|Etendeka Round-eared Elephant Shrew or Sengi Macroscelides|
micus. Image credit John P. Dumbacher
|Midgestation conceptus of the Four-toed Elephant Shrew Petrodomus|
tetradactylus. The embryo and fetal membranes are enclosed in the embryo
chamber by the decidua pseudocapsularis. Reproduced from
Oduor-Okelo et al. (here) (c) 2004 with permission from Elsevier
The report (here) mentions two pregnant females carrying one fetus in each horn. This suggests they may resemble other elephant shrews in that implantation of the blastocyst occurs in a preformed embryo chamber as shown above for Petrodumus tetradactylus. There is one such chamber in each horn.
Should a female fail to become pregnant, the chamber is discarded in a process akin to menstruation. In most mammals transformation of the endometrial stroma to decidua occurs only following implantation. Exceptions are the catarrhine primates, including humans; if pregnancy does not ensue the decidua is shed together with blood and fluids (see previous post). In the 1940's, when human menstruation was poorly understood, Professor C. J. van der Horst of the University of Witwatersrand proposed using elephant shrews as a model. His suggestion was not followed as the establishment of a breeding colony of macaques at the Carnegie Institution of Washington provided a better alternative.
Placentation in elephant shrews was studied by van der Horst and others and more recently has been described by Dominic Oduor-Okelo (here and here). The placental disc has a labyrinth with a haemochorial structure and a spongy zone. In addition there is a paraplacenta. The allantoic sac is large and divided into four lobes. This last feature is a synapomorphy for the superordinal clade Afrotheria (discussed here).