Parvancorina and Primicaris

When we read the web page where Sam Gon III discusses the origins of trilobites we also gain insight on how the curiosity built into us humans leads to a never-ending quest for knowledge and understanding. For God's creation is such that when an answer is found it frequently raises new questions. In this manner, combined with exploration and analysis, our knowledge and understanding of the matter increases.

From his presentation we learn that there is a group of fossils that may be classified as ancestors of Cambrian trilobites. If this turns out to be true the rather recent discovery is, of course, another major step forward in bridging Ediacaran enigma with the Cambrian explosion of life. Here is just a short quote from Sam's text (check the page itself for full discussion and a very illuminative chart):

Parvancorina: a Precambrian trilobite ancestor?

The similarity of the Precambrian Parvancorina to the Cambrian Chengjiang arthropod Primicaris larvaformis, and a protaspid of a Cambrian trilobite is seen to the left. [Protaspid is an early period in the growth of a trilobite in which larva lacks articulated segments]

All three have an ovoid form, and an anchor-like structure made up of an axial lobe and lateral lobes running along the anterior and lateral edges of the body.

Primicaris was first thought to be a larval naraoid (e.g., Hou & Bergstrom 1997), but it was recognized more recently as taxon in its own right (Zhang et al 2003).

Recapitulating phylogeny, the trilobite protaspid resembles Primicaris.

If the similarity of Parvancorina to Primicaris is more than superficial, it is perhaps the best candidate for an early arthropod in the Precambrian.

Two Comments
1. The text is again a good example of how research goes on in search of answers to increasingly specific questions as our knowledge increases. The many "ifs" are actually exclamation marks that here is something that should still be verified and studied carefully before we can say that we know.

2. I like very much this sentence in Sam's expert text

"Recapitulating phylogeny, the trilobite protaspid resembles Primicaris."

It is half English, half Latin and as such fully Hebrew to most people.

So where did Trilobites come from?

Trilobites are a true Leitfossil for the period of early life on planet Earth called Paleozoic which is Greek for Old Life.

"Trilobites were one of several families of arthropods in the early Cambrian oceans." But when exactly do they first appear in the fossil record and where in the arthropods tree of life did trilobites come from?


Earliest known Trilobites
Sam Gon III writes in his website and I quote (I have added emphasis. For the complete story it is highly recommended to visit the page on trilobite origins.)

The earliest trilobites appear in the lower Cambrian record.

[Note. In another page Sam tells that not in earliest Cambrian but in the so-called Series 2: 
"The first appearance of trilobites defines the start of Series 2 of the Cambrian (521 mya), and they can be found in strata up to the upper Permian (251 mya), after which trilobites (among a large number of marine organisms) went extinct in the great catastrophe that removed over 90% of all species on earth.]

These oldest trilobites include members of
Order Redlichiida, Suborder Olenellina, Superfamily Fallotaspidoidea and
Order Ptychopariida, Suborder Ptychopariina, Superfamily Ellipsocephaloidea.

Even these early representatives bear all of the defining characters of trilobites.


Probably the key distinguishing character, one that also allowed trilobites to be preserved so well (and which accounts for their sudden prominence in the Cambrian), is calcification of the exoskeleton.

It is interesting that some of the most primitive of trilobites lack a few characters that more advanced trilobites bear. Fallotaspidoids lack facial sutures, for example, and their protaspides are apparently uncalcified.

If the ancestors of trilobites in the Precambrian were uncalcified, then their preservation would be restricted to konservat-lagerstätten, which are very rare indeed. Cambrian konservat-lagerstätten such as the Burgess Shale (Canada) and Chengjiang (China) demonstrate the huge diversity of non-calcified arthropods that would have escaped detection if those sites did not exist. Many of these are arachnomorphs closely related to trilobites and relevant in a search for trilobite ancestors. But where did these arachnomorphs come from?

Three comments
1. The general observation Sam makes on the significance of what I call "Divine nature reserves" is of great importance here - the preservation of evidence. As he writes, without the Konservat-lagerstätten researchers of the origins and evolution of trilobites would be left without evidence about life forms that lack the calcified parts which survive better among the fossil record.


2. In a way it is, of course, tautology to say that first recognized trilobites have the defining characters of trilobites.

Of course! Otherwise they would not be defined as trilobites, would they?

Sam goes on describing some typical characteristics missing from the trilobites classed as Fallotaspidoidea but also these have the signs needed to make the fundamental Aristotelean classification into families, subfamilies etc.

The logic is simple
Superfamily A has characteristics ABCD
Superfamily B has characteristics ABCEFG
Specimen X has characteristics ABCD so it is an example of superfamily A.


3. It is quite remarkable that the known record of Cambrian life forms represents such a collection of "ready" organisms that then continue to live and develop from generation to generation. As Sam says, trilobites are a very successful designs and survived about three hundred million years flourishing in thousands of variations to the end of Permian.

Sam Gon III Guide to the Trilobites

Dr Sam Gon III "serves as the Senior Scientist for The Nature Conservancy's Hawai‘i Field Office in Honolulu... The [Web] site was first unveiled in August 1999 and has attracted feedback from around the world, generating ongoing updates. For all the accolades this site has gathered, Sam is not a professional trilobitologist, but a devoted trilobitophile! In 2006 this culminated in his first paleontological publication, dealing with trilobite origins."
From about the author page

Sam Gon III has created a comprehensive, very interesting, highly recommended, and publicly rewarded science site

Guide to the Orders of Trilobites 
and invites us to their fascinating world with these introductory words:

"Trilobites are the most diverse group of extinct animals preserved in the fossil record. Ten orders of trilobites are recognized, into which 20,000+ species are placed.

• Learn more about trilobite morphology, anatomy, ecology, behavior, reproduction, and development, and how they relate to trilobite origins, evolution, and classification. 
• Explore trilobite biostratigraphy, paleobiogeography, persistence across geological time, and their ultimate extinction. 
• View galleries of trilobite images from the web, examine fact sheets, pictorial guides, and an identification key for each order, 
• refer to a family listing, a genus listing, 
• or consult a trilobite glossary and bibliography, 
• tour world famous trilobite localities, 
• explore links to other web resources on trilobites, 
• and review books on trilobites, including an exclusive hardcopy pictorial adaptation of this website."

Period of the trilobites

"The first appearance of trilobites defines the start of Series 2 of the Cambrian (521 mya), and they can be found in strata up to the upper Permian (251 mya), after which trilobites (among a large number of marine organisms) went extinct in the great catastrophe that removed over 90% of all species on earth.

The Great Permian Extinction marks the end of the Paleozoic and the start of the Mesozoic.

Trilobites are one of the few major groups of organisms that span the majority of the Paleozoic Era. The greatest numbers of trilobite species occurred during the Cambrian and Ordovician periods, after which trilobite extinction trends exceeded radiation events.

Toward the end of the Devonian most of the families and orders of trilobites were gone. There were much fewer species in the lone surviving order Proetida in the Carboniferous and Permian periods.

Nevertheless, to have persisted for nearly 300 million years is a testimony to the successful design and adaptability of trilobites. Some scientists even hold out the faint hope that in poorly explored deep sea environments, trilobites may still exist, a holdover from truly ancient times."
From the Geotime page

Oldest known multi-cellular animal found in Namibia

Photo St. Andrews University

Otavia antiqua
Photo St. Andrews University

Pre-cambrian multi-cellular sponge like animal found in Namibia.

Geologist Anthony Prave has told about the discovery in January issue of the South African Journal of Science. See for more information here.