These are terminal branches from the lycopsid Lepidodendron sternbergii, one of the great scale trees that dominated major global habitats for 40 million years. Forests of these 35-meter-tall plants contributed greatly to the Carboniferous-aged coal deposits of North America. Most scale trees became extinct before the end of the Carboniferous. The scale trees were not typical lycopsids — both fossil and extant forms tend to be small and inconspicuous. Find out more about lycopsids or lycophytes here and here. You can see a reconstruction of an entire Lepidodendron (Fig. 5-7) here.

You get bonus points if you noticed that this is not Lepidodendron's first appearance as a Mystery Fossil. Back in 2001 we looked at Lepidodendron's scaly "bark" (Mystery Fossil #7).
 

		Visit the Mystery fossil archives for more mysteries from the past!