Squamata: Pythonomorpha: Alethinophidia

Taxa on This Page

1. Alethinophidia
2. Aniliidae
3. Aniloidea
4. Anomochilidae
5. Cylindrophiidae
6. Dinilysia X
7. Uropeltidae

Descriptions 

Alethinophidia: 

Note: these are the primitive conditions, i.e. characteristics of the paraphyletic Aniloidea.

Links:Lab VII. Snakes a sampler); S0952836999005051d 49..58 taxonomy, feeding biology and evolution); Digimorph - Ramphotyphlops braminus (Brahminy blind snake) - head; Herpetology- Snakes; PII- S1631-0691(02)01510-X.

References: Holman 2000); Tchernov et al. 2000) [T] ATW030923

Dinilysia

Range: upK (Coniacian [C&A]) of SAm.

Phylogeny: Alethinophoidia :(Aniloidea + Macrostomata) + *.

Characters: slightly flattened skull [C&A]; palatine does not contact ectopterygoid; pterygoid with teeth; outer orbital (lateral) margin of prefrontal vertical; low medial foot process of prefrontal; supraorbital present(?); quadrate vertical; shaft of stapes not straight; inhabited seasonally (or sporadically?) arid interdune environment with wind-dominated sedimentation [C&A]; terrestrial, semi-fossorial mode of life, with active or ambush predation in loose groundcover [C&A].

Links: BBC Online - Walking with Dinosaurs - Fact Files; Mike Caldwell hunts fossil snakes in Argentina.;

References: Caldwell & Albino (2001) [C&A]; Tchernov et al. (2000) [T]

Note: shares almost no derived features with scolecophidians.

Aniloidea: Anilius > Crotalus.

Range: fr upK of NAm, Eur, SAm, India & SW Asia.

Phylogeny: Alethinophidia ::Macrostomata + * : Aniliidae + (Cylindrophiidae + Uropeltidae + Anomochilidae)). 010901.

Aniliidae:Anilius, Coniophis, Eoanilius (?).

Note: At this level, snake phylogeny is very unclear. Possibly the majority opinion is that the advanced snakes are more closely related to Boids than to *, although both groups are fairly primitive. Most aniliids use defensive display behaviors which attempt to mimic toxic or dangerous organisms. This group may also include Loxocemids. 010609.

Discussion:Aniliids today are represented only by the genus Anilius of South America. However, they are perhaps the oldest group of snakes known from reasonably distinctive fossil remains. They have a more or less continuous fossil record from the Upper Cretaceous to the present day.

The distinctive squarish vertebrae of Coniophis are known from numerous locations in the Upper Cretaceous, Paleocene and Eocene of North America. Hecht (1959); Holman (2000). Oddly, Coniophis is also known from the Cretaceous of South America -- one of several indications that a land bridge existed between the two continents at one or more times in the later Cretaceous. Holman (2000). The early Eocene was apparantly a good time for snakes in North America. However, the diversification seems to have been due to the evolution of larger, terresestrial forms. The fossorial aniliids are represented only by the familiar Coniophis. In the later Eocene, perhaps as the result of colder climates, many snake species became extinct, including Coniophis. Id.

Presumably, some relict population survived in South America, since Anilius, the False Coral Snake, is known from a number of locations in northern and Western South America today. However, with the exception of a few Miocene vertebrae (Colombophis) there does not appear to be any fossil record in the Western Hemisphere after the middle Eocene. It has been argued that Columbophis is more likely to be a uropeltid than a true aniliid. Szyndlar (1994). Given that Recent uropeltids are only found in a restricted area of South Asia, it is perhaps more likely yet that Columbophis represents some completely extinct branch derived from the the Coniophis stem.

About the same time as Coniophis was dying out in North America, Eoanilius was making its first appearance in Europe. Eoanilius is said to be a true aniliid and is a fairly common fossil snake (if any ophidian fossil can be referred to as "common") from the Eocene and Oligocene of England, France and Germany. Europe, like North America, suffered a devastating extinction of snake species during the later Eocene. However, through chance or some difference in circumstances, the aniliids appear to have hung on in Europe for at least some period of time. Szyndlar (1994). In fact, a possible aniliid, Michauxophis, has been reported from as late as the Pliocene of France. Bailon (1988).

Unfortunately, as with most areas of snake taxonomy, it is not clear that all workers are speaking about the same thing. The traditional practice was to lump the Cylindrophiidae, Aniliidae, Anomalochilidae, and Uropeltidae under a general heading: usually "Aniloidea," but also frequently "Aniliidae." There is certainly a distinct possibility that the Aniloidea, in this sense, are a clade which diverged early from the boids and their progeny. Cundall et al (1993) make a good case that any "aniloid" group would be paraphyletic. However, their cladistic analysis rests on the combination of skeletal and soft tissue traits. As they are careful to point out, their skeletal data, considered alone, would support an aniloid clade. Their soft tissue data, taken only from highly derived extant species, makes almost no sense at all if considered alone. It is only the combination of skeletal and non-skeletal characters which yields the paraphyletic aniloidea as used in these Notes. However, the combined tree is fairly robust, especially for a snake phylogeny. Furthermore, the supposition that all "aniloids" form a separate branch of the family tree requires us to accept an odd, mosaic distribution of traits.

In the last analysis, the apparant similarity of the aniloids is quite possibly due to the fact that all known members of the constituent groups are fossorial to one degree or another. The difficult business of crawling around underground creates some rather severe constraints on biological design. As touched on elsewhere, the pressures of becoming fossorial followed by regaining terrestriality, are likely to result in a radically re-engineered skull. However, the re-engineering is not possible without the initial step of fossorial existence. Thus the unique and radical kinesis of the advanced snakes sets them apart from the "aniloids," but also argues that advanced snakes descended from a fossorial stem group, presumably part of the original aniloid radiation. ATW 010108.

Note added in disproof: The Rieppel people, e.g. Tchernov et al. (2000), disagree on almost everything in Lee's trees, e.g. Scanlon & Lee (2000) -- everything except the monophyly of the aniloids. On this subject, they speak with one voice. Accordingly, I grudgingly concede error, with much whining and snarling, and have accordingly restored the Aniloidea to their presumably rightful place.

Links: Aniliidae; Animal Diversity Web: Anilius scytale: Media; Lab VII. Snakes; espacio.ya.com - Bienvenido a la página de aligatorjazz; s102110100043.pdf.

References: Bailon 1988); Cundall et al. (1993); Hecht (1959); Holman 2000); Scanlon & Lee (2000); Szyndlar (1994); Tchernov et al. (2000). ATW 010901.

Cylindrophiidae(= Cylindrophiinae): Coniophis (?), Cylindrophis.

Phylogeny: Aniloidea ::(Uropeltidae + Anomochilidae) + *.

Note: Eoanilius (upEc of Eur) has been referred to this taxon, but the assignment is strongly disputed.

Image: Cylindrophis rufus from foto-bibliotheek.

Links: Cylindrophiidae; Cylindrophis sp; Lady Di Body Art (Dutch); Cylindrophis maculatus (Best on the Web); Cylindrophis rufus (Japanese); Herpetofauna of Myanmar several images); 两栖动物分类 Chinese).

References: Cundall et al (1993); Cundall & Rossman (1993); Hecht (1959); Lee et al. (1999a) [LBC]. ATW040114.

Uropeltidae (= Uropeltinae): "shield-tail" snakes.

Phylogeny:Aniloidea :::Anomochilidae + *.

Links: Docent Webpage; Uropeltidae; espacio.ya.com - Bienvenido a la página de aligatorjazz (Spanish).

References: Cundall et al (1993); Cundall & Rossman (1993).

Image: Uropeltis from foto-bibliotheek. ATW020123.

Anomochilidae: Anomochilus.  

Phylogeny:Aniloidea :::Uropeltidae + *.

Links: Anomochilidae.

References: Cundall et al (1993); Cundall & Rossman (1993). 010107.