Sphenodiscus

SphenodiscusWedge Disc
Classification
Domain	Eukaryota
Kingdom	Animalia
Phylum	Mollusca
Class	Cephalopoda
Order	Ammonitida
Family	Sphenodiscidae
Species	Sphenodiscus sp.
Presence
Location	North America, South America, Europe, Asia and Africa
Temporal Range	83.5 - 64.5 million years ago, Campanian - Danian Stage, Late Cretaceous - Early Paleocene Period
Episodes	Oceans (Segment 5) North America (Segment 2) What Do We Really Know About Ammonites?
Characteristics
Diameter	20 - 40 centimeters (8 - 15.8 inches)
Diet	Carnivorous

Sphenodiscus (Wedge Disc), also called tiger ammonites on the show because of the design given to their depiction in the series, is an extinct genus of sphenodiscid ammonite cephalopod that lived in various parts of the world, around 83.5 - 64.5 million years ago, from the Campanian stage of the Late Cretaceous Period to the Danian Stage of the Early Paleocene Period.

It is unknown which specific species was depicted on Prehistoric Planet. The species featured in the fifth segment of Oceans (set within the Tethys Ocean) may be S. binkhorsti of the Netherlands or some other European species, while the species featured in the second segment of North America (set in the Western Interior Seaway) may be any of the common species found in North America, like S. lobatus, S. lenticularis, S. pleurisepta, etc.

Paleobiology

“ Tiger ammonites are themselves hunters. The combination of a streamlined profile and a powerful siphon enables them to shoot through water at great speed. But so can the mosasaur. ”

― David Attenborough, North America

Sphenodiscus can attain a shell diameter of up to 40 centimeters (15.8 inches), though the size of the average specimen is only half of that.

Paleoecology

Paleoenvironment

As shown on Prehistoric Planet, Sphenodiscus thrived in the warm, shallow waters of the Gulf of Mexico, which was, by that time, part of the Western Interior Seaway, an inland sea that split North America into two landmasses (Laramidia in the west and Appalachia in the east). It was also present in similar seas across the globe, thriving in the waters of Trinidad and Brazil in South America, the Netherlands in Europe, Nigeria in Africa, and India (which by that time was an island isolated from the rest of Asia).

Appearances

Oceans

In the fifth segment of Oceans, several Sphenodiscus briefly appear alongside other ammonites in a seagrass meadow in the Tethys Ocean.

North America

	North America, Segment II
	Setting Gulf of Mexico, Western Interior Seaway, USA

North America, Segment II

Setting
Gulf of Mexico, Western Interior Seaway, USA

In the second segment of North America, a Globidens swims in the waters of the Gulf of Mexico, seeking out shoals of "tiger ammonites", Sphenodiscus. Every year, from the deep levels of the ocean, thousands of females come up to the coast, each ammonite carrying hundreds of fertilized eggs that need to be laid in the shallows, right where Globidens is waiting for them.

The Sphenodiscus use their own predatory traits (their streamlined profile and powerful siphon) to get to their destination faster and evade incoming threats. Unfortunately for them, Globidens is also quick enough to catch up to them and attack. With its globular teeth, the mosasaur easily crunches through the shells of the ammonites, releasing the buoyant air within its prey, disabling and sinking as many Sphenodiscus as it can instead of taking time to consume each ammonite it catches. Once the shoals of ammonites have passed through the area, with no more prey to cripple, Globidens feeds on the ammonites it sunk to the ocean floor. Despite the mosasaur having killed dozens of the ammonites, hundreds more make it to the shallows to successfully lay their eggs.

Uncovered: What Do We Really Know About Ammonites?

	What Do We Really Know About Ammonites?
	Subject Various facts and knowledge about ammonites. Experts Dr. Darren Naish, Zoe Hughes

What Do We Really Know About Ammonites?

Subject
Various facts and knowledge about ammonites.

Experts
Dr. Darren Naish, Zoe Hughes

TBA