This is a pretty cool story in the field of paleoentomology and ecology:
Paleoecological and Taphonomic Implications of Insect-Damaged Pleistocene Vertebrate Remains from Rancho La Brea, Southern California (Journal Article)
(If you don't want to slog through the jargon of a scientific journal article, here's a link to a news piece covering the story, in more accessible language!)
Researchers from the LA County Natural History Museum used modern dermestid* and tenebrionid beetle larvae to reconstruct the succession of insect larvae feeding on dead but as-yet-unsubmerged large vertebrates caught in the tar pits, based on damage done to the bones of these specimens by prehistoric beetle larvae.
A few thoughts:
The majority of the damage is on the feet of the larger vertebrates, which (to me) would seem to indicate that they were belly-up in the tar pits. Seems odd, but also appropriate given that...
Their findings indicate that some of these carcasses may well have been stuck in the tar, still not completely submerged, for 17 to 20 weeks! The animal would likely have been long dead by the time the beetles were chewing away at its bones, but it certainly does make the prospect of dying in a tar pit a bit grimmer than I would have envisioned. If sinking at such a slow rate, it seems that the animal may well have starved to death before drowning/suffocating. Neither is glamorous, but the drawn out death of starvation seems much worse, once your fate is sealed in tar anyways. Anyways, once the animal died, but still had a lot of sinking to do, I can imagine it would have fallen over into the tar, thus potentially exposing the feet for the beetle larvae to consume. A researcher on the paper also postulates that opportunistic vertebrate predators or scavengers would have turned over some of these carcasses to get at the belly, and maybe dismembered the carcass, thus exposing the feet in the process. This is obviously supported by the large number of smilodon and dire wolf fossils recovered from the tar pits, as well.
On a related note, I would have initially guessed that a beetle who laid her eggs on an animal carcass which was sinking into a pit of tar had simply made a poor choice, dooming her offspring to "go down with the ship", as it were. Accidental landings in suboptimal habitat are not unknown, especially among flying insects which are easily blown about (there was a popular anecdote in the entomology lab I worked in as an undergraduate about a former professor at the university finding low-elevation grasshopper species packed into a snowdrift on top of Mt. Evans). With a solid 17-20 weeks, though, I would revise that guess - one has to imagine they had plenty of time to feed and pupate into adults (for reference, the development period (from egg-laying to pupation) for modern dermestids ranges from as little as the development period (from egg-laying to pupation) for modern dermestids ranges from as little as 7-8 weeks up to about a year). It would not be surprising at all to find that there were sub-species, or at least populations, which thrived specifically on such carcasses. The whole scenario becomes pretty reminiscent of large organic matter falls, such as a whale carcass that sinks to the sea floor, supporting a wide array of scavengers and decomposers (and potentially as a stepping stone for the larvae of hydrothermal vent species!).
Anyways, that's enough rambling from me - hope you enjoyed the story! Next time you're in LA, visit the Page Museum and think about those poor ground sloths and glyptodons, sinking for several months on end.
* Interestingly, these guys are a major pest, and a problem in many museum collections as they can cause a lot of damage to all manner of specimens.
No comments:
Post a Comment