Trilobite Soft Part Preservation main content.

Trilobite Soft Part Preservation

     There is a temptation among those who collect and study trilobites to occasionally treat these Paleozoic arthropods as little more than their fossilized exoskeletons. After all, the pervasive remains of those hard, calcite carapaces are certainly the most recognizable, accessible and dramatic evidence we have through which to both confirm and celebrate the existence of these long-gone oceanic inhabitants. But there was clearly more to trilobites than just their outer shells…  and judging by a number of recent scientific discoveries, there was much more.
    We know that from their earliest stages in the Lower Cambrian that trilobites had eyes… quite impressive ones, at that. And ever since the discoveries made within the famed Burgess Shale over a century ago we've been aware that trilobites possessed an impressive array of soft body parts -- including antennae, multiple walking legs and even basic respiratory systems. Recent finds in the Ordovician strata of upstate New York have provided even more dramatic insight into trilobite morphology, showing clear evidence of both eggs and primitive yet highly efficient reproductive systems.
     And in 2016, discoveries made in the fossil-rich, 478 million year old Fezouata formation of Morocco, supplied even more information about what trilobite internal body design - and subsequent behavior -- may have been like in those long-distant seas. Working with three exceptionally preserved Megistaspis hammomndi specimens found in Ordovician outcrops located in the southeastern corner of that African nation, a pair of Spanish scientists, Diego Garcia-Bellido and Juan Carlos Gutierrez-Marco, uncovered evidence of a previously unseen midgut gland, which is known to secret enzymes used for the digestion of food. Their investigations also found signs of a crop, an internal organ commonly found in modern sediment feeders that live along the ocean floor. 
     These discoveries presented clear-cut evidence supporting the long-held belief that at least some species of trilobites foraged through the organism-rich mud along the sea bottom. And judging by the size that some of these Moroccan Megistaspis trilobites attained - occasionally up to 10 inches in length, including a long, graceful tail spine - it appears that such a bottom dwelling lifestyle suited their nature remarkably well. 
    These new findings also made note of three pairs of short, powerful spines located within the cephalon of these Megistaspis specimens - the first time that such an anatomical feature has been detected within a trilobite fossil. These head spines differ radically in shape, design and apparent function from the longer, smoother spines that adorn the underside of the trilobites' thorax and pygidium. The Spanish scientists speculated that these newly noted head spines may have been responsible for creating the trace fossils known as Cruziana rugosa… or trilobite trackways. It has long been surmised that trilobite movements were the cause of these trace fossils, but these new discoveries supply the proverbial “smoking gun” that paleontologists have long sought to confirm their theories.
   Despite this intriguing new information, it is clear that not all trilobites were sediment-feeding bottom dwellers like Megistaspis hammondi. Indeed, it's believed that during their 270 million year crawl through geologic time, trilobites successfully inhabited virtually every available niche within their ever-changing water world. Some were “floaters” who rode atop the oceanic waves, while others darted in and out of primal crinoid beds and coral reefs. Others may well have been the scourges of the early seas, praying on small soft-bodied arthropods, as well as upon their fellow trilobites. 
    However, in contrast to the exciting evidence supplied by the recent Moroccan finds, the definitive proof for such trilobite lifestyle diversity has yet to be found within the fossil record. But perhaps one day soon, in some distant corner of the globe, we will find specimens that provide additional insight into trilobite anatomy… discoveries that will demonstrate the incredible diversity of these amazing creatures that inhabited the ancient seas some half a billion years ago. 

A dorsal example of Megistaspis hammondi from the 478 million year old Fezouata formation of Morocco.