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Diving with Bull Sharks - Youtube Video

Gray Shark (Carcharhinus sp.) Introduction

The Carcharhinus genus, or the Gray sharks, is a highly successfull group. There are at least 31 different species (ITIS) that inhabit tropical and temperate waters across the globe. Well known species include the Bull Shark (C. leucus), Sandbar Shark (C. plumbeus), Blacktip Reef Shark (C. melanopterus), Spinner Shark (C. brevipinna), and many others. Most species closely resemble one another and range in size from 3 to 11 feet. They typically eat small fish and crustaceans, while larger ones will eat marine mammals.

Most Gray sharks have triangular, serrated upper teeth suitable for cutting and slender lower teeth with few serrations suitable for clutching. The teeth of many species are difficult to distinguish from one another as they have a high morphological overlap.

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Fossil Specimens and Identification Issues

The first defninitive occurrence of Carcharhinus in the fossil record comes from the Eocene. In the Eocene, they were already globally distributed and have been found in places including Egypt (Stromer, 1905), Antarctica (Kriwet, 2005), Jamaica (Underwood and Gunter, 2012), and Madagascar (Samonds et al., 2019). After the Eocene, they rapidly diversified in all tropical and temperate waters. The Miocene especially saw a rapid diversification of this genus.

This rapid diversification creates problems for shark tooth identification. For example, the Carcharhinus sharks of the Miocene Chesapeake Group (Calvert Cliffs) are likely composed of many localized species with the teeth of these species having overlapping characteristics (Kent, 2018). There are also differences in teeth between males and females, and juveniles and adults.

Because of this high morphological overlap and individual variation, it is sometimes not possible to identify isolated teeth to a single species (Kent, 2018). This is especially true for lower teeth, as the overlap in characteristics is much more prominent. In fact, some authors don't attempt to identify lower teeth to an individual species.

What this means for the casual shark tooth collector is it's safest to simply call most Carcharhinus teeth "Carcharhinus sp." and not attempt to make a species identification.

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The Species:

If you want to try to identify some of your Carcharhinus teeth, below is an identification guide to the more common and accepted fossil species. Please note there are many more fossil species than what is shown below.

The Bull Shark:
C. leucas

Reaching lengths of nearly 12 feet, Bull sharks are one of the larger species of Carcharhinus. They are found in tropical and temperate coastal waters worldwide. They are known to eat fish, smaller sharks, small mammals, and sea turtles. Bull sharks can live in fresh water and can be found in coastal rivers and lakes where they give birth. One was found to have swum 700 miles up the Mississippi river! Due to their large size, nearshore habits, and the ability to venture into fresh water, they are responsible for the majority of shark attacks.

Bull shark fossils are common in Miocene deposits of Maryland and Virginia. They are also found in Miocene and Pliocene deposits of North Carolina, the Pliocene of California and Pleistocene deposits of Florida. In Florida they are among the most common and largest Carcharhinus teeth found.

Description: The upper teeth of Bull sharks are large. In Pliocene deposits, Purdy et al., 2001 indicates a maximum height of around 24 mm, However, in Miocene deposits, Kent, 2018 indicates these teeth are much smaller and top out at around 18 mm. Upper teeth are broad and triangular with coarse serrations that get finer toward the tip of the crown. The distal heal is separated from the crown by a very weak notch and there is an obvious neck with a high root (Kent, 2018). The mesial cutting edge is relatively straight and does not have a notch between the heal and the crown. The roots have a short nutrient groove with nutrient pores toward the bottom of the root. Descriptions based from Kent, 2018 and Purdy et al., 2001.

Calvert Cliffs Note: These teeth were not reported from the cliffs in many older publications. They were usually grouped with C. perezii. The differences in these teeth tend to be a higher root, wider crown, and no notch between the heal and the crown.

The Dusky Shark:
C. obscurus

The dusky shark, also known as the Bronze Whaler, is another large shark that can reach lengths around 11 feet. They were once common in tropical and temperate coastal waters worldwide. The Dusky shark is a popular fishing target and their numbers have been decimated. It is estimated their population has declined by 80%. These sharks undergo seasonal migrations along the Eastern United States.

The dusky shark is not a Miocene species and is only found in the Pliocene to recent. Fossils are abundant in the Pliocene of North Carolina, and are common in Florida and North Carolina. In North Carolina Pliocene deposits, they are the most common Gray shark species found.

Description: With a maximum height of around 22 mm these are large teeth. The upper teeth are very triangular with "vertical or almost vertical distal cutting edges" and the tip of the teeth ‘deflect distally’ (Purdy et al., 2001). The roots are fairly wide and robust looking. Another key identification characteristic is many of the teeth have a very convex shaped cutting edge on the mesial side.

The Caribbean Reef Shark:
C. perezii

This is a very common shark found near coral reefs today. These teeth appear to be common in the Miocene of Maryland, Virginia, North Carolina, and most likely South Carolina. They are also reported from the Pliocene of North Carolina and the Pleistocene of Florida.

Description: The upper teeth have fairly narrow crowns that are finely serrated with serrations becoming slightly coarser toward the base. The transition between the shoulder and the mesial heel is very gradual (kent 2018), although the distal side may have a notch. The mesial cutting edge is usually straight or slightly convex. There is a distinct neck in these teeth, and they have a shallow nutrient groove. These teeth have a maximum height of around 18 mm. Descriptions based from Kent, 2018 and Purdy et al., 2001.

Copper Sharks:
C. brachyurus and C. priscus

The fossil record of C. brachyurus is global in tropical and temperate marine formations from the Miocene to recent. In the United states, it is abundant in Miocene deposits of North Carolina, Maryland, and probably South Carolina and Florida. It is also found in Miocene and Pliocene deposits of California (Landini et al. 2020). The fossil species C. egertoni is considered synonymous with C. brachyurus.

C. priscus is a problematic species. Many authors consider C. priscus synonymous with C. brachyurus. However, Reineke et al., 2011 found slight differences between the two species teeth and kept the name priscus. Kent, 2018 followed Reinecke and used the C. priscus name for the Calvert Cliffs area.

Description: The slight differences between C. brachyurus and C. priscus (if indeed it is a different species) are beyond the scope of this article. In general, C. brachyurus upper teeth are smaller than many other species, with a maximum height of around 10 mm. The upper teeth have a relatively narrow crown with fine serrations that become coarser toward the root, with the heels of the crown having more coarse serrations. There is also a distinct neck between the crown and the root, and a relatively deep nutrient groove in the root. Descriptions based from Kent, 2018 and Purdy et al., 2001.

The Silky Shark:
C. falciformis

This shark is very common in East Coast Miocene deposits such as Maryland, Virginia, North Carolina, South Carolina, and Florida. It has also been found in Pliocene deposits in California.

Description: With a maximum height of around 15 mm, C. falciformis are smaller than many other species. They also look similar to C. brachyurus. Upper teeth have a deep nutrient groove and a finely serrated blade. The mesial cutting edge is relatively straight, but has a small gap at the midpoint between the tip and the base of the crown. The serrations are larger toward the root and become coarse on the enamel shoulder. The key to identifying this tooth is the serration gap and relatively straight mesial cutting edge (Purdy et al., 2001). Descriptions based from Kent, 2018 and Purdy et al., 2001.

The Hardnose Shark:
C. macloti

This is a small, slender species of Gray shark found in tropical waters of the Indian and Pacific Ocean. Fossil specimens are uncommon in the Miocene of Maryland, Virginia, North Carolina, and probably South Carolina. They are also uncommon in Pliocene deposits of North Carolina and Florida.

Description: Teeth of this species are easy to distinguish from others. The upper teeth are very small, with a maximum height of around 8 mm. They have narrow crowns with smooth cutting edges. The shoulders have "cusplet-like" serrations or very coarse serrations, particularly on the distal shoulder (kent 2018). The mesial shoulders have smaller serrations, which are sometimes absent.

The Sandbar Shark:
C. plumbeus

Today the Sandbar shark is the most common shark found in the mid-Atlantic, including the Chesapeake Bay. It prefers shallow coastal waters such as estuaries and bays. They grow to a maximum size of around 7 feet.

C. plumbeus is an uncommon fossil found in Miocene of Maryland and North Carolina. This means the casual shark tooth collector may not find one at these locations. However, they appear to be more common in certain places in Florida (Pers. Obs.).

Description: These uncommonly found teeth are medium sized with a maximum height of around 19 mm. They are narrower and more elongate than that of C. obscurus, and also lack the convexity of the cutting edge that C. obscurus has (Purdy et al., 2001). The mesial edge has a steeply angled shoulder and the root has a week nutrient groove (Kent, 2018). These are also some of the largest Carcharinus teeth found at the Calvert cliffs.

C. cf. altimus Note: altimus is a problematic fossil species. It so closely resembles C. plumbeus that most authors synonymize them. However, Kent 2018 points out slight differences between the fossil teeth and keeps C. cf altimus, so it is technically reported from the Miocene Chesapeake group of Maryland and Virginia.

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Lower Gray Shark Teeth

Most lower Gray shark teeth are nearly impossible to identify to a species level. These are a few lower teeth of unknown species.

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Common Gray Shark Pathology

A common pathology in Gray shark Teeth is the mesial cutting edge will have a small protrusion, or bump. The three imaged below all have a small protrusion, but sometimes they are more noticeable, nearly creating a double blade. This is not a dramatic pathology, but it's a pathology nontheless.

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Gray Shark Vertebra

There are two general forms of shark vertebra; the Lamnoid-Type and Scyliorhinoid-Type.

These two forms are easy to tell apart. Lamnoid-Type have lots of "ridges" or septa running through the vertebral disk, while Scyliorhinoid-Type are more solid. View the image below for comparison.

Carcharhinidae (Requim sharks), which include the genus Carcharhinus (Gray Sharks) have the Scyliorhinoid form.

Other than sorting the vertebra forms, it's not possible to identify an isolated shark vertebra down to a genus.

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Fossil Hunting Locations for Gray Shark Teeth

Gray shark fossil teeth are very common and are found world wide in marine Tertiary deposits. In the United States, fossil teeth and sometimes vertebra are found from California on the Pacific to Florida, northwards to Delaware on the Atlantic.

Notable places to find Gray Shark fossils include Venice Beach in Florida, the Peace River of Florida, the Calvert Cliffs of Maryland, the mine tailings at the museum in Aurora, North Carolina, and Coastal South Carolina.

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High Quality Shark Teeth by Fossilera

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Jurgen Kriwet (2005) Additions to the Eocene selachian fauna of Antarctica with comments on Antarctic selachian diversity, Journal of Vertebrate Paleontology, 25:1, 1-7, DOI: 10.1671/0272-4634(2005)025[0001:ATTESF]2.0.CO;2

Kent. B. W. (2018). Chapter 2: The cartilaginous fishes (chimaeras, sharks, and rays) of Calvert Cliffs, Maryland, USA. In: S. Godfrey (ed.), The Geology and Vertebrate Paleontology of Calvert Cliffs, Maryland. Smithsonian Contributions to Paleobiology, 100: 45-157. (PDF Here)

Purdy, R., Schneider, V., Appelgate, S., McLellan, J., Meyer, R. & Slaughter, R. (2001). The Neogene Sharks, Rays, and Bony Fishes from Lee Creek Mine, Aurora, North Carolina. In: Geology and Paleontology of the Lee Creek Mine, North Carolina, III. C. E. Ray & D. J. Bohaska eds. Smithsonian Contributions to Paleobiology, No 90. Smithsonian Institution Press, Washington D.C. pp. 71-202.

Samonds KE, Andrianavalona TH, Wallett LA, Zalmout IS, Ward DJ (2019) A middle - late Eocene neoselachian assemblage from nearshore marine deposits, Mahajanga Basin, northwestern Madagascar. PLoS ONE 14(2): e0211789. DOI: doi.org/10.1371/journal.pone.0211789

Stromer, E. (1905) Die Fischreste des mittleren ubd oberen Eocans von Agypten, I. Die selachier, B. Squaloidei. Beitrag Paleontologische und Geologische Osterreich-Ungarns 18: 163-92.

Unerwood, C.J. & Gunter, G.C. (2012) The shark Carcharhinus sp. from the Middle Eocene of Jamaica and the Eocene record of Carcharhinus. Caribbean Journal of Earth Science, 44: 25