#caves

Convergence of form in groundwater wildlife from different regions of the world.

A quick definition... characters that are considered a result of permanent life in subterranean habitats are referred to as "troglomorphisms."

Dr. Ron Brandon wrote of the suite of characteristics that tended to be observed in North America's diverse, obligate subterranean, groundwater-inhabiting salamanders: An elongation of the head, a flattening of the head, a general trend toward a "shovel shaped" head, an increase in the number of teeth, a reduction of pigmentation and of eyes, and an elongation and attenuation of the body and limbs. These are common troglomorphisms observed in said salamanders. The same trend is also observed in Europe's "Olms." The "duck-biled" mouth is a characteristic observed in various groundwater fishes as well - see the image here comparing the face and mouth shape of obligate groundwater fishes from opposite sides of the planet (China and North America). Why? Dr. Brandon's hypothesis (H₁): The flattening of the head and the increased teeth (relative to surface-inhabiting related species) leads to more efficient prey capture and handling. This confers an evolutionary advantage in a habitat where feeding opportunities might be scarce, even rare in some systems. Every opportunity is significant; maximizing said events is key to surviving in the habitat. If this is true, strong evolutionary pressures toward improved prey capture and handling will influence head shape in evolutionary time. In fact, that is what we observe in unrelated groups of organisms. This doesn't mean that there can't be other hypotheses for the observed head shape and the convergence on it by multiple species in unrelated groups of salamanders.... OR that this is absolutely why we observe what we observe; however, the hypothesis does explain the convergence of head shape. Hope you enjoy these amazing inhabitants of subterranean waters from around the world. Here is what the "salamander circle" is represented by: the following...

Clockwise, starting at 12 noon:

European Olm (Proteus anguinus), Tennessee Cave Salamander (Gyrinophilus palleucus palleucus), Cascade Cavern Salamander (Eurycea latitans), Georgia Blind Salamander (Eurycea wallacei), Comal Blind Salamander (Eurycea tridentifera), Texas Blind Salamander (Eurycea rathbuni), Western Grotto Salamander-larva (Eurycea spelaea), Western Grotto Salamander-adult (Eurycea spelaea)