Dibamids
Temporal range:
Mexican blind lizard (Anelytropsis papillosus)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Family: Dibamidae
Boulenger, 1884
Genera

Anelytropsis
Dibamus
†Hoeckosaurus

Synonyms

Anelytropidae Cope, 1885

Dibamidae or blind skinks is a family of lizards characterized by their elongated cylindrical body and an apparent lack of limbs.[1] Female dibamids are entirely limbless and the males retain small flap-like hind limbs, which they use to grip their partner during mating.[1][2] They have a rigidly fused skull, lack pterygoid teeth and external ears. Their eyes are greatly reduced, and covered with a scale.[2]

They are small insectivorous lizards, with long, slender bodies, adapted for burrowing into the soil.[3] They usually lay one egg with a hard, calcified shell, rather than the leathery shells typical of many other reptile groups.[2][4]

The family Dibamidae has two genera, Dibamus with 23 species native to Southeast Asia, Indonesia, the Philippines, and western New Guinea and the monotypic Anelytropsis native to Mexico.[5] Recent phylogenetic analyses place the dibamids as the sister clade to all the other lizards and snakes[6][7][8] or classify them as sharing a common ancestor with the infraorder Gekkota, with Dibamidae and Gekkota forming the sister clade to all other squamates.[9] Hoeckosaurus from the Oligocene of Mongolia represents the only fossil record of the group.[10]

Characteristics

General appearance

Dibamids are burrower lizards characterized by their elongated bodies with blunt head and tail, and an apparent lack of limbs.[1][3] Relatively small, blind skinks can reach a maximum length of 250 mm (9.8 in) from head to tail[3] and the snout vent length (SVL) is variable between both genus Anelytropsis and Dibamus.[2] In Anelytropsis, the tail is longer than in Dibamus and represents between 34 and the 38% of the snout vent length which can range from 77 to 180 mm (3 to 7 in).[2] In Dibamus, the tail corresponds to 9 to 25% of the SVL that varies from 52 to 203 mm (2 to 8 in).[2]

Usually dibamids are dark colored, from brown to dark purple, with little to no variation along their body and frequently lack elaborate patterns.[2] It is common to find a color gradation from the darker back towards a lighter ventral side.[2] Scales are shiny and smooth and very similar and overlapping along with some variation in number and shape in the head and anal regions where males usually have additional scales to cover anal pores.[1][2] Scale row counts varies between both genera; Anelytropsis has 19 to 25 rows whereas Dibamus has 18 to 33.[2] In both groups osteoderms are absent.[1][2]

General characteristics of the soft tissue includes a tongue that is covered in lamellae except in the tip, heavily modified ears without external openings or middle ear cavity or eustachian tubes,[2] and highly reduced eyes that are covered by a scale and lack internal structure, particularly in Dibamus.[11]

Limbs

Dibamids are lizards with highly reduced limbs but they are not completely limbless. Males and females have rudimentary poorly developed hind limbs containing a femur, tibia and fibula in males, and distal cartilage cap. These elements are more developed on Dibamus than in Anelytropsis.[12] Female Dibamus lack the tibia and the fibula.[12]

Skull

The skull is approximately 5 – 7 mm in length[13] with reduced kinesis and a more rigid skull for burrowing.[13][14] The combination of fossorial habits and small size, contributes to the development of a skull configuration that is frequently found in other groups of burrowers and miniaturized species.[14][15][16] Among those characteristics are the closure of the supratemporal fenestra and the post-temporal fenestra, the relative large braincase, tubular or scroll-like palatines and modified jaw suspension mechanism with the quadrate articulating with the lateral wall of the braincase.[13][14][16]

Other characteristics of the skull of blind skinks include the absence of a parietal foramen,[2] a well developed secondary palate formed by three different bones, the maxillae, vomers and palatines which are expanded ventromedially to form a scroll, and the lack of palatal teeth.[13] Nasal and frontal bones are paired and contact each other in a W-shape suture with no overlap between the two bones, and several bones are lost (lacrimal, postorbital and jugal) or highly reduced (supratemporal and squamosal).[13] The main cranial differences, besides sizes, between Anelytropsis and Dibamus is the presence of epipterygoid and postfrontal in the Central American genus.[2]

The mandible of Dibamidae bears less than 10 teeth and is composed of only three bones, the dentary, the coronoid and the compound bone.[2] A remnant of the splenial bone is only present in one species of Dibamus, Dibamus novaeguineae.[12]

Classification

The family Dibamidae contains two genera, Anelytropsis and Dibamus, and the close relationship of the genera was based on two morphological characteristics that are unique to these groups, the secondary palate and the lamellae covering the tongue, and additional cranial characteristics that can be shared with other groups of lizards.[2]

The anatomical characteristics that dibamids share with other squamates contributed to the formulation of different taxonomic hypothesis.[2] Dibamids, and particularly Dibamus was considered to be part of geckos and precisely the family of legless geckos;[17] snakes, considering the organization of the skull and jaw muscles;[18] or was proposed to be closely related to a group of fossorial skinks with elongated bodies and reduced limbs.[19][16]

Phylogeny

Relationships among Dibamidae

Anelytropsis papillosus

Dibamus greeri

Dibamus montanus

Dibamus bourreti

Dibamus bourreti

Dibamus tiomanensis

Dibamus novaeguineae

Dibamus seramensis

Dibamus celebensis

Phylogeny of Dibamidae[20]

The relationships within Dibamidae have only be assessed until recently in a phylogenetic analysis that included DNA sequences from seven nuclear genes and one mitochondrial gene for 8 species, seven species of Dibamus and the one species of Anelytropsis.[20] This analysis shows that there are two major clades within Dibamidae, one that includes the one species form the genus Anelytropsis, Analytropsis papillous, and the species of Dibamus that are distributed along continental Southeast Asia (Dibamus greeri, Dibamus montanus, and Dibamus bourreti). The other clade includes species that are currently distributed in the peninsular Southeast Asia and Islands (Dibamus tiomanensis, Dibamus novaeguineae, Dibamus seramensis, and Dibamus celebensis).[20] These clades diverged 72 million years ago.[20] Anelytropsis diverged from all mainland Dibamus at approximately 69.2 million years ago.[20]

Dibamidae and its relationship with Squamata

The relationship of Dibamidae with other Squamata (lizards and snakes) has a long history of phylogenetic studies in which the morphological characteristics are used to determine those relationships.[21] Those analysis found close relationships between Dibamidae and all other lizards with elongated bodies, limb reduction and usually, a fossorial habit like amphisbaenians, snakes or fossorial skinks.[15][22][21] In morphology based phylogenies, dibamids are sister taxa to amphisbaenians and the clade that includes amphisbaeninas and dibamids is sister to all snakes.[21] The close relationships of this groups are the result of convergent evolution among this groups since some of the morphological traits have evolved independently in different groups.[15]

More recent phylogenies using DNA sequences of nuclear and mitochondrial genes include a large taxonomic sample of squamates and place dibamids as the sister group to all other lizards and snakes, or with Gekkota as the sister group to all other squamates.[6][23][9] Phylogenetic evidence supports dimabids being the most basal squamates, being sister to all other lizards and snakes, and indicates that they diverged during the late Triassic, around 210 million years ago.[8]

Biodiversity

There are two recognized genera within the family, Anelytropsis and Dibamus.[1] According to The Reptile Database,[5] Anelytropsis is monotypic and Dibamus includes 23 species:

Anelytropsis[24]

Dibamus[25]

For additional details, see here

An extinct monotypic genus, Hoeckosaurus was recently proposed from the description of fossil material from the early Oligocene of the Valley of Lakes in Central Mongolia.[10]

Biogeography

Dibamids have a disjunct distribution with one genus living in Northern Mexico, Anelytropsis, and the other one, Dibamus, living in South East Asia.[1] Biogeographical studies suggest that the separation between Anelytropsis and Dibamus, specifically the clade with species that are distributed in continental South East Asia, occurred approximately 69 million years ago during the late Cretaceous and the migration from Asia to North America took place during the Late Paleocene or Eocene through Beringia.[20]

Biology

Blind skinks are insectivorous and feed on arthropods and earthworms.[3] Blind skinks are characterized by their fossorial or burrowing habits.[1] They can dig their own burrows, use old burrows or other openings in the ground,[1] or dwell under the leaf litter or logs.[2]

Species of the genus Dibamus are frequently found in primary and secondary forests in a wide range of altitudinal variation (from the sea level to approximately 1300 meters above sea level).[2] Anelytropsis is found in drier environments and is adapted to xeric conditions of different environments in northern Mexico.[2]

Little is known about the reproduction of this group of lizards, but the inspection of female specimens from herpetological collections indicate that dibamids lays single egg[2] with hardened shell,[1] and eggs are laid frequently, at least in Dibamus.[1]

Conservation

None of the species of Dibamidae are listed as endangered species in the Convention on International Trade in Endangered Species of Wild Fauna and Flora CITES.[26]

The International Union for Conservation of Nature (IUCN) include some of the species of the genus Dibamus and the single species of Anelytropsis in the red list of endangered species, most are in the category of least concern, and two species, Dibamus kondaoensis and Dibamus tiomanensis are listed as nearly threatened and endangered respectively.[27]

References

  1. 1 2 3 4 5 6 7 8 9 10 11 Vitt, Laurie J.; Caldwell, Janalee P. (2014). Herpetology : an introductory biology of amphibians and reptiles (4th ed.). Amsterdam. ISBN 9780123869197. OCLC 839312807.{{cite book}}: CS1 maint: location missing publisher (link)
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Greer, Allen E. (1985). "The Relationships of the Lizard Genera Anelytropsis and Dibamus". Journal of Herpetology. 19 (1): 116–156. doi:10.2307/1564427. ISSN 0022-1511. JSTOR 1564427.
  3. 1 2 3 4 Pough, F. Harvey (2015-11-18). Herpetology (Fourth ed.). Sunderland, Massachusetts, USA. ISBN 9781605352336. OCLC 908397943.{{cite book}}: CS1 maint: location missing publisher (link)
  4. ↑ Cogger, Harold G.; Zweifel, Richard George, eds. (1998). Encyclopedia of Reptiles & Amphibians (2nd ed.). San Diego, CA. ISBN 0121785602. OCLC 39559811.{{cite book}}: CS1 maint: location missing publisher (link)
  5. 1 2 "The Reptile Database". reptile-database.reptarium.cz. Retrieved 2019-02-08.
  6. 1 2 Tonini, João Filipe Riva; Beard, Karen H.; Ferreira, Rodrigo Barbosa; Jetz, Walter; Pyron, R. Alexander (2016-12-01). "Fully-sampled phylogenies of squamates reveal evolutionary patterns in threat status". Biological Conservation. Advancing reptile conservation: Addressing knowledge gaps and mitigating key drivers of extinction risk. 204: 23–31. doi:10.1016/j.biocon.2016.03.039. ISSN 0006-3207.
  7. ↑ Portik, Daniel M; Wiens, John J (2020-08-14). Faircloth, Brant (ed.). "Do Alignment and Trimming Methods Matter for Phylogenomic (UCE) Analyses?". Systematic Biology. 70 (3): 440–462. doi:10.1093/sysbio/syaa064. ISSN 1063-5157. PMID 32797207.
  8. 1 2 Vidal, Nicolas; Hedges, S. Blair (2009-02-01). "The molecular evolutionary tree of lizards, snakes, and amphisbaenians". Comptes Rendus Biologies. La théorie de Darwin revisitée par la biologie d'aujourd'hui / Darwin's theory revisited by today's biology. 332 (2): 129–139. doi:10.1016/j.crvi.2008.07.010. ISSN 1631-0691. PMID 19281946. S2CID 23137302.
  9. 1 2 Reeder, Tod W.; Townsend, Ted M.; Mulcahy, Daniel G.; Noonan, Brice P.; Wood, Perry L.; Sites, Jack W.; Wiens, John J. (2015-03-24). Wilf, Peter (ed.). "Integrated Analyses Resolve Conflicts over Squamate Reptile Phylogeny and Reveal Unexpected Placements for Fossil Taxa". PLOS ONE. 10 (3): e0118199. Bibcode:2015PLoSO..1018199R. doi:10.1371/journal.pone.0118199. ISSN 1932-6203. PMC 4372529. PMID 25803280.
  10. 1 2 Čerňanský, Andrej (2019-10-25). "The first potential fossil record of a dibamid reptile (Squamata: Dibamidae): a new taxon from the early Oligocene of Central Mongolia". Zoological Journal of the Linnean Society. 187 (3): 782–799. doi:10.1093/zoolinnean/zlz047. ISSN 0024-4082.
  11. ↑ Gans, Carl; Parsons, Thomas (1970). Morphology B. Academic Press. OCLC 610352006.
  12. 1 2 3 Gasc, J. P. (1968). "Contribution a l'ostéologie et a la myologie de Dibamus novaeguineae Gray (Sauria, Reptilia)". Annales des Sciences Naturelles, Zoologie. 10: 127–150.
  13. 1 2 3 4 5 Gans, Carl (2008). Biology of the Reptilia. Volume 20. Morphology H. The Skull of Lepidosauria. Gaunt, Abbot S., and Adler, Kraig. Ithaca, New York: Society for the Study of Amphibians and Reptiles. p. 758. ISBN 978-0-916984-76-2.
  14. 1 2 3 Rieppel, Olivier (1984). "Miniaturization of the lizard skull: its functional and evolutionary implications". In Ferguson, M. W. J. (ed.). The Structure, Development and Evolution of Reptiles. Symposium No. 52, The Zoological Society of London. Academic Press. pp. 503–520. ISBN 978-0-12-613352-3. OCLC 729488307.
  15. 1 2 3 Lee M Y (1998). "Convergent evolution and character correlation in burrowing reptiles: towards a resolution of squamate relationships". Biological Journal of the Linnean Society. 65 (4): 369–453. doi:10.1006/bijl.1998.0256. ISSN 0024-4066.
  16. 1 2 3 Rieppel, Olivier (1984). "The cranial morphology of the fossorial lizard genus Dibamus with a consideration of its phylogenetic relationships*". Journal of Zoology. 204 (3): 289–327. doi:10.1111/j.1469-7998.1984.tb02376.x. ISSN 0952-8369.
  17. ↑ Underwood, Garth (1957). "On lizards of the family pygopodidae. A contribution to the morphology and phylogeny of the squamata". Journal of Morphology. 100 (2): 207–268. doi:10.1002/jmor.1051000203. ISSN 0362-2525. S2CID 83508772.
  18. ↑ Haas, Georg. 1973. Muscles of the jaws and associated structures in the Rhynchocephalia and Squamata. In: Gans, C and Parsons, T. S. Biology of the Reptilia, v.4, (.1. M.): 285-490, fig 1-169.
  19. ↑ Camp, Charles Lewis (1923). "Classification of the lizards. Bulletin of the AMNH ; v. 48, article 11". hdl:2246/898. {{cite journal}}: Cite journal requires |journal= (help)
  20. 1 2 3 4 5 6 Townsend, T. M.; Leavitt, D. H.; Reeder, T. W. (2011-01-26). "Intercontinental dispersal by a microendemic burrowing reptile (Dibamidae)". Proceedings of the Royal Society B: Biological Sciences. 278 (1718): 2568–2574. doi:10.1098/rspb.2010.2598. ISSN 0962-8452. PMC 3136834. PMID 21270029.
  21. 1 2 3 Gauthier, Jacques A.; Kearney, Maureen; Maisano, Jessica Anderson; Rieppel, Olivier; Behlke, Adam D. B. (2012). "Assembling the Squamate Tree of Life: Perspectives from the Phenotype and the Fossil Record". Bulletin of the Peabody Museum of Natural History. 53 (1): 3–309. doi:10.3374/014.053.0101. ISSN 0079-032X. S2CID 86355757.
  22. ↑ Hallermann, Jakob (1998). "The ethmoidal region of Dibamus taylori (Squamata: Dibamidae), with a phylogenetic hypothesis on dibamid relationships within Squamata". Zoological Journal of the Linnean Society. 122 (3): 385–426. doi:10.1006/zjls.1996.0109. ISSN 0024-4082.
  23. ↑ Pyron, R; Burbrink, Frank T; Wiens, John J (2013). "A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes" (PDF). BMC Evolutionary Biology. 13 (1): 93. doi:10.1186/1471-2148-13-93. ISSN 1471-2148. PMC 3682911. PMID 23627680.
  24. ↑ "Anelytropsis papillosus". The Reptile Database. Retrieved 2019-02-08.
  25. ↑ "Search results | The Reptile Database". reptile-database.reptarium.cz. Retrieved 2019-02-08.
  26. ↑ "The CITES species | CITES". www.cites.org. Retrieved 2019-02-09.
  27. ↑ "The IUCN Red List of Threatened Species". IUCN Red List of Threatened Species. Retrieved 2019-02-10.
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