Sunday, November 29, 2020

The Troost Starfish Fossil

The picture above is published drawing of an American starfish fossil. It was identified as Palaeaster antiqua in the publication Smithsonian Institution United States National Museum Bulletin 64 A Critical Summary of Troost's Unpublished Manuscript on the Crinoids of Tennessee by Elvira Wood (1865-1928), a graduate student at Columbia University, New York City 1909. A PDF scan can be found at this PDF link on the Internet.

Gerard Troost (1776-1850) described it as on pages 105-106 (Bulletin 64): "I described the Asterias antiqua in a memoir read before the Geol. Soc. of Pennsylvania, which was published in the transactions of that society in April, 1834 (vol. 1, pag. 232). Since that time two naturalists have given the name of Asterias antiqua to different species of Asterias - Hisinger in his Lethaea Sveciaca Holmiae 1837 pag. 89 Tab. 26, fig. 6, and Professor Locke of Cincinnati. (I do not recollect where the latter was published his description.) As the Tennessee fossil has priority, I will continue to consider it as Asterias antiqua. ...

It occurs in Decatur County, Tennessee in Silurian Limestone. The second above mentioned although very mutilated, I will now describe under the name of Comatula? prisca - and the third under the name of Asterias tennesseeæ.

The Asterias antiqua is a rare fossil. -The specimen here figured is the only one that I have seen - very rarely fragments of it are found. They are generally so incorporated with the limestone, that is a impossible to develop any from its matrix. The one which is here figured was brought to light by erosion; it fortunately lying parallel to the eroded at its surface; -the fossil, being likewise carbonate of lime, is also more or less eroded at its surface. It was found in the Silurian limestone on Harpeth River, Davidson County, Tennessee. Associated with Spirifer lynx [Platystrophia biforata lynx], Cyathophlla [Streptelasma], Orthis [Dalmanella testudinaria], &c."

Elvira Wood on page 106 (Bulletin 64) states, "The only starfish in the Troost collection is in the possession of Prof. Charles Schuchert. He informs the writer that Hall's description of this specimen is erroneous and that it belongs to a new genus. A description of both genus and species will soon be published by Professor Schuchert."

As it turns out in 1915 Charles Schuchert (1858-1942) published Bulletin 88 (Google Book link) entitled Revision of Paleozoic Stelleroidea with Special Reference to North American Asteroidea and as he told Ms. Wood he describes it on pages 86-87. He lists it as Mesopalæaster (?) antiquus (Troost). Dr. Schuchert writes "Although this is the first recorded American fossil starfish, very little is known about it and that little is mostly of a misleading nature. The specimen lies on a limestone slab and is very badly weather-worn or it may haven been treated with hydrochloric acid so that now is a nothing more than a polished section of a starfish. An illustration that will show its actual characters can not be made.

Professor Hall errs in stating that Asterias antiqua has "ambulacral grooves occupied by a single row of subquadrate ossicula, which extend across and alternate with adambulacral plates of each margin. * * * It is possible that this character may prove to be a generic importance." It may have been this character on which Hall thought of basing the genus Argaster, but he does not characterize it nor even mention that the name in parenthesis is intended as a new term with Asterias antiqua Troost as the genotype. This species, like all other Paleozoic starfishes, has double columns of ambulacral plates. This the specimen clearly demonstrates on the edge of the slab where the distal parts of the rays are broken away. Argaster should therefore be regarded as a nomen nudum, and should A. antiqua prove to be a Mesopalæaster, it should not be made to displace this genus.

Asterias antiqua has about 15 inframarginal plates in each column and about 32 in each adambulacral column. Two of the latter plates meet as usual in a pair of triangular oral armature pieces.

Each axil is occupied by two large, quadrangular, basal inframarginal plates. Between these proximally there is a large, widely triangular, interbrachial plate the apex of which may or may not attain the margin. Proximal to each axillary interbrachial plate and between the four or five pairs of axillary adambulacral plates, there is in the specimen an open space in each of the five areas. What additional plates, if any, occupied this area is not determinable. It may be that the axillary interbrachial plates occupied the entire interbrachial areas and that the present hiatus is due to the worn condition of the specimen. This appears to be the most natural interpretation as it is the normal interbrachial structure of Mesopalæaster. In Promopalæaster there are always two, three, five, or seven interbrachial marginal plates in each area, a fact which excludes Asterias antiqua from that genus.

The abactinal area is not visible, but many of these plates are squeezed beyond the inframarginals, showing the presence of numerous small plates recalling Mesopalæaster and Promopalæaster."

Charles Schuchert mentions locality [described by Troost earlier in this posting] as "This is apparently the same horizon as that about the city reservoir in Nashville, which is now regarded as of Upper Trenton (Catheys) age. The specimen is in the United States National Museum Cat. No. 39914."

Below is the image of the actual fossil from the Smithsonian National Museum of Natural History database of USNM PAL 39914 of holotype fossil of Asterias antiqua. It has a title IRN 3114318 1 by Suzanne McIntire. It is listed as having Other Content – Usage Conditions Apply if one wants to use the image for educational, non-commercial use. This image is available at this link

If you compare the drawing from Troost's original work and picture of the actual Troost fossil they match up in terms of shape and rough detail. Comparing a modern day digital camera picture to a hand etched image made on plate for printing from 1835-1849 shows a loss of detail on the drawing. Dr. Schuchert made a reference that it appears the fossil he studied in 1909-1915 had been etched with acid. The drawing shows a more three-dimensional starfish while the picture is more 2-D. Dr. Troost mentions the fossil being of "carbonate of lime" and being a trained chemist would put acid on a fossil like this. So maybe it was acid treated when it was with Dr. Hall in New York from 1855-1898?

Dr. Schuchert listed this fossil as being of a new genus he called Mesopalæaster. Checking on the web site Fossilworks they list is as being a synonym of Hudsonaster Stürtz 1899.