Mucrospirifer renaming

[Shamalama]

Hi All,

 

I spent some time this afternoon to do some research on the brachiopod Mucrospirifer mucronatus as I was writing a blog post. I'd heard from friends a while back that someone was combining a number of species of Mucrospirifer into M. mucronatus due to similarities.  I decided to see if I could find anything to verify this and would up locating a paper from 1964 where John Tillman did just that. 

 

("Variation in Species of Mucrospirifer from Middle Devonian Rocks of Michigan, Ontario, and Ohio", John R. Tillman, Journal of Paleontology, Vol. 38, No. 5 (Sep., 1964), pp. 952-964)

 

The TLDR of the paper is that, M. arkonensis, M. alpenensis, M. attenuatus, M. multiplicatus, and M. prolificus are combined into M. mucronatus. As well as M. profundus, M. grabaui, M. intermedia, M. latus are combined into M. thedfordensis.

 

Furthermore I found a doctoral thesis by Delpfine Ellen Welsh from Virginia Tech that further summarized these changes as part of her study of the evolution of Mucrospirifer across West Virginia, Maryland, Pennsylvania, New York, Michigan, and Ontario.

 

Welch, Delpfine Ellen. Geographical variation and evolution in the middle Devonian brachiopod, MUCROSPIRIFER. Diss. Virginia Tech, 1991

 

"The most recent systematic work is that of Tillman (1964) who studied the variation
of Mucrospirifer from the Middle Devonian rocks of Michigan. Ontario. and Ohio by measuring
previously described species and constructing histograms for each set of measurements.
Tillman studied characters emphasized in previous descriptions: number of costae, width of
costae, length of interarea, presence or absence of medial ridge in the sulcus and medial
groove on the fold, presence or absence of mucronate points at the cardinal extremities, size
of shell, width/length ratios, and the shape of the fold and sulcus.
Tillman (1964) concluded that number of costae depends on the age and/or size of the
individual, as does length of interarea. Width of costae was not constant even within a given
population. Development of the medial ridge and groove in the sulcus and fold, respectively,
was quite variable except in specimens from the Arkona Shale and Genshaw Formation where
they are usually well formed. In observing growth lines on individual specimens. Tillman
found that all previously described specimens of Mucrospirifer are mucronate at some stage

in their development. This includes specimens from the Arkona Shale which as adults do not
appear mucronate because of the addition of lamellae that decrease the degree of deflection
at the anterior border at the cardinal extremities and increase the shell thickness wi'thout
significantly changing the length or width of the specimen. Because the cardinal extremities
are rarely preserved and the growth lines are very difficult to trace, Tillman determined
width/length ratios to be of doubtful value. He found that as the angle made by the plane of
commissure at the fold increases, the height of the fold decreases, and he also found that
angle to be highly variable in all populations.
The shape of the fold and sulcus and the shape and general proportions of the shell
were the characters determined by Tillman (1964) to be most useful in distinguishing species.
Because he observed such an overlap among the species in the range of variation for the
characters studied, Tillman felt that no more than two species could be identified. Tillman
retained the species M. mucronatus and M. thedfordensis and considered all the rest to be
variations of these two. He placed arkonensis, attenuatus, multiplicatus, alpenensis, and
prolificus into synonymy with M. mucronatus; and thedfordensis, profundus, intermedia, latus,
and grabaui into synonymy with M. thedfordensis.
Tillman (1964) states that "M. mucronatus (Conrad) differs from M. thedfordensis
(Shimer and Grabau) in having a broadly U-shaped sulcus with flattened floor and subangular
edges and a gently convex to flattened fold"; "M. thedfordensis (Shimer and Grabau) differs
from M. mucronatus (Conrad) in having a U-shaped to V-shaped sulcus, never with a flattened
floor; a low moderately convex fold, never with a flattened surface."

 

This was all news to me but is helpful when identifying what I have found. This is very much a "lumper" situation where Tillman found that the variation used by others to differentiate species was not valid as it all represented different growth stages or were influenced by local environments. I don't like having to change labels every time a species or genus gets it's name changes (I'm talking about you Eldredgeops and Vinlandostrophia!) but this makes sense to me due to the similarities visually of specimens from distant locations. Besides, at least we get to keep the Mucrospirifer genus name.

 

Thus this specimen from the Mahantango of Mucrospirifer mucronatus  from the Mahantango formation in Pennsylvania is now the same species ....

 

As this this formerly Mucrospirifer arkonensis example from the Arkona formation of Ontario is.

[Fossildude19]

Thanks for this, Dave!

Cheers, and Happy New Year!

[siteseer]

Mucrospirifer has to be the coolest brachiopod.  It looks like a spaceship out of Buckaroo Banzai.

 

[Ludwigia]

8 hours ago, siteseer said:

Mucrospirifer has to be the coolest brachiopod.  It looks like a spaceship out of Buckaroo Banzai.

 

I like to call them stealth bombers.

[Al Tahan]

Very interesting. Thank you for sharing!! Love me some mucros