Cells from a woolly mammoth that died more than 28,000 years ago have been partially reactivated inside of mouse egg cells, according to a study published Monday in Scientific Reports.

The achievement shows that biological activity can be induced in the cells of long-dead creatures, but that does not mean that scientists will be resurrecting extinct animals like mammoths any time soon.

A team led by Kazuo Yamagata, a biologist at Kindai University in Japan, extracted cells from the remains of “Yuka,” a young female mammoth discovered in 2010 on the coast of the Dmitry Laptev Strait in the Russian Far East.

Yuka was entombed in permafrost, a frozen ground layer that can often keep the skin, fur, brains, and other softer tissues of dead animals intact. Because Yuka is in particularly great condition, Yamagata’s team was able to extract 88 nucleus-like structures from her preserved muscle tissues.

The mammoth cells were implanted into mouse oocytes, which are ovarian cells involved in embryonic development. The researchers also implanted elephant cells into mouse eggs to provide a control sample.

Once the cell nuclei were incubated, they seemed to reawaken—but only slightly. The cells did not divide, but completed some steps that precede cell division. For instance, the mammoth nuclei performed a process called “spindle assembly,” which ensures that chromosomes are correctly attached to spindle structures before a parent cell breaks into two daughter cells.

About ten years ago, another team tried the same technique using a 15,000-year-old mammoth mummy, but were unsuccessful in stimulating cellular activity from that specimen.

The fact that Yuka’s cells were able to spring back into partial action is both an exciting and challenging development for scientists interested in cloning extinct animals. On one hand, some degree of cellular reactivation is clearly possible. But Yuka is also an exceptionally pristine specimen, and even her cells were not able to complete cell division—a major hurdle that scientists must clear to accomplish de-extinction.

Read More: The Mission to Clone the Woolly Mammoth

“The results presented here clearly show us again the de facto impossibility to clone the mammoth by current [nuclear transfer] technology,” Yamagata and his colleagues admitted in the study. However, the “approach paves the way for evaluating the biological activities of nuclei in extinct animal species.”