Scientific Classification
| Kingdom: Animalia |
| Phylum: Arthropoda |
| Class: Trilobita |
| Order: Phacopida |
| Family: Phacopidae |
| Genus: Eldredgeops |
| Species: Eldredgeops rana Green, 1832 |
Information
Geological Range
Paleogeographic Distribution
Stratigraphic Occurrences
References
Eldredge, N. 1972. Systematics and evolution of Phacops rana (Green , 1832) and Phacops iowensis Delo, 1935 (Trilobita) from the Middle Devonian of North America. Bulletin of the American Museum of Natural History, 147:45–114.
Green, J. 1832. A monograph of the trilobites of North America: with coloured models of the species. J. Brano, Philadelphia, p. 41
Struve, W. 1992. Neues zur Stratigraphie und Fauna des rhenotypen Mittel-devon. Senckenbergiana lethaea, 71:503–624.
Description
From Eldredge (1972): “Eye with 17 dorsoventral files in normal adult. Trace of facial suture across ocular platform moderately incised. Tuberculation generally densely distributed over glabella. Transverse elongation of tubercles developed partially up front slope of glabella, becoming progressively more elongate approaching anterior cephalic margin. Tuberculation of genae and palpebral areas variably developed. Genal angles bluntly rounded. Axial rings of thorax and pygidium covered with tubercles moderately elongate transversely. Interpleural furrows obsolescent on pygidium. Pleural furrows moderately incised; pleura gently rounded. Tuberculation obsolescent on pygidial margins.”
Remarks
Notes from Emily Cavanaugh (July 2025): Eldredgeops rana ("rana" meaning “frog” in Latin, in reference to the species’ frog-like eyes and overall appearance) is an abundant and charismatic trilobite fossil that is primarily found in the middle Devonian of the northeastern United States. Assemblages of this species are most abundant in the Appalachian basin during the Givetian, and their paleogeography extends throughout central New York and Pennsylvania. As sea level rose and fell during the middle Devonian, it is likely that some populations of E. rana migrated farther west, leading to occasional assemblages of E. rana in the Michigan basin.
Eldredgeops is named after Niles Eldredge, who conducted critical work on the genus (then known as Phacops). He noticed that the genus experienced long periods of morphological stability (“stasis”), followed by brief intervals of rapid morphological change. This became one of two “type cases” of punctuated equilibria, a theory developed by Eldredge in collaboration with Stephen Jay Gould and published in 1972.
It is important to note that Eldredge originally recognized five subspecies within Phacops: Phacops rana crassituberculata Stumm, 1953; Phacops rana milleri Stewart, 1927; Phacops rana norwoodensis Stumm 1953; Phacops rana paucituberculatus Eldredge 1972; and Phacops rana rana (Green, 1832). Four of the five subspecies recognized by Eldredge (Eldredgeops milleri, E. crassituberculatus, E. rana, and E. paucituberculatus, with *E. paucituberculatus8 being “of questionable placement”) were raised to the species level, in addition to E. africanus and E. tindoufensis by Struve (1992). However, this designation is still questioned in the literature (see McKellar and Chatterton 2009, Levi-Setti 2014).
From Wilson (2014, p. 204): “Generally resembling Viaphacops cristatus … but marked by the absence of genal and axial spines, and the simple annulations of the pygidium. Formerly known as Phacops rana, this is perhaps the most common trilobite in the Middle Devonian Hamilton Group.” Maximum size 100 mm.
See Hendricks and Lieberman (2025) in Paleobiology for preliminary details about the stratigraphic occurrences of this species and its higher taxa.
Online Resources
[Punctuated Equilibria: an Alternative to Phyletic Gradualism by Eldredge and Gould, 1972] (https://www.blackwellpublishing.com/ridley/classictexts/eldredge.pdf)
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