Beyond Shark Teeth: The Complete Fossil Beachcomber's Guide

Rays are close relatives of sharks and share their polyphyodont, continuous-replacement dentition — but their teeth look nothing like typical shark teeth. Instead of blade-shaped cutting teeth, rays have flat, pavement-like crushing plates (technically called durophagous dentition) designed to crack open clams, oysters, and crabs.

Three genera dominate Florida Miocene fossil beaches. Myliobatis (eagle rays) produce roughly hexagonal flat tiles with a smooth enamel top and a fibrous root bottom. Rhinoptera (cownose rays) produce similar but narrower tiles with distinctive parallel ridges running across the enamel surface — unmistakable under a loupe. Aetobatus (spotted eagle rays) produce elongated rectangular plates, wider than Rhinoptera, also smooth-topped.

All three look like flattish oval or rectangular pebbles at first glance. The giveaway is the enamel surface: smooth, slightly lustrous, often darker than the root material. Hold one up and catch the light at a low angle — the enamel reflects differently from calcite or quartz. Ray plates are extremely common at Venice-area beaches and are routinely mistaken for smooth pebbles by beginners.

The Miocene and Pliocene seas of the Southeast US hosted a diverse cetacean fauna including early baleen whales (mysticetes), sperm whale relatives (physeteroids), and a variety of dolphins and porpoises. Their bones preserve well in phosphate-rich formations, but casual collectors rarely recognize them.

The most diagnostic — and beautiful — cetacean fossil is the tympanic bulla, the ear bone of an ancient whale. These dense, smooth bones are roughly the size and shape of a chicken egg, with a distinctive circular attachment scar on one end. They are extraordinarily dense: much denser than any rock of comparable size. The weight when you first pick one up is startling — it feels like picking up a stone twice its apparent volume. Color is usually creamy tan to dark brown. The inner surface shows a faint trabecular (sponge-like network) texture.

Vertebrae from small Miocene cetaceans are relatively common: round disc shapes with a distinctive spool or reel form showing two raised projections where the neural arch attached. Large flattened rib fragments from baleen whales can reach several inches and are often mistaken for driftwood or waterlogged bark until you notice the distinct cortical bone surface.

The warm Miocene seas of Florida hosted sea cows (Sirenia) — relatives of modern manatees in genera such as Metaxytherium and Dusisiren — in considerable numbers. Their remains are among the most common large-mammal fossils in the Florida Miocene, and their bones have unusual properties that make them easy to recognize.

Dugong ribs are extraordinarily dense and heavy (a condition called pachyostosis) — an adaptation that provided ballast for slow-swimming, bottom-grazing animals. A dugong-rib fragment the size of your fist may have the weight of a comparable piece of iron ore. The bone texture is smooth and compact, lacking the spongy marrow structure of most mammal bones. Color in Miocene specimens is usually dark gray to black, frequently the same color as associated megalodon teeth.

Sirenian vertebrae are similarly dense and disc-like. Some Peace River localities produce recognizable sections of dugong rib so regularly that experienced hunters consider them incidental finds while targeting shark teeth.

The Pleistocene epoch (2.6 million–11,700 years ago) saw Florida — then a substantially wider peninsula owing to lower sea levels — hosting a spectacular megafauna: Columbian mammoths (Mammuthus columbi), mastodons (Mammut americanum), giant ground sloths (Eremotherium laurillardii and Nothrotheriops), glyptodonts, native horses (Equus), tapirs, flat-headed peccaries, and dire wolves (Aenocyon dirus).

Mammoth and mastodon teeth are among the most dramatic fossils a Peace River diver can find. Mammoth molars have distinctive parallel enamel ridges (lophodont teeth) that look like a coarse file or washboard pattern. Mastodon molars have large rounded cusps arranged in paired rows — a completely different shape, sometimes described as looking like a cluster of rounded domes. Tusk fragments — off-white, moderately dense ivory — show characteristic Schreger-line cross-hatching pattern (concentric ovals) visible in cross-section, which is definitive for proboscidean ivory.

Giant ground sloth bones (Eremotherium) are large, dense, and irregularly shaped. Claw bones (unguals) from ground sloths look like curved, talon-shaped stones and are occasionally found in Peace River gravels. Horse teeth are relatively common: tall-crowned, highly ridged with complex enamel folding patterns that differ considerably from both shark teeth and mammoth teeth.

Fossil sea turtles made appearances in both the Cretaceous and the Cenozoic faunas of the Southeast US. Fragments of sea turtle shell costal and peripheral scutes are flat, roughly textured on one surface, smooth on the other, with a characteristic honeycomb internal structure in cross-section. Leatherback ancestors produced shell fragments relatively frequently at some Miocene sites.

Crocodilian material — scutes (dermal armor plates, with their distinctive deeply pitted surface texture on one face) and conical, root-heavy teeth — appears at Florida Miocene and Pleistocene sites. Crocodilians have a continuous fossil presence in Florida from the Oligocene onward. Their teeth are easily distinguished from shark teeth by their solid, non-bifurcated roots.

For invertebrate collectors, Miocene-age fossil scallops (Chesapecten jeffersonius, the official state fossil of Virginia), large oysters, and gastropods appear alongside shark teeth at Calvert Cliffs and similar sites. Sea biscuits (Clypeaster) — fossil sand dollars up to three inches across — are common at some Gulf coast sites. And don't overlook shark vertebrae: round, calcified cartilage centra with a distinctive asterisk-shaped central pattern — fascinating pieces that document the shark alongside its teeth.