Q: How do you arrive at a family tree of reptiles?
1. You can look at hundreds of taxa and score them for hundreds of characters and let maximum parsimony recover the family tree, as I did here. This is following in the paths of dozens of others who have created their own subsets of the reptile family tree with their own taxon and character lists. Because morphology is an expression of genetics, morphology is really the only genetics that counts. Morphology helps you survive in your niche and enhances secondary sexual characteristics to help you get laid to create replicants of your own naturally selected self.
2. You can look at the molecular DNA of several distinct specimens (all currently living) and let maximum parsimony recover a much more unfocused family tree leaving out hundreds of extinct taxa with no known living counterparts. Of course some of this DNA doesn’t express anything. Some of it jumps around the chromosomes. And DNA cannot be recovered from the vast majority of extinct taxa, so we’re left with huge ghost lineages, during which “things” happen (see below). Even the sex chromosomes are different between birds, mammals and lizards.
Male mammals have the XY combination while females have XX. Male birds carry what’s known as the ZZ pair and females have the ZW pair. The green anole X chromosome is a microchromosome. Yes, it’s nothing compared to having a skull, tail, four feet, five toes and relative constants like those when it comes to DNA.
BTW I freely admit to not knowing much about molecular studies except that they sometimes don’t replicate morph studies.
The DNA problems don’t end there…
We’re talking about reptiles here: DNA study results do not replicate morphological study results. Often DNA study results do not replicate other DNA study results. DNA is changing even when morphology does not (Hays 2008). This alone could be the reason for the discrepancy in DNA and morphology among reptiles (and not among mammals and humans involved in paternity suits).
Is this why reptile DNA studies don’t match morph studies?
A recent article on genetic sequencing of an anole lizard DNA reports, “We’ve now sequenced a lizard genome for the first time ever. The anoles shed light on non-coding sequences of genes. What they might be are the husks of special DNA sequences known as transposons. These can only be described as “jumping DNA”, able to actually move through the genomes and copy and paste themselves elsewhere. Transposons can give any genome that carries them great agility and resilience in dealing with unexpected environmental challenges.”
Lizard egg proteins
From the same article, “It appears that, as far as egg genes are concerned, reptiles are in a constant state of evolutionary flux, with the proteins revealing clear signs of rapid evolutionary change.”
The Hays et al. 2008 abstract
“The tuatara of New Zealand is a unique reptile that coexisted with dinosaurs and has changed little morphologically from its Cretaceous relatives. Tuatara have very slow metabolic and growth rates, long generation times and slow rates of reproduction. This suggests that the species is likely to exhibit a very slow rate of molecular evolution. Our analysis of ancient and modern tuatara DNA shows that, surprisingly, tuatara have the highest rate of molecular change recorded in vertebrates. Our work also suggests that rates of neutral molecular and phenotypic evolution are decoupled.”
I take this to mean DNA genetic evolution is decoupled from morphological genetic evolution in the Lepidosauria (but not necessarily decoupled in other living things). With that hanging over our collective decision making processes, maybe morphological genetic studies should trump DNA genetic studies in non-mammalian reptiles.
Reptile DNA studies might be interesting, but let’s not hang our hats on them. Let’s stick with fossils and phylogenetic analysis. That covers all the bases down to the specimen.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.
Hay JM, Subramanian S, Millar CD and Mohandesan E 2008. Rapid molecular evolution in a living fossil. Trends in Genetics, 24(3):106-109.