Zalambdalestidae

Zalambdalestidae is a clade of Asian eutherians occurring during the Cretaceous. Once classified as Glires, features like epipubic bones and various cranial elements have identified these animals as outside of Placentalia, representing thus a specialised clade of non-placental eutherians without any living descendants, and potentially rather different from modern placentals in at least reproductive anatomy.^[1][2]

Zalambdalestes Temporal range: Aptian–Campanian PreꞒ Ꞓ O S D C P T J K Pg N
Zalambdalestes lechei skull and lower jaw, Museum of Evolution Warsaw.
Life reconstruction of Zalambdalestes lechei
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Clade:	Eutheria
Order:	incertae sedis
Family:	†Zalambdalestidae Gregory & Simpson, 1926

Taxonomy

The exact position of Zalambdalestidae within Eutheria varies, though they are generally agreed to be more basal than zhelestids.^[3] Currently, the clade includes the genera Alymlestes, Anchilestes, Barunlestes, Kulbeckia, Prozalambdalestes, Zalambdalestes, Zhangolestes and Zofialestes.^[4]

Palaeobiology

Zalambdaltestids were insectivores, having zalambdodont molars much as various modern insectivorous species. They are uniquely suited to a saltatorial, cursorial lifestyle, bearing long, semi-digitigrade limbs and a spinal column similar to that of modern lagomorphs.^[5] Like most non-placental mammals, the presence of epipubic bones probably meant that they gave birth to poorly developed young much like modern marsupials and monotremes, though a study on multituberculate reproduction may suggest they and other early eutherians reproduced like modern placentals.^[6]

A study on Zalambdalestes suggests they had a unique axial morphology. This allowed for quick prey capture, and may suggest they had spines or bristly fur in life.^[7]