Development of this project was supported by the National Science Foundation. Pronged marine snail about 100 million years old. Marine snail collected by . Varied aspects of the shapes of bivalve shells. The large block is 3 X 3 1/2 X 5 and weighs three pounds. There are about 12 irregular ridges on the exterior of the valve (shell) in a spread fan pattern. Remarkably, the mantles of some freshwater mussels are modified to resemble small fish. When God created the scallop kind He designed its DNA to allow for the variation seen in the photo. Bivalves are also of major economic importance to humans, as sources of food and other products, and as damaging invasive species. Hc``Pc``Y36XD/0c`v`cR In most bivalves, the plane of symmetry is between the two valves (that is, the shells lie laterally on the body, and the right and left sides are nearly symmetrical, whereas in most brachiopods it is across the valves (i.e., the valves lie dorsally and ventrally on the body). Fossil snails, scallops, whelks, tusk shellsand corals are also commonly found. They are found mostly in tropical and subtropical ocean waters. Texas Cretaceous beds that hold bivalve, ammonite and possible . Bivalves There are many types of bivalve fossils in Texas. The adductor muscle is the part of the scallop that is consumed in the US; the entire scallop body is consumed elsewhere in the world. Access here. The ligament is considered a partly organic component of the shell (see image above under "Ligament"). You can check the current water level for the Brazos river by following this link here. Although these growth lines look rather like tree rings, they do not necessarily reflect years of growth (see Sclerochronology, below). Some bivalves are symetrical, like clams, while others have different shaped sides, but most have a hinge that connects the two valves. Neithea texana. The gillshave evolved into ctenidia, specialized organs for feeding and breathing. Cretaceous Era (65 - 150 Million Years Ago), Fossil finds from Dallas, Ft. Worth, Lake Benbrook. Specimen is from the collections of the Paleontological Research Institution, Ithaca, New York. More typically, clues about the ligament of fossil bivalves come from structures of the shell around the ligament, such as fossettes, nymphs, resilifers, etc. ), A Turquoise Standoff: The Story of a Woman Standing Her Ground in Nevadas Mining World. An elastic ligament connects the two valves, allowing them to spring open when the adductor muscles relax. While the collector may want to give a skip to Lake Whitney and its temptations, its definitely worth a trip for the fossil enthusiast. Image provided by Paul Harnik. CaCO3 precipitated in warmer water is relatively high in 16O and depleted in 18O (isotopically light); CaCO3 precipitated in cooler water is relatively high in 18O and depleted in 16O (isotopically heavy). Texas Fossil Bivalve Texigryphaea ONE PER PURCHASE Dinosaur Age Shell $2.99 $3.98 shipping or Best Offer Lucina saltwater clam Bivalve fossils 380 million years old agatized 1 pound $17.48 Nice Fossil Large Bivalve Sea Shell From Pliocene Age / Sarasota Florida $30.00 $12.00 shipping or Best Offer The Journal seeks to appeal to a broad international audience, and to publish comprehensive systematic treatments of taxa, which employ modern analytical techniques and have broad evolutionary, environmental, and/or geographic significance. At first glance, bivalves do not appear to have much in common with these other groups besides having a shell made of calcium carbonate, which most possess. The larval shell, which is frequently retained on the umbo in older individuals, is called the prodissoconch. It looks very similar to cockles that inhabit our oceans today. The shell is prominently ribbed with 20 ribs on the convex (back) side and six ribs on the concave (visible) side. Other Texas Fossils. [1] By 1935, the formation had been included in the Washita Group.[9]. 2008. [6], Foraminifera are poorly preserved, but may include Globigerina. ", A number of fossil pelecypods similar in design to, Chalcedony is a variety of quartz, and quartz is crystalline silica which is an important material for forming both rocks and fossils. [7] While the vertical wells relied on the porosity of the formation (up to 6%), the horizontal wells exploit a system of natural vertical fractures in the formation. bivalve species are named, Panopea anacachoensis new species and Spondylus siccus new species, and two potentially new gastropod . Always The Best Prices. There are 20 remaining ribs, but both ears of the valves and the hinges are missing. Photo by Chandler Olson, courtesy of Kathryn Estes-Smargiassi, Academy of Natural Sciences of Drexel University. Some bivalves, such as the scallops, can swim. This is also where youll be able to access the dig site, which will be along the embankments. Left image by Brocken Inaglory (Wikimedia Commons; Creative Commons Attribution-Share Alike 3.0 Unported license). The Society holds an Annual Meeting, which is ordinarily in the fall at the same time and place as the Annual Meeting of The Click here for a list of fossils from this site. Some of the external shell features of the bivalveMercenaria mercenaria, including the valves, commissure, and umbones. Photograph by "Shellnut" (Wikimedia Commons; Creative Commons Attribution-Share Alike 3.0 Unported license). If an extant animal has died the hinge ligaments that open and close the valves always relax so that the valves will then pop open. More. Since, ICR COMMITS TO NEW CREATION ENGINEERING THEORY, CREATION ENGINEERING HALLMARKS OF DESIGN, THE DELETERIOUS CONSEQUENCES OF EVOLUTION, NATURAL SELECTION: DEAD AT ITS INCEPTION-PART 1, NATURAL SELECTION: DEAD AT ITS INCEPTION-PART 2, NATURAL SELECTION: DEAD AT ITS INCEPTION-PART 3, NATURAL SELECTION: DEAD AT ITS INCEPTION-PART 4, NATURAL SELECTION: DEAD AT ITS INCEPTION-PART 5, NATURAL SELECTION: DEAD AT ITS INCEPTION-PART 6, NATURAL SELECTION: DEAD AT ITS INCEPTION-PART 7, NATURAL SELECTION: DEAD AT ITS INCEPTION-PART 8, NATURAL SELECTION: DEAD AT ITS INCEPTION-PART 9, NATURAL SELECTION: DEAD AT ITS INCEPTION-PART 10. Ammonites and Nautiloids - Jacksboro, Jack County, TX, Ammonites - Old Toll Bridge Road Creek, Cooke County, TX, Ammonites - Oliver Creek, Denton County, TX, Ammonites - Spring Creek, Cooke County, TX, Nautiloids and Ammonites - Rayzor Ranch, Denton County, TX, Baculites - North Sulphur River Fannin Co., TX, Ammonites- Fort Worth, Cedar Hill, and Midlothian, Gastropods -Lake Grapevine, Denton Co., TX, Gastropods - Spring Branch, Comal Co., TX, Echinoids - Oliver Creek and Rayzor Ranch, Denton Co., TX. Bivalve Fossils This Specimen has been sold. Specimen is from the Quaternary of St. Marys County, Maryland (PRI 76728), with external shell features annotated. 0000014582 00000 n Thefossilshereareverysmall;nothingbiggerthanaquartermaybefound. Lopha oysters are still found alive today, thus it is a living fossil. List of pterosaur-bearing stratigraphic units, "Reconnaissance in the Rio Grande coal fields of Texas, including a report on igneous rocks from the San Carlos coal field by C.E. Click here for a more detailed list of fossils from this site. The Society's official newsletter, Priscum, is issued to all members twice yearly. 0000001893 00000 n One or two adductor muscles hold the shell tightly closed when they contract. If these Turritella Agate fossilized sedimentary blocks were the result of catastrophic burial, then it would be difficult to determine if they were freshwater or marine or if they could have adapted in their various forms to both types of water. Along with the hinge teeth, the ligament forms the hinge system that holds the two shell valves together. Information about your use of this site is shared with Google. Right: Ruditapes philippinarumwith separate incurrent and excurrent siphons extended; image by Stefan Didam (Wikimedia Commons; Creative Commons Attribution-Share Alike 3.0 Unported license). Bivalve Phylogeny and Classification- 2. The Paleontological Society Memoirs (issued as supplements to the Journal), Short Course Notes, and Special Publications. Description: The fossil clam Anadara is 1 7/8 wide X 1 5/8 high. Location: Astoria formation near Newport, Oregon. Pterosaur remains are among the fossils that have been recovered from the formation. in Flugsaurier: Pterosaur papers in honour of Peter Wellnhofer. 0000001633 00000 n This paper expands the distribution of many eastern Gulf Coast and Atlantic Coast taxa westward into Texas and shows strong ties between the Anacacho fauna and that of the Campanian Tar Heel and Bladen Formations of the Black Creek Group in North Carolina. Most bivalves have a byssus as larvae, and many lose it as adults. Holding the crystals together is organic matrix, composed of polysaccharide and protein (kind of like mortar to the crystal bricks), that also gives the shell its color; the crystals themselves are colorless. This technique uses the temperature-dependence of the ratio between two stable (i.e., non-radioactive) isotopes of oxygen when it is incorporated into the calcium carbonate (CaCO3) of the bivalve shell. The bay scallop Argopecten irradians. Fossil Trips Jamie's Favorites. Location: Walnut formation in Bell County, Texas. 0000003411 00000 n 1.5" Cretaceous Bivalve Mollusk (Neithea) Fossil - Texas SOLD 11 months ago SOLD. What was left behind is fossilized evidence of a seabed teaming with life. Click here for Whiteside Museum of Natural History website. Appropriate clothing should be worn during all hikes based on temperature and time of year. The lowest is 25 feet (7.6m) of hard microgranular grayish-white limestone that breaks with a conchoidal fracture. And as an Amazon Associate, we earn a commission on qualifying purchases after clicking on those links, at no additional cost to you. Interpretation: This particular genus has been found in many locations throughout the world and is alive yet today, so is another example of a living fossil. 17. As their name implies, bivalves have two shells that are called valves. The byssus is a set of elastic or calcified fibers secreted by a gland in the foot, used to anchor the bivalve to a hard substrate. Trigonia. Waco Research Pit The Waco Research Pit (aka The Waco Pit) is probably one of the most popular places near Waco to dig for fossils. Exceptional Fossil Reveals Fish-Eating-Fish Moment Frozen in Time, The Great Meteorite Hunt: Museum Offers $25,000 Reward for Rare Fireball Remains in Maine, Why Petrified Logs Look Like Theyve Been Cut (The How and The Why). Besides the permit there are no other fees or other restrictions to dig for fossils at this location. Fossil specimen of the gastropod Trepospira depressa from the Pennsylvanian Graham Formation of Coleman County, Texas (PRI 70109). The area is an Eocene maritime site with an abundance of tiny gastropod shells, indicating it was formerly a marine location. 1.5" Cretaceous Bivalve Mollusk (Neithea) Fossil - Texas SOLD SOLD . The incurrent siphon brings water and suspended food into the mantle cavity, and the excurrent siphon carries out water and waste. Growth lines on a specimen of Mercenaria mercenariafrom the Quaternary of St. Marys County, Maryland (PRI 76728), with external shell features annotated. . The mantle covers the body and secretes the shell. 3 0 obj << /Linearized 1 /O 5 /H [ 1197 225 ] /L 897791 /E 897473 /N 1 /T 897614 >> endobj xref 3 40 0000000016 00000 n Analysis of the macrofossil components from these eastern localities has expanded the number of invertebrate species known from the Anacacho Limestone by nearly three-fold. Width of specimen is approximately 10 cm. Bivalves include clams, scallops, mussels, oysters, and their relatives. To book a trip or inquire more details, email me at: Self-provided transportation, park fees, hotel, food and beverages. For most creation scientists, the created kind is established at, or near, the Family level rather than the Genus level. Diagrams showing how mantle fusion forms siphons in many infaunal bivalves (shell removed). Location: Blockley, Gloucestershire, United Kingdom. Request Permissions. In species with a large siphon the pallial line shows an embayment (the pallial sinus) which allows for connection of larger retractor muscles. The Digital Atlas of Ancient Life project is managed by thePaleontological Research Institution, Ithaca, New York. Blue arrows indicate movement of water. The inner fold is usually the thickest and is muscular. Figure fromYamanashi et al. The right valve fits inside the left like a lid. This is Myria Prez o, Day one of PermianFest has been awesome! These gastropods are wonderful examples of the tremendous variety within a created kind as allowed for by the information in their DNA. The folding is not seen in the Buda Formation below it and may be due to slumps and slides that occur due to differential compaction and the contrasts between the more ductile shale layers and the less ductile limestone layers. An exception is provided by several remarkably preserved specimens of Laevitrigonia gibbosa from the Jurassic of England, which show evidence of gills and other soft parts. The bivalve shell is usually composed of several layers of crystals of calcium carbonate (CaCO3). Class Bivalvia: Introduction and Morphology 1. The Boquillas Formation contains abundant marine fossils including the extinct bivalve fossil seen below in Figure 2. [5], In the Big Bend National Park area, the formation is divided into three informal members. Barrett, P.M., Butler, R.J., Edwards, N.P., & Milner, A.R. [1] Cretaceous Fossil Oyster and Gastropod Association - Madagascar SOLD SOLD. "Visualization of Freshwater Mussel Water Movement from In-current Siphon to Ex-current Siphon" by Jared McGovern (YouTube). 1.68 0.48 SIZE: 51 x 18 x 9mm (2.01 x 0.71 x 0.35 inches) Add to basket Exogyra, Cretaceous, USA (May differ to photo) Rated 5.00 out of 5 Sale! Modern bivalves live in a variety of depositional settings in fresh, brackish, and marine water. This is one of the top museumsin Texas and does active excavations on a local ranch. 0000001144 00000 n Unlike all other mollusks, bivalves lack a distinct head with all of its associated organs (tentacles, radula, etc. Specimen is from the collections of the Paleontological Research Institution, Ithaca, New York. These eastern Anacacho deposits are interpreted to represent more offshore, deeper water environments than those to the southwest, where reef and lagoonal deposits have been reported. 0000022432 00000 n In just two days we will explore the fossil history of North Texas by collecting 300-million-year-old marine invertebrates and walking in 110 million year old dinosaur tracks. HERE ARE SOME OTHER SIMILAR FOSSILS FOR SALE, 4.3" Cretaceous Rudist (Durania) - Kansas, 9.4" Cretaceous Rudist (Durania) - Kansas, Two Fossil Clams (Mercenaria) - Ruck's Pit, FL. [8], The formation was originally named the Shoal Creek Limestone, but this name was preempted, and the formation was renamed the Buda Limestone by T.W. By using this site, you agree to its use of cookies. The small piece is 1 X 1 1/4 X 3. So what are the ways to connect to these long lost creatures? Many of these pieces are then sliced, tumbled and polished into various items of beauty such as rings and bracelets. The Waco Research Pit (aka The Waco Pit) is probably one of the most popular places near Waco to dig for fossils. Texas Cretaceous Fossils : Bivalves - Clams Texas Cretaceous Fossils : Bivalves - Clams Share Followers 2 Album created by JamieLynn 88 1 0 Texas Cretaceous Fossils : Bivalves - Clams A selection of bivalves from Cretaceous Formations of Texas : Glen Rose, Walnut, Comanche Peak, Georgetown, Del Rio and Austin Chalk. (2020.). A roughfile clam from the Flower Garden Bank National Marine Sanctuaryjust one of many different bivalve mollusk species. Pink line indicates the sampling transect." Bivalves are members of the phylum Mollusca, which also includes cephalopods (squids, octopuses, nautiloids, and ammonoids), gastropods (snails, slugs, and nudibranchs), scaphopods (tusk shells), polyplacophorans (chitons), the extinct rostroconchs, and three minor groups, the monoplacophorans, Caudofoveata, and Solenogastres (the latter two are generally collectively called aplacophorans). "Cockle Jumping" by Fritz Rivera (YouTube). Protobranch gills are typically rather small and simple, and used primarily for respiration. Autobranch gills are usually used for suspension feeding in addition to respiration. The Journal emphasizes specimen-based research and features high quality illustrations. This item is part of a JSTOR Collection. Transportation provided in the form of a 12 to 15 passenger van. 0000031359 00000 n References and Further Reading Image above: A fossil scallop (Pectinidae) from the Eocene Ocala Limestone of Florida. They include clams,oysters,cockles,mussels,scallops, and numerous other familiesthat live in saltwater, as well as a number of families that live in freshwater. Bivalvia. Description: This beautifully formed and permineralized Spirifer fossil is 2 wide X 1 3/8 deep. Scanning electron photomicrograph of the prodissoconch of the modern bivalve Nuculana acuta. 2023 Texas A&M University. Left: Dissected Mercenaria mercenaria, with the siphon held out in life position; photograph by Warren D. Allmon. But people who appreciate the beauty and design of a multitude of things in the universe are not fools if they attribute them to the true Creator. Erika Locke, Nature Lover & Geology Professor Del Mar College, Corpus Christi, Texas. A small inland sea covered what is now Waco, Texas during the Late Cretaceous era. You can help Wikipedia by expanding it. Photograph (left) and drawing (right) of a blue mussel (Mytilus edulis) secured to a rock by its byssal fibers. Two new bivalve species are named, Panopea anacachoensis new species and Spondylus siccus new species, and two potentially new gastropod species are identified but not named herein due to inadequate material. 47. The mantle is comprised of two or three layers or folds. This paleontological site article is a stub. The valves are not equal in width. There are many types of bivalve fossils in Texas. We guarantee the authenticity of all of our, 2.4" Fossil Hadrosaur Caudal Vertebra w/ Metal Stand - Texas, Devil's Toenail Fossil Oyster (Gryphaea) - Medium Size, Devil's Toenail Fossil Oyster (Gryphaea) - Large Size, 7.5" Cluster of Fossil Clams With Fluorescent Calcite - Ruck's Pit, FL, Bargain, 2.4" Fossil Oreodont (Leptauchenia) Skull - Unprepared, Two Cretaceous Fossil Oysters (Rastellum) - Madagascar. Evolutionary History of Bivalves - 4. Interpretation: These brachiopods are usually found in the lowest fossil-bearing sediments, indicating that these animals lived at the bottom of the oceans. Since Goniobasis is found in numerous sedimentary layers of the rock record, that indicates that there was a lot of mixing of the habitat of these snails during the global Flood. The banks along the lake are teeming with them. Various arrangements of hinge teeth have been named (see images below). If you havent been to Waco or the surrounding area, then I highly suggest you go ahead and put it towards the top of your Places-To-Visit list. Are there areas near Waco that are good for digging fossils? The top panel shows the carbon isotopes accumulated in the shell of theTridacnaclam. Description: A mass assemblage of Turritella gastropods from France displayed at the Wyoming Dinosaur Center. The left and right valves of aMercenaria shell may be determined by holding the shell with the umbo pointing away from you and the ventral shell margin (i.e., most recent area of shell growth) pointing downward. Always respect private property! Matrix failed the acid test and so is not limestone. Shell description Most bivalve fossils from central Texas are like these. Again, we see a bivalve that was fossilized with both valves tightly closed, indicating rapid burial while the clam was still alive an evidence for the worldwide Flood. p61-107. The foot primarily functions as a burrowing organ in infaunal species. For comments on the text we thank Chris McRoberts. Bivalves Showing 1-28 of 56 results 1 2 Small Jurassic Coast Fossil Oyster, Frome Clay (Actual as seen) Sale! The total number of taxa identified from these two sources far ex- All taxonomic groups are treated, including invertebrates, microfossils, plants, and vertebrates. Left image source: "Pallbo" (Wikimedia Commons; public domain). This study focuses on the molluscan paleontology of the middle Campanian interval in the eastern part of the Anacacho exposure belt in Medina County, Texas. In some cases the fossil clams are so identical to living clams that they have been assigned the same genus names and are called living fossils by the experts because they are thought to have lived millions of years apart. This increase in diversity, based on a small amount of new work, suggests that many more taxa are yet to be identified, particularly in the western part of the exposure belt in Uvalde and Kinney Counties. This paper documents the bivalve and gastropod fauna, discussing and illustrating 24 bivalve taxa and 11 gastropod species. Description: The fossilized Lopha oyster is 3 end-to-end X 1 1/2 maximum thickness. 0000010552 00000 n In the rock record it can be found throughout many levels comprising the secular Geologic Column yet is an index fossil for specific sedimentary layers thought by evolutionists to be millions of years old. Since North Texas and Central Texas are both predominantly Cretaceous Era and consequently share many of the same fossil species, I am only posting images of fossils I have specifically found in North Texas. Right image source: "shellnut" (Wikimedia Commons; Creative Commons Attribution-Share Alike 3.0 Unported license), Creative Commons Attribution-Share Alike 3.0 Unported license, Creative Commons Attribution 4.0 International license, Creative Commons Attribution 2.0 Generic license. Difference between a bivalve mollusk (left two diagrams), in which the plane of symmetry (blue line) is usually between the valves and corresponds with the commissure, and a brachiopod (right two diagrams) in which the plane of symmetry is usually across the valves. That is not how scallop shells are found today on the ocean beaches. Five growth rings are visible. All bivalves live in or very close to the water, and have lamellar gills for respiration (which are also used for feeding in many species). 0000026292 00000 n In: The Digital Encyclopedia of Ancient Life. There is significant folding and faulting seen in the Boquillas Formation (Figures 3 and 4). Oysters, Clams, Scallops,and other mollusks are all considered bivalves. Geological Society of America (GSA). For years most rock shops have identified this conglomerate of snail fossils encased in a cryptocystalline variety of quartz as Turritella Agate. The reason is that the snails looks very much like the marine fossil Turritella shown above. The Society also publishes, on an irregular basis, Even the smaller creeks in the area are a great source for fossils. Video shows a cockle using its foot to escape a sea star predator. The modern hard-shelled clam (also known as the quahog or cherrystone),Mercenaria mercenaria (family Veneridae), is used here as an example of a typical bivalve. These adaptations serve as lures to attract real fish, which are hosts for the bivalve's parasitic larvae. (PRI 70109) by Digital Atlas of Ancient Life on Sketchfab. 0000010678 00000 n Abundant bivalve fossils are found in the formation east of Big Bend National Park. The valves are also damaged on the ends that open. Large specimen is 1 1/4 diameter X 2 long. Bivalve Fossils (clams, oysters, mussels, scallops) for sale. Bulk bivalve fossils// Exogyra, Texigryphaea, Oyster, Clam fossils// Devil's toenail fossils NatureEnframed (244) $8.99 $9.99 (10% off) FREE shipping Original Shell Material Exogyra Ponderosa Cretaceous Oyster Fossil Central Texas Hill Country Gulf Coast Plain Bi-Valve Austin RelicsAntiques (1,761) $29.99 "Natural Fish Lure | Lampsilis Mussel and Bass" by Michael Backus (YouTube). Bivalve Cardium congestum. Magnified view shows annual growth patterns (one year spanned by black arrow); the dark bands identified by white arrows represent the periods of slowest growth, in this case, summer. Just pay close attention to the exposed gravel beds and embankments. The author has noticed that many of the fossil clams from the rock record have different genus names from extant clams that look very similar. / Cretaceous fossil gallery / Cretaceous bivalves gallery. The gut or digestive system in bivalves runs from mouth to anus, including labial palps surrounding the mouth for initial particle sorting. These sites that have been known to be decent producers of various types of fossils for rockhounds. Exposures in Hays County, Texas have yielded fossil remains of Pterodactyloidea, Ornithocheiroidea and Ornithocheiridae. During the early Cretaceous an inland sea called The Western interior Seaway covered what is now the center of North America. Many species of animals have lost body parts during the course of their evolution. Photographs by Jonathan R. Hendricks. The complete fossils consist of two articulated valves: a larger gnarly-shaped shell (the "toenail") and a smaller, flattened shell, the "lid". 0000037408 00000 n Marine snails collected by Taff in 1892. The shell looks to have had 20 to 25 whorls prior to being buried when Liracassis was alive. Just North of the town of Gatesville along CR215 you will find multiple cutouts in the road that expose the chalky layers that contain fossils. From Wikipedia: Bivalvia, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a classof marine and freshwater mollusksthat have laterally compressed bodies enclosed by a shell consisting of two hinged parts. Habitat(s):marine (salt water), freshwater (lakes, rivers, and streams). Growth lines parallel to the shell margins mark increments of growth of the shell, similar to tree rings. Interactive 3D model of a fossil specimen of the bivalve Mercenaria mercenaria from the Quaternary of St. Mary's County, Maryland (PRI 76728), with external shell features annotated. The total thickness is about 100 feet (30m). Ernst Tinaja is a narrow slot canyon in the eastern part of Big Bend National Park. Right image from Cooke et al. When the rudist became a fossil, all the hollow spaces were filled with sediment, creating a cast of the original animal. However, in Gods grace the post-Flood earth still had many beautiful things that we can enjoy today including this wonderful Spirifer brachiopod that sparkles in the light. Description: The Gryphaea fossil pelecypod is 1 1/4 long X 1 1/16 wide X 11/16 thick. 0000002075 00000 n The periostracum provides protection against abrasion, and/or camouflage by attached sponges, algae, and other epibionts. Upper and Lower Glen Rose Formation . Looking for the perfect addition to your crystal collection? Trigonia costata ranges from the Lower Jurassic ( Toarcian) to Middle Jurassic ( Callovian ). It can also function as an escape organ for some epifaunal forms (e.g., cockles, Cardium spp., family Cardiidae).