''Juravenator'' is a

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 small (75 cm long)

coelurosaur Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyrann ...

ian

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

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

(although a 2020 study proposed it to be a hatchling

megalosauroid Megalosauroidea (meaning 'great/big lizard forms') is a Taxonomic rank, superfamily (or clade) of Tetanurae, tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period. The group is defined as ''Megalosaurus, M ...

), which lived in the area which would someday become the top of the

Franconian Jura The Franconian Jura ( , , or ) is an upland in Franconia, Bavaria, Germany. Located between two rivers, the Danube in the south and the Main in the north, its peaks reach elevations of up to and it has an area of some 7053.8 km2. Emil Meyne ...

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

(

Painten Formation The Painten Formation is a geologic formation in Germany. It preserves fossils dating back to the Tithonian stage of the Late Jurassic period. ''Juravenator'' was a small bipedal predator. The holotype of ''Juravenator'' represents a juvenile individual, about seventy-five centimetres in length. In 2006 and 2010 Göhlich established some diagnostic traits. The four teeth of the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

in the front of the snout had serrations on the upper third of the back edge of the tooth crown. Between the tooth row of the premaxilla and that of the

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates 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 t ...

there was no hiatus. The maxillary teeth were few in number, eight with the holotype. The depression or ''fossa'' for the large skull opening, the ''fenestra antorbitalis'', was long and extended far to the front. The

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

was relatively short. The claws of the hand were high at their bases and suddenly narrowed transversely in the middle. The zygapophyses in the middle of the tail were bow-shaped.

Feathers and scales

''Juravenator'' was originally classified as a member of the

Compsognathidae Compsognathidae is a family of coelurosaurian theropod dinosaurs. Compsognathids were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Periods. The bird-like features of these species, along with other d ...

, making it a close relative of ''

Compsognathus ''Compsognathus'' (; Greek ''kompsos''/κομψός; "elegant", "refined" or "dainty", and ''gnathos''/γνάθος; "jaw") is a genus of small, bipedal, carnivorous theropod dinosaur. Members of its single species ''Compsognathus longipes'' c ...

'', which preserved evidence of scales on the tail of one specimen, but also of ''

Sinosauropteryx ''Sinosauropteryx'' (meaning "Chinese reptilian wing", ) is a compsognathid dinosaur. Described in 1996, it was the first dinosaur taxon outside of Avialae (birds and their immediate relatives) to be found with evidence of feathers. It was cover ...

'' and ''

Sinocalliopteryx ''Sinocalliopteryx'' (meaning 'Chinese beautiful feather') is a genus of carnivorous compsognathid theropod dinosaurs from the Lower Cretaceous Yixian Formation of China (Jianshangou Beds, dating to 124.6 Ma). While similar to the related ''Huax ...

'', for which there is fossil evidence of a downy, feather-like covering. However, a patch of fossilized ''Juravenator'' skin (from the tail, between the eighth and twenty-second vertebra, and lower hind leg) shows primarily normal dinosaur scales, as well as traces of what may be simple feathers. Paleontologist Xu Xing, in his comments on the find in the journal ''Nature'', initially suggested that the presence of scales on the tail of ''Juravenator'' could mean that the feather coat of early feathered dinosaurs was more variable than seen in modern birds. Xu also questioned the interpretation of ''Juravenator'' as a compsognathid, suggesting the extensive scaly hide could be a primitive trait. Xu considered it most likely that ''Juravenator'' and other primitive feathered dinosaurs simply possessed more extensive scales on their bodies than modern birds, which retain scales only on the feet and lower legs.Xu, X. (2006). "Scales, feathers, and dinosaurs". "Nature", 440: 287-288. Xu's interpretation was supported by further study of the ''Juravenator'' fossil. The first follow-up study to the initial description reported that faint impressions of filamentous structures, possibly primitive feathers, were present along the top of the tail and hips. A more in-depth study, published in 2010, included an examination of the specimen under ultra-violet light by Helmut Tischlinger. The examination under UV revealed a more extensive covering of filament-like structures, similar in anatomy to the primitive feathers of other compsognathids, including ''Sinosauropteryx''. The investigation also discovered additional patches of soft tissue, on the snout and the lower leg, and vertical collagen fibres between the chevrons of the tail vertebrae. Foth ''et al.'' (2020) reinterpreted purported scales preserved with the holotype specimen of ''J. starki'' as remains of

adipocere Adipocere (), also known as corpse wax, grave wax or mortuary wax, is a wax-like organic substance formed by the anaerobic bacterial hydrolysis of fat in tissue, such as body fat in corpses. In its formation, putrefaction is replaced by a permanent ...

, possibly indicating the presence of a fat body. Christophe Hendrickx and Phil R. Bell reexamine the specimen of ''Juravenator'', they find that the scaly integument on the tail show the presence of ISOs.

Discovery and naming

In the summer of 1998, the Jura-Museum Eichstätt at

Eichstätt Eichstätt () is a town in the federal state of Bavaria, Germany, and capital of the district of Eichstätt. It is located on the Altmühl river and has a population of around 13,000. Eichstätt is also the seat of the Roman Catholic Diocese ...

organised a paleontological expedition to the nearby chalk quarry of Schamhaupten. Near the end of the planned excavations, two volunteers, Klaus-Dieter Weiß and his brother Hans-Joachim Weiß, found a chalk plate in which clear vertebrate remains were visible. A first preparation uncovered the head of a small theropod. However, due to the vulnerability of the bones, removing the hard

calcium silicate Calcium silicate is the chemical compound Ca2SiO4, also known as calcium orthosilicate and is sometimes formulated as 2CaO·SiO2. It is also referred to by the shortened trade name Cal-Sil or Calsil. It occurs naturally as the mineral larnite. ...

matrix was slow and expensive. To see whether it was worthwhile to proceed, a CT-scan of the fossil was made. This seemed to show that only the neck and a small part of the rump were still present and accordingly the preparation was discontinued. In 1999 the find was reported in the scientific literature by Günther Viohl. By 2001 the fossil had generated some publicity and was nicknamed ''Borsti'' in the German press, a name commonly given to bristle-haired dogs, on the assumption the creature was endowed with bristly protofeathers. In 2003, the new director of the museum, Martina Kölbl-Ebert, decided to finish the preparation. Preparator Pino Völkl then discovered, during seven hundred hours uncovering the remaining bones, that almost the entire skeleton was present. In 2006 the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

''Juravenator starki'' was named and described by Ursula Göhlich and

Luis Chiappe Luis María Chiappe (born 18 June 1962) is an Argentine paleontologist born in Buenos Aires who is best known for his discovery of the first sauropod nesting sites in the badlands of Patagonia in 1997 and for his work on the origin and early evo ...

. The generic name is derived from the name of the

Jura Mountains The Jura Mountains ( , , , ; french: Massif du Jura; german: Juragebirge; it, Massiccio del Giura, rm, Montagnas da Jura) are a sub-alpine mountain range a short distance north of the Western Alps and mainly demarcate a long part of the Frenc ...

and the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''venator'', "hunter". The specific name honours the Stark family, owners of the quarry. 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 ...

, JME Sch 200, was found in the ''Malm Epsilon 2'', a

marl Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. Marl makes up the lower part o ...

layer of the

Painten Formation The Painten Formation is a geologic formation in Germany. It preserves fossils dating back to the Tithonian stage of the Late Jurassic period.Kimmeridgian In the geologic timescale, the Kimmeridgian is an age in the Late Jurassic Epoch and a stage in the Upper Jurassic Series. It spans the time between 157.3 ± 1.0 Ma and 152.1 ± 0.9 Ma (million years ago). The Kimmeridgian follows the Oxfordian ...

, about 151 to 152 million years old. As the bones were accessed from below — the specimen having landed on its back on the seafloor — and the plate was not split further, a counterslab is lacking. The fossil consists of an almost complete articulated skeleton with skull of a juvenile individual. Only the tail end is missing. In small areas impressions or remains of the soft parts are present. The fossil was considered the most complete specimen of a non-avian theropod ever found in Europe.

Classification

While first classified as a member of the

, subsequent studies have found problems with the initial study that produced those findings. Rather than grouping it with ''Sinosauropteryx'' and other compsognathids, Butler ''et al.'' found that it was not a compsognathid, but rather a basal member of the group

Maniraptora Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Deinonychosauria, Oviraptoros ...

. Studies conflict on whether or not compsognathids belong to this later group or are more primitive. Additional work published by Luis Chiappe and Ursula Göhlich in 2010 found that ''Juravenator'' was most similar in anatomy to ''Compsognathus'', and that it probably did belong to the Compsognathidae if that is actually a natural group. They also suggested that "compsognathids", including ''Juravenator'', may form a grade of primitive coelurosaurs rather than a monophyletic

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, ...

. In 2011

Cristiano dal Sasso Cristiano Dal Sasso (born 12 September 1965) is an Italian paleontologist. Biography He was born in Monza, Italy and has been working since 1991 for the Milan Natural History Museum where he is the curator of fossil reptiles and birds. He was ...

and Simone Maganuco published an analysis which recovered the Compsognathidae as a natural group and ''Juravenator'' belonging to it as a sister species of ''Sinosauropteryx''. However, a large analysis of coelurosaurs published in 2013 again found ''Juravenator'' to be a coelurosaur closely related to, but not a member of, the Compsognathidae. Instead, it was recovered as a close relative of ''

Ornitholestes ''Ornitholestes'' (meaning "bird robber") is a small theropod dinosaur of the late Jurassic (Brushy Basin Member of the Morrison Formation, middle Kimmeridgian age, about 154 million years agoTurner, C.E. and Peterson, F., (1999). "Biostratigraph ...

'' outside the clade

Maniraptoriformes Maniraptoriformes is a clade of dinosaurs with pennaceous feathers and wings that contains ornithomimosaurs and maniraptorans. This group was named by Thomas Holtz, who defined it as "the most recent common ancestor of '' Ornithomimus'' and bird ...

. Foth ''et al''. (2020) considered it plausible that ''Juravenator'' may have been a non-coelurosaurian tetanuran, potentially part of the

group along with the similar ''

Sciurumimus ''Sciurumimus'' ("Squirrel-mimic," named for its tail's resemblance to that of the tree squirrel, ''Sciurus'') is an extinct genus of tetanuran theropod from the Late Jurassic of Germany. It is known from a single juvenile specimen representing t ...

''.

Paleobiology

Comparisons between the

scleral ring Sclerotic rings are rings of bone found in the eyes of many animals in several groups of vertebrates, except for mammals and crocodilians. They can be made up of single bones or multiple segments and take their name from the sclera. They are bel ...

s of ''Juravenator'' and modern birds and reptiles indicate that it may have been

nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

. However, this may be due to the only known specimen being a juvenile. A 2020 study by Bell & Hendrickx noted small, round structures preserved on the sides of the tail. They interpreted these as "integumentary sense organs" like those on the scales of crocodiles. If this identification is correct, these would be the first sensory organs found in the skin of any dinosaur. ''Juravenator'' may have used these to detect the movement of aquatic prey, such as fish, as it waded in the water.

Taphonomy

Reisdorf and Wuttke, in 2012, provided an extensive discussion on the

taphonomy Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov t ...

of the ''Juravenator'' specimen, i.e. the events that lead to its death, transportation, and fossilization. The specimen was deposited within a lagoon, to where it must been transported, possibly from the nearby islands. It is possible that a flash flood swept the animal into the sea, in which case it likely died by drowning. It is also possible that the animal swam or drifted onto the sea, or that it rafted on plants, and was then transported by surface currents to its place of burial. The rafting hypothesis is supported by tree trunks found at the Schamhaupten locality. The specimen would have arrived on the sea floor within a few hours after its death, as otherwise gases forming in its body cavity would have prevented it from sinking in one piece. Water depth at the burial site would have been large enough to prevent refloating of the carcass after such gases were produced. The specimen was found in almost in full (bones still connected together), only the skull, pelvic girdle, and front section of the tail were disarticulated to some degree. The skeleton is nearly complete, and missing parts in the tail were likely lost during excavation. Some discussion have revolved around the original orientation of the fossil within the rock, that is if the slab was prepared from its top or bottom site, or whether the individual lay on its back or its belly. Chiappe and Göhlich, in their 2010 description, assumed that it lay on its belly, an interpretation that is further supported by an

aptychus An aptychus is a type of marine fossil. It is a hard anatomical structure, a sort of curved shelly plate, now understood to be part of the body of an ammonite. Paired aptychi have, on rare occasions, been found at or within the aperture of ammo ...

(body part of an

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

) found within the slab; aptychi are almost always embedded with their concave sides pointing upwards. However, the original excavator later confirmed that the specimen is on the bottom site of the slab, and that it therefore lay on its back. Reisdorf and Wuttke, in 2012, discovered small, rounded stones within the belly area that they interpreted as

ooid Ooids are small (commonly ≤2 mm in diameter), spheroidal, "coated" (layered) sedimentary grains, usually composed of calcium carbonate, but sometimes made up of iron- or phosphate-based minerals. Ooids usually form on the sea floor, m ...

s. These ooids formed in shallow water and were likely transported with the individual to the place of burial. The authors speculate that ''Juravenator'' might have lived on the shores, where the ooids might have been swallowed. It is also possible that the individual drowned in shallow water, inhaling ooids suspended in the water. Chiappe and Göhlich identified fossils of

isopod Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, an ...

s found with the specimen, and concluded that these animals likely have scavenged the carcass while it was still floating. Reisdorf and Wuttke, in 2012, stated that the isopods could alternatively have parasitising the living animal. When the cadaver arrived at the seafloor, its head came to rest on its right side and the tail bent to the left. The seafloor was devoid of life except for a covering of microbial mats, preventing disruption by scavengers. In contrast to many other specimens from the Solnhofen archipelago, including ''Compsognathus'', the ''Juravenator'' specimen was not found in a typical death pose with the neck and tail curved over the torso. Reisdorf and Wuttke concluded that death poses resulted from the release of elastic ligaments during decay that spanned the vertebral column. The ''Juravenator'' specimen does not show such a pose because it was lying on its back, preventing the spine from bending.

References

External links

Article on ''Juravenator'' from ''National Geographic''
{{Taxonbar, from=Q132891 Compsognathids Kimmeridgian life Late Jurassic dinosaurs of Europe Feathered dinosaurs Fossils of Germany Fossil taxa described in 2006 Taxa named by Luis M. Chiappe