Pteraspidomorphi is an extinct class of early jawless fish ancestral to jawed vertebrates. Homologous trochlear nerves are found in all jawed vertebrates. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates. CFTR orthologs occur in the jawed vertebrates. Lymphocyte receptors, Ig and TCR, are found in all jawed vertebrates. Like TCR and Ig, the MHC is found only in jawed vertebrates. The diversity of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth. Evolution of the adaptive immune system occurred in an ancestor of the jawed vertebrates. Testosterone and the classical nuclear androgen receptor first appeared in gnathostomes (jawed vertebrates). Placodermi is a paraphyletic group of the clade Gnathostomata, which includes all jawed vertebrates. The cyclostomata evolved oxygen transport hemoglobins independently from the jawed vertebrates. YouTube was founded by Chad Hurley, Jawed Karim and Steve Chen in 2005. Chen was an employee at PayPal, where he first met Chad Hurley and Jawed Karim. Hurley founded YouTube in 2005 with Steve Chen and Jawed Karim. Wells was played by Adilah Barnes in the 2004 film "Iron Jawed Angels".