Misplaced Pages

Symmetrolestes Temporal range: Late Barremian-Late Aptian 125–115 Ma PreꞒ Ꞓ O S D C P T J K Pg N
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
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 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. The holotype is kept 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.

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.

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.

Paleoecology

The type specimen of Symmetrolestes was found in Barremian-Aptian layers in the Kitadani Formation, the formation belongs to the Tetori Group in which is located in Central Japan. The formation shows a wide array of faunae, mainly many species of plants like cycads and conifers, which are mainly represented by cones and shoots. The animal fauna mainly consisted of dinosaurs such as the medium-sized theropod Fukuiraptor, the small ornithopod Fukuisaurus, and the giant sauropod Fukuititan. Smaller dinosaurs and basal birds like Fukuivenator and Fukuipteryx also coexisted with Symmetrolestes. The formation also preserves fossils of crocodilians belonging to the group Eusuchia, turtle shells and the remains of prehistoric mollusks. Two other mammals from the Kitadani Formation remain undescribed. 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.

References

1. Han, Gang; Meng, Jin (May 24, 2016). "A new spalacolestine mammal from the Early Cretaceous Jehol Biota and implications for the morphology, phylogeny, and palaeobiology of Laurasian 'symmetrodontans'". Zoological Journal of the Linnean Society. 178 (2): 343–380. doi:10.1111/zoj.12416.
2. ^ 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. Azuma, Yoichi; Xu, Xing; Shibata, Masateru; Kawabe, Soichiro; Miyata, Kazunori; Imai, Takuya (April 2016). "A bizarre theropod from the Early Cretaceous of Japan highlighting mosaic evolution among coelurosaurians". Scientific Reports. 6 (1): 20478. Bibcode:2016NatSR...620478A. doi:10.1038/srep20478. ISSN 2045-2322. PMC 4763874. PMID 26908367.
5. Shibaba, Masateru; Azuma, Yoichi (2015). "New basal hadrosauroid (Dinosauria: Ornithopoda) from the Lower Cretaceous Kitadani Formation, Fukui, central Japan" (PDF). Zootaxa. 3914 (4): 421–40. doi:10.11646/zootaxa.3914.4.3. 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. Miyata, Kazunori; Azuma, Yoichi; Shibata, Masateru (2016-02-17). "New mammalian specimens from the Lower Cretaceous Kitadani Formation, Tetori Group, Fukui, Japan". Historical Biology. 28 (1–2): 139–150. doi:10.1080/08912963.2015.1012509. ISSN 0891-2963. S2CID 130464170.
9. "Kitadani Dinosaur Quarry (lower, BB I) (Cretaceous to of Japan)". PBDB.org.

v t e Mammalia
Kingdom: Animalia Phylum: Chordata Clade: Synapsida Clade: Therapsida Clade: Cynodontia Clade: Mammaliaformes Synapsida see Synapsida Cynodontia see Cynodontia Mammalia see below↓
Mammalia Australosphenida? †Ambondro †Tendagurutherium? Monotremata? †Henosferidae Asfaltomylos Henosferus †Ausktribosphenidae Ausktribosphenos Bishops? Kryoparvus? Monotremata †Kollikodontidae? Kollikodon Kryoryctes? Sundrius †Steropodontidae Parvopalus? Steropodon †Teinolophidae Stirtodon? Teinolophos Ornithorhynchoidea †Opalios Ornithorhynchidae †Dharragarra? †Monotrematum? †Obdurodon Ornithorhynchus †Patagorhynchus? Tachyglossidae †Megalibgwilia †Murrayglossus Tachyglossus Zaglossus †Allotheria? see Allotheria includes multituberculates Theriimorpha see below↓
Theriimorpha Theriimorpha †Acinacodus †Amphidon †Amphilestes †Aploconodon †Chaoyangodens †Comodon †Condorodon †Dyskritodon? †Fruitafossor? †Hakusanodon †Indotriconodon †Juchilestes †Jueconodon †Kemchugia †Kryptotherium †Liaoconodon †Liaotherium †Manchurodon †Nakunodon †Phascolotherium †Sangarotherium †Tendagurodon †Allotheria? Monotremata? †Gobiconodontidae Fuxinoconodon Gobiconodon Hangjinia Huasteconodon? Meemannodon Repenomamus Spinolestes †Jeholodentidae Jeholodens Yanoconodon †Klameliidae? Ferganodon Klamelia †Triconodontidae Alticonodon Arundelconodon Astroconodon Corviconodon Eotriconodon Jugulator Meiconodon Priacodon Triconodon Trioracodon Victoriaconodon Volaticotheria? †Volaticotheria Argentoconodon Ichthyoconodon Triconolestes? Volaticotherium †Tinodontidae Gobiotheriodon? Tinodon Trishulotherium Yermakia Trechnotheria Monotremata? †Zhangheotheriidae Anebodon Kiyatherium Maotherium Ningchengodon Origolestes Zhangheotherium †Spalacotheriidae Akidolestes Aliaga Cifellitherium Heishanlestes Infernolestes Lactodens Shalbaatar Spalacolestes Spalacotheridium Spalacotherium Spalacotheroides Symmetrodontoides Symmetrolestes Yaverlestes Cladotheria see below↓
Cladotheria †Dryolestida Brancatherulum? Dorsetodon Drescheratherium Euthlastus Henkelotherium Paurodon Tathiodon Dryolestidae Achyrodon Amblotherium Anthracolestes Beckumia Crusafontia Dryolestes Groebertherium? Guimarotodus Hercynodon Krebsotherium Lakotalestes? Laolestes Minutolestes Phascolestes Portopinheirodon Treslagosodon †Meridiolestida Amarillodon Austrotriconodon Bondesius Casamiquelia Cronopio Groebertherium? Lakotalestes? Leonardus Necrolestes Paraungulatum Quirogatherium Solanutherium Mesungulatoidea Coloniatherium Mesungulatum Orretherium Peligrotherium Reigitherium †Donodontidae Amazighodon Anoualestes Donodon Stylodens Prototribosphenida †Abelodon †Amphibetulimus †Amphitherium †Arguimus †Brancatherulum? †Chunnelodon †Magnimus †Minimus †Mozomus †Nanolestes †Palaeoxonodon †Vincelestes Monotremata? †Peramuridae Afriquiamus? Kouriogenys Peramuroides Peramus Tendagurutherium? Tribosphenida / Boreosphenida †Aegialodon †Argaliatherium †Brasilestes †Carinalestes †Eomaia †Holoclemensia †Hypomylos †Juramaia †Kermackia †Kielantherium †Pappotherium †Picopsis †Tirotherium †Tribactonodon Theria †Patagomaia Eutheria see Eutheria includes placentals Metatheria see Metatheria includes marsupials
Other taxa Incertae sedis †Atlasodon †Chronoperates †Microderson †Thereuodon †Tingamarra Saint Bathans Mammal UA 8699 Other taxa Prototheria Yinotheria Eutriconodonta Amphilestidae Theriiformes Pantotheria Symmetrodonta Eupantotheria Paurodontidae Amphitheriidae Marsupionta

• Spalacotheriidae
• Fossil taxa described in 2004
• Fossils of Japan
• Cretaceous mammals
• Cretaceous mammals of Asia
• Early Cretaceous mammals of Asia
• Prehistoric mammal genera