Dinosorex, the “terror shrew”, was a genus of eulipotyphlan mammal found across much of Europe for most of the Miocene, ranging from about 23 to 9 million years ago. Part of a family of stem-shrews known as heterosoricids, it was larger than most of its living relatives – probably around 15-20cm long (6-8″) – and inhabited subtropical swampy forest environments.
Dinosorex kaelini here was one of the later species in this lineage, living in what is now Switzerland around 12-10.5 million years ago.
It had massive incisor teeth at the front of its jaws and crushing teeth further back, specialized for grabbing, immobilizing, and cracking open prey like hard-shelled invertebrates. Similar to some modern shrews the tips of these teeth were also reinforced with iron in their enamel, which would have given them a striking dark red coloration.
But while Dinosorex was quite abundant and successful during its time, it seems to have had such a specific ecological preference that it couldn’t adapt when the climate shifted towards the end of the Miocene. Drier conditions and more open savannas quickly took over, and the terror shrews disappeared along with the lush humid forests they were so dependent on.
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.
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.
…Insectivora?
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.
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.
Lipotyphla
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.
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.
Thanks to the absence of large terrestrial carnivores on the Gargano-Scontrone island(s) during the Late Miocene, animals that were usually small had the opportunity to become larger, moving into the vacant ecological niches and evolving into predators unlike anything existing on the mainland.
Deinogalerix was a giant member of the gymnures – close relatives of hedgehogs without the quills – with a proportionally big head and a long snout full of large fangs at the front and bone-crushing molars at the back.
Several different species have been found, with the largest Deinogalerixkoenigswaldi having a head-and-body length of around 60cm (2′). Along with its tail that would have made it at least 90cm long (2′11″), making it the biggest eulipotyphlan ever discovered.
It would probably have hunted smaller mammals, birds, and reptiles, filling a niche on the island similar to dogs or cats.
The modern solenodons, today found only on the Caribbean/Antillean islands of Cuba and Hispaniola, represent the last living survivors of a very ancient branch of placental mammals. Although they’re part of the eulipotyphlans – the lineage that also contains shrews, moles, and hedgehogs – their last common ancestor with the other members of that group dates back to over 70 million years ago.
And during their early evolutionary history, somewhere between the Late Cretaceous and mid-Eocene (~68-43 mya), the ancestors of the solenodons diverged into two different lineages: the solenodons themselves, and the nesophontids.
Known only from skulls and jumbled partial skeletal remains, nesophontids seem to have been fairly similar to their solenodon cousins. They would have been shrew-like in appearance, varying in total size from 5 to 20cm long (2-8″), with slender flexible snouts that they used to sniff out their small invertebrate prey. They also probably had a venomous bite like the solenodons, since their canine teeth had distinctive grooves for injecting toxic saliva.
Their remains have been found in various islands around the Caribbean, in Cuba, Hispaniola, Puerto Rico, the United States Virgin Islands, and the Cayman Islands. Between six and twelve different species are represented, all in a single genus called Nesophontes (meaning “island murderer”) – and all of the known specimens are actually subfossils from the Holocene, dating to less than 12,000 years old.
These relatively young ages mean that pieces of nesophontid DNA have been successfully recovered from bones within preserved owl pellets, which is how we could confirm their close relationship to solenodons and the dates of their ancestors’ probable divergence. But we have absolutely no idea about the rest of their family history during the entire Cenozoic, such as how and when they originally colonized the Caribbean or whether they had any other extinct relatives in the Americas.
(There is one possible partial specimen from a piece of Dominican amber, dating to the Oligocene or Early Miocene, 29-18 million years ago, but it’s not clear whether it’s a nesophontid, a solenodon, or something else entirely.)
Nesophontes edithae was the only species of nesophontid living in Puerto Rico and the United States Virgin Islands. It was the largest known member of the genus, at least 20cm long (8″), and may have been able to reach such a size due to the absence of competition from solenodons on those particular islands.
Along with its relatives around the Caribbean it seems to have survived frustratingly close to modern times, even existing alongside indigenous humans, with some remains only about 500 years old. But when the islands were colonized by Europeans from the 1490s onwards, the combination of the introduction of invasive Old World rats, new predators like domestic cats and dogs, and extensive deforestation probably killed off the nesophontids very quickly (along with all but two of the solenodon species).
Despite claims of fresh-looking remains in owl pellets and searches for surviving populations, there’s currently no convincing evidence for any living nesophontids, and radiocarbon dating has never found anything younger than 500-600 years old.
