This display shows mammals found in Pennsylvania. How many have you seen in your backyard?
mammals
Armadillos: Identical Quadruplets Every Time
Armadillos are placental mammals that first appeared in the fossil record in South America 60 million years ago. Today, there are 21 species, only one of which is found in North America—the nine-banded armadillo, Dasypus novemcinctus.
All armadillos have a protective shell, or carapace, made of bony plates in the skin. These osteoderms not only cover the trunk, but the head, limbs, and, except for the naked-tail armadillo, even the tail. Armadillo in Spanish means “little armored one,” but the Aztec name is more descriptive, translating to “turtle-rabbit.” The carapace of the nine-banded armadillo has two major shields, one at the shoulders and the other at the pelvis, connected by a series of overlapping bands, which provide some degree
of flexibility. As you can guess from its name, there are usually nine such bands in Dasypus novemcinctus (as in the mother pictured here), but this varies from seven to 10. The underbelly is not similarly protected with osteoderms, but the skin is tough and leathery.
Dasypus novemcinctus, Nine-banded Armadillo
The evolution and biology of the nine-banded armadillo, the state small mammal of Texas, have fascinated me for years. However, because we just celebrated Mother’s Day, I want to comment on the amazing armadillo mother. Dasypus novemcinctus is the only vertebrate that gives birth to identical quadruplets every time! A female produces a single egg that, once fertilized, splits into four genetically identical embryos that share one placenta. How and why this unique pattern evolved and continues to be maintained is a mystery. We usually consider genetic diversity a plus for organisms with multiple births as
it increases the chances that some offspring will survive in an ever-changing environment, but the nine-banded armadillo bucks this by producing clones.
Other than making milk for her young, the nine-banded armadillo mother is not particularly attentive, and the father is even less so. Yet, perhaps her major role is providing sufficient nutrition for her young to grow and prosper. Building a bony carapace requires extra nutrients, primarily calcium, and phosphate. Although ossification of the osteoderms begins in utero, you can imagine that birth (of four babies no less!) is facilitated by them having a thin and flexible carapace, that is, one that
is not fully formed. Indeed, thankfully, most of the carapace’s development occurs after birth.
The armadillo mother makes this all happen largely on an insectivorous diet, a generally poor source of calcium. Add to that, armadillos have a lower metabolic rate than most mammals. Somehow, despite these perceived handicaps, the young born at 100 grams (less than a quarter pound) grow rapidly and are able to forage for themselves at two months. How the armadillo mother is able to do all this for her four identical babies is as mysterious as how she had four identical babies in the first place.
John Wible, PhD, is curator of mammals at Carnegie Museum of Natural History. He studies the evolutionary history of mammals and lives in a house full of them, some human (wife and two sons) and some non-human (cats, rabbits, and guinea pigs).
Carnegie Museum of Natural History Blog Citation Information
Blog author: John WiblePublication date: May 22, 2017
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More Mammals with Venom
by John Wible
The duck-billed platypus, Ornithorhynchus anatinus, is no doubt one of the world’s oddest mammals, with a suite of adaptations to its life in streams in eastern Australia and Tasmania. Its suede-like bill is packed with electro- and mechanoreceptors, which help the platypus find small invertebrates and fish in murky waters. It has webbed forefeet and hind feet and a hairy, beaver-shaped tail, all great for swimming and diving, and a lush, thick coat for insulation on cold mornings.
As with other mammals, the female platypus produces milk to nurture its young. However, its young are hatched from leathery eggs! Along with the echidna or spiny anteater from Australia and New Guinea, the platypus is one of the two types of living monotremes or egg-laying mammals. This is in contrast to the other groups of extant mammals, marsupials, and placentals, which have live births.
Along with egg-laying, the skeleton of the platypus is a throwback to its mammal-like reptile origin. The bones in its arms and legs, the humerus and femur, are set perpendicular to the trunk, giving the platypus a sprawling posture and a waddling gait on land. Marsupials and placentals have more upright postures with less waddling.
But where is the venom? If you look closely at the ankle of the male platypus, you will see a deadly looking weapon made of keratin, just like your fingernails. This tarsal spur sticks out from the body and sits on a small, flat bone—the os calcaris. The spur is hollow and connected to a gland below the knee that produces venom during the platypus breeding season. Because
of this seasonal activity, the venom is thought to be used in male-male competition for females.
For humans that make the mistake of picking up male platypuses at the wrong time of year, the venom is not deadly, but it is excruciatingly painful. One unfortunate soldier said it is worse than shrapnel! A small remnant of the spur is retained in juvenile female platypuses for only a few months after hatching, and the supporting bone, the os calcaris, without a spur occurs in the echidna. In recent years, tarsal spurs and support bones have been found in the fossil record for numerous groups of extinct primitive mammals that lived during the Age of Dinosaurs. Rather than being unique to the male platypus, venom manufactured in the leg may have been a widespread component of early mammalian weaponry for survival in the hostile Mesozoic landscape. Why this apparatus was lost in early marsupials and placentals is a mystery. One group, the bats, have reinvented a tarsal spur, where it is used in support of the wing membrane.
John Wible, PhD, is the curator of the Section of Mammals at Carnegie Museum of Natural History. John’s research is focused on the tree of life of mammals, understanding the evolutionary relationships between living and extinct taxa, and how the mammalian fauna on Earth got to be the way it is today. He uses his expertise on the anatomy of living mammals to reconstruct the lifeways of extinct mammals. John lives with his wife and two sons in a house full of cats and rabbits in Ross Township.
Mammals with Venom
Did you know that some mammals are venomous?
The Section of Mammals has one specimen in its collection of the solenodon, which at 21 inches long is the largest member of the group of mammals that includes shrews and moles.
Our specimen, Solenodon paradoxus, comes from the Caribbean island of Hispaniola (which includes Haiti and the Dominican Republic), but there is second solenodon species in Cuba, Solenodon cubanus. Solenodons have a mobile proboscis, obviously much shorter than an elephant’s trunk, and a powerful sense of smell, which makes up for their tiny eyes. They occupy a shrew-like niche, rooting in leaf litter for insects and earthworms—their primary prey.
Both solenodon species are highly endangered and at various times have been thought to be extinct. Problems for the solenodons started in the 1800s when small Asian mongooses were introduced by humans to control the snake and rat populations; feral dogs and cats aggravated the issue, as the solenodons did not fare well against any of these three carnivores. Habitat destruction has nearly been the final blow.
Prior to the introduction of the carnivores, solenodons were the top mammalian predator on their islands. Part of what helped them was their ability to produce venom in one of their salivary glands, making the solenodon one of the very few venomous mammals. They have a snake-like delivery system for their venom. The tallest tooth in the lower jaw (the second incisor) has a deep groove on its inner surface, which accommodates the duct of the venomous salivary gland. In fact, the name solenodon in Greek means “grooved tooth.” When the solenodon bites, the venom is injected from that tooth and slows down its prey. Unfortunately for the solenodons, their venom and fighting prowess has not been sufficient to protect them from the introduced carnivores.
John Wible, PhD, is the curator of the Section of Mammals at Carnegie Museum of Natural History. John’s research is focused on the tree of life of mammals, understanding the evolutionary relationships between living and extinct taxa, and how the mammalian fauna on Earth got to be the way it is today. He uses his expertise on the anatomy of living mammals to reconstruct the lifeways of extinct mammals. John lives with his wife and two sons in a house full of cats and rabbits in Ross Township.
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Squirrels at CMNH
by John Wible
Like many people in western Pennsylvania, I share my yard with gray squirrels (Sciurus caroliensis). Other than the mammalian pets in our houses, gray squirrels are the mammals we are most likely to see on a daily basis. They amuse us with their acrobatic antics at our bird feeders, their chattering vocalizations, and their skirmishes with their squirrel neighbors.
Gray squirrels are rodents with large, ever-growing incisors that help them open nuts and seeds. They belong to the squirrel family (Sciuridae), which also includes chipmunks, woodchucks, and flying squirrels. In fact, there are more than 200 species of squirrels that inhabit all continents except Antarctica, although humans brought them along to Australia.
A typical adult gray squirrel in western Pennsylvania is about two feet from head to tail tip. That is not a baby gray squirrel below it in the picture above. That is an adult of the world’s smallest squirrel, the African pygmy squirrel (Myosciurus pumilio)! It measures about 5 inches and weighs 16 grams, less than half an ounce. They are found in lowland tropical forests in west central Africa (Cameroon, Gabon, Congo, and Equatorial Guinea). They are omnivores, foraging constantly, eating bark, fruits, and insects. Their conservation status is generally okay, but deforestation is a threat.
The African pygmy squirrel is the only squirrel that travels frequently both upside down and right side up along branches. What a treat it would be to see how one of these would get to my bird feeder!
John Wible, PhD, is the curator of the Section of Mammals at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.
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Armadillos: Identical Quadruplets Every Time
Carnegie Museum of Natural History Blog Citation Information
Blog author: Wible, JohnPublication date: March 15, 2017
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Craniums and mandibles
Craniums and mandibles of various mammals on display in the Hall of North American Wildlife.
