Sciurumimus

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Sciurumimus
Temporal range:
Ma
↓
The juvenile type specimen
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Orionides
Genus: †Sciurumimus
Rauhut et al., 2012
Species:
†S. albersdoerferi
Binomial name
†Sciurumimus albersdoerferi
Rauhut et al., 2012

Sciurumimus ("Squirrel-mimic," named for its tail's resemblance to that of the tree squirrel, Sciurus[1]) is an extinct genus of tetanuran theropod from the Late Jurassic Torleite Formation of Germany. It is known from a single juvenile specimen representing the type species, Sciurumimus albersdoerferi, which was found in a limestone quarry close to Painten in Lower Bavaria.[2] The specimen was preserved with traces of feather-like filaments.[3]

The Sciurumimus specimen was first announced in an informal presentation by Rauhut and Foth (2011),

phylogenetic analyses dispute this placement.[5] However, a recent analysis on immature coelurosaurs, including compsognathids, finds Sciurumimus back in Megalosauroidea.[6]

Description

Life restoration of a juvenile Sciurumimus, with two Pterodactylus in the background

Sciurumimus is known from a single holotype fossil that is exceptionally well-preserved, with full skeleton in complete articulation along with fine details of soft tissue. It is comparable in size and proportions to the juvenile coelurosaur Juravenator, although differs significantly in several anatomical details. The skull of Sciurumimus is proportionally large, at 156% of the length of the femur and longer than the cervical vertebrae series. These body proportions, along with short forelimbs, lack of fusion in the skeleton, and regular tooth morphology indicate the specimen represents a very young, probably early-posthatchling individual.[2]

The fossil preserves filamentous plumage at the tail base and on other parts of the body. These structures are described as being identical to the

therizinosauroid Beipiaosaurus. Skin is also preserved.[7] Although most of the preserved soft tissue on the Sciurumimus holotype likely represent integumentary structures, a small patch of what may be muscle tissue is observed along the rear edge of the tibia.[2]

Classification

Close up of the skull

When first discovered, a phylogenetic analysis suggested that Sciurumimus may have been a primitive member of the Megalosauroidea, a clade of large carnivorous dinosaurs more primitive than many other well-known theropods like the

carnosaurs, making it the most basal known feathered theropod.[2] This classification was supported by one of three initial analyses conducted by the scientists who described it. The other two analyses, which the authors regarded as less well supported, found it as more closely related to Monolophosaurus and Avetheropoda, and in an unresolved position among avetheropods and megalosauroids, respectively. The exact position in the various analyses was difficult to determine due to the fact that the only known specimen is a very young juvenile.[2]

This initial study was criticized by several researchers, who noted that some of the old analyses the scientists used to plug in data from the new fossil were incomplete and missing relevant data on various species.

neocoelurosaurs.[13] A detailed reanalysis of the taxon was done in the supplementary material of Hartman et al. (2019) which found several characters to be misscored, and when the uncorrected Sciurumimus was placed in the matrix Juravenator was also found to be a basal tetanuran, while if Sciurumimus was absent Juravenator would be found to be a basal coelurosaur. The analysis found Sciurumimus to be a compsognathid, though they noted that this position was tentative.[5] Foth et al. (2020) again placed, albeit tentatively, Sciurumimus in Megalosauroidea, this time accompanied by Juravenator.[14]

Andrea Cau, in 2024, recovered Sciurumimus, along with Compsognathus and Scipionyx all within different positions within Megalosauroidea. [6]

Here is a simplified phylogeny of Cau (2024) with Sciurumimus in bold.

Tetanurae

References

  1. ^ "Newly Discovered Dinosaur Implies Greater Prevalence of Feathers". American Museum of Natural History. July 2, 2012. Retrieved February 2, 2019.
  2. ^
    PMID 22753486
    .
  3. S2CID 123219913
    .
  4. ^ Rauhut and Foth, (2011). New information on Late Jurassic theropod dinosaurs from Southern Germany. IV Congresso Latinoamericano Paleontologia de Vertebrados.
  5. ^
    PMID 31333906
    .
  6. ^
    doi:10.4435/BSPI.2024.08
    .
  7. S2CID 245820672
    .
  8. ^ Mortimer, M. 2013. "Coelurosauria Archived 2013-09-29 at the Wayback Machine", The Theropod Database. Accessed online 09-AUG-2013.http://archosaur.us/theropoddatabase/Coelurosauria.htm#Sciurumimusalbersdoerferi
  9. ^ Mortimer, M. and Marjanovic, D. (in prep.) http://archosaur.us/theropoddatabase/Coelurosauria.htm#Sciurumimusalbersdoerferi Archived 2013-09-29 at the Wayback Machine
  10. S2CID 4364892
    .
  11. S2CID 56480710
    .
  12. S2CID 174811556
    .
  13. ISBN 978-0-691-16766-4
    .
  14. S2CID 216245045
    , retrieved 2020-11-12
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