Zuolong

Source: Wikipedia, the free encyclopedia.

Zuolong
Temporal range: Late Jurassic[1]
~161.2 to 158.7 Ma - Oxfordian
Skeletal diagram of known material in white and light grey
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Coelurosauria (?)
Genus: †Zuolong
Choiniere et al., 2010
Type species
†Zuolong salleei
Choiniere et al., 2010

Zuolong is an extinct

Chinese word "long" which means dragon. The specific epithet "salleei" is in honor of Hilmar Sallee, who funded the expedition which led to the specimen's discovery.[2]

Discovery

Zuolong was discovered in the upper part of the Wucaiwan member of the Shishugou Formation in Xinjiang, China. 40Ar/39Ar dating of volcanic feldspar at this locality places it at the span between the Callovian and Oxfordian boundary, and Zuolong was discovered in the upper part of this unit, which is interpreted as being Oxfordian in age.[1] The specimen was discovered in 2001 by the Sino-American field expedition, but it was not described until 2010 when Jonah Choiniere, James Clark, Catherine Forester, and Xu Xing published a full analysis of the bones.[2]

Choiniere and colleagues noted that, at the time of its description, Zuolong was one of the oldest

coelurosaurs known to science, but that the implications of its discovery cannot be fully understood until more fossil material is discovered. The Middle Jurassic preserves very few coelurosaurs, and the ones which are known are almost all from China, with the exception of Proceratosaurus and Kileskus.[2]

The holotype of Zuolong, given the designation IVPP V15912, consists of a partially complete skull and numerous post-cranial elements. The skull preserves a

metatarsals from the right foot, three toes, and a single toe claw.[2]

Description

Life restoration of Zuolong with a hypothetical coat of feathers

Zuolong was not a large theropod. Choiniere and colleagues used two regression analyses based on the work of P. Christiansen and R.A. Fariña[3] as well as François Therrien, and Donald M. Henderson[4] to estimate the body mass of Zuolong and they calculated a range of between 16–50 kilograms (35–110 lb) based on the length of the femur and the size of the skull. This would make it about half the estimated size of its contemporary, Guanlong.[2] Later, Gregory S. Paul suggested that the holotype is a juvenile and estimates a total adult length of 3 metres (9.8 ft) and a mass of 60 kilograms (130 lb).[5] Other authors have suggested a larger adult size, giving a total length of 3.35 metres (11.0 ft) meters and a mass of 43 kilograms (95 lb) kilograms.[6] The holotype is also considered by Thomas R. Holtz Jr. to almost certainly be from a juvenile theropod.[7]

Choiniere and colleagues provide the following traits as autoapomorphies for the skull: a slit-like depression on the surface of the

vertebral centra, a straight humeral and femoral shaft, and a high and rounded ilium.[2]

Skull

Several parts of the skull of the holotype are preserved completely, albeit with very poor preservation quality. This makes some aspects of the skull anatomy difficult to determine, but enough is known that the authors who described it noted several distinct features. There are very few primitive

theropods such as Guanlong, Coelurus, and Tanycolagreus. The skull is overall triangular-shaped, with a significant tapering towards the end of the snout. It has very large orbits which face laterally and a pronounced anterior process of the lacrimal, which gives the appearance of a small crest above the eyes, a trait very common among theropods.[2]

The preserved

megalosauroids.[2]

Post-Cranial Skeleton

Map showing the Wucaiwan locality
Map showing the Wucaiwan locality in China, where Zuolong was found

Twenty-two vertebrae are preserved, coming from all four vertebral segments. Choiniere and colleagues noted multiple features of the

caudal vertebrae, like the dorsals, lack both fossae and formania on their lateral surface, and they also preserve sharply inclined neural spines, though these are not as pronounced as they are in allosauroids.[2]

The left humerus and radius are both preserved, and the radius is about 88% the length of the humerus, which is a ratio that is conserved across a wide variety of theropods. The manual claws which are preserved are strongly curved and have lateral grooves down their length.[2]

The hip bones display a supraacetabular crest which extends from the posterior end of the

fovea capitis, is known to be a pathological condition in male turkeys, so the authors say they cannot rule this out as a possibility, although they think it is relatively unlikely and cannot be proven until a second specimen is found.[2]

The rest of the leg bones display a patchwork of characteristics seen in other theropods. The

tyrannosauroids. The tibia is not complete, so it is not possible to know if Zuolong had a tibia which exceeded the femur in length, which is more common in derived coelurosaurs and is commonly viewed as a cursorial adaptation. The metetarsals are generally similar to other basal coelurosaurs such as Coelurus and Tanycolagreus, however they do have a unique feature in this part of the body which is a flange on the front-medial edge of the distal condyle of the third metatarsal, which is not seen in similar taxa.[2]

Classification

The classification of Zuolong has been uncertain and controversial since its description.[2] Almost every analysis including it in its matrix has recovered this species in a different position.[8][9][10] Different hypotheses of its classification can be seen below.

As a Basal Coelurosaur

The most common hypothesis of the taxonomy of Zuolong is that it is a basal member of coelurosauria.[2][8][11][7]

In their description of Zuolong in 2010, Choiniere and colleagues included a wide variety of taxa in their phylogenetic analysis. Zuolong exhibits several

avetheropods. They also included numerous coelurosaurs of uncertain classification in an attempt to use their analysis to resolve the phylogeny hypotheses at the base of coelurosauria. These included Bagaraatan, Tugulusaurus, Tanycolagreus, and Aniksosaurus, although a few of these taxa were eventually excluded from the final analysis.[2]

The resulting analysis recovered Zuolong within a

astragalus, and a lack of a horizontal groove on the astragalar condyles. Another novel result of this phylogeny included a recovery of Proceratosaurus at the base of coelurosauria outside of tyrannosauroidea. A reduced consensus tree compiled from 421 of the most parsimonious trees in their analysis is shown below.[2]

Coelurosauria

In 2020, a group of several authors led by the Brazilian paleontologist Juliana Manso Sayão described a new genus of coelurosaur from the Romualdo Formation, Aratasaurus.[8] They conducted a phylogenetic analysis using the data set presented in a 2012 paper about the anatomy and relationships of Nqwebasaurus, another enigmatic early coelurosaur, some supplementary data about Santanaraptor, and added the recently described Bicentenaria to the dataset.[8][12]

In the resulting analysis the conducted, they recovered this new taxon as the

caudal vertebrae, a shelf-like fossa on the ilium, and a lack of an anterior process on the pubic boot.[8]

Other novel results of this analysis included finding a

stem-maniraptoran and the sister taxon of Ornitholestes. A consensus tree compiled from the 1,056 most parsimonious trees is shown below.[8]

Coelurosauria

The most recent phylogeny including Zuolong was contained in the paper which described the new taxon Maip, a large megaraptoran from the Late Cretaceous by Rolando and colleagues in 2022. They performed two analyses, one which included fragmentary taxa, and one which did not. Although the discussion of their results focused most heavily on its implications for megaraptoran taxonomy, both of their analyses resolved the same relationships for Zuolong and other basal coelurosaurs. The results of their analysis, compiled from a consensus of the 2,560 most parsimonious trees is shown below,[11]

Tetanurae

As a Basal Maniraptoromorph

Zuolong is a part of the analysis conducted by Fernando Novas and colleagues in their description of the basal coelurosaur Bicentenaria in 2012. Their phylogenetic analysis was relatively unresolved as a result of coding Santanaraptor as a wildcard taxon, so it was removed from their final analysis. In this analysis, they observed that femur length, which is viewed as a proxy for body size exhibited a continuous two-step decline at the base of coelurosauria and then again at the base of paraves. This seemingly unbroken trend was used to classify Zuolong as a stem-maniraptoran based on the size estimates published for the holotype. This decrease in size is also explained as the cause of the rapid diversification of coelurosauria in the Middle or Late Jurassic.[9]

Coelurosauria

In

compsognathid, Xunmenglong. Their paper included a phylogenetic analysis based on the data set provided by Choiniere and colleagues in their 2014 description of Aorun.[13][14] This analysis was unique in its inclusion of a dual analytical framework; the authors of both papers conducted a conventional phylogenetic analysis as well as one which coded several primary characters to account for the ontogeny of the sampled taxa.[14] This was done because the holotype of Aorun was shown by histology to be a juvenile.[13]

This resulted in very different results depending on the analysis used. In the ontogeny analysis, Zuolong is recovered in the conventional position as a very early-diverging coelurosaur outside of

synapomorphies for this clade. Xing and colleagues use the discrepancy between their two analyses as an example of the need for additional specimens to be described before phylogenetic relationships can be confidently established.[14]
The results of both of their analyses can be seen below.

Full Analysis[14]
Coelurosauria
Ontogeny Analysis[14]
Coelurosauria

As a Basal Tetanuran

sauropodomorphs.[10][16] Cau's analysis differs substantially from those conducted by Matthew Baron in 2017[16] and Paul Dieudonné and colleagues in 2020[17] by recovering the enigmatic Chilesaurus as a basal member of tetanurae.[10]

Cau recovered Zuolong as being slightly more basal than Chilesaurus, which itself is found to be the sister taxon of

cervical vertebrae, a reduced shelf over the acetabulum, a perforation of the pubic apron, a medially-facing head of the femur, and a reduction of the femoral trochlea.[10] Darren Naish and Cau also recovered a basal tetanuran position for Zuolong in their 2022 re-description of Eotyrannus.[18] The consensus tree from Cau's original analysis, compiled from the 3,072 most parsimonious trees, can be seen below.[10]

Theropoda

Paleoecology

Paleoenvironment

A climatological map of the world during the middle to late Jurassic, with the Shishugou labeled "C1"

The only remains of Zuolong so far described were discovered near the town of Wucaiwan in Xinjiang, China.[2] This locality is a part of the upper member of the Shishugou Formation,[19] which ranges from 164 to 159 million years ago. This interval spans the transition from the Middle Jurassic to the Late Jurassic, though most of it has been recently dated to the Late Jurassic.[20] This region is inland and arid today, but in the Late Jurassic, it formed a coastal basin on the northern shores of the Tethys Ocean.[21]

The lower (or Wucaiwan) member of the Shishugou consists primarily of red

sauropods which created "death pits" that trapped and buried small animals.[20][22]

A depiction of some of the animals of the Shishugou Formation in their environment

There have also been significant volcanic ash deposits found in the Wucaiwan member, indicating that volcanic activity in the western part of China was increasing at this time.[20]

Contemporary Fauna

A variety of small animals have been uncovered from the

ornithopods, tetanurans, and a putative ornithomimosaur.[19][25]

Named fossils include the primitive mammal-relative

ceratosaur Limusaurus, which was preserved in one of the muddy "death pits".[20]

See also

References

  1. ^ a b Clark, J. M.; Xu, X.; Eberth, D. E.; Forester, C. A.; Machlus, M.; Hemming, S.; Yuan, W.; Hernandez, R. (2006). "The Middle-to-Late Jurassic terrestrial transition: new discoveries from the Shishugou Formation, Xinjiang, China". 9th International Symposium, Mesozoic Terrestrial Ecosystems and Biota. University of Manchester: 26–28.
  2. ^
    S2CID 86543963
    .
  3. S2CID 84322349
    .
  4. S2CID 86025320
    .
  5. ISBN 978-0-691-13720-9
    .
  6. ISBN 978-0691180311
    .
  7. ^
    ISBN 978-0-375-82419-7
    .
  8. ^
    PMID 32651406
    .
  9. ^
    doi:10.22179/REVMACN.14.372
    .
  10. ^
    doi:10.4435/BSPI.2018.01
    . Retrieved 2023-08-12.
  11. ^
    PMID 35474310
    .
  12. doi:10.1016/j.jafrearsci.2012.05.005
    .
  13. ^
    S2CID 53538348. Figures available at: Figshare.com
  14. ^
    S2CID 210615455
    .
  15. S2CID 225281618
    .
  16. ^
    S2CID 205254710
    .
  17. S2CID 221854017
    .
  18. PMID 35821895
    .
  19. ^
    ISBN 0-520-24209-2
    .
  20. ^
    S2CID 251934171
    .
  21. ^
    PMID 20838442
    .
  22. S2CID 131520314
    .
  23. S2CID 129583852
    .
  24. S2CID 4358448
    .
  25. ISBN 0-520-24209-2
    .
Retrieved from "https://en.wikipedia.org/w/index.php?title=Zuolong&oldid=1221008313"