Modern or fossil sand dollars?

[Bone Daddy]

I ran across these in a thrift store for a hot buck, so I grabbed them up. It's five sand dollars. One is a little different the others. Are any of these fossil? They seem very clean to be fossil, so I suspect they are modern. Can anyone confirm?

 

Thanks!

 

Edit : the backs are very clean like the fronts.

 

Edited April 28, 2023 by Bone Daddy

[Meganeura]

They look too perfect to me to be fossils - but I haven’t found many sand dollars so I really can’t say for sure. I’d guess Modern though 

[Thomas.Dodson]

I vote modern as well.

[FossilDAWG]

I also vote for modern.  There are some Pleistocene fossil sand dollars like that, but they are not common due to their fragility.  On the other hand these can be picked up by the hundreds on many modern beaches.

 

Don

[doushantuo]

I suggest one does an internet search of "James Nebelsick,echinoid,taphonomy"

Not likely of any great age,IMO

[Bone Daddy]

Thanks folks. That pretty much confirms my suspicions. Modern sand dollars. Still not bad for a buck though. 

 

I've found a few partial fossil echinoids down here, but never anything complete.

[Coco]

Current ones.

 

On the right you have 4 Mellita quinquiesperforta and on the left 1 Encope michelini which was eaten on the right side (predation during its lifetime and probably lived with its injury).

 

Coco

[Shellseeker]

2 hours ago, Coco said:

Current ones.

 

On the right you have 4 Mellita quinquiesperforta and on the left 1 Encope michelini which was eaten on the right side (predation during its lifetime and probably lived with its injury).

 

Coco

Crab ?

Quote

Covering behavior refers to the propensity of echinoids (Echinoidea) to lift materials from the surrounding environment onto their aboral surfaces using their tube feet and spines. This behavior has been widely documented in regular echinoids from a variety of well-lit, shallow- marine habitats. Covering behavior in the deep sea, however, is rarely observed, and the functional significance of covering when it does occur remains speculative. During a photographic survey of the seafloor off Anvers Island and Marguerite Bay along the western Antarctic Pen - insula, we imaged 11 benthic transects at depths ranging from 390 to 2100 m. We recorded the number of echinoid species, incidence of covering behavior, types of materials used for covering, potential predators of echinoids, and potential prey items for predators. The echinoid Sterechinus spp. was found at all depths, and the percentage of individuals exhibiting covering behavior increased with depth between 390 and 1500 m. There was a significant positive correlation between the incidence of covering behavior in Sterechinus spp. and the density of king crabs (Anomura: Lithodidae), crushing predators that may be expanding their bathymetric range up the Antarctic continental slope as a consequence of ongoing climatic warming. In contrast, covering behavior was not positively correlated with the densities of non-crab predators, the total densities of predators, or the availability of prey. Our results document rarely observed covering behavior in echinoids living in the deep sea and suggest that covering could be a behavioral response to predation pressure by king crabs.

https://www.researchgate.net/publication/301716907_Covering_behavior_of_deep-water_echinoids_in_Antarctica_Possible_response_to_predatory_king_crabs

Is the crab after the echinoid or minerals in the shell or both?

[Coco]

I’m not familiar with sea urchin predators, but I’m thinking more of a fish or something like that. Your sea urchin is eaten on the right, but it is also eaten on the top right.

 

I don’t know the size of your sea urchins, but I have, for example, a large Echinodiscus auritus from the Philippines of 15 cm that has two bites, one of 6 cm wide on the edge of the sea urchin and 2.5 cm inside the bite, which is about 2 cm deep. I can’t imagine a crab making such a dent in such a sea urchin. On this one, we see that he lived with his wounds because the thorns grew back.

 

 

Moreover, I saw in the lagoons of the de La Réunion regular sea urchins protect themselves by covering themselves with everything they could find: small stones, pieces of plastic, small dead shells etc... Predators probably don’t have a problem finding them, and maybe camouflage helps them survive.

 

Coco

Edited April 29, 2023 by Coco

[Harry Pristis]

I agree with Encope michelini for the example with the fish nibbles.  E. michelini still lives in Florida waters and elsewhere.

 

Occurrence.—Encope michelini is widely distributed in Florida in strata as old as the late Pliocene. The species occurs in the Tamiami, Caloosahatchee, Anastasia, Bermont, Nashua, and Fort Thompson Formations, as well as the Miami Limestone. A few specifc locations follow: Tamiami Formation: uppermost indurated bed of the formation exposed at the Quality Materials Quarry, Charlotte County (FM locality CH080); Peace River, southwest of Arcadia, DeSoto County; Anastasia Formation at Vero Beach Landfll, Indian River County (FM locality IR003); Dickerson Quarry, St. Lucie County (FM locality SL003); Bermont Formation at101 Ranch Pit 02, Okeechobee County (FM locality OB013); Fort Thompson Formation at Glenwood Heights, Dade County (FM locality DA012); Caloosahatchee Formation, banks of the Caloosahatchee River near LaBelle. Miami Limestone at Buena Vista, near Miami (USGS locality 4867). This species also occurs in the middle Pleistocene Canepatch Formation of South Carolina.

[PODIGGER]

Bone Daddy,

I would agree definitely modern, like the ones below.  These were found in the surf at low tide just off the beach at Long Boat Key. Most summers there seems to be plenty for the taking laying on the bottom.

 

 

 

 

[Harry Pristis]

Note the single example of Leodia sexiesperforata in the upper right of the image and the smaller example at 8 o'clock from it.

 

Occurrence.—Mooi and Peterson (2000) discussed questionable occurrences of L. sexiesperforata in the upper Pleistocene Miami Limestone and Fort Thompson Formation in Florida. However, we have been unable to validate the presence of this species in the Fort Thompson Formation. The species does occur in the Miami Limestone at Buena Vista, near Miami (USGS locality 4867). Considering the abundance of this species throughout the Caribbean region as far north as the Florida Keys (though it does more rarely occur farther north to the Carolinas), its near absence in the fossil record of the region is surprising. Donovan et al. (2015) documented the occurrence of this species in the Pleistocene of the Cayman Islands.

[PODIGGER]

That is really interesting Harry.  I had no idea and never did any research on these. Thanks!

[doushantuo]

e.g. fig 3 in:

 

Phylogeography of the sand dollar genus Encope: implications regarding the Central American Isthmus and rates of molecular evolution

Simon E. Coppard & H. A. Lessios 
Nature Scientific Reports volume 7, Article number: 11520 (2017) 

s41598-017-11875-w.pdf

obviously,it concerns the taxonomy/systematics of the species,but there are sparse remarks on ecology and taphonomy

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Edited April 30, 2023 by doushantuo