Stingray stinger and teeth

Stingrays belong to the cartilaginous fishes [Class Chondrichthyes], which includes sharks, stingrays, electric stingrays, skates, and sawfish. Cartilage is soft, unlike true bone, and is very difficult to preserve. Fossilized remains of cartilaginous fishes consist mainly of their teeth, spines, dermal scales, and, in some cases, vertebrae.

Stingrays evolved from sharks, when the shark's dorsal fin developed into a whip-like tail. Sharks have a long geologic history, extending back to the Devonian (about 400 million years ), whereas stingrays extend back only to the Early Cretaceous (about 140 million years or so). 

Bat rays, named for their wing-shaped pectoral fins, are a variety of stingrays. Bat rays are euryhaline, which means that they can tolerate a wide rang of salinities, hence they are found in estuaries, bays, and rocky-bottom shorelines (including kelp beds).
  
Bat rays feed on mollusks, crustaceans, and small fish. They use their wing-shaped fins to move sand and mud, thereby exposing their prey. Bat rays are common along the eastern Pacific coast between Oregon and the Gulf of California. 

The maximum size of a bat ray is about 200 pounds, with a wingspan of about 6 feet (see my artwork below).

All stingrays have a venomous stinger (spine) near the base of their tail. The two views (lateral and side) shown above are of a complete stinger, 8.3 cm long and 4 mm wide, are from a modern-day, full-sized adult specimen of the bat ray Myliobatis californicus from Ventura, southern California.  

As shown below, stingray teeth are flat and form tightly-packed rows. Unlike sharks, which have sharp and piercing teeth for eating fish, stingray teeth are used only for crushing and grinding shells (clams, crabs, etc.). The crushed shell is inedible and is ejected, whereas the soft parts of these shelled animals are then swallowed. 

Articulated stingray teeth in both jaws of a full-sized, modern-day adult Myliobatis californicus from Ventura, southern California. 

Stingray teeth fall out and are replaced continuously in living specimens. Fossil stingray teeth are, therefore, moderately common locally. They occur mainly as fragments of partial sets of teeth.

Miocene Round Mountain Silt (14 million years old); largest set of teeth 24 mm length. 

Middle Eocene Llajas Formation (47 million years old), Simi Valley; 45 mm length.

Middle Eocene Gosport Sand (42 million years old), Little Stave Creek, Alabama; longest set of teeth 15 mm. 

Fossil freshwater stingrays, some of which are nearly complete and articulated, are known from deposits as old as Paleocene age (about 60 million years old) in Italy and Germany. Other well preserved freshwater specimens are known from Eocene deposits in Wyoming and Miocene deposits in Indonesia.

Colorful Land Snails

Ancient land snails (air-breathing terrestrial pulmonate gastropods) originated during the Carboniferous Period, probably about 310 million years ago, which was about 165 million years after the first marine gastropods appeared.

More-modern land snails, like those mentioned below, are rare before the Cretaceous but are more plentiful in Cenozoic age (post- 66 million years ago) deposits. As fossils, they are useful to geologists because they are excellent indicators of the terrestrial environment, but their shells are susceptible to having been transported by streams into the marine environment. 

Many modern-day, air-breathing land snails from the tropics have intricate color bands on their shells. Unfortunately, color bands of both terrestrial (and marine shells) are only rarely preserved by fossilization.

The biggest shell is 3.5 cm in height.

Liguus virgineus (Linnaeus, 1758), also called the "rainbow snail" or "candy-stripes snail" air-breathing pulmonate is restricted to the islands of Haiti and Dominican Republic in the Caribbean Sea. They live in trees, thus they are arboreal. They feed on moss, fungi, an microscopic algae that cover the bark. In recent years, they have been over harvested for shell-craft trade. Also, the destruction of forests have become a major threat. The background color of the shell is creamy white, with narrow bright spiral stripes of red, green, blue, yellow, and purple. The slug-like animal itself is brown with black streaks. Genus Liguus belongs to family Orthalicidae.

Both shells are 3.5 cm in height.

 Amphidromus perversus (Linnaeus, 1758) is another tree snail, but its genus belongs to family Camaenidae. It lives in eastern India to northern Australia and especially in Indonesia (e.g., Sumatra, Java, Bali). The two specimens shown above display the asymmetry in shell coiling, which is common among this species. In fact, some populations simultaneously include the left-hand shell coiling (sinistral) and the right-hand shell coiling (dextral). This is a rare biologic phenomenon, and the reasons for it are still being researched. There is also much color variation among this species and its subspecies.

2.7 cm height

Helicostyla roissyana (Férussac, 1840) is the "chocolate-swirl" snail. It is another air-breathing land snail, but it belongs to family 
Bradybaenidae. This snail is endemic to the Philippines. 

The largest shell is 3.2 cm height.

Helicostyla annulata (Sowerby, 1841) is a tree snail, belonging to family Bradybaenidae. The unbounded  yellow to pale-yellow forms are shown here, but there is also a banded form. Helicostyla annulata is common in the Philippines.

                    

   

Ryssota ovum Valenciennes, 1854 is a tree snail restricted to rain forests in the Philippines. It can also live in branch and leaf debris at the tree base. This species is large sized, and the specimen shown here is 7 cm in diameter. The common name of this snail is the "Polished Muffin Snail." Some people consider the meat of this snail to be a delicacy, and its shell is used as a water vessel. The genus belongs to family Helicarionidae.

Yaadia and Quadratotrigonia Cretaceous bivalves

This post concerns two species of "knobby" bivalves (clams) of Cretaceous age. They have medium-sized, sturdy shells with ovate or quadrate shape, and their shells are ornamented with widely spaced, oblique radial ribs bearing large nodes (knobs). Early workers referred to these kinds of bivalves as "knobby trigoniids."

 Two views (left vs. right valves) of a plaster cast of a complete specimen (length 7.4 cm = from left margin to right margin) of the "knobby trigoniid" known as Yaadia leana (Gabb), Early Cretaceous (late Albian?) from Alaska. 

Two views (left vs. right valves) of a plaster cast of a complete specimen (length 100 cm) of Quadratotrigonia mearnsi (Stoyanow), Early Cretaceous (early Albian) age, Guadalupe  Mts., southeastern corner of Arizona. This species, which also occurs nearby in Texas, differs from the preceding species by having more rows of knobs, more closely spaced rows, and a few widely spaced rows of nodes on the dorsal area, including the edge of the dorsal margin. 

Both of these knobby genera were partial burrowers, most likely with one half or less of their shell protruding into the water column. Their shells were not streamlined enough for rapid nor total burial. For a time, the sturdy and knobby shells resisted predation by gastropods and fish, which lived in the nearshore warm-temperate ocean waters preferred by this bivalve. The predation, however, became too severe (i.e., the Mesozoic Marine Revolution), and knobby trigoniids went extinct during the Maastrichtian, the last interval of the Cretaceous.

"Knobby" bivalves, in general, were very diverse during the Mesozoic. Nearly all of them went extinct at the end of the Cretaceous, most likely because of over predation by carnivorous gastropods and vertebrates (i.e., the “Mesozoic Marine Revolution.”) Today, a few relic species related to the "knobby" bivalves survive and live only in Australia. One of these species is illustrated below. 

Exterior and interior views of both valves (left on the left side, etc.) of a modern-day specimen of Neotrigonia margaritacea from southeastern Australia. Notice the "mother-of-pearl" luster on the insides of the valves. The hinge teeth of this small-sized species (2.4 cm height) are stout, long, and fit snuggly inside the sockets of the opposite valve. Neotrigonia margaritacea is a burrower but, unlike most bivalves, it can actually jump.

My post on August 19, 2017 dealt with the morphologic differences between two species of the same genus of a Cretaceous trigoniid. You can always access my previous posts by using the "Search This Blog" box in the upper right-hand side of each posting.