‘ Based on DNA , fossils and other evidence , CROCODILES are more
CLOSELY RELATED TO BIRDS than snakes and lizards !’
and had feathers on just certain body regions ( especially the forearms , hind legs and tail ), and whilst some species had just one type of feather , others featured a number of different types . By the Early Cretaceous ( 124- 128 million years ago ) for example , Sinornithosaurus and Microraptor gui had both plumulaceous as well as pennaceous feathers .
The most likely scenario for the evolution of feathered flight is that as lineages became increasingly arboreal , this would have favoured more aerodynamic feathers that assisted in leaping amongst branches . The development and modification of pennaceous feathers on the limbs and tail would have enhanced arboreal locomotion by permitting first parachuting , then gliding , and finally powered flight .
Birds are reptiles too !
Not only are birds dinosaurs , but they , like dinosaurs , are also reptiles . Surprisingly , based on multiple lines of evidence – DNA , fossils and various embryonic and morphological features – birds are classified within the group Archosauria , which includes crocodiles ! This means that crocodiles are more closely related to birds than they are to other reptiles , like snakes and lizards . Molecular and fossil data date the divergence of the lepidosaurs ( including snakes and lizards ) from archosaurs at about 270-
275 million years ago , whereas crocodiles and dinosaurs last shared a common ancestor about 230-220 million years ago . Despite superficial appearances , crocodiles share more features with birds than lizards , in particular in relation to their bone and muscular structures . Another common feature is a single penis ( for those birds that have not lost the penis as an intromittent organ ), whereas lizards and snakes have two hemipenes .
‘ Based on DNA , fossils and other evidence , CROCODILES are more
CLOSELY RELATED TO BIRDS than snakes and lizards !’
More broadly , there are multiple features that birds share in common with reptiles . These include eggs with a calcareous shell , the protein betakeratin ( in feathers and scales ), a ‘ diapsid ’ skull ( which differs to that of mammals ), scales ( retained on birds ’ legs ), and the production of uric acid in order to eliminate nitrogenous waste . It is well established among zoologists that birds are completely nested within the reptilian clade ; over a century ago T . H . Huxley , a renowned zoologist and close colleague of none other than Charles Darwin , was moved to declare birds to be ‘ glorified reptiles ’.
This points to the inaccuracy of the field of ‘ herpepology ’: our organisms of interest , the herpetofauna , are thus a group inconsistent with evolutionary relationships . Combining amphibians and reptiles , these two disparate clades , which diverged approximately 360 million years ago , were grouped together as those ‘ creeping ’ animals ( the name being derived from the Greek herpeton or herpein ; to creep ). This makes herpetofauna a polyphyletic clade , while the traditional view of Reptilia , excluding birds , is consequently a paraphyletic clade ( i . e . a grouping with a common ancestor but that does not include all descendents ).
These evolutionary relationships reveal another inaccuracy in the very name of the group we know as dinosaurs , for the name Dinosauria derives from the Greek words deinos , meaning terrible , and sauros , meaning lizard . Dinosaurs , especially of the avian kind , are hardly ‘ terrible ’, and are strictly not lizards either . These flaws are unsurprising given that the term dinosaur was coined by Richard Owen , a religious man opposed to his contemporary Charles Darwin ’ s theory of evolution .
The successful survivors .
Birds were not entirely immune to the cataclysmic consequences unleashed when the ancient asteroid crashed into Mexico . By the end of the Cretaceous , a number of distinct
Left : specimens preserved in amber ( like this grasshopper ) exhibit extremely fine structural detail . Image by Roy Palmer . Above right : pterosaurs had mastered flight well before birds . This species of Zhenyuanopterus dinosaur lived during the Cretaceous period in China . Image by Linda Bucklin .
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