Anastasia, a lemur at the Maryland Zoo in Baltimore, died of an illness that experts said is not common in her species, which is native to Madagascar.

       Officials at the zoo said Anastasia was one of its two Coquerel’s sifakas (CAH-ker-rells she-FAHKS). She died Aug. 12 and was 17 years old.

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       Anastasia had been treated by experts for what was suspected to be kidney disease and gland issues. But vets were looking for a definitive diagnosis even as they cared for her, according to Ellen Bronson, the senior director of animal health, conservation and research at the zoo.

       “Ultimately, we concluded that she had a rare disease that has not been reported before in this species, commonly referred to as ‘Addison’s disease,’” said Erin Grimm, a mammal collection and conservation manager at the zoo. According to Grimm, the disease causes the adrenal gland to stop excreting hormones such as adrenaline and cortisol, which are “essential to many body functions.”

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       At first, Anastasia responded well to replacement therapy and care, but at her “advanced age she was not able to fully recover,” Grimm said.

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       Female Coquerel’s sifakas are known to take on “dominant roles in their troop,” and Anastasia was “no exception,” Grimm said in a statement.

       Grimm said Anastasia, who was called Ana for short, came to the Maryland Zoo in 2009. She and a male lemur, Gratian, mated and produced five offspring at the zoo. Those baby lemurs were sent to other zoos, officials said.

       Ana was known to “rule the roost” in her enclosure at the zoo, officials said in a statement. She was often the first to pick her favorite foods and the first to eat. And zookeepers said she was “adept at breaking up family squabbles.”

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       But Grimm said Ana could also be “gentle,” noting that the lemur was “fiercely protective of her offspring.” Grimm called Ana’s death “quite a loss for all of us.”

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       Coquerel’s sifakas are unique-looking. They’re brown and white and are different from other lemurs because of how they move — they stay in a very “upright posture and only use their back legs,” as they leap through treetops, according to zoo officials.

       They’re also known for being able to jump more than 20 feet at a time, and on the ground, officials said, “they spring sideways off their back feet to cover distance.”

       In the wild, they’re native to Madagascar. They’re an endangered species, experts said, and in the wild they spend most of their time in treetops in forests. Their habitats have been harmed by deforestation, zoo officials said.

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       The Maryland Zoo is one of 13 accredited zoos in the United States to have them. And the Maryland Zoo’s other Coquerel’s sifaka — a male — will be moving to another zoo to be part of a breeding pair, zoo officials said. The Maryland Zoo said it hopes to get more Coquerel’s sifakas at some point through the association of zoos and aquariums.

       An earlier version of this report misspelled Ellen Bronson’s last name as Brownson. This version has been corrected.