An amorphus globosus (from Greek: αμορφή (amorphē) 'formless' and Latin: globus 'sphere'), also known as a globosus amorphus, ^[1] or an amorphus globosus monster, ^[1] is a malformation occurring in veterinary medicine, especially in domestic cattle. Instead of a normally developed fetus, it results in the formation of a more or less spherical structure covered with hairy skin, which contains parts of all three germ layers; the differentiation of its contents can vary greatly. An amorphus globosus is not viable due to the lack of functional organs. ^[2]

The teratological reasons for the development of amorphus globosus are not fully understood, but it is believed that the malformation is generally associated with twin gestation, ^[3] in which one embryo does not develop normally. In two cases, the karyotype of the amorphus was identical to its normally developing twin, ^{[4] [5]} while in another case, the karyotype deviated from the normal twin, ^[6] so an emergence from fraternal twins also seems possible.

Amorphus globosus is more common in livestock than generally assumed. ^[2] It occurs most commonly in cattle, but there are also case reports in goats ^[2] and horses. ^[7] A case of amorphus globosus has also been described in human medicine, where it was also a twin pregnancy. ^[8]

• Birth defect
• Twin reversed arterial perfusion
• Schmallenberg orthobunyavirus

• Image of an amorphus globosus in cattle on website of Cornell University