''Acteosaurus'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of aquatic

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...

that lived in the

upper 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'', the ...

period. Its species, ''A. tommasinii'' and ''A. crassicostatus'', were described in 1860 and 1993. Though ''A. crassicostatus'' is probably a

junior synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...

for '' Adriosaurus suessi'', ''A. tommasinii'' was found to be similar to coniasaurs,

mosasauroid Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Ancient Greek, Greek ' meaning 'lizard') comprise a group of extinct, large marine reptiles from the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Ma ...

s, and a sister taxon to modern

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 joi ...

in 2010.

Etymology

The primary portion of ''Acteosaurus name comes from

Actaeon Actaeon (; grc, Ἀκταίων ''Aktaion''), in Greek mythology, son of the priestly herdsman Aristaeus and Autonoe in Boeotia, was a famous Theban hero. Like Achilles in a later generation, he was trained by the centaur Chiron. He fell to ...

(; Greek: ), a famous Theban

hero A hero (feminine: heroine) is a real person or a main fictional character who, in the face of danger, combats adversity through feats of ingenuity, courage, or Physical strength, strength. Like other formerly gender-specific terms (like ...

who was hunted and killed by the

goddess A goddess is a female deity. In many known cultures, goddesses are often linked with literal or metaphorical pregnancy or imagined feminine roles associated with how women and girls are perceived or expected to behave. This includes themes of s ...

Artemis In ancient Greek mythology and religion, Artemis (; grc-gre, Ἄρτεμις) is the goddess of the hunt, the wilderness, wild animals, nature, vegetation, childbirth, care of children, and chastity. She was heavily identified wit ...

. The second part of the name is the

Greek Greek may refer to: Greece 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 ...

word ' (), which means "

" or "

reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...

". The type species was named after the botanist Muzio Giuseppe Spirito de Tommasini (1794—1879), the

Podestà Podestà (, English: Potestate, Podesta) was the name given to the holder of the highest civil office in the government of the cities of Central and Northern Italy during the Late Middle Ages. Sometimes, it meant the chief magistrate of a city ...

—or magistrate—of

Trieste Trieste ( , ; sl, Trst ; german: Triest ) is a city and seaport in northeastern Italy. It is the capital city, and largest city, of the autonomous region of Friuli Venezia Giulia, one of two autonomous regions which are not subdivided into provi ...

under the

Habsburgs The House of Habsburg (), alternatively spelled Hapsburg in Englishgerman: Haus Habsburg, ; es, Casa de Habsburgo; hu, Habsburg család, it, Casa di Asburgo, nl, Huis van Habsburg, pl, dom Habsburgów, pt, Casa de Habsburgo, la, Domus Hab ...

Taxonomy

As a genus, Acteosaurus was described in 1860 by

German German(s) may refer to: * Germany (of or related to) **Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ger ...

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Christian Erich Hermann von Meyer Christian Erich Hermann von Meyer (3 September 1801 – 2 April 1869), known as Hermann von Meyer, was a German palaeontologist. He was awarded the 1858 Wollaston medal by the Geological Society of London. Life He was born at Frankfurt am Ma ...

. There exist two known species of Acteosaurus called ''A. tommasinii'' (type species) and ''A. crassicostatus'', the latter of which suggested as a junior synonym of ''Adriosaurus suessi''. A 2010 redescription of the type species found "

monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...

of the

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 term, ...

Ophidiomorpha". This included the Dolichosauridae, ''

Pontosaurus ''Pontosaurus'' is a now extinct genus of pythonomorph from the Late Cretaceous period. It was originally named ''Hydrosaurus'', but that name was preoccupied by an agamid lizard, so it was renamed. It is known from two species, both Cenomania ...

'', ''

Aphanizocnemus ''Aphanizocnemus'' is an extinct genus of lizard from Lebanon. It is a marine lizard that lived during the Late Cretaceous. It is often classified in the family Dolichosauridae as a close relative of snakes, although some studies have placed it ...

'', and ''

Adriosaurus ''Adriosaurus'' is an extinct genus of squamate which lived in what is now Slovenia and other parts of Europe during the Late Cretaceous. It was snake-like and grew up to in length. This is the first fossil record of vestigial limbs in lizards. ...

''. ''Acteosaurus'' was found to be a basal ophidiomorph (similar to ''Adriosaurus'') and sister taxon to the Ophidia, or modern snakes.

Description

''Acteosaurus'' is described as slender or snake-like, similar to other dolichosaurids. Its shortened forelimbs and long tail help to distinguish it from other genera, and its vertebral column is similar to more modern

varanid The Varanidae are a family of lizards in the superfamily Varanoidea within the Anguimorpha group. The family, a group of carnivorous and frugivorous lizards, includes the living genus '' Varanus'' and a number of extinct genera more closely relat ...

lizards. It was a small reptile measuring long. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

, when it was discovered, was unfortunately missing its head. So, while Meyer was unable to come up with an exact number, he noted that ''Acteosaurus'' has at least 10

cervical vertebrae In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...

, and 27 dorsals. There are small

articular processes The articular processes or zygapophyses (Greek ζυγον = "yoke" (because it links two vertebrae) + απο = "away" + φυσις = "process") of a vertebra are projections of the vertebra that serve the purpose of fitting with an adjacent vertebr ...

on the

trunk Trunk may refer to: Biology * Trunk (anatomy), synonym for torso * Trunk (botany), a tree's central superstructure * Trunk of corpus callosum, in neuroanatomy * Elephant trunk, the proboscis of an elephant Computing * Trunk (software), in rev ...

vertebrae, and it has long, narrow

neural spine The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

s, and posteroventrally positioned, unfused

haemal arch A haemal arch also known as a chevron, is a bony arch on the ventral side of a tail vertebra of a vertebrate. The canal formed by the space between the arch and the vertebral body is the haemal canal. A spinous ventral process emerging from the hae ...

es on the vertebrae of the tail. There is no

pachyostosis Pachyostosis is a non-pathological condition in vertebrate animals in which the bones experience a thickening, generally caused by extra layers of lamellar bone. It often occurs together with bone densification (osteosclerosis), reducing inner ca ...

, or bone thickening, in the vertebrae and ribs. The limbs are reduced in size, and though the

forelimb A forelimb or front limb is one of the paired articulated appendages (limbs) attached on the cranial ( anterior) end of a terrestrial tetrapod vertebrate's torso. With reference to quadrupeds, the term foreleg or front leg is often used instead. ...

s of ''Acteosaurus'' are fully developed, they are smaller than the hind limbs. ''Acteosaurus

pelvic bone The hip bone (os coxae, innominate bone, pelvic bone or coxal bone) is a large flat bone, constricted in the center and expanded above and below. In some vertebrates (including humans before puberty) it is composed of three parts: the ilium, ischi ...

is flattened, has square-shaped pubic process, and a rectangular descending ramus.

Distribution and habitat

Both ''Acteosaurus tommasinii'' and ''A. crassicostatus'' were found in the upper section of

karst Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

platy

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

, in

Komen Komen (, it, Comen or ''Comeno'') is a settlement in Slovenia. It is the seat of the Municipality of Komen. It is located on the Karst Plateau in the Slovenian Littoral. Name Komen was attested in written sources in 1247 as ''Cominum'' (and as ...

Slovenia Slovenia ( ; sl, Slovenija ), officially the Republic of Slovenia (Slovene: , abbr.: ''RS''), is a country in Central Europe. It is bordered by Italy to the west, Austria to the north, Hungary to the northeast, Croatia to the southeast, an ...

. Komen is part of

Istria Istria ( ; Croatian language, Croatian and Slovene language, Slovene: ; ist, Eîstria; Istro-Romanian language, Istro-Romanian, Italian language, Italian and Venetian language, Venetian: ; formerly in Latin and in Ancient Greek) is the larges ...

, a peninsula on the

Adriatic sea The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Sea) to t ...

, and also a section of the

Karst Plateau The Karst Plateau or the Karst region ( sl, Kras, it, Carso), also locally called Karst, is a karst plateau region extending across the border of southwestern Slovenia and northeastern Italy. It lies between the Vipava Valley, the low hills sur ...

. During the late Cretaceous, most of Europe was an

island chain An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster, or collection of islands, or sometimes a sea containing a small number of scattered islands. Examples of archipelagos include: the Indonesian Archi ...

in the

Tethys ocean The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents ...

, and ''Acteosaurus aquatic nature and similarity to mosasauroids suggests that it lived on the coast of one of these islands.

References

External links