mysqldump silently corrupts 4-byte UTF-8 data

[dvaneeden@dve-mac msb_ma10_0_20]$ ./my sqldump --skip-extended-insert unicodedata | grep DOLPHIN

INSERT INTO `ucd` VALUES ('1F42C','?','DOLPHIN','So','0','ON','','','','','N','','','','','');

[dvaneeden@dve-mac msb_ma10_0_20]$ ./my sqldump --skip-extended-insert --default-character-set=utf8mb4 unicodedata | grep DOLPHIN

INSERT INTO `ucd` VALUES ('1F42C','��','DOLPHIN','So','0','ON','','','','','N','','','','','');