Juravenator

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Juravenator
Temporal range:
Ma
↓
Holotype specimen
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Orionides
Genus: †Juravenator
Göhlich & Chiappe, 2006
Type species
†Juravenator starki
Göhlich & Chiappe, 2006

Juravenator is a

theropod dinosaur (although a 2020 study proposed it to be a hatchling megalosauroid[1]), which lived in the area which would someday become the top of the Franconian Jura of Germany (Painten Formation
), about 151 or 152 million years ago. It is known from a single, juvenile specimen.

Description

Size of the juvenile type specimen, with a human for scale

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

zygapophyses in the middle of the tail were bow-shaped.[2][3]

Feathers and scales

Life reconstruction based on the juvenile holotype, showing both feathers and scales.

Juravenator was originally classified as a member of the Compsognathidae, making it a close relative of Compsognathus, which preserved evidence of scales on the tail of one specimen, but also of Sinosauropteryx and Sinocalliopteryx, for which there is fossil evidence of a downy, feather-like covering.[2] 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.[4] 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.[5]

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.

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.[3]

Foth et al. (2020) reinterpreted purported scales preserved with the holotype specimen of J. starki as remains of adipocere, possibly indicating the presence of a fat body.[1] Christophe Hendrickx and Phil R. Bell reexamine the specimen of Juravenator, they find that the scaly integument on the tail show the presence of integumentary sense organs.[6]

Discovery and naming

Close-up of the skull

In the summer of 1998, the

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.[7]
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

Luis Chiappe. The generic name is derived from the name of the Jura Mountains and the Latin venator, "hunter". The specific name honours the Stark family, owners of the quarry.[2]

The holotype, JME Sch 200, was found in the Malm Epsilon 2, a marl layer of the Painten Formation dating to the late Kimmeridgian, about 151 to 152 million years old. As the bones were accessed from below — the specimen having landed on its back on the seafloor[8] — 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.[2]

Classification

Skeletal reconstruction

While first classified as a member of the

Cristiano dal Sasso 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.[10] 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 outside the clade Maniraptoriformes.[11] Foth et al. (2020) considered it plausible that Juravenator may have been a non-coelurosaurian tetanuran, potentially part of the megalosauroid group along with the similar Sciurumimus.[1]

Paleobiology

Comparisons between the

nocturnal.[12]
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.[13]

Taphonomy

Reisdorf and Wuttke, in 2012, provided an extensive discussion on the taphonomy 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.[8]

The specimen was found in almost in full

ammonite) 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.[8]

Reisdorf and Wuttke, in 2012, discovered small, rounded stones within the belly area that they interpreted as

isopods found with the specimen, and concluded that these animals likely have scavenged the carcass while it was still floating.[3] Reisdorf and Wuttke, in 2012, stated that the isopods could alternatively have parasitising the living animal.[8]

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.[8]

References

  1. ^
    S2CID 216245045
    , retrieved 2020-10-24
  2. ^
    S2CID 4427002
    .
  3. ^
    S2CID 130486197
    .
  4. ^ a b Goehlich, U.B.; Tischlinger, H.; Chiappe, L.M. (2006). "Juravenator starki (Reptilia, Theropoda) ein neuer Raubdinosaurier aus dem Oberjura der Suedlichen Frankenalb (Sueddeutschland): Skelettanatomie und Weichteilbefunde". Archaeopteryx. 24: 1–26.
  5. ^ Xu, X. (2006). "Scales, feathers, and dinosaurs". "Nature", 440: 287-288.
  6. S2CID 233860853
    .
  7. ^ Viohl, G. (1999). "Discovery of a new small theropod". Archaeopteryx. 17: 15–19.
  8. ^
    S2CID 129785393
    .
  9. S2CID 85684021
    .
  10. ^ Cristiano dal Sasso & Simone Maganuco (2011) "Scipionyx samniticus (Theropoda: Compsognathidae) from the Lower Cretaceous of Italy — Osteology, ontogenetic assessment, phylogeny, soft tissue anatomy, taphonomy and palaeobiology" Memorie della Società Italiana de Scienze Naturali e del Museo Civico di Storia Naturale di Milano XXXVII(I): 1-281
  11. S2CID 4364892
    .
  12. S2CID 33253407
    .
  13. S2CID 222137370
    .

External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Juravenator&oldid=1140481179"