It Came From The Wastebasket #01: Is This An Insectivore?

Most of the wastebasket taxa featured this month are completely extinct and known only from fossils, but to start things off let’s take a look at a major example of how even groups with living members could have their classification muddled up for centuries.

The name Insectivora first came into use in the early 1820s, and was used to refer to various “primitive-looking” small insect-eating mammals, with modern shrews, moles, hedgehogs, tenrecs, and golden moles as the original core members.

An illustration showing the animals that originally made up "Insectivora". From left to right it pictures a shrew, a tenrec, and a hedgehog on the top row, and a mole and a golden mole on the bottom row. Text at top of the the image reads "Insectivora".

Then over the next few decades solenodons, treeshrews, sengis, and colugos all got lumped in with them too.

By the early 20th century insectivorans were considered to represent the “primitive” ancestral stock that all other placental mammals had ultimately descended from, and any vaguely similar fossil species also got dumped under the label. Extinct groups like leptictids, cimolestans, adapisoriculids, and apatemyids all went into the increasingly bloated Insectivora, too, making the situation even more of a wastebasket as time went on.

An illustration showing the animals that made up the expanded historical version of "Insectivora". From left to right it pictures a leptictidan, a shrew, a tenrec, a hedgehog, and a sengi on the top row, an apatemyid, a mole, a golden mole, and a solenodon in the middle row, and a cimolestan, a colugo, and a treeshrew on the bottom row. Text at top of the the image reads "…Insectivora?", styled like a typewritten label that has been stuck over the previous image's text.

The problem was that the only characteristics that really united these various animals were very generic “early placental mammal” traits – small body size, five clawed digits on the hands and feet, relatively unspecialized teeth, and mostly-insectivorous diets – and attempts at making sense of their evolutionary relationships were increasingly convoluted.

An image of a diagram from a 1967 academic paper, showing a complicated attempt to figure out the evolutionary relationships of "insectivores", with many different group names linked by arrows. For comparison next to it is the "Pepe Silvia" conspiracy wall meme.
…They’re the same image.

(Image sources: &

The rise of cladistic methods from the 1970s onwards resulted in a lot of “insectivores” finally being recognized as unrelated to each other, removing them from the group and paring things back down closer to the name’s original definition. The idea that insectivorans were ancestral to all other placentals was abandoned, instead reclassifying them as being related to carnivorans, and the remaining members were recognized as just retaining a superficially “primitive” mammalian body plan.

Just shrews, moles, hedgehogs, solenodons, tenrecs, and golden moles were left, and to disassociate from the massive mess that had been Insectivora this version of the group was instead now called Lipotyphla.

An illustration showing the animals that made up "Lipotyphla". From left to right it pictures a solenodon, a tenrec, and a hedgehog on the top row, and a shrew, a mole, and a golden mole on the bottom row. Text at top of the the image reads "Lipotylpha", styled like an embossed label-maker sticker that has been stuck over the previous images' text.

But there were still no unique anatomical links between the remaining lipotyphlans. And then once genetic methods became available in the late 1990s, something unexpected happened.

Studies began to suggest that tenrecs and golden moles were actually part of a completely different lineage of placental mammals, the newly-recognized afrotheres, with their closest relatives being sengis and aardvarks. Meanwhile the rest of the lipotyphlans were laurasiatheres, closely related to bats, ungulates, and carnivorans.

Lipotyphla was suddenly split in half. For a while it was unclear if even the remaining shrew-mole-hedgehog-solenodon group was still valid – hedgehogs’ relationships were especially unstable in some studies – but by the mid-2000s things began to settle down into their current state.

Finally, after almost 200 years of confusion, the insectivore wastebasket has (hopefully) now been cleaned up. The remaining “true lipotyphlans” do seem to all be part of a single lineage, united by their genetics rather than by anatomical features, and are now known as Eulipotyphla.

A few fossil groups like nyctitheriids and amphilemurids are generally also still included, but since this classification is based just on their anatomy it isn’t entirely certain. The only exception to this are the nesophontids, which went extinct recently enough that we’ve actually recovered ancient DNA from them and confirmed they were eulipotyphlans closely related to solenodons.

An illustration showing the animals that now make up Euipotyphla. From left to right it pictures a solenodon, and a hedgehog on the top row, and a shrew, a mole, and an amphilemurid on the bottom row. Text at top of the the image reads "Eulipotylpha", with the letters "E" and "U" hastily scribbled onto the front of the previous image's text.

And a bonus image with species IDs:

Continue reading “It Came From The Wastebasket #01: Is This An Insectivore?”

Month of Mesozoic Mammals #30: Strange Relations


A group known as the leptictidans were probably some of the weirdest early eutherians. With their tiny forelegs, big hindlegs, and long counterbalancing tails, they somewhat resembled jerboas or small kangaroos – except they also had long slender snouts that probably ended in sengi-like proboscises, and their feet were structured more like those of running animals than jumping ones. They’re also thought to have been mainly bipedal, convergently evolving a similar posture and movement style to non-avian theropod dinosaurs.

Leptictidium (Eocene, 50-35 mya) by Tim Bertelink || CC BY-SA 4.0

First appearing in the Late Cretaceous, they made it through the end-Cretaceous extinction and survived up until the mid-Cenozoic across the northern hemisphere, going extinct around 33 million years ago. They were probably omnivores, eating a mixture of insects, small vertebrates, and soft plant matter such as fruit and leaves.

Their mix of “primitive” skull features and highly specialized skeletons makes classifying them particularly difficult. They’ve been proposed to be placentals related to primates and rodents or afrotheres, a very early branch of the eutherians, or close to placentals but not quite true members themselves. The latter interpretation currently seems most likely, but they could also be a paraphyletic group at the base of placentals (suggesting that they could even be ancestral to placentals, and therefore all placentals would technically be leptictidans).

Gypsonictops was one of the earliest leptictidans, living during the Late Cretaceous of North America (70-66 mya). Known only from teeth and jaw fragments, we don’t know much about its appearance or full size – although it was probably smaller than its later relatives, perhaps about 35cm long (1′2″).

Any reconstruction of such fragmentary remains is going to be very speculative, but I’ve restored it here as a sort of transitional form, not yet quite as specialized. A more sengi-like animal, mainly quadrupedal but able to run and hop on its hind legs to flee from danger or chase after small fast-moving prey.