''Sciurumimus'' ("
Squirrel
Squirrels are members of the family Sciuridae, a family that includes small or medium-size rodents. The squirrel family includes tree squirrels, ground squirrels (including chipmunks and prairie dogs, among others), and flying squirrels. Squ ...
-mimic," named for its tail's resemblance to that of the tree squirrel, ''
Sciurus
The genus ''Sciurus'' contains most of the common, bushy-tailed squirrels in North America, Europe, temperate Asia, Central America and South America.
Species
The number of species in the genus is subject to change.
In 2005, Thorington & Hoffma ...
''
) is an extinct genus of
tetanuran
Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans (including birds). Tetanurans ar ...
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 ...
from the
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987.
In European lithostratigraphy, the name ...
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
Lower Bavaria (german: Niederbayern, Bavarian: ''Niedabayern'') is one of the seven administrative regions of Bavaria, Germany, located in the east of the state.
Geography
Lower Bavaria is subdivided into two regions () – Landshut and Donau-W ...
.
The specimen was preserved with traces of feather-like filaments.
The ''Sciurumimus'' specimen was first announced in 2011 in an informal presentation, but not formally described and named until the following year. Although originally classified as a basal
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 ...
,
[ later ]phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
analyses dispute this placement, suggesting it was a basal member of the Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.
Relationships
Although many phylogenetic analyses found basal tetanurans that were outside ...
.
Description
''Sciurumimus'' is known from a single 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 ...
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
''Juravenator'' is a genus of small (75 cm long) coelurosaurian theropod dinosaur (although a 2020 study proposed it to be a hatchling megalosauroid), which lived in the area which would someday become the top of the Franconian Jura of Ger ...
'', although differs significantly in several anatomical details. The skull of ''Sciurumimus'' is proportionally large, at 156% of the length of the femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
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.[
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 stage 1 feathers preserved in some ]ornithischian
Ornithischia () is an extinct order 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 ...
s, the basal tyrannosaur
Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent ...
''Dilong
''Dilong'' (; lit. "earth dragon") is a Chinese dragon name that is also used to mean "earthworm" in traditional Chinese medicine and ''Geosaurus'' in zoological nomenclature.
Dragon
In Chinese mythology, ''dilong'' "earth dragon" is one of m ...
'', and the basal therizinosauroid
Therizinosaurs (once called segnosaurs) were large herbivorous theropod dinosaurs whose fossils have been found across the Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs, skull and pelvis unite t ...
'' Beipiaosaurus''. Skin is also preserved. 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.[
]
Classification
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 tyrannosauroid
Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent b ...
s and carnosaur
Carnosauria is an extinct large group of predatory dinosaurs that lived during the Jurassic and Cretaceous periods. Starting from the 1990s, scientists have discovered some very large carnosaurs in the carcharodontosaurid family, such as ''Gig ...
s, making it the most basal known feathered theropod.[ 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
''Monolophosaurus'' ( ; meaning "single-crested lizard") is an extinct genus of tetanuran theropod dinosaur from the Middle Jurassic Shishugou Formation in what is now Xinjiang, China.Holtz, Thomas R. Jr. (2011) ''Dinosaurs: The Most Complete, Up ...
'' and Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.
Definition
Avetheropoda was named by Gregory S. Paul in 1988, and was first defined as a clade by Currie and Padian i ...
, 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.[
This initial study was criticized by several researchers, who noted that some of the old analysis the scientists used to plug in data from the new fossil were incomplete and missing relevant data on various species.][Mortimer, M. 2013.]
Coelurosauria
", The Theropod Database. Accessed online 09-AUG-2013.http://archosaur.us/theropoddatabase/Coelurosauria.htm#Sciurumimusalbersdoerferi[Mortimer, M. and Marjanovic, D. (in prep.) http://archosaur.us/theropoddatabase/Coelurosauria.htm#Sciurumimusalbersdoerferi ] In an analysis published in 2013 ''Sciurumimus'' was obtained as one of the most primitive members of the Coelurosauria, more derived than the megalosauroids. However, this analysis focused on the Coelurosauria and the dataset on which it was based contained only one megalosaurid and only four terminal taxa outside the Coelurosauria.[See pages 3 and 11 in th]
supplementary material
of Other analyses found it to be an allosauroid
Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Metriacanthosauridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae. Allosauroids, alongside the family Megalosauroidea, were among th ...
or a tetanuran outside Avetheropoda. Paul (2016) placed it among basal neocoelurosaurs. 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
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 ...
, though they noted that this position was tentative. Foth ''et al''. (2020) again placed, albeit tentatively, ''Sciurumimus'' in Megalosauroidea, this time accompanied by ''Juravenator
''Juravenator'' is a genus of small (75 cm long) coelurosaurian theropod dinosaur (although a 2020 study proposed it to be a hatchling megalosauroid), which lived in the area which would someday become the top of the Franconian Jura of Ger ...
''.
References
{{Taxonbar, from=Q133894
Prehistoric coelurosaurs
Late Jurassic dinosaurs of Europe
Fossils of Germany
Feathered dinosaurs
Fossil taxa described in 2012
Taxa named by Mark Norell