The Scolecophidia, commonly known as blind snakes or thread snakes, are an infraorder of

snakes Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...

. They range in length from . All are

fossorial A fossorial () animal is one adapted to digging which lives primarily, but not solely, underground. Some examples are badgers, naked mole-rats, clams, meerkats, and mole salamanders, as well as many beetles, wasps, and bees. Prehistoric evid ...

(adapted for burrowing). Five families and 39 genera are recognized. The Scolecophidia infraorder is most likely

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

Taxonomy

The infraorder name Scolecophidia derives from the two

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...

words or σκώληκος (, genitive ), meaning "earthworm", and (), meaning "snake". It refers to their shape and fossorial lifestyle.

Families

Evolution

Despite only having fossils as early as the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

, Scolecophidia itself likely originated in the

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively ...

, with Anomalepididae, Leptotyphlopidae, and

Typhlopoidea The Scolecophidia, commonly known as blind snakes or thread snakes, are an infraorder of snakes. They range in length from . All are fossorial (adapted for burrowing). Five families and 39 genera are recognized. The Scolecophidia infraorder is mos ...

diverging from one another during the

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

. Within Typhlopoidea, Gerrhopilidae likely diverged from the Xenotyphlopidae-Typhlopidae

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

during the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145& ...

, and

Xenotyphlopidae ''Xenotyphlops'' is a genus of snakes, the only genus of the family Xenotyphlopidae, comprising two species found only in Madagascar. These snakes are also known as the Malagasy blind snake. Physical characteristics The family Xenotyphlopidae ...

and Typhlopidae likely diverged from one another during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

. Scolecophidians are believed to have originated on

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...

, with anomalepidids and leptotyphlopids evolving in west Gondwana (South America and Africa) and typhlopids, gerrhopilids, and xenotyphlopids on east Gondwana, initially on the combined India/Madagascar land mass, during the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

. Typhlopids then dispersed to Africa and Eurasia. South American typhlopids appear to have evolved from African typhlopids that rafted across the Atlantic about 60 million years ago; they, in turn, dispersed to the Caribbean about 33 million years ago. Similarly, typhlopids appear to have reached Australia from Southeast Asia or Indonesia about 28 million years ago.

Fossil record

The extinct fossil species '' Boipeba tayasuensis'' from the

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

was described in 2020, marking the earliest fossil record of Scolecophidia. It was a

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

and was over 1 meter in length, making it much larger than most modern blindsnakes, with only '' Afrotyphlops schlegelii'' and '' Afrotyphlops mucruso'' rivaling it in size. Prior to this, the earliest scolecophidian fossils were only known from the

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pala ...

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to A ...

and the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

. Possible Typhopid skin has been identified in Dominican amber.

Phylogeny

This phylogeny combines the ones recovered by Vidal ''et al.'' in 2010 and Fachini ''et al.'' in 2020.

Description

The common name of Scolecophidia, blind snakes, is based on their shared characteristic of reduced eyes that are located under their head scales. These head scales are found in all snakes and are referred to as spectacles, but within this infraorder, they are opaque, resulting in decreased visual capabilities. Reduced eyes of the Scolecophidia have been attributed to evolutionary origins of snakes, which are hypothesized to have arisen from fossorial ancestors, causing a loss of genes related to eyesight that later evolved again in higher snakes to be similar to other vertebrates due to convergent evolution. Newer research shows that seven of the 12 genes associated with bright-light vision in most snakes and lizards are not present in this infraorder, and the common ancestor of all snakes had better eyesight.Burrowing snakes have far worse eyesight than their ancestors
/ref> Other shared characteristics include an absent left oviduct in four of the five families, aside from the Anomalepididae, which have a well developed yet reduced left oviduct. Aside from this, these snakes range in length from 10 to 100 cm (3.9 to 39.4 in). Their typical body shapes include slender, cylindrical bodies and small, narrow heads. All these families either lack or have a vestigial left lung and lack cranial infrared receptors.

Behavior

The main shared characteristic found across all Scolecophidia is a fossorial nature, either living underground or within logs and leaf litter. Aside from this, thus far the reproduction remains understudied with all Scolecophidia studied thus far being noted to be oviparous, with elongate eggs noted in both leptotyphlopids and typhlopids. Foraging behaviors vary across families, but all feed on invertebrates. Some of their main food sources include ant or termite eggs, which are tracked down by following chemical cues left by these invertebrates to create trails. ''Tricheilostomata macrolepis'' has been seen climbing up trees and waving its head side to side vertically to detect chemical cues in the air to locate insect nests. In a study on the Leptotyphlopidae, some species were found to specialize in eating only termites or ants; some rely on binge feeding patterns, while others do not. While these snakes are often difficult to locate due to their burrowing habits, they are more often seen above ground after rain due to flooding that occurs in burrows. The ancestral nature of the Scolecophidia has resulted in the use of these organisms as models for evolutionary studies in Serpentes to better understand evolution of reproduction, morphology, and feeding habits.

References

{{Taxonbar, from=Q201636 Taxa named by Edward Drinker Cope Extant Coniacian first appearances