloration.

In all species of Anomalepididae the snout is bluntly rounded in shape, and in all genera except Typhlophis the scales surrounding the snout are somewhat enlarged. These enlarged scales not only reduce friction between the snake's head and the soil during burrowing, they also house numerous pressure-sensitive sensory organs. The tail is universally short (1–3.4% of the snake's total length) and may terminate in a sharp, needle-like apical spine (T. squamosus and the seven species of Liotyphlops), or end more bluntly as in other snakes (Anomalepis, Helminthophis, and T. ayarzaguenai).

Early blindsnakes are also characterized by a suite of unique internal anatomical features. The most noteworthy of these features are an elaborate, M-shaped hyoid (the skeletal element that supports the tongue, and which in other snakes is V- or Y-shaped), a relatively short tongue, and a pair of peculiar "orbital bones" that are involved in the suspension of the upper jaws. (Though traditionally called "orbital bones," it has recently been established that these bones have nothing to do with the formation of the bony orbit.) Additionally, like many other basal snakes, at least some species of Liotyphlops retain a vestigial pelvic girdle. However, no pelvic elements have been found in Anomalepis, Helminthophis, or Typhlophis.

Distribution

Anomalepididae is an exclusively Neotropical family, with an apparently discontinuous distribution in central and northern South America and southern Central America. The genus Anomalepis includes four species, which range from northern Costa Rica southward through northern Peru. Helminthophis contains three species, which are distributed from Costa Rica southward through Colombia and Venezuela. In addition, one species of this genus (H. flavoterminatus) may have been introduced onto the Indian Ocean island of Mauritius during the nineteenth century. Liotyphlops is the most speciose of the four anomalepidid genera, including three species that range from southern Costa Rica southward through Venezuela, Colombia, and Ecuador and four species that are distributed throughout southern Brazil, southeastern Paraguay, and northeastern Argentina. Finally, the genus Typhlophis includes only two species, which are distributed from central Venezuela eastward through French Guiana and southward through northeastern Brazil. T. squamosus has also been reported to be present on Trinidad, but the validity of this claim remains questionable. The altitudinal distribution of early blindsnakes is poorly known, but available data suggest that these snakes inhabit a relatively wide range of elevations, from sea level to at least 5,968 ft (1,819 m). It should be emphasized, however, that these tiny, secretive snakes inhabit areas that have relatively low human population densities. Furthermore, like other blindsnakes, anomalepidids are probably frequently transported to areas outside of their natural range through human activities (especially through the agricultural trade). Therefore, the known geographical distributions of early blindsnakes may not accurately reflect the natural or complete range of the family.

Habitat

The little information that is available about the natural history of early blindsnakes suggests that these serpents utilize a wide range of macrohabitats. They have been collected in hot, humid rainforests, dry forests, pasturelands, and even rocky, mountainous regions. However, throughout these many macrohabitats, they apparently inhabit a relatively narrow range of microhabitats. They are most commonly encountered in soil, often during the course of digging operations, or hidden beneath logs, stones, or forest debris. It is not known to what depths they may retreat beneath the ground, but one species (T. ayarzaguenai) was unearthed by an excavator from a depth of about 1.6 ft (0.5 m) in Venezuela. Although there have been no reports of arboreality for anomalepidids, it is likely that they also occasionally climb trees, as this behavior has been noted in numerous species of leptotyphlopid and typhlopid blindsnakes.

Behavior

Because early blindsnakes occur predominantly in areas with relatively low human population densities, the behavior of these small, secretive serpents is very poorly known. In captivity, L. beui behaves similarly to comparably sized typhlopids, exhibiting strong fossorial tendencies and responding to human handling by frantically writhing its body, voiding the contents of its cloaca, and jabbing the sharp terminal spine on the tip of its tail into the skin of its captor. Given their tropical distribution, it is likely that early blindsnakes are active throughout the year. However, like other blindsnakes, they are probably more active at night than during the day.

Feeding ecology and diet

Very little information is available concerning the natural diet or feeding ecology of early blindsnakes. However, both L. ternetzii and T. squamosus are known to feed on the eggs, larvae, and pupae of ants, suggesting that the trophic ecology of early blindsnakes is similar to that of other blindsnakes (Leptotyphlopidae and Typhlopidae), nearly all of which prey almost exclusively on social insects.

Reproductive biology

The reproductive biology of early blindsnakes is almost completely unknown. All species are presumed to be oviparous, but specific details about reproductive seasonality, courtship and mating behavior, oviposition, clutch size, and incubation time are lacking.

Conservation status

No early blindsnakes are listed as Endangered or Vulnerable by the IUCN. However, six of the 16 species of Anomalepididae are known only from the vicinities of their type localities, and one (A. aspinosus) has not been found since 1916. Therefore, the status of many species of early blindsnakes is unknown.

Significance to humans

None known.

Resources

Books

Greene, Harry W. Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press, 1997.

McDiarmid, Roy W., Jonathan A. Campbell, and T'Shaka A. Touré. Snake Species of the World: A Taxonomic and Geographic Reference. Vol. 1. Washington, DC: Herpetologists' League, 1999.

Pérez-Santos, Carlos, and Ana G. Moreno. Ofidios de Colombia. Museo Regionale di Scienze Naturali, Monografia 6. Turin, Italy: Museo Regionale di Scienze Naturali, 1988.

Peters, James A., and Braulio R. Orejas-Miranda. Catalogue of the Neotropical Squamata. Vol. 1, Snakes. Washington, DC: Smithsonian Institution Press, 1970.

Periodicals

Cunha, Osvaldo R. da, and Francisco P. do Nascimento. "Ofídios da Amazônia. X.—As cobras da região leste do Pará." Museu Paraense Emílio Goeldi Publicações Avulsas 31 (1978): 1–218.

Dixon, James R., and Christopher P. Kofron. "The Central and South American Anomalepid Snakes of the Genus Liotyphlops." Amphibia-Reptilia 4 (1983): 241–264.

Hahn, Donald E. "Liste der rezenten Amphibien und Reptilien: Anomalepididae, Leptotyphlopidae, Typhlopidae." Das Tierreich 101 (1980): 1–93.

Kofron, Christopher P. "The Central and South American Blindsnakes of the Genus Anomalepis." Amphibia-Reptilia 9 (1988): 7–14.

List, James C. "Comparative Osteology of the Snake Families Typhlopidae and Leptotyphlopidae." Illinois Biological Monographs 36 (1966): 1–112.

Robb, Joan, and Hobart M. Smith. "The Systematic Position of the Group of Snake Genera Allied to Anomalepis." Natural History Miscellanea 184 (1966): 1–8.

Señaris, J. Celsa. "A New Species of Typhlophis (Serpentes: Anomalepididae) from Bolívar State, Venezuela." Amphibia-Reptilia 19 (1998): 303–310.

Nathan J. Kley, PhD