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.
Taxonomy The exact position of Zalambdalestidae within Eutheria varies, though they are generally agreed to be more basal than zhelestids. A 2026 paper suggested that zhelestids were the sister group to zalambdalestids.
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. 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.Urton, James (July 25, 2022). "New study challenges old views on what's 'primitive' in mammalian reproduction". UW News. University of Washington. Retrieved April 6, 2024.
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.Arnold, Patrick; Janiszewska, Katarzyna; Li, Qian; O'Connor, Jingmai K.; Fostowicz-Frelik, Łucja (April 16, 2024). "The Late Cretaceous eutherian Zalambdalestes reveals unique axis and complex evolution of the mammalian neck". Science Bulletin. doi:10.1016/j.scib.2024.04.027.
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