Pregnant tenrecs run hot and cold

Tailless tenrec (Tenrec ecaudatus)
Photo by Markus Fink (Wikimedia Commons CC)

Tenrecs do not maintain a constant body temperature. It waxes and wanes throughout the day. A recent study found this applies even to pregnant tenrecs. Yet after they give birth their body temperature becomes stable and warm.

As mentioned in a recent post, this tenrec (Tenrec ecaudatus) has large litters. In the present study up to 19 young. They grow quickly from 12 g at birth to 400 g at 5 weeks (weaning). Perhaps thermoregulation becomes more important when the mother is lactating.

In the closely related species Echinops telfairi, gestation length varies in the range 50-79 days (here). Just speculating, but if body temperature varies could this affect fetal growth rate and thereby the timing of delivery?

Reproduction in tenrecs is quite interesting as we discuss for the ovary here and placenta here.

Litter size in the tailless tenrec and a Jurassic tritylodont

Tailless tenrec (Tenrec ecaudatus) with litter
Photo (C) by H. Schütz. From Goodman, Benstead and Schütz
The Natural History of Madagascar

The record for litter size in mammals - 32 viable fetuses - is held by the tailless tenrec. The source for this is Bluntschli (Revue Suisse de Zoologie 1937; 44: 271-282). The tailless tenrec polyovulates and an even larger number of unimplanted blastocysts has been observed (Nicoll & Racey).

Small litter size is nonetheless typical for mammals and is currently in focus because of a remarkable fossil from the Early Jurassic (Hoffman & Rowe). This comprised a clutch of at least 38 perinates and the presumed mother in the genus Kayentatherium. 

The mammals derive from the synapsids and Kayentatherium is on a non-mammalian side branch called tritylodontids. The trees in Prothero (previous post) suggest they diverged from the branch leading to mammals way back in the Triassic. So the finding does not exactly pinpoint when a reduction in litter size started to happen. 

The abstract claims that 38 is "well outside the range of litter sizes documented in recent mammals." Except one might add in the tailless tenrec.