Solenodons have a few unusual traits, one of them being the position of the two teats on the female, almost on the buttocks of the animal, and another being the venomous saliva that flows from modified salivary glands in the mandible through grooves on the second lower incisors ("solenodon" derives from the Greek "grooved tooth"). Solenodons are among a handful of venomous mammals. Fossil records show that some other now-extinct mammal groups also had the dental venom delivery system, indicating that the solenodon's most distinct characteristic may have been a more general ancient mammalian characteristic that has been lost in most modern mammals and is only retained in a couple of very ancient lineages. The solenodon has often been called a "living fossil" because it has endured virtually unchanged for the past 76 million years.