Mesolithic or Secondary Epoch. Chalk Period. Jurassic Period. Triassic Period. Palæolithic or Primary Epoch. Permian Period. Coal Period. Devonian Period. Archilithic or Primordial Epoch. Silurian Period. Cambrian Period. Laurentian Period. [Legend:] Single or MONOPHYLETIC PEDIGREE of the Stem of the BACK-BONED ANIMALS Based on Palæontology. Relative lengths of the 5 Epochs in per centages. Quarternary Epoch 0.5 Tertiary Epoch 2.3 Secondary Epoch 11.5 Primary Epoch 32.1 Primordial Epoch 53.6 ------ _Total_ 100.0] In the first order, that of _Primary Reptiles_, or _Primary Creepers_ (Tocosauria), we class the extinct _Thecodontia_ of the Trias, together with those Reptiles which we may look upon as the common primary form of the whole class. To the latter, which we may call _Primæval Reptiles_ (Proreptilia), the Proterosaurus of the Permian system very probably belongs. The seven remaining orders must be considered as diverging branches, which have developed in different directions out of that common primary form. The Thecodontia of the Trias, the only positively known fossil forms of Tocosauria, were Lizards which seem to have been like the still living monitor lizards (Monitor, Varanus). SYSTEMATIC SURVEY _Of the 8 Orders and 27 Sub-orders of Reptiles._ (Those groups marked with * became extinct even during the Secondary Period.) ----------------------------------------------------------------------------------- | _Sub-orders_ | _Systematic Name_ | _A Generic Name_ _Orders_ | _of_ | _of the_ | _as_ _of Reptiles._ | _Reptiles._ | _Sub-orders._ | _an example._ ----------------------------------------------------------------------------------- I. =Primary= { 1. Primæval reptiles 1. Proreptilia * (Proterosaurus?) =Reptiles= { +Tocosauria+ { 2. 2. Thecodontia * Palæosaurus { 3. Cleft-tongued 3. Fissilingues Monitor { 4. Thick-tongued 4. Crassilingues Iguana II. =Lizards= { 5. Short-tongued 5. Brevilingues Anguis +Lacertilia+ { 6. Ringed lizards 6. Glyptodermata Amphisbæna { 7. Chameleons 7. Vermilingues Chamæleo { 8. Adders 8. Aglyphodonta Coluber { 9. Tree serpents 9. Opisthoglypha Dipsas III. =Serpents= { 10. 10. Proteroglypha Hydrophis +Ophidia+ { 11. Vipers 11. Solenoglypha Vipera { 12. Worm serpents 12. Opoterodonta Typhlops