The Beacon

Online “Tree of Life” is Your Ultimate Guide to Sharks, Rays, and Skates

A Galapagos shark (Carcharhinus galapagensis). (Photo: Oceana / Eduardo Sorensen)

When you think of Shark Week, the chances are that you're picturing a great white or a hammerhead shark. Or, if you’re thinking about the ancient oceans, you’re likely picturing the Megalodon thanks to Shark Week. But the handful of celebrity shark species that get the most attention this week don't even begin to cover the incredible range of shark and ray species out there. Fortunately, there’s an online resource that serves as the ultimate Shark Week guide, but you’ll need more than just a week to learn about all of these amazing animals.

Chondrichthyes: Tree of Life is an online database showcasing the complex evolutionary history of sharks, skates, rays and chimaeras, and was recently presented at the 2014 Sharks International Symposium in Durban, South Africa. Using the Tree of Life, you can learn about more than 1,200 shark species through interactive illustrations, CT scans, maps, and other information. Created by College of Charleston marine biology professor Gavin Naylor in collaboration with students in his lab in an effort to better understand the evolutionary history of Chondrichthyes, it’s the ultimate guide for any shark lover.

Sharks have been roaming the world's oceans for over 420 million years. During this time, they've adapted to different environments and developed different traits, evolving into approximately 500 shark species and 600 ray and skate species, all divided into 52 families.

Though these families are all related, they're quite diverse. Sharks, for example, range from 40-foot long whale sharks (Rhincodon typus) to nine-inch long green lanternsharks (Etmopterus virens). The same goes for rays and skates. They are closely related, but rays give birth to live young and are typically much larger than skates, which lay eggs in egg cases. Skates and rays are also closely related to sharks, but differ in that they are dorsoventrally flattened (like a pancake, which is why some people refer to them as 'pancake sharks') and can be characterized by their large, flattened pectoral fins that are fused to the side of the head, looking more like wings than fins.

To complicate things even further, some sharks are flattened like rays, such as the Pacific angelshark (Squatina californica), but they can still be distinguished visually by the location of their gill openings and shape of their pectoral fins. Similarly, some rays actually look much more like sharks, such as the sawfish (Pristis and Anoxypristis).

Explore the Tree of Life on your own to learn more about the evolution of sharks and rays and, if you’re up to the challenge, use it to help you answer the following questions about Chondrichthyes. Be sure to check back on Friday afternoon for answers to these questions:

1. Sawfish aren’t sharks, but rays. How many species of sawfish are there? 

A: There are seven recognized species of sawfish, but some are so similar that some scientists say there are five. 

2. Dusky sharks (Carcharhinus obscurus) are part of the requiem shark family. How many species are in that family? 

A: There are 37 species within the requiem shark family.

3. The giant manta ray (Manta birostris) is the largest ray species in the world with a wingspan of up to 23 feet. How many other species of manta are alive today? 

A: There are two species of manta raysManta birostris, the giant manta, and the smaller Manta alfredi, known as the reef manta. 


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