Bison at La Brea Tar Pits

I recently visited the La Brea Tar Pits with my family. We had a great time and learned a lot. One interesting thing we noticed was the ages of the bison found there. Next to some of their jawbones was a sign that said this:

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Migration

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Not all the animals lived at Rancho La Brea year round. Some were migratory, traveling in and out of the area. How do scientists know this?

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At Rancho La Brea, paleontologists have found fossils of many young bison. They can tell the age of the bison by the number and kind of teeth in the jaw and the amount of wear shown by the teeth. 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.

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These clusters of ages indicate that the bison were present at Rancho La Brea only during a few months of the year. 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.

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My husband and I found it interesting that there were no bison found with ages of 5 to 13 months or with ages of 17 to 25 months. So we did a bit of research. Here's what we discovered:1. This statement:

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These clusters of ages indicate that the bison were present at Rancho La Brea only during a few months of the year

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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. If there was any variation (as there is with modern bison) they would've had to move very rapidly through Rancho La Brea staying only a few days at the most. Also they would've had to go through the area during the same few days every year for 30,000 years.2. This statement:

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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.

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is false and misleading. 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. 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) even if all the calves were born in April, the earliest they could've traveled through Rancho La Brea would be June . For them to be present at Rancho La Brea during late spring, they would've had to have been born in February or March, which is not when modern bison are born.3. Their scenario doesn't seem very likely. What seems more likely is that there was 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.I would like to point out that I want this to be a very narrow topic. I don't want to be asked to prove how the flood could cause the animals to be trapped in tar. That is not something I have researched. I simply want people to agree with me that a sudden event is more likely if you only consider the ages of the bison babies, and that the scenario given at the museum doesn't adiquately explain what was found.

The idea I was trying to portray was that any variation in times of births, would necessitate a shorter stay at Rancho La Brea. If they were born within a couple of weeks (a much shorter span than we see in modern bison) they would only be able to stay at La Brea for 1.5 months max. But the sign says that they stayed a few months. Seems misleading to me. No. Because there were no newborn and no one month old calves. Also this scenario has them traveling and giving birth at the same time. Yes but that is not what the sign indicated. The sign indicated that they stayed there for a few months every year. Also they would have to give birth within the same two months and travel through La Brea within the same few days every year for 30,000 years (or 44,000 according to Chiroptera) I've looked at several. Here's one:
Requested Page Not Found (404)That's all the time I have tonight. I am curious about your statement "Not when modern bison are born on the great plains." Do you have a source stating that modern great plains bison are born in Feb. and March?

No, that's not what I think, but I'm not discussing that at this point. I have limited time and have to discuss one thing at a time. Have a nice day.

So it doesn't have to provide accurate information? MY 1.5 month stay? I don't think it's very likely that they stayed for 1.5 months. Bison these days are born over a period of at least 2 months, which wouldn't give them more than a day or two to stay at La Brea each year. And even if they were staying there 1.5 months, their statement would be in disagreement. "A few" generally indicates between 3 and 5. Even if we assume that all the calves were born in May. There are problems with the statment on the sign. If they were born anytime in May that gives a 1 month span for them to be born. They would have to arrive at La Brea in July (which is not late Spring)They would have to arrive towards the end of July so that the youngest calves (born end of May) would be 2 months old. They could only stay until mid September at the latest, because after that the oldest ones (born beginning of May)would look more like 5 month olds than 4 month olds. That only gives them 1.5 months which is less than "a few" . Notice that I'm allowing for some calves to actually be 4.5 months old. They would have to continue these narrow patterns for many thousands of years. The more year to year variation you allow for, the smaller the window of time for them to be born and the smaller the window of time for them to remain at the tar pits. I'm only pointing out that their scenario doesn't work very well, and that their info is misleading and false. That was you. Message 3 It was yours. And I don't think bison migrating patterns are that precise. They seem to vary from year to year. Whatever the case, the conditions would have to be almost exactly the same every year for many thousands of years. Do you know of any modern bison which are born in Feb and March? I agree that ancient bison could've calved earlier, but the sign said:

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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.

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Which is false. What they have up there is clearly false. Maybe YOU can provide some information which excuses them from lying to the public? What "information" am I adding that's not there? If it's helpful we can just forget my alternative. I'll just stick with pointing out that the museum is posting false information and that their migration scenario seems inadequate given the ages of the animals found. I hope you're not accusing ME of intelectual dishonesty. It would be nice to see percentages. Maybe our next field trip should be a bison ranch. this one http://www.nature.org/aboutus/travel/almanac/nea.php?requ... says the babies are born May through July. Yes, I would like to see that information too. I looked and couldn't find anything. I wonder why it's so hard to get that info? But it does say

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No bison have yet been recovered that are of intermediate ages- 5 to 13 months old or 17 to 25 months old.

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But then why does the sign say

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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.

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Also I would be very interested to see that published data.This message has been edited by Christian, 04-17-2006 12:26 PM

Yes, I'm still around. I'm even a moderator! Though I don't have time to do much moderating.

Thanks Modulous, I would like to see what those other factors are.

Then let's not assume it's true. Lets assume the migration scenario is true and see how well that fits the evidence. I'd rather take things one step at a time. I want to know if I am right that their scenario is unsatisfactory. That's all. no, but He is good.

Oh yeah, I almost forgot to reply to that one. yes, nature of teeth wearing would help. But I have a book on Bison that says the calves nurse for about 8-12 months. So If the ancient bison nursed for that long too, it wouldn't work because most of the bison were between 2-4 months. I have a picture of a graph which illustrates that, but I don't have time to get the picture up for you now. It will have to wait. I'm not sure how this would explain anything.

I am going to request information from the museum as to the exact numbers and ages of animals found. I'll ask for the numbers of all large mammels. I think this will help. I'll also ask what the error margin is for judging the ages of the bison calves. I'm glad to see that at least some of you can see problems with the clarity of the information given on the sign.

Thanks for asking. I'm still working slowly through that book (Ancient Earth Ancient Skis). It's a bit over my head, but is also raising some questions which I am looking into.

In case anyone is interested, this is the email I sent to the museum. Hopefully they will provide me with the requested information soon.

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I recently visited your museum with my family. One display about bison migration sparked my interest, and I have been doing some research regarding it. I am having trouble, however, finding some of the desired information. Could you please provide me with the following:

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-The number of bison found in the tar pits divided into the various ages found. (how many 2-4 month olds; how many 14-16 month olds, etc)
-the ratio of male vs. female bison found
-the margin of error in determining the ages of the bison calves
-the numbers and ages of other large mammals found at the Rancho La Brea tar pits

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Thank you very much for your time

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Yes, it would be interesting to see what their answer would be. I didn't have time today, however to articulate my problem to them, but I did get an answer to my email. Here's what they said:

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I was very pleased to learn that your visit to the Page Museum stimulated your further research into the bison migration story.

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I was not involved in the original research but believe the information you seek may be found in the following publication:

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Jefferson, G. T. and J. Goldin 1989. Seasonal migration of Bison antiquus from Rancho La Brea.
Quaternary Research, 31: 107-112.

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The numbers of the different kinds of large mammal fossils changes annually as our excavation progresses but a summary of the numbers of fossils before our current excavation started may be found in:

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Marcus, L. F. 1960. A census of the abundant large Pleistocene mammals from Rancho La Brea. Contributions in Science No. 38 pp 1-11.

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Kind regards,
John Harris

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I don't have time now to look for the sources he referenced, but maybe one of you want to do that. Perhaps this info will clear up the problem, otherwise I'll send them another email.

Do either of those papers have the specific information I requested?

Ok, so the sample size is smaller than what I would've thought. I would like to know how many of those were calves and of which ages. Of course a bigger sample would give us more accurate information. With a smaller sample, it's hard to draw any conclusions. I would like to read those papers myself. Hopefully I'll get a chance to do that. I also may ask again for the requested information if it isn't on those papers. It has to be somewhere. My contention is that the information on the sign is still incorrect.