Juramaia

Juramaia is an extinct genus of very basal eutherian mammal known from the Late Jurassic (Oxfordian stage) deposits of western Liaoning, China. It is a small shrew-like mammal with a body length of approximately 70–100 mm,[1][2] making it similar in size to the modern De Winton's shrew.[3] Juramaia is known from the holotype BMNH PM1343, an articulated and nearly complete skeleton including incomplete skull preserved with full dentition.

Juramaia
Temporal range: Late Jurassic, 160.89–160.25 Ma
↓
Restoration
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Clade: Eutheria
Genus: †Juramaia
Luo et al., 2011
Species
  • †J. sinensis Luo et al., 2011 (type)

Discovery

It was collected in the Daxigou site, Jianchang, from the Tiaojishan Formation dated at about 160 million years ago.[4] It was first named by Zhe-Xi Luo, Chong-Xi Yuan, Qing-Jin Meng and Qiang Ji in 2011 and the type species is Juramaia sinensis.[5]

Evolution

The discovery of Juramaia provides new insight into the evolution of placental mammals by showing that their lineage diverged from that of the marsupials 35 million years earlier than previously thought.[5] Furthermore, its discovery fills gaps in the fossil record and helps to calibrate modern, DNA-based methods of dating the evolution.[6][7] Based on climbing adaptations found in the forelimb bones, it has been suggested that the basal stock of Eutheria was arboreal,[5] in a manner resembling that of modern rats.[8]

Classification
 
Metatheria
 

Sinodelphys szalayi

 
 

Cenozoic metatherian

 
 
Eutheria
 

Juramaia sinensis

 
 

Montanalestes keeblerorum

 
 
 

Murtoilestes abramovi

 
 

Eomaia scansoria

 
 

Prokennalestes trofimovi

 
 
 

Cenozoic placentalia

 
 
 

See also

References
  1. "Juramaia sinensis - 160-Million-Year-Old Fossil Pushes Back Mammal Evolution". Archived from the original on 2012-03-27. Retrieved 2011-09-09.
  2. Welsh, Jennifer (24 August 2011). "Skinny 'Shrew' Is Oldest True Mammal". LiveScience. Retrieved 5 December 2017.
  3. Smith, Andrew T.; et al. (2010-04-23). A Guide to the Mammals of China. p. 308. ISBN 978-1400834112.
  4. Chu, Z.; He, H.; Ramezani, J.; Bowring, S.A.; Hu, D.; Zhang, L.; Zheng, S.; Wang, X.; Zhou, Z.; Deng, C.; Guo, J. (2016). "High-precision U-Pb geochronology of the Jurassic Yanliao Biota from Jianchang (western Liaoning Province, China): Age constraints on the rise of feathered dinosaurs and eutherian mammals". Geochemistry, Geophysics, Geosystems. 17 (10): 3983–3992. doi:10.1002/2016GC006529.
  5. Zhe-Xi Luo; Chong-Xi Yuan; Qing-Jin Meng; Qiang Ji (25 August 2011). "A Jurassic eutherian mammal and divergence of marsupials and placentals" (PDF). Nature. 476 (7361): 442–445. doi:10.1038/nature10291. PMID 21866158. Archived from the original (PDF) on 10 November 2013. Electronic supplementary material
  6. "Fossil redefines mammal history" BBC News
  7. Discovery of a 160-million-year-old fossil represents a new milestone in early mammal evolution
  8. Bonnan MF, Shulman J, Varadharajan R, Gilbert C, Wilkes M, Horner A, et al. (2 March 2016). "Forelimb Kinematics of Rats Using XROMM, with Implications for Small Eutherians and Their Fossil Relatives". PLOS ONE. 11 (3): e0149377. doi:10.1371/journal.pone.0149377. PMC 4775064. PMID 26933950.
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