Here's a link to the Science mag news article on it.
Apparently, yes it seems the spiders were splitting from the scorpions.
This guy had spinnerets (make silk) which I guess is kind of defining form spiders.
The tail is like scorpions, or maybe
Eurypterids which are scorpion relatives that lived in the sea until the end
Permian extinction (252 MYA).
What they discuss in this article is this relationship and the changes in the body plan of the animals.
This would reflect evolutionary changes in the developmental changes that generate the body plans of the two groups and how that became different (genetically, molecularly, cell biologically).
Starting with Drosophila (fruit fly), Developmental and Genetic controls many of the developmental processes that generate the larval or adult body forms have been revealed.
The Arthropods as a group (including insect, crutaceans, spiders, and a whole bunch of other things with jointed bodies) have body plans that are strongly arranged on a
segmental plan. They have a front/back and top/bottom distinction (body axes).
But along their length (anterior/posterior axis), they have repeated units of organization (segments) repeated along the A-P axis. Among these segments (in Drosophila), each segment has an individual segmental identity, which is controlled by which genes are on. This, in turn, controls other genes generating later processes and/or genes more involved with producing some kind of structure of function.
Each segment might possibility produce a leg in a particular position, or a gill, or a spicule (breathing hole) in other positions. These are often patterned based on locations in a segment, but the way they develop can be different in each segment.
Each segment can develop each of these parts of the segment in different (but segmentally stereotypical) ways, generating a diversity of (complexly generated) segments (each possibly fulfilling different functions) along the A-P body axis in a reliable manner.
All these different steps have been controlled through genetics in Drosophila (and other well researched animals) in the lab.
Other groups of Arthropods (animals with a hard cuticle (exoskeleton) and obvious body and legs segments) have different ways of making segments and different numbers of segments and different regions of the body (head, thorax, abdomen) where the segments have obvious similarities. The same genes are used in the differing developmental programs of the different species. Some times there might be a whole row of virtually identical segments, End segments are always unique (they have unique and very primordial functions that would have to be fulfilled by any large metazoan (eating and pooping)).
Changes in the genetic programs, that through developmental processes, generate the body plan differences, underlie the changes these guys are looking at in their perfectly preserved example, by looking at their fossils.
Very cool!
