Artica gibbosa - Clam Steinkern
Quick Facts
Fossil Name: Arctica gibbosa (Steinkern)
Common Names: Cretaceous Heart Clam, Gibbous Clam
Scientific Name: Arctica gibbosa
Geological Period/Age: Early Cretaceous (Albian Stage), approximately 110 million years old
Location/Formation: Lower Glen Rose Formation, Texas, USA
This fossil is a classic example of marine life from the age of dinosaurs. Arctica gibbosa was a common clam that lived in the shallow sea that once covered central Texas. Its robust, heart-shaped form makes it a recognizable and frequent find for collectors.
Composition & AppearanceFossil Type: Bivalve (a mollusk with two hinged shells).
Preservation: This specimen is a steinkern, a German term meaning "stone kernel." This type of fossil forms when sediment fills the inside of the clam's empty, articulated shells. Over millions of years, the original shell material dissolves away, leaving a perfect internal mold of the clam's interior, cast in solid rock.
Appearance: The steinkern is typically heart-shaped, inflated, and rounded, reflecting the "gibbous" (swollen or convex) nature of the original clam. You are not seeing the outer shell, but rather the shape of the space inside the shell, often with impressions of the internal hinge teeth and muscle scars visible.
Composition: It is composed of the lithified sediment of the Glen Rose Formation, typically a hard limestone or marl.
Significance of the FossilPaleoenvironmental Indicator: The presence of Arctica gibbosa is a clear indicator of a specific ancient environment. It tells us that the area was a shallow, warm, near-shore marine ecosystem, such as a lagoon or bay with a soft, muddy seafloor.
A Piece of a Famous Ecosystem: The Glen Rose Formation is world-famous for its spectacular dinosaur trackways, left by giants like Acrocanthosaurus and Sauroposeidon. This humble clam lived on the seafloor of the very same body of water whose muddy shorelines preserved these iconic footprints. Finding one places you directly in the world the dinosaurs inhabited.
Paleo-Ecological Associations(The following information is based on scientific reconstructions of the ancient Glen Rose ecosystem.)
Environment: Lived buried in the soft mud and sand on the floor of the shallow, subtropical Western Interior Seaway that covered much of North America during the Cretaceous.
Associated Fauna: It shared its habitat with a diverse community of marine invertebrates, including other bivalves (Trigonia, Protocardia), oysters (Exogyra), gastropods (Tylostoma), echinoids (sea urchins), and ammonites. The most famous neighbors were, of course, the dinosaurs walking along the coastlines.
Lifestyle: Arctica gibbosa was an infaunal suspension feeder. This means it lived buried just beneath the surface of the seafloor, extending a siphon up into the water column to filter out plankton and other microscopic bits of food.
Fossil Name: Arctica gibbosa (Steinkern)
Common Names: Cretaceous Heart Clam, Gibbous Clam
Scientific Name: Arctica gibbosa
Geological Period/Age: Early Cretaceous (Albian Stage), approximately 110 million years old
Location/Formation: Lower Glen Rose Formation, Texas, USA
This fossil is a classic example of marine life from the age of dinosaurs. Arctica gibbosa was a common clam that lived in the shallow sea that once covered central Texas. Its robust, heart-shaped form makes it a recognizable and frequent find for collectors.
Composition & AppearanceFossil Type: Bivalve (a mollusk with two hinged shells).
Preservation: This specimen is a steinkern, a German term meaning "stone kernel." This type of fossil forms when sediment fills the inside of the clam's empty, articulated shells. Over millions of years, the original shell material dissolves away, leaving a perfect internal mold of the clam's interior, cast in solid rock.
Appearance: The steinkern is typically heart-shaped, inflated, and rounded, reflecting the "gibbous" (swollen or convex) nature of the original clam. You are not seeing the outer shell, but rather the shape of the space inside the shell, often with impressions of the internal hinge teeth and muscle scars visible.
Composition: It is composed of the lithified sediment of the Glen Rose Formation, typically a hard limestone or marl.
Significance of the FossilPaleoenvironmental Indicator: The presence of Arctica gibbosa is a clear indicator of a specific ancient environment. It tells us that the area was a shallow, warm, near-shore marine ecosystem, such as a lagoon or bay with a soft, muddy seafloor.
A Piece of a Famous Ecosystem: The Glen Rose Formation is world-famous for its spectacular dinosaur trackways, left by giants like Acrocanthosaurus and Sauroposeidon. This humble clam lived on the seafloor of the very same body of water whose muddy shorelines preserved these iconic footprints. Finding one places you directly in the world the dinosaurs inhabited.
Paleo-Ecological Associations(The following information is based on scientific reconstructions of the ancient Glen Rose ecosystem.)
Environment: Lived buried in the soft mud and sand on the floor of the shallow, subtropical Western Interior Seaway that covered much of North America during the Cretaceous.
Associated Fauna: It shared its habitat with a diverse community of marine invertebrates, including other bivalves (Trigonia, Protocardia), oysters (Exogyra), gastropods (Tylostoma), echinoids (sea urchins), and ammonites. The most famous neighbors were, of course, the dinosaurs walking along the coastlines.
Lifestyle: Arctica gibbosa was an infaunal suspension feeder. This means it lived buried just beneath the surface of the seafloor, extending a siphon up into the water column to filter out plankton and other microscopic bits of food.
