Too many dinosaurs

Maggie Koerth-Baker has a very nice piece in FiveThirtyEight about the high proportion of dinosaur genus names that have eventually been discarded over the years: “All Those New Dinosaurs May Not Be New — Or Dinosaurs”. She focuses on the work of Michael Benton, who has worked to document the number of named dinosaur genera that have fallen into disuse over the years.

Facts like this make paleontology seem hopelessly flawed. But there are good reasons to think that we’re getting better at naming dinosaurs, not worse, Benton said. Compared with 50 years ago, dinosaur names are now based on larger quantities of fossil evidence, and that evidence is evaluated in far more detailed, scientific ways. The theropod-herbivore imbalance suggests there is still something deeply wrong, but it’s not unfixable.

The bottom line is that nearly half of dinosaur genera named between 1850 and 1980 have been “sunk” by later scientists.

Is that a bad thing?

Actually, I view it as a very good thing that taxonomic proposals are subjected to strong testing as our knowledge increases. This is the way that biological science works. New discoveries that provide previously unknown parts for old fossil organisms allow them to be compared in new ways. New discoveries about the variation within known taxa can cause us to change what we see as sufficient to test a phylogenetic hypothesis. And new insights about biogeographic connections cause us to look at old data in a new light.

If we look at human evolution, the proportion of genera lost over the years is much greater. At a maximum today scientists accept just eight, with more than a dozen having been cast aside, also mostly before 1980. As in the case of dinosaurs, we are likewise in the midst of a taxonomic burst in naming hominin genera. Five of the eight hominin genera now accepted by many anthropologists were named after the year 1990, four after 2000.

Of course, the way that scientists have used the genus as a taxonomic category has changed over the years. Taxonomists were very free with genus names before the New Synthesis in the 1940s, and tightened up to some degree afterwards. Later, after the 1980s, genera took on a different role in taxonomic practice, as systematists began to insist that a genus should always be a monophyletic group.

That shift has particularly driven the increase in hominin genus naming over the last twenty years. The pattern of relationships in the hominin clade, with only one surviving species, has been hard to resolve. When a single cladistic analysis can change the sister groupings of different hominin species, it makes it easy for many anthropologists to attack large grade-based genera like Australopithecus. This phenomenon has caused one “sunk” genus to be revived, Praeanthropus, and others to be named, like Kenyanthropus. With the earliest hominins, each may arguably occupy a position branching from the stem of the later hominin tree, making it impossible to say they belong to a monophyletic group with other early species, even if they collectively may represent very similar adaptive patterns.

We may later discover more evidence of these early hominin taxa, discovering (as some have claimed) that they are in fact close relatives that should be placed within the same genus. If so, we may see a resurgence of the days when hominin genera were sunk.