Symmetrolestes

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Symmetrolestes
Temporal range: Late
Ma
Symmetrolestes parvus (NSM PV 20562, holotype). A. Lingual stereo view of the
dentary
. B. Drawing of the jaw in approximately the same position as in A.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: †Symmetrodonta
Family: †Spalacotheriidae
Genus: †Symmetrolestes
Type species
†Symmetrolestes parvus
Tsubamoto and Rougier, 2004

Symmetrolestes is an extinct genus of small

spalacotheriid mammal[1] from the Early Cretaceous period of Japan. The genus contains one species known as S. parvus, the type fossil (which is only fossil known) is from fluvial deposits located in the Dinosaur Quarry in the Kitadani Formation, near the city of Katsuyama which lies alongside valley of the Sugiyamagawa River
. It was described by Tsubamoto and Rougier in 2004 keeping the holotype at the National Science Museum, Tokyo, Japan.

Description

The type specimen (NSM PV 20562, holotype) is known from a fragmentary right jaw with the first incisor and five postcanine teeth preserved. Symmetrolestes is more derived than zhangheotheriids as it had acute−angled molariform teeth with completely developed shearing surfaces, taller crowns on its teeth and more complete cingulids. It differs from other spalacotheriids due to the fact it had fewer molariform teeth, a higher number of premolariform teeth and gradual transition between premolariforms and molariforms. The jaw is gracile, slender, and never reaches more than 1.5 times the height of the teeth.[2]

Etymology

Symmetrolestes means "symmetric hunter", The root Symmetro is in reference to the symmetric aspect of the molars and the root lestes meaning "hunter", a common ending of the taxonomic names of most Mesozoic mammals based on the dubious hunting habits of these of such mammals. The species name parvus means small, in reference to its small stature.[2]

Classification

A cladistic analysis that was made shows that Symmetrolestes is a sister group to other Spalacotheriidae. The scientists went on to say that the combination of the occurrences of the more primitive spalacotheriids and Symmetrolestes, in Japan and of Zhangheotheriidae, which is the sister taxon of Spalacotheriidae, in China suggests a possibility the East Asian origins of the group Spalacotheriidae.[2]

Paleoecology

dinosaurs
shared their habitat with Symmetrolestes and other mammals

The type specimen of Symmetrolestes was found in

mollusks. Two other mammals from the Kitadani Formation remain undescribed.[8]
The Kitadani Formation was likely not an arid environment, but one that was more wet with meandering rivers. Volcanic sediments have also been found in the formation in the form of tuffs.[9]

References

  1. doi:10.1111/zoj.12416
    .
  2. ^ a b c T. Tsubamoto, G. W. Rougier, S. Isaji, M. Manabe, and A. M. Forasiepi. 2004. New Early Cretaceous spalacotheriid "symmetrodont" mammal from Japan. Acta Palaeontologica Polonica 49(3):329-346
  3. ^ Yabe, A., Terada, K. and Sekido, S., 2003: The Tetori-type flora, revisited: a review. Memoir of the Fukui Prefectural Dinosaur Museum, 2:23–42.
  4. PMID 26908367
    .
  5. PMID 25661952
    .|
  6. ^ Sonoda T, Azuma Y, Hirayama R, Ando H. (2015) New trionychoid specimens and turtle fauna from the Lower Cretaceous Kitadani Formation of the Tetori Group in central Japan. PeerJ PrePrints 3:e949v1 https://doi.org/10.7287/peerj.preprints.949v1
  7. ^ Hirayama, R. (2002) Preliminary report of the fossil turtles from the Kitadani Formation (Early Cretaceous) of the Tetori Group of Katsuyama, Fukui Prefecture, Central Japan. Memoirs of the Fukui Prefectural Dinosaur Museum. 1: 29-40.
  8. S2CID 130464170
    .
  9. ^ "Kitadani Dinosaur Quarry (lower, BB I) (Cretaceous to of Japan)". PBDB.org.
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