Slowworm Anguis fragilis, copyright Hans Hillewaert.

Belongs within: Anguimorpha.

The Anguidae, glass lizards and allies, are a group of lizards found in Eurasia, northern Africa and the Americas that are characterised by rectangular scales, osteoderms in the ventral skin, a reduced supratemporal arch and striations on the medial face of the tooth crowns (Animal Diversity Web). Many have limbs reduced or lost whereas others retain well-developed legs.

Glass worms, slow worms and scheltopusiks
Published 27 July 2023

A case could be made that lizards are something of the poor relation among terrestrial vertebrates. They receive nowhere near the attention paid towards birds or mammals but are in fact spectacularly diverse. Close to 11,000 species of lizard are known to be alive today (including snakes, which are really just lizards with ideas above their station). This is a comparable number of species to birds, and nearly twice the diversity of mammals. So let’s make a gesture towards repairing this neglect by giving a brief consideration to the family Anguidae.

Scheltopusik Pseudopus apodus, copyright Jakob Fahr.

The anguids are about 100 species of lizard found in Eurasia, northern Africa and the Americas, with significantly more diversity in the last region. They vary in size from medium (about ten centimetres in length) to arguably gigantic. The largest, the scheltopusik Pseudopus apodus of Europe and central Asia, grows over 1.3 m in length and is also the world’s largest legless lizard (excluding snakes this time). Anguids are united as a group by the presence of imbricate (overlapping like roof tiles) scales and osteoderms both dorsally and ventrally (Gauthier 1982). In many species, the osteoderms become less imbricate on the sides of the body where a distinct fold of skin allows for mobility. In those species where lateral osteoderms remain imbricate, the fold disappears.

Shasta alligator lizard Elgaria coerulea shastensis, copyright Damon Tighe.

In recent years, the circumscription of the anguids has differed between authors. Two subfamilies are consistently included in the family. The Anguinae, including the slow worms and glass lizards, are legless lizards found across the Holarctic realm (some species retain vestigial hind legs only). The Gerrhonotinae, alligator lizards, are found in the Americas and retain functional limbs, albeit relatively short ones. Two further New World subfamilies are included by some authors but treated as distinct families by others. The Diploglossinae, galliwasps, are skink-like, often brightly coloured lizards. The Anniellinae, American legless lizards, are represented in the modern fauna by a single genus Anniella of small legless lizards found in deserts of California and Baja California. A fifth extinct subfamily, the Glyptosaurinae, is known from the Palaeocene to the Miocene of Eurasia and North America (Sullivan 1979). Glyptosaurines are distinguished by a covering of thick, tuberculate osteoderms making them look not dissimilar in appearance to a modern gila monster.

Northern legless lizard Anniella pulchra, copyright Kuoni W.

The majority of living anguids are insectivores; larger species will also eat small vertebrates. Sullivan (1979) suggested that glyptosaurines primarily fed on terrestrial gastropods during the wetter Palaeogene, transitioning to a more vertebrate-focused diet as the climate cooled in the Oligocene and snails became less abundant. Most are terrestrial though the gerrhonotine genus Abronia is arboreal. Leglessness (at least to the extent of losing the fore limbs) has evolved on at least three occasions among the anguids in the broad sense, and under varying circumstances (Wiens & Slingluff 2001). The species of Anniella are sand-swimmers, burrowing just under the surface in loose sediment. The anguines and the diploglossine genus Ophiodes, in contrast, are crawlers above ground, often ‘swimming’ through grass. The difference in habits is reflected by differences in morphology: Anniella, like snakes, has an elongate trunk but a relatively short tail, whereas anguines and Ophiodes have become stretched both along the trunk and tail. All appear similar at first glance but have taken different paths to get where they are today.

Systematics of Anguidae
    |--Diploglossus [Diploglosseae, Diploglossinae]H81
    |    |--D. bilobatusMH11
    |    |--D. occiduus (Shaw 1802)H81
    |    `--D. pleeiMH11
    |    |--Helodermoides Douglass 1903 [Glyptosaurini]SH96
    |    |    `--H. tuberculatus Douglass 1903 [incl. Glyptosaurus giganteus Gilmore 1928, G. montanus Douglass 1908]SH96
    |    `--MelanosauriniSH96
    |         |--MelanosaurusLBG12
    |         `--Peltosaurus Cope 1873SH96
    |              `--*P. granulosus Cope 1873 (see below for synonymy)SH96
    |--Ophisaurus Daudin 1803 [incl. Dopasia Gray 1853; Ophisaureae, Ophisaurinae]RB05
    |    |--O. attenuatusJP79
    |    |--O. canadensisSH96
    |    |--O. compressusDO99
    |    |--O. formosensis Kishida 1930TYM08
    |    |--O. harti [=Dopasia harti]SH96
    |    |--O. roqueprunensis Augé 1992SH96
    |    `--O. ventralisAM99
         |--Parophisaurus Sullivan 1987SH96
         |    `--*P. pawneensis (Gilmore 1928) [=Xestops pawneensis, Machaerosaurus pawneensis, Pancelosaurus pawneensis]SH96
         `--Anguis Linnaeus 1758 [Anguieae]L58
              |--A. bipes Linnaeus 1758L58
              |--A. cephallonica [incl. A. fragilis peloponnesiacus]N10
              |--A. cerastes Linnaeus 1758L58
              |--A. colchica [=A. fragilis colchica, A. fragilis colchicus]N10
              |--A. colubrina Linnaeus 1758L58
              |--A. eryx Linnaeus 1758L58
              |--A. fragilis Linnaeus 1758BB03
              |--A. graecaN10
              |--A. jaculus Linnaeus 1758L58
              |--A. laticauda Linnaeus 1758L58
              |--A. lumbricalis Linnaeus 1758L58
              |--A. maculata Linnaeus 1758L58
              |--A. meleagris Linnaeus 1758L58
              |--A. reticulata Linnaeus 1758L58
              `--A. scytale Linnaeus 1758L58
Anguidae incertae sedis:
  Odaxosaurus piger Gilmore 1928B93 [=Pancelosaurus pigerG88]
  Gerrhonotus [Gerrhonoteae]LBG12
    |--G. liocephalusMH11
    |--G. multicarinatusGWN71
    `--G. principisW06
    |--A. deppiDD61
    `--A. gramineaMH11
    |--B. gadoviDD61
    `--B. imbricataMH11
    |--C. enneagrammusMH11
    |--C. occiduusFS01
    `--C. sagraeF15
  Pseudopus Merrem 1820RB05
    |--P. apodus (Pallas 1775)RB05 [=Ophisaurus apodusB89]
    |--P. laurillardi (Lartet 1851) [=Anguis laurillardi, Ophisaurus laurillardi]RB05
    |--P. moguntinus (Boettger 1875)RB05 [=Ophisaurus moguntinusB89; incl. Propseudopus fraasi Hilgendorf 1883RB05]
    `--P. pannonicus (Kormos 1911)RB05 [=Ophisaurus pannonicusB89]
    |--E. coeruleaMH11
    |--E. kingiiMH11
    |--E. multicarinataMH11
    |--E. panamintinaMH11
    `--E. paucicarinataMH11
  Ophisauriscus quadrupesSH96

*Peltosaurus granulosus Cope 1873 [incl. P. abbotti Gilmore 1928, P. abbottii (l. c.), P. floridanus Vanzolini 1952]SH96

*Type species of generic name indicated


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[L58] Linnaeus, C. 1758. Systema Naturae per Regna Tria Naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. Laurentii Salvii: Holmiae.

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Wiens, J. J., & J. L. Slingluff. 2001. How lizards turn into snakes: a phylogenetic analysis of body-form evolution in anguid lizards. Evolution 55 (11): 2303–2318.

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