I’ve posted a lot about extant arthropod orders at this point. So I decided to do a detour and do something a little bit different for a change. I download all fossil occurrences of Panarthropoda from the Paleobiology Database (PBDB) and mapped on QGIS the median age (in millions of years) of all the panarthropod fossil occurrences within each grid cell.
Areas dominated by older fossils: Appalachians, Utah, Midwest, Canadian Arctic, Yukon, Andes, Morocco, British Isles, Portugal, Scandinavia, Baltics, most of China, Russia and Australia
Areas dominated by newer fossils: Japan, New Zealand, Indonesia, India, Patagonia, most of Europe, coastal US (both coasts), Caribbean, small oceanic islands in general
I think these are more reflective of geological history than anything about arthropods in particular. To double check I made one for mollusks too.
It shows largely similar patterns to the arthropod one, though with a few differences like more newer stuff across Europe. Between these two maps, there are some interesting though perhaps obvious in retrospect observations one can make.
Coastal areas that were recently submerged have accumulated fossils of abundant shallow water taxa
Small islands are very geologically young so they simply would not have had time to accumulate deep time fossils
Areas that used to be part of the central Pangaean mountains (Appalachians, Scotland, Ireland, Morocco) show the same color as each other.
Perhaps the strangest thing is that fossil mollusks and panarthropods are somehow both entirely absent in Finland. What’s up with that?
Final note: There is a lot more fossil mollusks than fossil panarthropods. They are both more abundant in general and more abundant in areas under sampled for arthropods like africa and southeast asia
iNaturalist’s mission is centered around recent, personal encounters with nature, so we don’t often have discussions about paleontology. But since I’m a volunteer at a paleontology museum and our collection is overwhelmingly mollusca, I’ll offer my amateur reply.
First of all, what you’re doing appears to be a roundabout way of recreating the stratigraphic record. Each of the fossils from this database were dated based on the stratigraphic formations they came from. You’re downloading that data and then recreating a chronostratigraphic map from that. That seems like lots of extra work.
Stratigraphy is extensively studied and frequently revised, on a local/regional level. Trying to take that all in at a glance on a global level, to make sense of billions of years of plate tectonics–well, it’s messy!
You mentioned mapping the “median age” of fossils in each grid cell. I’m not sure what that’s supposed to accomplish. Let’s say you’re looking at a grid cell here in New York State, where the bedrock is Devonian Age, roughly 380 million years old. And perhaps there’s also a Pleistocene glacial deposit, where fossils are less than a million years old. The median may be 190 million, which is Jurassic, but what would that mean? There are no fossils at all in the area from that age.
Well, I took a glance at the geologic map at Macrostrat, and it looks like nearly all of Finland is Precambrian bedrock, so there would be no fossils preserved in that rock, at all! I went to PBDB and searched for fossil collections from Finland, and the results show only one collection from the Early Cambrian (with taxa I’m unfamiliar with) and all other collections from the Holocene. So, yes, by and large, Finland just doesn’t have fossils.
