Dolichosauridae (from

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

, ''dolichos'' = "long" and

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

''sauros''=

lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...

) is a family of

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

aquatic lizards. They are widely considered to be the earliest and most primitive members of Mosasauria, though some researchers have recovered them as more closely related to snakes.

Description

''Dolichosaurus'' was a small marine squamate at about 0.5 to 1 meter in total length. ''Coniasaurus'' was similarly sized at about 0.5 meters in length. They were elongated (especially apparent in the neck) marine lizards with reduced limbs and small, thin heads. Dolichosaurs may have occupied a niche similar to the earlier nothosaurs and modern

sea snakes Sea snakes, or coral reef snakes, are elapid snakes that inhabit marine environments for most or all of their lives. They belong to two subfamilies, Hydrophiinae and Laticaudinae. Hydrophiinae also includes Australasian terrestrial snakes, w ...

, in using their thin heads to feed in crevices and narrow spaces along coral reefs and rocky shores. One of the earliest dolichosaurs, '' Kaganaias'' from

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 125.77 Ma (million years ago) and 121.4 ± 1.0 Ma (Historically, this stage was placed at 129.4 million to approximately 125 million years ago) It is a ...

, probably lived in

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

environment unlike other members in the family. Despite their aquatic nature, fluctuations in sea level did not appear to have any significant effects on dolichosaurid evolution during the Cenomanian and Turonian. The degree to which the limbs were reduced suggest that the dolichosaurs would have been unable to generate any significant movement on land, and they thus likely spent most of their time underwater. Though the reduction of the limbs have no obvious evolutionary advantage, it is an adaptation that might be shared with early

snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...

History of discovery

Both of the genera routinely referred to the Dolichosauridae, '' Dolichosaurus'' and '' Coniasaurus'', were described by

Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomy, comparative anatomist and paleontology, palaeontologist. Owen is generally considered to have been an outstanding naturalist with a remarkabl ...

in 1850 based on specimens of

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

age collected from the Lower Chalk of southeastern

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

.Owen, R. 1850. Description of the Fossil Reptiles of the Chalk Formation; pp. 378–404 in F. Dixon (ed.), ''The Geology and Fossils of the Tertiary and Cretaceous Formations''. The unusually large number of dorsal and cervical vertebrae present in ''Dolichosaurus'' prompted it to be named as a new genus and ''Coniasaurus'' could be distinguished from known Cretaceous lizards by dental characteristics. Nopcsa (1908)Nopcsa, F. 1908. Zur kenntnis der fossilen Eidechsen. Beitra¨ge zur Pala¨ontologie und Geologie O¨sterreich-Ungarns und des Orients 21: 33–62. restudied the specimens discovered by Owen and described several new specimens of ''Coniasaurus'' and ''Dolichosaurus''.

Classification

Many authors have suggested the dolichosaurs to be a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

group. Both known species of ''Coniasaurus'', ''C. gracilodens'' and ''C. crassidens'', are known from disarticulated skulls with isolated vertebral elements. In contrast, ''Dolichosaurus longicollis'', the only species of ''Dolichosaurus'', is known from postcranial skeletons with only very fragmentary skulls and no teeth. This has made the exact nature of their relation difficult to determine. ''Coniasaurus'' and ''Dolichosaurus'' are generally considered to be either nested within basal mosasauroids as a third group alongside mosasaurs and aigialosaurs, or as the sister group to the mosasauroids. The difficulties in establishing more certain relationships not only between the Dolichosauridae and the Mosasauroidea, but also between ''Dolichosaurus'' and ''Coniasaurus'', arise from the nature of the fossil remains referred to the genera. With ''Coniasaurus'' largely lacking postcranial material and ''Dolichosaurus'' largely lacking cranial material, they are difficult to compare with each other. Studies that propose a close relation between

s and mosasauroids in a group dubbed

Pythonomorpha Mosasauria is a clade of Aquatic animal, aquatic and semiaquatic squamates that lived during the Cretaceous period. Fossils belonging to the group have been found in all continents around the world. Early mosasaurians like Dolichosauridae, dolich ...

demonstrate the importance of ''Dolichosaurus'', ''Coniasaurus'' and other Late Cretaceous marine squamates in squamate phylogeny and evolutionary history. The hypothesis suggesting that snakes, mosasaurs, aigialosaurs and dolichosaurs share a common aquatic ancestor is not universally accepted and stands in stark contrast with the previously widespread hypothesis of snakes having a

fossorial A fossorial animal () is one that is adapted to digging and which lives primarily (but not solely) underground. Examples of fossorial vertebrates are Mole (animal), moles, badgers, naked mole-rats, meerkats, armadillos, wombats, and mole salamand ...

origin. The

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

below is based on Palci and Caldwell (2010a), Caldwell and Palci (2010b), placing the Dolichosauridae as a sister group to modern

s and their closest ancestors. Other authors have disagreed with this hypothesis, instead placing dolichosaurs at the base of Mosasauria, with Mosasauria unrelated to snakes. Cladogram following Augusta et al. (2022):

References

{{Authority control † Barremian first appearances Campanian extinctions Prehistoric reptile families