Cosmoselachus mehlingi
- 演化之聲
- Mar 19
- 3 min read
Age
Carboniferous（Late Visean-Early Serpukhovian）
331-326 Ma
Taxonomy
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Symmoriiformes
Family: Falcatidae
Genus: Cosmoselachus
Species: Cosmoselachus mehlingi
Morphological description
The fossil of Cosmoselachus mehlingi was originally recovered from the Fayetteville Shale as early as 1979. It was initially part of a private collection and was not examined by specialists at the American Museum of Natural History until 2013. The species was formally recognized in 2024. The specimen was damaged during transport, and over time has undergone pyrite decay, in which pyrite (FeS2) within the fossil oxidized to produce iron sulfate (FeSO4) and sulfur dioxide (SO2).
The teeth of Cosmoselachus mehlingi are of the cladodont type, small and with unfused bases. Each tooth bears three cusps that are slightly recurved lingually. These are arranged along elongate Meckel's cartilages with scalloped margins. The spacing between tooth families is relatively wide, and buccopharyngeal denticles occur between them. There are ten tooth families in both the upper and lower jaws, housed in large and widely spaced alveoli, a feature characteristic of falcatid sharks.
The lower jaw is slender, with the jaw joint located posterior to the rear margin of the cranium. A depression is present on the ventral surface of Meckel's cartilage, likely representing the attachment site of the adductor musculature. Although the branchial arches are partially collapsed, at least three pharyngeal arches can be identified. The pectoral fins are exceptionally well preserved, with 15 to 18 distal fin radials and a length of at least 24 cm. They retain three-dimensional structure without evidence of compression.
Parts of the posterior cranial skeleton are also preserved. The occipital region is elongate and terminates in a rounded end. There appears to be only a single dorsal aortic canal, and no pronounced cranial dome or other projections are present.
The holotype specimen is catalogued as AMNH FF 20509.
Etymology
The genus name Cosmoselachus derives from the nickname "Cosm" of Carl Mehling, a senior specialist at the American Museum of Natural History, in recognition of his contributions to the collection and identification of fossil chondrichthyans, as well as his longstanding dedication to unusual vertebrates. The suffix "-selachus" is derived from Greek, meaning shark.
The species name mehlingi also honors Carl Mehling.
Biological description
Cosmoselachus mehlingi is a symmoriiform chondrichthyan from the Late Mississippian (late Viséan to early Serpukhovian) Fayetteville Shale of northwestern Arkansas, United States. The fossil was recovered from the bed of Cove Creek in Searcy County.
This species possesses a shark-like dentition and elongated lower jaws, but also exhibits an opercular structure resembling that of holocephalans. The gill cover is formed by elongate cartilaginous rays derived from multiple branchial arches, not limited to the hyoid arch. These rays are fused along their length, forming a continuous corrugated surface that may have been capable of fully sealing the gill openings. This type of structure is unknown in both modern sharks and holocephalans, indicating a unique evolutionary feature.
The dentition is consistent with falcatid sharks, and the arrangement of tooth families shows some similarity to that of the extant frilled shark (Chlamydoselachus).
In life, this species likely inhabited shallow marine environments. The elongated opercular structure may have functioned to prevent water from flowing back into the pharyngeal cavity during respiration.
The three-dimensional preservation of the fossil suggests that the depositional environment of the Fayetteville Shale was characterized by low oxygen conditions and rapid burial, which facilitated the preservation of delicate cartilaginous structures.
(Author: Shui-Ye You)
Reference
Bronson AW et al. (2024). A new operculate symmoriiform chondrichthyan from the Late Mississippian Fayetteville Shale (Arkansas, United States). Geodiversitas.
35.83, -92.56
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