Brain Research on Lizards 
7 
destroy them and to steal their niches. Some 
of the smaller mammal-like reptiles pre- 
sumably “went underground” and gradually 
became mammals, keeping their young 
nearby so that they too would not be gobbled 
up. Other animals derived from a different 
stock appear to have taken to the trees and 
gradually became birds, with nests for the 
young representing an extension of the 
amnion. 
REPTILIAN BEHAVIOR 
It is, of course, disappointing that there 
are no existing reptiles directly akin to the 
mammal-like reptiles (Fig. 5). The croco- 
dilia are derived from the archosaurs, and 
the Rhynchocephalia (of which the famous 
tuatara is the only existing form) also 
betray some affinity to the archosaurs 
(Colbert, 1969). The turtles (Chelonia) 
seem to have maintained their characteristic 
independence since branching off from the 
stem reptiles. Only the lizards appear to 
bear any resemblance to the primitive 
synapsids. One of the primitive Pelycosaurs 
was the Varanosaurus which Romer has 
described as having proportions not unlike 
those of many lizards (1966, p. 174). Colbert 
refers to these animals as being about 5 ft. 
in length, with a slender body, fairly slender 
limbs, and a long tail. “In fact,” he con- 
tinues, “we might say that Varanosaurus 
was lizard like in his general aspect, though 
this characterization must not be taken as 
an indication of any close relationships with 
lizards.” (Colbert, 1969, p. 130) 
On the basis of the foregoing comments 
and other considerations, it would appear 
that lizards — and particularly the Varanus 
lizards (Auffenberg, this volume) — would 
bear the closest resemblance to the mammal- 
like reptiles. It is also to be noted that 
present-day lizards occupy niches similar to 
those of the carnivorous mammal-like rep- 
tiles. 
The scientific method partly relies on the 
recognition of commonalities and differences 
in things. As described elsewhere in this 
volume, examination of the brains of lizards 
provides an excellent opportunity to identify 
differences in structures that appear to cor- 
relate with behavior called upon in a variety 
of niches. For our studies, however, we are 
particularly interested in identifying kinds 
of behavior that lizards have in common 
with other terrestrial vertebrates. 
From an evolutionary standpoint it is 
curious that ethologists have paid little at- 
tention to reptiles, focusing instead on fishes 
and birds. Lizards and other reptiles provide 
illustrations of patterns of behavior com- 
monly seen in mammals, including human 
beings. In Table 1, I have listed 24 types of 
behavior seen among reptiles that involve 
self-preservation and the preservation of the 
species. Those that primarily involve self- 
preservation are placed at the beginning of 
the list. 
Five Interoperative Behaviors 
There is an important pentad of proto- 
typical forms of behavior of a general nature 
that may be variously operative in the activi- 
ties listed in Table 1. They may be denoted 
as: (1) isopraxic, (2) perseverative, (3) 
reenactment, (4) tropistic, and (5) decep- 
tive behavior. The word “isopraxic” refers 
to behavior in which two or more individ- 
uals engage in the same kind of activity 
(MacLean, 1975a, 1977a). As a purely 
descriptive term, isopraxic avoids precon- 
ceptions and prejudices commonly attached 
to such terms as “social facilitation” and 
“imitation” (MacLean, 1975a). Persevera- 
tive behavior applies to repetitious acts like 
those that occur in displays and would in- 
clude so-called displacement or adjunctive 
behavior seen in conflictive situations. Re- 
enactment behavior refers to the repetition 
on different occasions of behaviors seeming 
to represent obeisance to precedent as, for 
example, following familiar trails or return- 
ing year-after-year to the same breeding 
grounds. Tropistic behavior is characterized 
by positive or negative responses to partial 
or complete representations, whether alive 
