No. 406.] DINOSAUR-AVIAN STEM. 781 
II. RISE oF THE THEORY or HomopLasy. 
The theory of direct descent was more or less strongly sup- 
ported by many anatomists, but there were also many dis- 
senters. Seeley (Fiirbringer, '88, p. 1595) pointed out with 
truth that the direct descent theory rested upon resemblances 
of certain bones of the pelvis and posterior extremities which 
are found only in certain genera and are not characteristic of 
the whole group. 
Vogt also advocated the homoplastic view. Their opinions 
(79) were given by Seeley (81) as follows : 
* * All the characters whereon are based the claim of dino- 
saurs to be regarded as the ancestors of birds are only related 
to the power of keeping an üpright position upon the hind 
feet.’ 
* Vogt believes that certain dinosaurs were leaping or perch- 
ing animals, and infers that the avian characters of the pelvis 
and hind limbs thus came to be evolved from community of 
habit with birds. He is, however, not indisposed to see in 
dinosaurs possible parents of the ratites; while the Archzop- 
teryx would be the ancestor of the birds that fly." 
In 1882 Dollo also (82, '83) advanced the more modern idea 
that the resemblances in the pelvis and hind limbs might as 
well be considered adaptive as genetic. Baur, however (83, 
PP. 417 f.; '85 (2), pp. 446 f.), held firmly to the idea of direct 
descent, singularly enough, not through the carnivorous dino- 
saurs, but through the herbivorous iguanodont types. Dames, 
in opposition to Baur (84) concluded with Vogt, Seeley, and 
Dollo that the resemblances were due to adaptation, and that 
the direct ancestors of the birds could not be designated. A 
Still more conservative view, that the resemblances were alto- 
gether due to adaptation and not at all indicative of genetic 
descent, was taken by Richard Owen, by W. K. Parker (87), 
by Cleland (87), and by Mehnert (88). In the mean time, 
however, Owen, Cope, Mivart, Wiedersheim, had more or less 
strongly advocated the theory of the derivation of the carinate 
birds from the pterosaurs. Thus arose the extreme theory of 
Mivart (81) that the carinate birds sprang from pterosaurs, 
