Horse Metacarpal 3 Found - Equus Simplicidens?

[100%Texan]

On another one of my canoe trips down Brazos, Texas a friend of mine found a bone and tossed it to me. I've been able to confirm it is a horse metacarpal 3. I've done the stone to bone test and it does "click" like a stone. I was asked if it is completely minieralized. One test that was mentioned was "scaping test". Does anyone know what this means? What would a scape test on mineralized result in? what would happen if not fully mineralized?

The reason for this "true fossil test", horses were introduced back to Texas area around 500 years ago. If this is a fossil, which I do believe that it is, means that this is a fossil of a Hagerman Horse also called American Zebra which went extinct 10,000 years ago.

While the largest find of Hargerman Horse was found in Idaho, there have been some found in North, Texas.

[RichW9090]

There are literally dozens of named Pleistocene horses from North America, and it could be any of them. The bone looks rather smallish to me, so I'd start looking at things like the stilt-legged onanger, Equus francisci. E. simplicidens is a much larger horse. What is the bone in the center photo? It looks like a navicular or an ectocunieform. Was it found with the metacarpal fragment?

Equus francisci has a proximal width of the metacarpal of from 32.2 to 38.4 mm. What does yours measure?

Edited February 15, 2013 by RichW9090

[Cris]

What is the bone in the center photo?

I think it's just a proximal view of the horse metacarpal.

[siteseer]

Yes and E. simplicidens is also one of the earliest species of Equus - present during the Pliocene. According to MacFadden (1992: p. 180) simplicidens was replaced by E. scotti during the Late Pliocene. I'm not certain but I think simplicidens was reported by another author from at least one Early Pleistocene site but not from any Late Pleistocene sites.

MacFadden, B.J. 1992.

Fossil Horses: Systematics, Paleobiology, and Evolution of the Family Equidae. Cambridge University Press.

There are literally dozens of named Pleistocene horses from North America, and it could be any of them. The bone looks rather smallish to me, so I'd start looking at things like the stilt-legged onanger, Equus francisci. E. simpliciens is a much larger horse. What is the bone in the center photo? It looks like a navicular or an ectocunieform. Was it found with the metacarpal fragment?

Equus francisci has a proximal width of the metacarpal of from 32.2 to 38.4 mm. What does yours measure?

[RichW9090]

Right Siteseer. The Equus complicatus we've been looking at on another thread is related to that simplicidens - scotti lineage.

And the Peace River sites are almost exclusively RLB, unlike many other Florida Rivers.

Cris, if you look at the center picture, the articulating surface is complete, but the proximal end of he MCIII shown in the first photo is erroded. Also, in the center photo, the back side of the bone (the side away from the camera) has a very sharp border. The bone is only a half inch or so in thickness (depth).

Edited February 15, 2013 by RichW9090

[100%Texan]

All,

Thanks for all your replies. All 3 pictures are of the same bone fragment. The bone at it's widest point is 1 3/4 inches and narrowest is 1 3/8 inches. The reason for the middle picture was to show a close up detail of bonetip, plus an attempt to show how flat is the end of the bone. I can actually stand the bone on end. Another point is from the end of bone narrows down slightly from the joint end and is a perfect circle until where the bone has broken off.

I was not sure if this would be a small animal or a young animal.

[Jesse]

If you want to see if it is completely mineralized, hold a match to the broken end and see if it gives off a burnt hair smell or no smell.

Without knowing the age of the surrounding strata an id would be difficult, but it is in the size range of simplicidens. I see the Hagerman horse several times a week, I'll compare your pictures to it the next time I say hello, lol!

[RichW9090]

Since you say that all three photos are of the same bone fragment, then the bone is the proximal end of a metatarsal, not metacarpal.

44.5 mm proximal width would be smaller than any horse in the E. simplicidens group or the E. laurentius group, but could be any of the horses in the other three groups.

Group..................................Metatarsal........................Metacarpal

Equus alaskae group:..................41.45 - 52.00...................42.70 - 52.60

Equus fancisci group:..................33.40 - 58.25...................31.35 - 53.60

Equus laurentius group:...............47.30 - 64.30..................44.90 - 67.90

Equus scotti group:......................41.75 - 62.60...................38.90 - 59.00

Equus simplicidens group:...........46.10 - 57.00...................46.20 - 60.4

These are the groups Melissa Winans used in her 1989 paper. There are many species in each of these groups, so this bone could be any one of them. Unfortunately, we can't narrow it down any more than that because we lack the measurement of greatest length, which would help refine the ID better. So it isn't E. simplicidens. I included measurements of the metacarpal in case anyone disagrees with my ID of it as a metatarsal, and you can see that the bone is still too small to be E. simplicidens, and just below the minimum for E. laurentius.

Edited February 16, 2013 by RichW9090

[Jesse]

That bone is fairly well river polished, I don't know that I would expect an accurate measurement from it.

What was her sample size in that study for each group? We have a pretty good amount of simplicidens material here at the IMNH and several of them are in the same size range of the one pictured. I don't think the groups would break down that cleanly, a similar study has been tried here with the different species of bison and failed as there is just to much overlap between them.

That being said, I doubt it is a simplicidens but with it being found out of stratigraphic reference it could go either way.

[RichW9090]

Jesse, her sample size was as small as 40 bones in one group to 150 in another group - all were statistically significant samples. Her paper has been ignored by most paleontologists, unfortunately, for I think it is the most reasonable approach to Equus taxonomy for North America currently available.

Edited February 16, 2013 by RichW9090

[Jesse]

Morphometric studies like that are tricky. The bison study here was never submitted for publication because the results look nearly identical to the results above. There is simply too much overlap between the species, and in blind tests the groups failed to hold up to scrutiny, I imagine that is why her research hasn't been taken seriously. With horses from simplicidens to modern, they all look nearly identical and are virtually indistinguishable from each other. One of our local paleontologists brought in a scotti astragulus that was at least 25% larger than every other astragulus in our collection. If it wasn't a fossil you would have thought it came from a clydesdale! That is why stratigraphical and geographical location is important with these guys.

If this was my find, I would call it equus sp. and go have a beer.

[100%Texan]

Thanks guys,

With the additional information and tools, I was able to measure the mid-shaft (approximation) width (37mm) and front to back (35mm) based on a paper on a dig in Neuces County, Texas digs. At 37mm, the bone falls in the width range for both metacarpal (37.3 - 42.3) and metatarsal (24.7 - 37.9) of the equus scotti. The francisci ranges are two small for this bone.

I did the match test.... no smell aside from the match.... no change except for soot that easily washed off.

I'd say this is the best it's going to get... time for that drink and to go paddling again.

I appreciate all the comments.

[RichW9090]

Be a little careful with the Neuces River paper - that was early on (2002) in Jon's work with the material, before he realized that there were also Hemphillian fossils there. For example, there are a large number of Pleistocene pronghorns, mostly Tetrameryx, but some Capromeryx. But nestled in amongst them are two specimens of the Hemphillian 6-horned form, Hexameryx/Hexabelomeryx. Another example is the giant flightless bird Titanis walleri. Originally thought to be Pleistocene, rare earth element analysis demonstrated that it was from the late Hemphillian (2006). So it is possible that one or more of the smaller horses Baskin described as E. francisci could be the slightly smaller Hemphillian horses like Dinohippus or Astrohippus, which would skew the ranges. Baskin had only 3 metatarsals of E. fancesci from the Neuces River, while Winans had around 40 E. fancesci from a much greater number of sites cleary including this bone fragment in its range of variation.

Edited February 16, 2013 by RichW9090

[fossillarry]

This is a metatarsal not a metacarpal. The j shaped posterior structure in the middel view is a dead give away for identifying horse metatarsal. The hook of the j points towards the cuboid facet. Nice specimen.