Deconstruction the Family Tree

• By Anne-Marie Luca

Did you know that dolphins are more closely related to cows than to sharks? And that crocodiles have more family ties to birds than to lizards? Over the past 50 years or so, discoveries in genetics have uprooted the universal tree of life as it was long imagined.

While traditional methods classify species according to their overall resemblance, phylogenetic classification, or cladistics, aims to identify family relationships among organisms by studying, sequencing and decoding their genomes, as French biologist Hervé Le Guyader, co-author of Classification phylogénétique du vivant, explained when he spoke at the Jardin botanique in 2013. This method also makes it possible to look at the evolution of life in a new way.

“Genes are much more reliable than physical characteristics,” says Jacques Dancosse, a veterinarian at the Montréal Biodôme. “Species that evolve under similar conditions will have the same physical structures, but will not be at all related. This is what we call evolutionary convergence. Genetics, on the other hand, proves family connections.”

This classification method has not only allowed us to completely rethink the history of life, but has revealed some surprising family connections between organisms with absolutely no resemblance. In fact it has led scientists to deconstruct some established groups of species.

So no more reptiles, fish or vertebrates… Who knows, we may all have to go back to school to learn biology all over again!

Curious connections

Flying crocodiles?

Crocodiles are much more closely related to birds than they are to lizards. And both crocodiles and birds are now considered part of the Archosauria group. About 250 million years ago, their common ancestor split into two branches, leading to dinosaurs – ancestors of birds – and crocodiles. Today, crocodiles and birds both have a gizzard, a pocket in their stomachs where their food is ground up. That’s one of crocodiles’ evolved characteristics that distinguishes them from their miniature look-alikes, lizards, which are now classified as part of the Lepidosauria.

Are you more surf, or turf?

Dolphins are the cows of the sea. Or almost! These two mammals’ genetics point to a common ancestor, the mesonychid, a carnivorous landdwelling ungulate. About 50 million years ago, the group it belonged to divided into two branches. One remained on land, while the other adapted to aquatic life.

Hands for swimming

The bone structure of these aquatic species, (i.e. all the ones in that branch) called cetaceans, bears traces of their past life on land. They have a pelvis, like their landdwelling cousins, although it is smaller and not attached to their spinal column. Moreover, their pectoral fins have five bones, as do hands. And, unlike fish, they swim by moving their tail fins up and down, indicating a spinal column built to move front to back, rather than left to right.

Cousins, but how close?

Trout are also cows’ cousins. In fact these fish are more closely related to cows than they are to sharks, for instance. “Their last common ancestor lived 476 million years ago, while the one with sharks was 525 million years ago,” explains Professor Guy Drouin, at the Biology Department of the University of Ottawa.

Nearer to animals!

And mushrooms are actually much more closely related to animals than to plants! (Remember that fungi aren't actually considered plants.) Their common ancestors, the opisthokonts, are more recent.