A passion for fossils of mammalian ancestors leads to prize-winning PhD

Steve Koppes (USA)

When he was still a high school student in Florida, Christian Kammerer turned his unusually keen, critical eye to reports about some enigmatic new synapsid fossils from Russia. He wondered — had the discoverers of these bizarre, mammal-like reptiles misinterpreted their finds?

Kammerer shot off an email to University of Chicago palaeontologist, James Hopson, to find out. Kammerer later characterised the exchange as one between “an upstart pretender” and “a titan of synapsid research.” However, Hopson, Professor in Organismal Biology & Anatomy, felt almost as if he had glimpsed the academic equivalent of a future Heisman Trophy winner. As he says:

I was truly amazed how familiar he was with the technical literature on synapsids and that he had informed opinions as to whether newly described Russian species were really new.”

The emails began a fruitful mentoring bond. Hopson encouraged Kammerer to apply for undergraduate studies at UChicago and later for graduate studies. Kammerer’s youthful spark of insight and enthusiasm never wore off. In his last quarter there, Kammerer received the Society of Vertebrate Paleontology’s Alfred Sherwood Romer Prize for his outstanding student talk on his PhD research.

As Hopson says:

He has become the most knowledgeable expert of non-mammalian synapsids I know, continuing a learning trend started in high school.”

First choice pick in palaeontology

After Kammerer received his PhD, he became what one might call a first choice pick among vertebrate palaeontologists. He is now the Gerstner-Kalbfleisch Postdoctoral Fellow in the Department of Vertebrate Paleontology at the American Museum of Natural History in New York City (AMNH).

Kammerer first encountered synapsids in a darkened corner of the AMNH as a Long Island native. This diverse group of vertebrates dominated terrestrial ecosystems from approximately 300 to 230 milion years ago.

As Kammerer says:

This group is perhaps best known for including the ancestors of mammals. The evolution of mammals from early synapsids is perhaps the best-documented major evolutionary transition in the vertebrate fossil record.”

In his Romer Prize acceptance remarks, he noted how:

these bizarre creatures from long before the age of dinosaurs latched onto my imagination.”

They became even more intriguing to him as he learned that, within their ranks, were our own distant ancestors.

He devoted his PhD research to broad-scale questions of synapsid evolution under the guidance of Neil Shubin, the Robert R. Bensley Professor of Organismal Biology & Anatomy. Along the way, Kammerer racked up some impressive statistics. He examined 4,540 synapsid specimens for his study, of which 2,907 included fairly complete skulls that he could use in his final analysis.

Statistically robust analysis

As Kammerer says:

Studying skulls provided the largest sample size, important for producing statistically robust results, as well as the broadest diversity of synapsid species. Skull shape is also extremely interesting from a theoretical standpoint, because it encompasses a great deal of important biological information about the animal, especially in terms of inferred feeding habits.”

Palaeontologists recognise synapsids as one of the hardest-hit groups during the most massive die-off in Earth history, which took place at the end of the Permian Period, approximately 250 million years ago. The non-mammalian synapsids survived the end-Permian mass extinction, but never again dominated terrestrial ecosystems as they had previously.

Kammerer examined the decline of the synapsids by analysing changes in the shape of their skulls, which provides clues to their eating habits. He found that, although the extinction survivors diversified into new species, synapsids as a whole displayed less variety in skull shape. He also found no signs of a second mass extinction once thought to have reduced synapsid diversity before the end of the Permian. In other words, reports of a mass extinction in the middle Permian Period have been greatly exaggerated.

It is a tribute to his early scepticism that Kammerer’s own work is helping undermine conventional wisdom about synapsids. Thirteen years after he sent those bold emails, the long-extinct ancestors of mammals are still fuelling his imagination.