''Helioscopos'' ( ) is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of ardeosaurid

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 ...

from the

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

Morrison Formation The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltston ...

of the United States.

Discovery and naming

The

type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

of ''Helioscopos'', given the designation DINO 15914 (previously DNM 15914), was discovered at

Dinosaur National Monument Dinosaur National Monument is an American national monument located on the southeast flank of the Uinta Mountains on the border between Colorado and Utah at the confluence of the Green River (Colorado River tributary), Green and Yampa River, Y ...

from a locality called "Quarry #317". This locality is part of the famous and well-studied

in Utah. When the specimen was originally reported on in

1998 1998 was designated as the ''International Year of the Ocean''. Events January * January 6 – The ''Lunar Prospector'' spacecraft is launched into orbit around the Moon, and later finds evidence for Lunar water, frozen water, in soil i ...

, it was suggested to belong to the genus '' Paramacellodus'', which is known from throughout the Northern Hemisphere in the

. However, the specimen was re-examined in

2023 Catastrophic natural disasters in 2023 included the Lists of 21st-century earthquakes, 5th-deadliest earthquake of the 21st century 2023 Turkey–Syria earthquakes, striking Turkey and Syria, leaving up to 62,000 people dead; Cyclone Freddy ...

by a team of authors including Dalton Meyer, Chase Brownstein, Kelsey Jenkins, and

Jacques Gauthier Jacques Armand Gauthier (born June 7, 1948, in New York City) is an American vertebrate paleontologist, comparative morphologist, and systematist, and one of the founders of the use of cladistics in biology. Life and career Gauthier is the ...

in the same publication that they named the new genus ''

Limnoscansor ''Limnoscansor'' (International Phonetic Alphabet, ) is an extinct genus of Ardeosauridae, ardeosaurid lizard from the Late Jurassic Solnhofen Limestone of Germany. Discovery and naming The holotype and only known specimen of ''Limnoscansor'', g ...

''. This re-examination included CT-scanning the specimen, which was preserved in 3D, to study each of bone more thoroughly. Meyer and colleagues determined that the specimen did not belong to ''Paramacellodus'' and should be given a new name. The name they gave the specimen was ''Helioscopus dickersonae''. The name is derived from the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

words ''"helios"'' meaning "sun" and ''"scopós"'' meaning "watcher". This name was given in reference to the large

pineal foramen A parietal eye (third eye, pineal eye) is a part of the epithalamus in some vertebrates. The eye is at the top of the head; is photoreceptive; and is associated with the pineal gland, which regulates circadian rhythmicity and hormone production ...

present in the fossil. The specific epithet ''"dickersonae"'' was given to honor two family members of the principal author (who had the last name Dickerson) as well as Mary Cynthia Dickerson, the first curator of herpetology at the

American Museum of Natural History The American Museum of Natural History (AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. Located in Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 21 interconn ...

. The genus name also mirrors the extant lizard species ''

Phrynocephalus helioscopus ''Phrynocephalus helioscopus'', the sunwatcher toadhead agama, Fergana toad-headed agama, or sunwatcher, is a species of agamid lizard found in Kazakhstan, S Russia, Turkmenistan, Uzbekistan, Kyrgyzstan, Tajikistan, Turkey, Iraq, China, Mongolia ...

'' (commonly called the "sunwatcher"). Shortly after the paper was published, it was discovered that the name ''Helioscopus'' was

preoccupied In biology, a homonym is a name for a taxon that is identical in spelling to another such name, that belongs to a different taxon. The rule in the International Code of Zoological Nomenclature is that the first such name to be published is the s ...

by another genus of prehistoric lizard. In a supplement to the original publication, the authors amended the name to be spelled ''Helioscopos''.

Description

The holotype and only specimen of ''Helioscopos'' is a partial

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

and

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

s. Among the bones preserved are the

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

e, prefrontals, the

parietal bone The parietal bones ( ) are two bones in the skull which, when joined at a fibrous joint known as a cranial suture, form the sides and roof of the neurocranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four bord ...

, the right postorbitofrontal and

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestra ...

, the left

jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...

, part of both

palatine A palatine or palatinus (Latin; : ''palatini''; cf. derivative spellings below) is a high-level official attached to imperial or royal courts in Europe since Roman Empire, Roman times.

s, the right

pterygoid Pterygoid, from the Greek for 'winglike', may refer to: * Pterygoid bone, a bone of the palate of many vertebrates * Pterygoid processes of the sphenoid bone ** Lateral pterygoid plate ** Medial pterygoid plate * Lateral pterygoid muscle * Medial ...

, both dentaries, the left postdentaries, and part of the

braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...

. In their description, Meyer and colleagues assessed the

ontogeny Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the ovum, egg to adult. The term can also be used to refer to t ...

of the specimen based on the degree of fusion of some of the skull bones. The sphenoid and basioccipital bones are fully fused, as are the

surangular The surangular or suprangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular bone, angular, splenial and articular. It is o ...

and prearticular bones. These skull characteristics are generally recognized as markers of skeletal maturity, based on study of the skulls of

western whiptail The western whiptail (''Aspidoscelis tigris'') is a species of lizard in the Family (biology), family Teiidae. The species is found throughout most of the southwestern United States and northern Mexico. Most of its populations appear stable, and ...

s, and the authors conclude that ''Helioscopos'' was a fully grown individual when it died.

Classification

In their description of ''Helioscopos'', Meyer and colleagues conducted a

phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

to determine the evolutionary relationships of the new taxon. They found it to be a member of the family

Ardeosauridae Ardeosauridae is an extinct family of lizards known from the Late Jurassic of Germany and North America and Early Cretaceous of Mongolia, with other potential species elsewhere from Europe and Asia over the same time period. The position of this ...

and suggested that this family was a stem-member of

Gekkota Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates. They range from . Geckos are unique among lizards f ...

. The affinities of Ardeosauridae are generally controversial among researchers. A simplified version of the phylogeny recovered by the authors is shown below.

Paleoenvironment

The only fossils of ''Helioscopos'' currently known were discovered at

in a quarry which corresponds to the

-aged

. The sedimentary geology of the area indicates that, during the Jurassic Period, the area was a seasonally-variable

alluvial plain An alluvial plain is a plain (an essentially flat landform) created by the deposition of sediment over a long period by one or more rivers coming from highland regions, from which alluvial soil forms. A ''floodplain'' is part of the process, bei ...

dominated by

conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...

fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...

s, and

cycad Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants o ...

s. Other vertebrate life from the area included other reptiles such as turtles,

rhynchocephalia Rhynchocephalia (; ) is an order of lizard-like reptiles that includes only one living species, the tuatara (''Sphenodon punctatus'') of New Zealand. Despite its current lack of diversity, during the Mesozoic rhynchocephalians were a speciose g ...

ns, and

crocodyliformes Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the only pseu ...

, such as the genera ''

Goniopholis ''Goniopholis'' (meaning "angled scale") is an extinct genus of goniopholidid crocodyliform that lived in Europe and North America during the Late Jurassic and Early Cretaceous. Like other goniopholidids, it resembled living crocodilians, and pro ...

'' and '' Hoplosuchus''. The dominant terrestrial life of the time were the non-avian

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s. Among the dinosaurs known from Dinosaur National Monument are the giant

sauropods Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...

Camarasaurus ''Camarasaurus'' ( ) is a genus of sauropod dinosaur that lived in North America during the Late Jurassic period. Its fossil remains have been found in the Morrison Formation, dating to the Kimmeridgian and Tithonian ages of the Jurassic, betwe ...

'', ''

Apatosaurus ''Apatosaurus'' (; meaning "deceptive lizard") is a genus of herbivorous sauropod dinosaur that lived in North America during the Late Jurassic period. Othniel Charles Marsh described and named the first-known species, ''A. ajax'', in 1877, a ...

'', ''

Diplodocus ''Diplodocus'' (, , or ) is an extinct genus of diplodocid sauropod dinosaurs known from the Late Jurassic of North America. The first fossils of ''Diplodocus'' were discovered in 1877 by S. W. Williston. The generic name, coined by Othnie ...

'', and ''

Barosaurus ''Barosaurus'' ( ) is a genus of giant, long-tailed, long-necked, herbivore, plant-eating Sauropoda, sauropod dinosaur closely related to the more familiar ''Diplodocus''. Remains have been found in the Morrison Formation from the Jurassic, Up ...

'', the

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

s ''

Allosaurus ''Allosaurus'' ( ) is an extinct genus of theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic period ( Kimmeridgian to late Tithonian ages). The first fossil remains that could definitively be ascribed to th ...

'' and ''

Ceratosaurus ''Ceratosaurus'' (from Greek 'horn' and 'lizard') is a genus of carnivorous theropod dinosaur that lived in the Late Jurassic period (Kimmeridgian to Tithonian ages). The genus was first described in 1884 by American paleontologist Othni ...

'', and several

ornithischian Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek st ...

genera including ''

Stegosaurus ''Stegosaurus'' (; ) is a genus of herbivorous, four-legged, armored dinosaur from the Late Jurassic, characterized by the distinctive kite-shaped upright plates along their backs and spikes on their tails. Fossils of the genus have been fo ...

'', ''

Camptosaurus ''Camptosaurus'' ( ) is a genus of plant-eating, beaked ornithischian dinosaurs of the Late Jurassic Period (geology), period of western North America and possibly also Europe. The name means 'flexible lizard' (Ancient Greek, Greek (') meaning ...

'', and ''

Dryosaurus ''Dryosaurus'' ( , meaning 'tree lizard', Greek ' () meaning 'tree, oak' and () meaning 'lizard', (the name reflects the forested habitat, not a vague oak-leaf shape of its cheek teeth as is sometimes assumed) is a genus of an ornithopod dinos ...

''.Foster, John. Jurassic West, Second Edition: The Dinosaurs of the Morrison Formation and Their World. NED-New edition, 2, Indiana University Press, 2020. JSTOR, https://doi.org/10.2307/j.ctv18sqxpx.

References

{{Taxonbar, from=Q131939542 Squamata Morrison fauna Jurassic reptiles of North America Prehistoric lizard genera Taxa named by Jacques Gauthier