The Fossorial Life - Portal to a Better Time?

[Badger] shuffled on in front of them, carrying the light, and they followed him, nudging each other in an anticipating sort of way, down a long, gloomy, and, to tell the truth, decidedly shabby passage, into a sort of a central hall; out of which they could dimly see other long tunnel-like passages branching, passages mysterious and without apparent end. But there were doors in the hall as well—stout oaken comfortable-looking doors. One of these the Badger flung open, and at once they found themselves in all the glow and warmth of a large fire-lit kitchen.

 

Kenneth Grahame, The Wind in The Willows (1908)

At some point, I added the phrase "fossorial life" to a list of interesting words, sayings, and topics for possible blog posts (yes, this list is a catchall).  Writing about this phrase took me from the Badger's comfortable and homey burrow, which offered shelter from a snow storm to the Mole and the Rat, on a journey of discovery, disaster, and speculation.

I've used "fossorial" once in this blog when I suggested that it's possible the turtle's carapace (top shell) originally evolved to further a "fossorial lifestyle."  I like the word for its sibilance and its music - "fa, so, la."  I assume the root word is the Latin foss meaning "trench or ditch" which, in turn, gives rise to the Latin fossul which is a "burrow" and fossor, "a digger."  And, certainly, a related Latin term is fossil defined as "dug up."   (Donald J. Borror, Dictionary of Word Roots and Combining Forms, original copyright 1960.)  The adjective, as all of these Latin words suggest, describes an animal "capable of, or characterized, by digging burrows."  (Oxford English Dictionary (OED).)  I was a bit surprised that it's a fairly recently coined word, first appearing, according to the OED, in 1834.

The fossorial life is one lived, at least in part, underground.  I am intrigued by, and drawn to, such a life in this age of catastrophes, actual and impending, a time marked by climate, social, and political upheaval that threatens all living creatures on the planet.  Its appeal goes beyond metaphorical burrowing or burying one's head in the sand.

Mammals have been burrowing and embracing the fossorial life for millions of years.  In an article on two fairly recently discovered, purportedly fossorial creatures from the Jurassic Period (201 to 145 million years ago (mya)), science writer Riley Black noted that both Docofossor brachydactylus, while not quite a mammal, but close, and Fruitafossor windscheffeli, just slipping in under the wire to qualify as a mammal, sported the hallmarks of the fossorial life among which are truly buff forearms and shovel-shaped forefeet.  These discoveries offer the earliest evidence of burrowing among proto- and early mammals.  (Sciencespeak:  Fossorial, Laelaps, National Geographic, February 16, 2015.)  (I would note that there are other features of mammals that signal a life lived in the soil including small eyes and poor eyesight, little external evidence of ears, and a fusiform or spindle-shaped body.)

Black characterized the Docofossor (living some 160 million years ago) as the "Jurassic equivalent of a mole," though he noted that it's not related to moles and is an evolutionary dead end, as is the Fruitafossor (living some 150 million years ago) which is often described as anteater-like.  Pictured below is the holotype fossil of D. brachydactylus on display at China's National Natural History Museum.  (It is reproduced under the Creative Commons Attribution-Share Alike 4.0 International License and can be found on Wikimedia Commons.)

What I found most compelling about Black's account is his observation that mammals and mammal-like animals have evolved to embrace a fossorial life multiple times.  Clearly, there's a robust and attractive payoff to living this way.

If I cast my net broader to include all vertebrates, the early roots of a fossorial existence go much further back into deep time, perhaps as far back as the Devonian (some 419 to 359 million years ago) or maybe the Carboniferous (about 359 to 299 million years ago), but, most certainly to the Permian (about 299 to 252 million years ago) when "vertebrate burrowing becomes more common and complex."  (Lorenzo Marchetti, et al., Origin and Early Evolution of Vertebrate Burrowing Behaviour, Earth-Science Reviews, Volume 250, 2024.)

What's the pull of going underground?  As paleontologist Marchetti and his colleagues observed, burrowing is used by animals for a host of reasons such as:  acquisition and storage of food, protection from predators, and escape from adverse climate conditions on the surface.  This last may be seasonal when animals hibernate to deal with food scarcity and cold during the winter, or when they aestivate (enter a state of torpor or dormancy) to cope with arid and hot periods above ground.

Sheltering from adverse surface conditions can be singularly important for the survival of species.  Marchetti et al. looked closely at the appearance of fossorial vertebrates in the fossil record and mapped that information to events in deep time.  What is striking is how often climate change (e.g., transition in the early Permian from an ice age to a greenhouse climate) and specific extinction events (e.g., end-Permian mass extinction) appear to be associated with an increase and proliferation of fossoriality.  They concluded, "In some instances, burrowing can be viewed as a potential survivor's gate through a mass extinction." (p. 32)

A gate or portal to a better time.  What a wonderful image.

Paleontologist Elsa Panciroli, in her masterful book Beasts Before Us:  The Untold Story of Mammal Origins and Evolution (2021, subject of a previous post in this blog) began her chapter on the end-Cretaceous mass extinction by recreating the experience of one, small, burrowing mammal the day the asteroid slammed into the Earth.  Reminiscent of The Wind in the Willows, the chapter opens with:

In a nest furnished with moss, a small circle of fur twitches.  Nose tucked against warm belly.  Whiskers flickering.  The sleeper is thrilled by memories of herbal scents and squirts of crushed bug.  Senseless dreams of scampering curl its minute toes.  The burrow is Goldilocks warm, just big enough to turn around and tuck in your tail.  It is mushroom dark, filled with musk.  The Earth clasps this sleeping body in her hand.

The little sleeper barely stirs as a rumble reaches it from another continent.  (p. 273)

When this insectivore finally leaves its burrow, it enters into a dark and devastated landscape, littered with decaying carcasses, which actually serves the animal well.  In Panciroli's telling, the animal survives and procreates, giving rise to generations more of these burrowing creatures.

Panciroli asserted:

From a mammal's point of view, the epic end-Cretaceous catastrophe might be nothing more than a harsh season to weather.  It's not that mammals were unaffected - like most animals they suffered catastrophic casualties.  Many lineages became extinct.  But we all know our own creation mythology:  our ancestors rose like a phoenix from dinosaurian ashes.  (p. 274)

The thought of those days, months, and many, many years when the environment was lethal or, at least, extremely difficult for myriad animals is actually quite terrifying.  I find some solace in the scene that Panciroli described: a warm burrow in the soil, hidden away from the devastation, a way for an animal and its species to survive.

Clearly, little mammal insectivores were not the only type of animal to pass through the portal.  For an analysis of which general types of animals could have survived the immediate aftermath of the asteroid's impact, I recommend a paper by earth scientist Douglas S. Robertson and his colleagues titled Survival in the First Hours of the Cenozoic (Geological Society of America Bulletin, May/June, 2004).  Perhaps no surprise that they found the vertebrate animal groups that did make it from the Cretaceous into the new era were much more likely to be those whose members had a life that involved sheltering in water or burrows.

It's appealing in some way to consider the advantages of a fossorial life as a way to endure climate change and make it through to the other side (assuming there is an other side), but it's not for us.  We haven't evolved to live that way, regardless of its advantages.  So, it's interesting, but idle speculation.  Yet there are those who take seriously the idea of a fundamental change in our existence as a means to survival.  As mentioned above, hibernation is a feature that some burrowing mammals experience as a way to deal with challenges on the surface (cold and food scarcity).  Vladyslav Vyazovskiy, a sleep physiology professor at the University of Oxford, has penned a provocative essay titled Could Humans Hibernate?  (Aeon Newsletter, November 18, 2024).  The takeaway is that, no, we cannot hibernate (yet), though perhaps our earliest ancestors did.  The attraction of it as a solution to a host of problem resonates with me.  Vyazovskiy wrote:

The revival of interest in hibernation in general, and human hibernation in particular, comes at the right time. The genre of science fiction is about imagining and predicting practical solutions for real-life problems when they cannot be solved with existing means. When the world is facing acute problems at a planetary scale, including climate change, technogenic disasters, wars, incurable disease, pandemics and mental health crises, and we are grappling with perennial questions, such as how to attain immortality (or at least extend high-quality life considerably), solve the mystery of consciousness or reach the far corners of the Universe, hibernation emerges as a potential opportunity, if not the only hope.

Whoa!