Why Names Change in Paleontology

Before reading this post, you might want to review what I wrote in my recent post on July 12, 2018. It is entitled "What's in a name."

If you collect fossils and utilize paleontologic literature, you will soon realize that the latinized names of fossils are subject to change. Some reasons why names get changed are summarized here, along with examples:

1) If genus-species names of identical spelling have been published for different fossils, they are homonyms. The earliest name is the senior homonym and has priority over the latter name, which is the junior homonym. This type of change is relatively common in the early literature, when authors would use poorly understood (at that time) genera names (e.g., Venus, Voluta, Cypraea, Trochus), in  combination with overused species names (e.g., rugosa, inornata, spinosa, elongata), which described very common morphologic features.

For example, the Cenozoic (Pliocene) Cancellaria crassa Nomland, 1917 (April) from California versus and the Late Cretaceous (Late Cretaceous, middle Campanian) Cancellaria crassa Waring, 1917 (July) from California. Nomland’s name is the senior homonym because it was named first (in this particular case, by three months), and Waring’s name is the junior homonym. The word "crassa" is Latin for "fat" or "stout," not exactly an unique feature.

The photo on the left is Cancellaria crassa Nomland, 1917. The photo on the right is Cancellaria crassa Waring, 1917. They cannot both have the same name; thus, Waring's species was renamed by Hanna (1924) as Cancellaria simiana Hanna, 1924.

2 If two or more genus-species names are the same thing, they are synonyms. The earliest name is the senior synonym and has priority over the other name, which is a junior synonym. These are very common changes and mostly created by workers who did not familiarize themselves with the previously known names of whichever group they were studying.

For example, the above two specimens are of the same Pacific Coast Late Cretaceous gastropod, Acirsa nexilia (White, 1889). The photo on the left is the senior synonym Acirsa nexilia (White, 1889), and the sketch on the right is Mesotoma? intermedium Whiteaves, 1903, the junior synonym. Note that White's species name has been transferred to a different genus than he originally used, therefore, his surname is now in parentheses. One of the most important rules of nomenclature is: If the species becomes transferred to another genus (previously named or new), the name of the original author is placed in parentheses. For example, is some other worker decided, after a thorough study, that Turritella andersoni actually belongs in genus Cerithium, then the proper format would be Cerithium andersoni (Dickerson, 1916).

Note: If a species is reassigned to a different subgenus, the original author’s name is not put in parentheses.

A list of name changes showing the history of a naming of a species  is called a synonymy = a list of synonyms (different names for the same thing). It is an elegant way of efficiently keeping track of all the changes. 

An example of a synonymy is the following, which was given by Squires in 2011, when he created the new genus Igonoia (a small-sized Cretaceous gastropod) and published the scientific proof in the journal "The Nautilus" 125 (3), p. 145:

                                Igonoia angulata (Gabb, 1869)

Margaritella angulata Gabb, 1869: 172, pl. 28, fig. 55.
Solariella angulata (Gabb). Stewart, 1927:317, pl. 24, fig. 17.

In this example, the sequence of events was: Gabb named angulata and incorrectly assigned it to genus Margaritella; Stewart incorrectly reassigned Gabb's species to genus Solariella; and Squires created a new genus.

3) If the original author misidentified the genus, there will have to be reassignment to the correct genus. Also, if the original author used the wrong gender for the species name, there will have to be changes. Note: the species name has to agree in gender with the name of the genus name.

The photo on the left is the holotype of Ficus plectatus Waring, 1917. Using better preserved specimens, Squires (2018, Journal of Paleontology, v. 92, no. 5, pp. 794–803) was able to transfer Waring's to genus Oniscidia Mörch. The photo on the right is a well preserved specimen of Oniscidia plectata (Waring, 1917). The species name plectata agrees in gender with the genus name, Oniscidia, which has a feminine ending. 

4) Another reason for a name to be changed is that, too often, authors rely on only a single specimen (the holotype) to represent a new species. This ill-advised procedure is prone to error, especially if the author did not have the skill or tools to clean the aperture of a fossil gastropod or the hinge of a fossil bivalve. If the holotype is finally cleaned, or if new specimens are found and show new unique morphologic information, then reassignment as to the genus or species can finally be made.  

The image on the left simulates what it would have looked like if the aperture of a fossil gastropod was left uncleaned. If one relied on this incomplete information, identification as to genus or species would be highly suspect and prone to error. The image on the right shows the same specimen after the aperture was carefully cleaned, and it revealed that this Late Cretaceous gastropod from Vancouver Island, British Columbia gastropod could be identified as Agathodonta. It is the first confirmed species (also a new species) of this extant genus in the Western Hemisphere (see Squires, 2011, The Nautilus, v. 125, no. 4, pp. 1-14).


5) Also, new technology allows for better study of the shells, thereby allowing for better family and generic assignment. For example, the invention of scanning electron microscopes have made it easier for paleontologists to examine the protoconchs of gastropods. These earliest whorls of a gastropod can yield very useful information essential for correct identification, and this kind of information was rarely even mentioned by most early workers.

The image on the left shows the upper whorls and tip (protoconch) of the Late Cretaceous gastropod Igonoia onoensis Squires, 2011. The image on the right shows (much clearer) an enlargement of the tip of the same specimen. The protoconch (about two whorls) is smooth, and the first whorl of the rest of the shell has ribs. The protoconch information helped to assign this gastropod to genus Igonoia. 

Yaadia and Quadratotrigonia Cretaceous bivalves

This post concerns two species of "knobby" bivalves (clams) of Cretaceous age. They have medium-sized, sturdy shells with ovate or quadrate shape, and their shells are ornamented with widely spaced, oblique radial ribs bearing large nodes (knobs). Early workers referred to these kinds of bivalves as "knobby trigoniids."

 Two views (left vs. right valves) of a plaster cast of a complete specimen (length 7.4 cm = from left margin to right margin) of the "knobby trigoniid" known as Yaadia leana (Gabb), Early Cretaceous (late Albian?) from Alaska. 

Two views (left vs. right valves) of a plaster cast of a complete specimen (length 100 cm) of Quadratotrigonia mearnsi (Stoyanow), Early Cretaceous (early Albian) age, Guadalupe  Mts., southeastern corner of Arizona. This species, which also occurs nearby in Texas, differs from the preceding species by having more rows of knobs, more closely spaced rows, and a few widely spaced rows of nodes on the dorsal area, including the edge of the dorsal margin. 

Both of these knobby genera were partial burrowers, most likely with one half or less of their shell protruding into the water column. Their shells were not streamlined enough for rapid nor total burial. For a time, the sturdy and knobby shells resisted predation by gastropods and fish, which lived in the nearshore warm-temperate ocean waters preferred by this bivalve. The predation, however, became too severe (i.e., the Mesozoic Marine Revolution), and knobby trigoniids went extinct during the Maastrichtian, the last interval of the Cretaceous.

"Knobby" bivalves, in general, were very diverse during the Mesozoic. Nearly all of them went extinct at the end of the Cretaceous, most likely because of over predation by carnivorous gastropods and vertebrates (i.e., the “Mesozoic Marine Revolution.”) Today, a few relic species related to the "knobby" bivalves survive and live only in Australia. One of these species is illustrated below. 

Exterior and interior views of both valves (left on the left side, etc.) of a modern-day specimen of Neotrigonia margaritacea from southeastern Australia. Notice the "mother-of-pearl" luster on the insides of the valves. The hinge teeth of this small-sized species (2.4 cm height) are stout, long, and fit snuggly inside the sockets of the opposite valve. Neotrigonia margaritacea is a burrower but, unlike most bivalves, it can actually jump.

My post on August 19, 2017 dealt with the morphologic differences between two species of the same genus of a Cretaceous trigoniid. You can always access my previous posts by using the "Search This Blog" box in the upper right-hand side of each posting.