How Can We Know That Dinosaurs Were Reptiles?

For amateur dinosaur lovers out there, there are many questions that come to mind when contemplating the existence of these giant extinct beasts. One such question revolves around the assertion that dinosaurs were reptiles. While the answer to this question may seem simple for those trained in biology and paleontology, today we’re going to take a look at the answer from a layman’s point of view.

Understanding Science to Determine Whether Dinosaurs Were Reptiles

Understanding Class

All living things in terms of biology are classified in to classes. There are currently a considerable number of animal classes each of which are divided up by phylum. A phylum is a way of categorizing living things by general specialization of their body plan. A class is a way of categorizing living things within a phylum that are alike in a number of ways, for example all mammals drink milk as newborns and have hair on their bodies. All birds are born from hard shelled eggs and have feathers on their bodies. All reptiles are cold blooded and have scaly skin.

Can We Prove That Dinosaurs Were Reptiles?

The answer to the question of whether dinosaurs were reptiles is a little tricky based on newer information that has recently been discovered in the field of paleontology. Let’s take a look at the defining characteristics of reptiles on a closer level to try and make sense of this.

Reptiles are Cold Blooded

A recent article from Science daily contests that while dinosaurs were reptiles by classification, they were sometimes warm blooded reptiles rather than cold blooded ones. This article is based on research from the Institut Català de Paleontologia (ICP) and Universitat Autònoma de Barcelona (UAB) and looks at the development of lines of arrested growth in living animals. To date there has been no definitive answer as to whether dinosaurs were cold blooded or warm blooded but the general consensus seems to be that among the different species both endothermic and ectothermic creatures can be found.

This assertion does not rule out the fact that dinosaurs could have been reptiles since not all dinosaurs are believed to have been warm blooded.

Reptiles Have Scales

The discovery of Yutyrannus and the theory that a number of Tyrannosaurs (and other dinosaur superfamilies) may have been feathered seems to throw a wrench in to the works as far as this classification criteria is concerned. If some dinosaurs had downy feathers and hatched from brittle hard shelled eggs wouldn’t this classify them as birds? Not necessarily. The feathers found on these dinosaurs were far different to the feathers found on modern day birds, hence why researchers refer to them as proto-feathers. There is also the consideration that these “feathered” dinosaurs may also have possessed scales (either modified or “traditional” scales) on their skin with only patches of these proto-feathers.

The presence of feathers on some dinosaur species does not rule out the majority of dinosaurs that had scales and therefore met this criteria to be classified as a reptile.

Reptiles Are Born on Land

There is no doubt here that dinosaurs were born on land from hard-shelled eggs. While most people like to believe that all birds hatch in nests above ground, there are a number of birds which do lay their eggs in nests on land – much like the image we have of dinosaurs from recovered nesting sites.

Being born on land helps to categorize dinosaurs as reptiles, however; it also draws a parallel to the development of birds.

Weren’t Dinosaurs Birds?

Considering the fact that dinosaurs may have been warm blooded, they may have had feathers and they hatched on land from hard shelled eggs, couldn’t we say that these “reptiles” were in fact birds? There is a slight complication with this assertion. If you are like most paleontologists then you believe that birds evolved from dinosaurs – that is before dinosaurs, there were no birds. So how could dinosaurs be birds if birds had yet to evolve?  Certainly there is the consideration that dinosaurs could have been the first birds, but based on the fact that not all dinosaurs were feathered or warm blooded, it is more likely that there is simply an overlap between reptiles and birds during the evolution process.

So what does this all mean? It means that using what we know currently about dinosaurs and birds and using deduction based on number of defining criterion, that dinosaurs were reptiles.