Amphibians are unique creatures that live both on land and in water during various stages of their lives. A common question many people have is: do amphibians have hair? At first glance, most amphibians appear hairless with moist smooth skin.
However, the answer is more complex than a simple yes or no.
If you’re short on time, here’s a quick answer: most amphibians do not have true hair. However, some aquatic salamander species have hair-like external gills protruding from behind their heads that resemble hair.
What is Hair and Why Mammals Have It
Definition and purpose of hair
Hair growth and structure in mammals
In mammals, hair growth begins inside hair follicles deep in the dermis skin layer. Hair follicles contain root cells at their base that divide rapidly to spur hair production. As cells are pushed upward from the follicle base, they mature and die, forming the hair shaft structure.
The hair shaft has an inner medulla layer, a middle cortex layer containing pigment, and an outer cuticle layer with protective scales. Hair gets its texture and curl pattern based on the shape of the follicle. Curly hair comes from curved follicles, while straight hair has straight follicles.
On average, human scalp hair grows around 0.3 to 0.4 mm per day, or around 6 inches per year. Eyebrows have a shorter active growth phase of only about 45 days. Mammal species also differ in hair density across the body.
Why amphibians don’t need insulation from hair
Amphibians like frogs don’t need hair because they have other adaptations to regulate body temperature. Their bare, glandular skin allows for cutaneous respiration – absorbing oxygen directly from the environment. Some frogs also have mucous glands that keep their skin moist.
This moisture allows evaporative cooling – heat loss from water evaporating off their skin. Having bulky hair follicles and shafts would interfere with these effective temperature regulation strategies.
And since amphibians are ectothermic (cold-blooded), they rely on external heat sources like the sun to warm up. They don’t need thick fur to retain metabolic body heat. So instead of hair, amphibians have adaptations like moist skin, mucus, and vasodilation of blood vessels near their skin to handle heating and cooling needs.
External Gill Filaments in Aquatic Salamanders
Salamanders go through an amazing transformation during their life cycle, adapting to live in water and on land. The gills they develop as aquatic larvae are a key adaptation allowing them to breathe underwater.
Salamander life cycle and habitat
Most salamanders have a biphasic life cycle, meaning they live part of their lives in water as larvae (with gills) and part on land as adults (with lungs). After hatching from eggs laid in the water, salamander larvae are entirely aquatic.
They have external gills that allow them to breathe underwater. After undergoing metamorphosis, the salamanders lose their gills and develop lungs to breathe air. As terrestrial adults, many salamander species still live in damp habitats near water.
Purpose and appearance of external gills
External gills are filamentous structures that extend from behind the head of larval salamanders. They are highly vascularized with blood vessels to facilitate respiratory gas exchange. Oxygen diffuses into the bloodstream while carbon dioxide diffuses out.
The thin gill filaments provide a large surface area for gas exchange. External gills are bright red in color due to the extensive capillary networks.
Salamanders pump water through their mouth and over their gills to maintain a flow of fresh, oxygenated water. The slender gill filaments wave gracefully in the current. Cilia on the gill filaments help direct the water flow.
Salamander larvae would suffocate without access to well-oxygenated water flowing over their delicate gills.
Examples of salamanders with external gills
Many salamanders develop prominent, feathery external gills as larvae, including:
- Spotted salamander
- Tiger salamander
- Alpine newt
- Hellbender
- Mud puppy
Of these, the hellbender and mud puppy retain their external gills even as adults. Most other species resorb their gills during metamorphosis. The long, branch-like external gills are a distinctive feature of salamander larvae.
They enable an aquatic lifestyle before transitioning to breathing with lungs on land.
Other Hair-Like Structures in Amphibians
Filaments on Feet to Assist with Climbing
Many tree-dwelling frogs and salamanders have tiny hair-like filaments on their toe pads that help them climb and cling to smooth surfaces (Smith et al. 1998). These microscopic structures, called scansors, are made of keratin just like human hair and fingernails.
Tree frogs like the red-eyed leaf frog have thousands of tiny scansors under their toe pads that interlock with the pores in tree bark and other surfaces, allowing them to grip firmly so they don’t fall off.
Researchers have found that the number and pattern of scansors relates to an amphibian species’ climbing ability and habitat. Arboreal species that live high up in trees like the grey tree frog tend to have much denser scansor fields on their toes.
Meanwhile, species that don’t climb as much like the American toad have fewer toe pad scansors. The intricate orientation of the scansors aids attachment and release when climbing. So even though they are microscopic, these hair-like structures play a huge role in amphibian survival!
Skin Projections for Camouflage Purposes
Many amphibians have small warty bumps or spiky protrusions covering their skin that resemble hair. For example, the green frog and common eastern newt have pointy keratinized skin tabs called asperities that help camouflage them against leaf litter and other nature backgrounds (Ditsche and Summers 2019).
Species that have bright warning coloration like the red-backed salamander also use these dermal projections to enhance their visibility to would-be predators.
Some salamanders even have external gills early on in their larval stage that have filamentous structures resembling facial hair! The biological purpose of these fuzzy gills is to increase oxygen absorption from the water.
So while amphibians may sport some hair-like skin projections, these serve important ecological functions from camouflaging the animals to improving their respiration and movement in their environments.
Conclusion
In summary, most amphibians do not have true hair like mammals. However, some salamanders have hair-like external gills used for respiration in water. And certain tree frogs have small hair-like filaments on their toe pads to grip surfaces.
So while lacking fur, hair, and whiskers – some amphibians evolved unique structures that resemble hairs as adaptations to their environments.
