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Merycoidodontoids have raised their cute stubby little faces on this
list. Once again we're way off topic, but, in the spirit of
deconstructing traditional textbook archetypes (cf. the amphibious
lystrosaur, the beach-basking plesiosaur, the erect-necked super-tall
moa, the vulture-like azhdarchid), it's interesting that some
mammalogists are now arguing that the old image of sheep-like herding
merycoidodontoids is unsubstantiated.
According to new evidence presented recently by Sundell (1997),
mercoidodontoids were, in fact, burrowers. Whole families of
merycoidodontoid have now been found preserved in burrows, and this
lifestyle is supported by the stocky merycoidodontoid body, their
broad, clawed feet and big heads with robust canines. I think
Sundell compared them to living warthogs.
I'm also intrigued by the fact that palaenodonts, an enigmatic group
of Palaeogene pangolin-like mammals that may be related to
xenarthrans, may also have been burrowers. Apparently they exhibit a
suite of characters suggestive of this lifestyle (a classic paper on
this subject was published in _Journal of Morphology_ some years
back, but I haven't yet gotten round to finding it).
One thing that may strike you as odd is that mammalogists are always
adding to the list of fossorial/semi-fossorial mammal taxa, yet the
Mesozoic seems strangely depauperate in its number of archosaurian
burrowers. Only one dinosaur, to my knowledge, has ever been regarded
as a burrower, but all I have to go on is a brief bit of blurb Bakker
came out with on a TV show broadcast in 1993. The crew were filming
in his house, and in his sink were a load of alligator legs, with a
hypsilophodontid tarsus and foot on the drainage board. He said, and
I am sure of this, that this hypsilophodontid represented the first
evidence for a dinosaur 'that lived in a burrow'. A little later I
thought he might be referring to _Drinker_, but in everything else
Bakker has written about _Drinker_ he maintains that it was a
marsh-dweller adapted for walking around on wet ground. Not the right
habitat to dig burrows.
I suppose you could also say that heterodontosaurs have been
considered as burrowers by some.
Crocodyliforms to the rescue. Gomani's (1997) recent work on
_Malawisuchus_ shows that this robust little animal denned in
burrows, and am I right in thinking that there is also some evidence
indicating that _Chimaerasuchus_ did the same? These crocs
(notosuchids) clearly do have burrowing adaptations, including
well-muscled forelimbs and stout, deep heads with big neck muscles.
And of course, what is funny is that these crocs are the only ones
that mammals ever managed to half-successfully mimic. Notosuchids are
not, you see, mammal-like crocs; it is mammals that are
notosuchid-like synapsids. Perhaps;)
"Insects live in a very ancient world, led by evolution along paths
that have been closed to us, until our own evolution has led us to
invent the means of exploring them"