When Was Central Fl Last Under Salt Water?

[aplomado]

I've posted a picture of a large whelk my dad found on a ranch just north of Lake Okeechobee before. When was this area last under salt water? I'm trying to find out the age.

Thanks!

[Auspex]

Late Pliocene, I think, maybe into the early Pleistocene?

[verydeadthings]

Yep, basically what auspex said. There's an older post that goes into some more detail about past sea levels in Florida: http://www.thefossilforum.com/index.php?/topic/51689-florida-teeth/?hl=barstow In that post, I reference this FGS publication which has more info: http://ufdc.ufl.edu/UF00000124/00001/30j

That whelk looks like a lightning whelk to me, Busycon perversum. They usually coil sinistrally (left-handed), as your specimen does. The shells are quite common in shallow marine environments of southwest Florida, like Sarasota bay. Regarding its age, if it was found at or near the surface, just north of Lake Okeechobee, the Florida geological map (http://sofia.usgs.gov/publications/maps/florida_geology/Florida_geology-xlg.jpg) indicates that it comes from "shelly sediments of Plio-Pleistocene age." You can find more detailed information about the mapped formation here (http://sofia.usgs.gov/publications/maps/florida_geology/OFR80.pdf).

Long story short, either Pliocene or Pleistocene. A more precise date would probably require first-hand knowledge of the local stratigraphy and collection of other fossils from the same site. Nice find!

[calhounensis]

Plio-Pleistocene. Sinistrofulgur sp. or S. contrarium.

[verydeadthings]

I'm not familiar with Sinistrofulgur. From a quick internet search, it seems to be a subgenus of genus Busycon (Hollister, 1958). I'm a bit confused by the taxonomy. According to Wise et al. (2004), "...Based on the evidence all left-handed whelks of North America should be referred to the oldest available nomen, Busycon perversum (Linne´, 1758), with three subspecies, B. perversum perversum along the Yucatan peninsula, B. perversum sinistrum (Hollister, 1958) in the northern and eastern Gulf of Mexico, and B. perversum laeostomum (Kent, 1982) in the Atlantic." Other people seem to use Busycon (Sinistrofulgur) contrarium to refer to the fossil species (http://www.marinespecies.org/aphia.php?p=taxdetails&id=747340), and use Busycon (Sinistrofulgur) sinistrum for the modern species.

Anyone feel free to correct me about any of this. Is Sinistrofulgur a subgenus within Busycon? Is Sinistrofulgur synonymous with Busycon, and therefore we shouldn't be using Busycon?

Until I have a better idea I'm going to keep calling lightning whelks from southern Florida, fossil or modern, Busycon perversum sinistrum.

Hollister S.C. 1958, A review of the genus Busycon and its allies - Part I: Palaeontographica Americana IV(28): 48-126, pls. 8-18.

Wise, J., M. G. Harasewych, and R. T. Dillon Jr. "Population divergence in the sinistral whelks of North America, with special reference to the east Florida ecotone." Marine Biology 145.6 (2004): 1167-1179.

[calhounensis]

It's been a while since I delved in Florida inverts. So I don't quite know the proper taxonomy. In the simplest way that I can explain it.. Sinistrofulgur are the very large whelks. Busycon are generally the smaller whelks. That explanation really has no scientific backing to it, just personal experience. TFF member MikeR would know the true taxonomy I would imagine.

Edited May 4, 2015 by calhounensis

[verydeadthings]

Thanks for the info, calhounensis! This might be a potato/potato thing for the same critter. At least now I'll know what people are talking about when they mention Sinistrofulgur

[MikeR]

TFF member MikeR would know the true taxonomy I would imagine.

Thanks Daniel! You have managed to drag me away from the sometimes frustrating aspects of my job to the equally frustrating world of Busycon taxonomy.

First let’s get the easy stuff out of the way. It is always difficult to make an age determination on a shell collected out of context. If it was dug up on the ranch itself from a very short distance from the northern shore of Lake Okeechobee, it would probably be from either the Lower Pleistocene Caloosahatchee Formation or the Middle Pleistocene Bermont Formation. I would think probably the latter however without any additional indicative fauna it is impossible to say for sure.

Now let’s talk about the recent species of left handed whelks. VDT is spot on in regards to calling the shell Busycon. WoRMS which I now closely follow lists “Sinistrofulgur” as invalid as either a genus or subgenus of Busycon. I will be the first to admit that I use the genus “Sinstrofulgur” based upon other publications including the recent Florida Paleontological Society faunal lists which use “Sinistrofulgur”. I suspect that part of the confusion originated with someone moving the subgenus to genus without a formal explanation and eventually this was incorrectly adopted by both professionals and hobbyists. The same thing has occurred with Turritella which would require an equally long explanation.

Prior to the DNA work by Wise et. al. 2004, the most detailed study on Busycon was performed by S.C. Hollister (1958). Based on morphology he recognized four recent sinistral Busycon species; B. perversum (Linne, 1758) from the Yucatan, B. sinistrum Hollister, 1958 from Cape Hatteras to the Yucatan, B. aspinosum Hollister, 1958 restricted to the Sarasota region, and B. pulleyi Hollister, 1958 in the Gulf of Mexico west of the Mississippi River. Hollister noted that B. contrarium (Conrd, 1840) is a Miocene (now recognized as Upper Pliocene) fossil and its use restricted as such. Regardless of Hollister’s suggestion, B. contrarium is still listed by many authors as recent as supurbly detailed in the following Jacksonville shell club article http://www.jaxshells.org/trava.htm. Another sinistral species B. laeostomum (Kent, 1982) was described more recently as occurring in the Mid-Atlantic. With a background in molecular biology I accept DNA results as gospel. Wise et. al. sequenced selected chromosomal and mitochondrial loci from five selected regional pools of “Sinistrofulgur”. Their results showed a less than 2% sequence divergence between all populations which is well within the published variation of other conspecific molluscan species and therefore proposed that all should be considered the same species Busycon perversum (Linne, 1758). Interestingly, the two populations with the greatest genotypic difference were the West Florida pool and the Atlantic pool possibly due to gene flow restriction by the mangrove and carbonate environment of South Florida while the Yucatan pool exhibited the greatest phenotypic difference. After determining through DNA that all left-handed Busycon are conspecific, Wise and coauthors looked at the physical characteristics of both shell and soft tissue from the regional pools to recommend three geographically separate subspecies or forms: B. perversum perversum (Linne, 1758) for the Yucatan form, B. perversum laeostomum (Kent, 1982) in the Atlantic, and B. perversum sinistrum (Hollister, 1958) in the Gulf of Mexico. For as much as I tout WoRMS, it is not perfect as it makes no mention of the Wise work from 11 years ago. It recognizes most of the Hollister species with the exception of B. aspinosum in which there is no mention. Since Wise et. al. uses both DNA sequence data as well as traditional morphometric analysis to make their determinations, I think I will ignore WoRMS at least for my Holocene sinistral Busycon.

As muddled as the modern taxonomy is for “Sinistrofulgur” the fossil record is worse. Hollister pictured a specimen originally described by Thomas Conrad (1840) from the Miocene of North Carolina (probably either Yorktown or Duplin Formation) as different from modern species based upon its small size, high spire and rounded shoulders. Many collectors including yours truly have called all fossil species as either Busycon or Sinistrofulgur contrarium which has simplified the identification process but in reading the Hollister paper for this post, obviously wrong. Many of the Plio-Pleistocene “Sinistrofulgur” are more similar to modern species. DNA testing cannot be used to determine variation leaving only description by physical characteristics of fossils from an extant family that is known to be highly variable. Add to this the nine species of “Sinistrofulgur” that Ed Petuch added in his 1994 Atlas of Florida Fossil Shells and the naming has become much more complicated. Questions this has raised include at what point in the Plio-Pleistocene does the modern species arise? Is B. contrarium present in Florida at any point of the Plio-Pleistocene? Are any of Petuch’s “Sinistrofulgur”truly valid?

I was in the process of creating a new blog post on the Bermont Formation however this line of discussion as piqued my interest. I have a very large number of sinistral Busycon from a wide range of locations and formations within the Plio-Pleistocene of the Southeastern United States. I think I will now do my next blog post using much of the same discussion and text on a deep dive where I can post images without a concern for overall image capacity.

Mike

Edited May 5, 2015 by MikeR

[calhounensis]

"Are any of Petuch’s species truly valid?"

[MikeR]

You're sounding like your mom

Edited May 5, 2015 by MikeR

[verydeadthings]

Many thanks to Mike for providing more information on the taxonomy of this group. As well as the fossils I've found, I've also seen living lightning whelks in Sarasota bay. I heard they were edible, but wasn't quite confident enough to boil one up and eat it