Lymph hearts are thought to have evolved in Rhipidistia. Mammals have lost the lymph heart as a centralized organ, instead having the lymph vessel themselves contract to pump lymph.[2]
^ abcHedrick, Michael S.; Hillman, Stanley S.; Drewes, Robert C.; Withers, Philip C. (1 July 2013). "Lymphatic regulation in nonmammalian vertebrates". Journal of Applied Physiology. 115 (3): 297–308. doi:10.1152/japplphysiol.00201.2013. ISSN8750-7587. PMID23640588.