Salt glands

In the section on tears you'll find that AAT/H proponents claim tears in humans are a method of actively excreting salt in response to a saltwater environment, but in fact, tears are never hypertonic and cannot do what AAT/H proponents claim for them. Tears are, however, strongly hypertonic in regard to potassium and that does indicate what environment we developed in. That environment is terrestrial, not aquatic. The salt glands of terrestrial birds and reptiles are specialized for excreting potassium, unlike those of their marine relatives.

Some AAT/H proponents, most notably Elaine Morgan, have insisted that salt glands do not exist in terrestrial birds and reptiles. I must admit I find it discouraging that someone who is making up a theory with which they wish to supplant the past several decades of paleoanthropology does so little research before making such claims. This info is readily available.

Of course, it may be that it isn't simply poor research, since Morgan continued to make the "salt glands only in marine birds and reptiles" claim long after the facts (with refs and accurate quotes) had been presented to her (in several newsgroup posts which she replied to and so presumably read). She did finally say that she was dropping these bogus claims, but these are related to her claims that human tears and sweat are aquatic adaptations, and she and other AAT/H proponents still make those claims. As always, the "false facts" generated by AAT/H proponents are persistent, and so I feel the facts must be stated once again.


1975 Salt Glands in Birds and Reptiles by M. Peaker and J.L. Linzell (Dept. of Physiology, Agricultural Research Council, Institute of Animal Physiology, Babraham, Cambridge). Monographs of the Physiological Society No. 32. Cambridge University Press: Cambridge, London, New York, Melbourne.

Mentioned in text:
Some terrestrial birds with salt glands:
1. Ostrich
2. a Partridge, Ammoperdix heyi (North Africa and the Middle East
deserts)
3. various Falconiformes (birds of prey), including Red-Tailed Hawks
4. North American Roadrunner, Geococcyx californianus (particularly
in nestlings)

Some terrestrial reptiles with salt glands:
1. Green or Linnean Iguana, Iguana iguana
2. Desert Iguana, Disposaurus dorsalis (North America)
3. at least one variety of Mastigure, Uromastyx aegytius (North Africa and the Middle East deserts)
4. Chuckwallas
5. False Iguana, Ctenosaura pectinata

pg. 259:
Table 13.3. Salt glands in lizards

Nasal salt secretion observed

Iguanidae Iguana iguana
Dipsosaurus dorsalis
Crotaphytus collaris
Sauromalus obesus
Sauromalus hispidus
Sauromalus varius
Sceloporus cyanogenys
Conolophus subcristatus
Amblyrhynchus cristatus (Marine)
Agamidae Uromastyx aegytius
Uromastyx acanthinurus
Scincidae Eumeces skiltonianus
Trachydosaurus rugosus
Xantusidae Species not stated
Lacertidae Acanthodactylus sp.
Teiidae Species not stated
Varanidae Varanus gouldii

Nasal salt secretion not observed

Gekkonidae Coleonyx sp.
Agamidae Amphibolurus ornatus
Lacertidae Lacerta viridus
Anguidae Gerrhonotus sp.

Other families with representatives lacking salt glands:
Anniellidae, Teiidae, Cordylidae, Helodermatidae.

pg. 261:

The evolution of salt glands, or indeed of any homeostatic system, is clearly a fascinating subject for speculation. Cranial salt glands are only known to exist in birds and modern reptiles. Therefore it is the reptiles to which we must concentrate most of our attentions. Nasal glands probably first appeared in the Amphibia serving to moisten and cleanse the nasal passages of the adults, which are usually terrestrial (see Bang & Bang, 1959). Judging by extant species the kidneys of reptiles and birds are much less 'efficient', in terms of concentrating ability, than those of mammals. Therefore evolution of amphibian nasal glands into salt-secreting glands might be inferred to have occurred in the early reptiles since, in truly terrestrial vertebrates, two major avenues for ionic and osmotic regulation present in lower vertebrates would have been lost -- the gills and the skin. In fact the development of the reptilian skin, which is relatively impermeable, from the amphibian type across which ions and water movements occur and can be controlled, must have meant a major alteration in the control of salt and water metabolism. Therefore any animal with an additional means of excreting ions would be at an advantage. It would enable such creatures to live on plants, which are rich in potassium and/or return to the sea and eat plants and invertebrates, which have the same ionic content as sea water. Therefore one might argue that the evolution of a salt gland together with all the other adaptations which enabled the initial colonization of land, was an important means of permitting the vast and complex adaptive radiation that occurred to fill all the varied ecological niches.