@article{TEXTUAL,
      recid = {14680},
      author = {Sharma, Neelima and Haridy, Yara and Shubin, Neil},
      title = {Synovial joints were present in the common ancestor of  jawed fish but lacking in jawless fish},
      journal = {PLOS Biology},
      address = {2025-02-25},
      number = {TEXTUAL},
      abstract = {Synovial joints, characterized by reciprocally congruent  and lubricated articular surfaces separated by a cavity,  can simultaneously provide mobility and load bearing. Here,  we study the early evolution of synovial joints by  examining the morphological, genetic, and molecular  features required for the development and function of the  joints in elasmobranchs and cyclostomes. We show the  presence of cavitated and articulated joints in the  skeleton of elasmobranchs, such as the little skate  (Leucoraja erinacea) and bamboo shark (Chiloscyllium  plagiosum). However, our results do not support the  presence of articular cavities between cartilaginous  elements in cyclostomes such as sea lampreys (Petromyozon  marinus) and hagfish (Myxine glutinosa). Immunostaining  reveals the expression of lubrication-related proteoglycans  like aggrecan and glycoproteins such as hyaluronic acid  receptor (CD44) at the articular surfaces in little skates.  Analysis of joint development in little skate embryos shows  the expression of growth differentiation factor-5 (Gdf5)  and β-catenin at the joint interzones like tetrapods.  Muscle paralysis in little skate embryos leads to joint  fusion, suggesting that muscle activity is necessary for  the formation of synovial cavity and development of normal  articular surfaces, in a manner similar to zebrafish and  tetrapods. Together, these data suggest that synovial  joints originated in the common ancestor of extant  gnathostomes. A review of fossils from the extinct clades  along the gnathostome stem suggests that joints with  reciprocally articulating surfaces arose in the dermal  skeleton of the common ancestor of all jawed vertebrates.  Synovial joints in cartilaginous tissue were a subsequent  gnathostome innovation.},
      url = {http://knowledge.uchicago.edu/record/14680},
}