Hello Christian,
Let's see if I can help.
quote:
The young bison from the asphalt deposits are either 2 to 4 months old, 14 to 16 months old, or 26 to 30 months old. Each group is thus 12 months (one year) apart. No bison have yet been recovered that are of intermediate ages- 5 to 13 months old or 17 to 25 months old.
Starting with a null hypothesis, there are several ways to explain this:
- The {prehistoric} bison herd migrated back then as the {modern} bison herds did in the recent past (before fences) moving to different areas in different times of the year,
- Something causes the bison to be less cautious during certain times of the year,
- The tar pits only trapped animals at certain times of the year, and
- There isn't enough data to judge for sure
These are theories to explain the data, now for some tests:
Regarding (2), while mating seasons have been observed to cause behavior in adults that could be deemed 'less cautious' and make them prone to being caught in the tar, this can be pretty well ruled out for newborns and yearlings, as it has not been observed in modern bison nor in other species.
Likewise regarding (3), this can be ruled out by the presence of other non-migratory animal remains that show a year-round pattern (I am assuming that this has been {considered\done\evaluated} because they talk about bison and not all the species found in the tar pits -- they single out a migratory species).
Regarding (4), while more data is always nice, there comes a point where the pattern emerges that further data only reinforces rather than alters the conclusions. Let's take your information provided:
Modern bison calves are born mostly in may but can be born any time from mid April through July or August. There were no newborn calves, no one month old calves.
What you should develop is a distribution curve of births against day of the year, this would show that, say, 90% of the births were in May, with some before and slightly more after.
The next thing to do then is to look at how a sampling of that population during a one month period, a two month period and a three month period at different times of the year would look, and then compare that with the tar pit results for a best match.
More data could provide a sample or two in the "off" months, but the numbers of other samples in the "on" months would still means it fits the pattern, yes?
This rather leaves us with (1) - which also matches observed patterns of behavior in {modern} bison - as the most likely scenario, unless you can think of other options.
... Also they would've had to go through the area during the same few days every year for 30,000 years. ...
I think if you play with the data for your births versus time of year curve (with a one month period for most births) and look for ways to get consistent 2 month groupings of ages that they could have stayed about a month in the area.
And we are talking a migratory species too, right?
This statement:
quote:
These clusters of ages indicate that the bison were present at Rancho La Brea only during a few months of the year
cannot be true unless all the bison were born on or very near the same day, every year for the 30,000 years represented by the tar pits.
No, it just means that there are ages that are missing from the data, as could
not occur in a non-migratory species. A non-migratory species would have young getting trapped all year round (I'm assuming this is a fact re (3) above), and thus would be all ages.
We know there are months when bison do not reproduce, and again, by matching the pattern of births vs time of year against age clusters shows that the bison were only there part of the year.
This statement:
quote:
If the calves of extinct bison were born at the same time of the year as modern bison calves, then the bison were present at Rancho La Brea every year during late spring.
... Modern bison calves are born mostly in may ... If all the calves were born in May, they would've had to go through Rancho La Brea in July, August, or September (mid summer to early fall)
You could have a point here - change late spring to summer - but this does not invalidate the conclusion of periodic visits, just the timing of them. We are still left with a migratory species leaving clustered ages of entrapments.
3. Their scenario doesn't seem very likely. What seems more likely is that there was some sudden event ...
I'm sorry, but you lost me there. You've just been arguing that this couldn't have occurred as described because it would have required a narrow window in time each year, and then you say a more likely theory is an even narrower time window?
Don't all the objections you raised above apply equally to this theory? If so, then it isn't any more likely, is it? What we need is a test that would differentiate results from the two theories to see which is more likely.
...some sudden event which killed all those animals, and there were bison ranging from 2-4 months which had been born that year, bison ranging from 14-16 months which had been born last year, and bison ranging from 26-30 months which had been born two years previously.
The problem here is that this does
not account for the data from non-migratory species that would have victims of all ages (see above re (3)). Given that this data would invalidate your theory, and given that it was likely a part of forming the conclusions regarding the bison (as oppossed to other species), I can't "agree with (you) that a sudden event is more likely" -- sorry.
k?
ps -- how goes the
time troubles?
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