Form and Function: A Tribute to Adolf Seilacher

It is with sorrow that we announce that Dolf Seilacher, one of the most influential paleontologists of his generation, recipient of the 1992 Crafoord Prize of the Royal Swedish Academy of Sciences and the 1993 Paleontological Society medal, died at his home in Tübingen on Saturday April 26th at the age of 89.  In a long and distinguished career at the University of Tübingen (as graduate student and assistant, and then professor from 1964-1990) and at Yale University (where he taught from 1987 until 2009) Dolf Seilacher’s research focused on the interplay between extinct organisms and the environment in which they lived, as revealed by the evidence in sedimentary rocks.  He made fundamental contributions on how fossils are preserved including exceptional fossil deposits (Fossil-Lagerstätten), on trace fossils (which provide evidence of ancient behavior), and on the evolution of form, including the nature and affinities of the oldest large organisms that first appeared during the Ediacaran Period some 575 million years ago before the Cambrian explosion.   He created a remarkable book and exhibit on Fossil Art which toured museums around the world.  We will remember his wonderful company as guide, raconteur and good friend, his remarkable teaching, and his unique skills and insights as an observer and interpreter of specimens, both living and fossil.


A chapter by Derek Briggs describing Dolf Seilacher’s research on form and function (just one aspect of his scientific contributions) was published by the Yale Peabody Museum to celebrate his 80th birthday in 2005.  This chapter, which includes a full list of Seilacher’s publications at that time, can be downloaded here.

Professor of Geology and Geophysics Adolf Seilacher.


Dr. Adolf Seilacher, of Yale University and the University of Tübingen, has spent his career investigating form and function in fossils. Displayed here are a few of the many Yale Peabody Museum specimens that he has studied.

Seilacher’s exceptional ability to elucidate concepts is seen in his detailed specimen drawings in this exhibit.

Photograph © Wolfgang Gerber. All rights reserved. Used with permission.

Innovative Adaptations


Scyphocrinites sp.
Upper Silurian, Morocco
YPM 202267
Purchased for the Yale Peabody Museum by Dr. Seilacher


Most of the great diversity of form that we see in the animal kingdom is the result of adaptation. An adaptation is a trait or group of traits that increases an organism’s chances of survival. Adaptation allows organisms to function well in the environment in which they live. However, the range of variation in form is limited by the basic body plan of the organism (jellyfish cannot develop legs and run around like a beetle) and by the materials available (such as the properties of a shell). Dr. Seilacher often uses unusual extinct organisms as examples to unravel the different factors that influence the evolution of form.

Natural selection favors variations that make an animal more likely to survive. Over the course of geologic history, some animals evolve to flourish in a very narrow range of conditions. When these conditions change extinction could result.

Tow-net Feeding


Illustration of Scyphocrinites sp.
(YPM 202267) by Dr. Seilacher.
Courtesy of SEPM (Society for Sedimentary Geology).


Many ancient crinoids, relatives of modern starfish, lived attached to the seabed by a long stalk (hence their popular name “sea-lilies”). Modern crinoids are free-living on the seafloor. Some unusual ancient crinoids, like Scyphocrinites, floated in the ocean with a water- and air-filled buoy. The arms were used in feeding in the same way that a net towed by a fishing trawler filters fish from the water. By casting an open mesh behind it, Scyphocrinites trapped food in the passing water. The arrangement of the branching arms was optimized for catching the maximum amount of food.

Rudists as Bivalvian Dinosaurs


Bournonia bournoni d'Orbigny
Late Cretaceous, France


Rudists are extraordinary clams from the Mesozoic that showed pronounced adaptations. Modern clams generally have 2 equal-sized shells (valves) held together by a flexible ligament. The 2 valves of rudists, in contrast, are dramatically different in size and shape. Most rudist families either lost or greatly reduced the ligament through the course of evolution. Like modern corals, rudists probably had symbiotic photosynthetic algae, which helped create ideal conditions for skeletal growth.

Rudists as Bivalvian Dinosaurs


Toucasia patagiata (White)
Early Cretaceous, Texas


Toucasia, an early rudist, lived attached to the sea floor in thickets. The larger valve grew in an elongated spiral form. In this Yale Peabody Museum specimen the attached valve is below, and the free valve (or “lid”) at the top.

Rudists as Bivalvian Dinosaurs


Requienia ammonia Nathorst
Early Cretaceous, France


Requienia was not permanently attached, but lived in soft-bottom sediments. Unlike in the thin-shelled Toucasia, the larger valve was thicker to provide weight to anchor it in the sediment.

Adaptation in Brachiopods


Richthofenia cf. communis
Late Permian, Italy


Brachiopods generally have two more-or-less equal-sized valves, although their symmetry differs from that of clams. Like rudists, some aberrant Permian brachiopods took the two-valve body plan to an extreme.

Adaptation in Brachiopods


Prorichthofenia sp.
Permian, Texas


Richthofenia lived with its larger cone-shaped valve in the sediment. The smaller valve functioned like a lid. Its lifestyle is referred to as a “sediment sticker.” As you look into the cavity of Prorichthofenia, you can see the small lid-like free valve.

Adaptation in Brachiopods


Prorichthofenia sp.
Permian, Texas


Some brachiopods evolved from sediment stickers to become reef-dwelling forms with spines cemented to a hard surface, as in Prorichthofenia.

Adaptation in Brachiopods


Leptodus nobilis americanus Girty
Permian, Texas


Here, several reef-dwelling Leptodus form a cluster. The attached valve of these bizarre brachiopods was shaped like a shoehorn and the free valve only partially covered the soft body of the organism, which may have allowed photosynthetic algae to flourish.

Epizoans Provide Evidence of Host Biology


Ceratites semipartitus
Middle Triassic, Germany


Since ammonoids are extinct, we cannot observe them directly. Dr. Seilacher used “hitch-hikers” on the ammonoid shell to interpret its lifestyle. This ammonoid is covered with epizoans (animals that attach themselves to the surface of other animals). These epizoans include bivalves, brachiopods, gastropods and serpulid worms.

Commonly, epizoans attach to shells of dead animals as they lie with one side on the sea floor. In this case epizoans encrust both sides of this shell, indicating that they attached to the shell while the ammonoid was alive and swimming. Most of the encrusters show a preferred orientation, that facilitated feeding and respiration. The orientation of the encrusters on the host indicates that the ammonoid did not jet quickly through the water, but floated and swam slowly near the seabed.

Epizoans Provide Evidence of Host Biology


Titanosarcolites sp.
Late Cretaceous, Habana Formation, Cuba


This is a partial specimen of Titanosarcolites, a rudist that reached about 20 inches (over a half a meter); rudists could be as much as 6 feet (2 meters) tall!. This specimen has been cut in half and polished to show circular canals in the shell that are thought to have harbored photosynthetic algae.