Austin Chalk stratigraphic column in Texas

The Glen Rose Formation is a shallow marine to shoreline

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

from the lower Cretaceous period exposed over a large area from South Central to North Central Texas. The formation is most widely known for the dinosaur footprints and trackways found in the

Dinosaur Valley State Park Dinosaur Valley State Park is a state park near Glen Rose, Texas, United States. History Dinosaur Valley State Park, located just northwest of Glen Rose in Somervell County, Texas, is a scenic park set astride the Paluxy River. The land f ...

near the town of Glen Rose, Texas, southwest of

Fort Worth Fort Worth is the fifth-largest city in the U.S. state of Texas and the 13th-largest city in the United States. It is the county seat of Tarrant County, covering nearly into four other counties: Denton, Johnson, Parker, and Wise. Accord ...

and at other localities in Central Texas.

Geology

The Glen Rose is the uppermost, thickest and most extensively exposed formation of the Trinity Group, a series of shallow-water marine formations deposited on a southeastward flank of the

Llano Uplift The Llano Uplift is a geologically ancient, low geologic dome that is about in diameter and located mostly in Llano, Mason, San Saba, Gillespie, and Blanco counties, Texas. It consists of an island-like exposure of Precambrian igneous and m ...

, through a number of sea regressions and transgressions. Wells drilled in eastern

Travis County Travis County is located in south central Texas. As of the 2020 census, the population was 1,290,188. It is the fifth-most populous county in Texas. Its county seat is Austin, the capital of Texas. The county was established in 1840 and is n ...

have encountered over 1,000 feet of the Glen Rose. In the northern part, the Glen Rose is laterally continuous with the Paluxy Formation. The Glen Rose overlies the Hensel Sand and is overlain in turn by formations of the Fredericksburg division. In 1974, Keith Young concluded, based on ammonite zonation, that the formation ranges from late Upper

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ag ...

into the Lower

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0 ...

, about 115-105 million years old. The formation consists mostly of hard limestone strata alternating with marl or marly limestone, but is replaced by sandy facies shoreward (to the northwest). Because of the differing strengths of the layers, the limestone weathers to form a staircase profile on hills. Individual steps that form this distinctive stair-step topography extend for many miles without any apparent change in expression. These strata were originally referred to as the "Alternating Beds", which term included the overlying Fredericksburg formations. The Glen Rose has been divided into upper and lower portions, separated by a one-foot layer of

Corbula ''Corbula'' is a genus of very small saltwater clams, marine bivalve molluscs in the family Corbulidae, the basket clams.Gofas, S. (2010). Corbula Bruguière, 1797. In: Bouchet, P.; Gofas, S.; Rosenberg, G. (2010) World Marine Mollusca database. ...

shells, a small bivalve. The formation was named in 1891 for the town of Glen Rose, Texas, by paleontologist

Robert T. Hill Robert Thomas Hill (August 11, 1858 – July 20, 1941) was a significant figure in the development of American geology during the late 19th and early 20th centuries. As a pioneer Texas geologist, Hill discovered and named the Comanche series of t ...

.Marion I. Whitney & Lewis B. Kellum, ''Echinoids of the Glen Rose Limestone of Texas,'' Mich. Acad. of Science, Arts & Letters,'' Vol. LI, p. 241 (1966). The type locality is a near shore section exposed in the Paluxy River near the town of Glen Rose. The stratigraphy of the formation was most recently revised in a 1971 study. A stratigraphic column at the Mount Bonnell location starts with the

Lower Cretaceous Lower may refer to: * Lower (surname) * Lower Township, New Jersey *Lower Receiver (firearms) * Lower Wick Gloucestershire, England See also *Nizhny Nizhny (russian: Ни́жний; masculine), Nizhnyaya (; feminine), or Nizhneye (russian: Н� ...

Trinity Group overlain by the Edwards Group.

Upper Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

formations follow, starting with the

Del Rio Clay The Del Rio Clay is a geologic formation in Texas. It preserves fossils dating back to the Cretaceous period. A stratigraphic column at the Mount Bonnell location starts with the Lower Cretaceous Trinity Group overlain by the Edwards Group a ...

Buda Limestone The Buda Limestone is a geological formation in the High Plains and Trans-Pecos regions of West Texas and in southern New Mexico, whose strata date back to the Late Cretaceous. Pterosaur remains are among the fossils that have been recovered ...

, and then the

Eagle Ford Group The Eagle Ford Group (also called the Eagle Ford Shale) is a sedimentary rock formation deposited during the Cenomanian and Turonian ages of the Late Cretaceous over much of the modern-day state of Texas. The Eagle Ford is predominantly c ...

. Formations within the Trinity Group include the Hammett Formation, Cow Creek Formation,

Hensel Formation The Hensel Formation or Hensel Sand is a Mesozoic geologic formation in Texas. Fossil ornithopod tracks have been reported from the formation.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607. A stratigraphic column at the Mount Bo ...

, and Lower and Upper Glen Rose Formation. The Hammett and the lower portion of the Upper Glen Rose act as confining units (or

aquitard An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characte ...

) for the Middle Trinity

Aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characte ...

. The Upper Glen Rose contains the Upper Trinity Aquifer, which appears to have inter-aquifer

groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit ...

flow with the

Edwards Aquifer The Edwards Aquifer is one of the most prolific artesian aquifers in the world. Located on the eastern edge of the Edwards Plateau in the U.S. state of Texas, it is the source of drinking water for two million people, and is the primary water s ...

as water levels are at the same elevation.

Caves and caverns

There are a number of

caves A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...

in the Glen Rose, some of which are open to the public, including

Cascade Caverns Cascade Caverns is a historically, geologically, and biologically important limestone solutional cave south of Boerne, Texas, United States, on 226 Cascade Caverns Road, in Kendall County, Texas, Kendall County. It has been commercially operated ...

and Cave Without a Name, both in

Kendall County, Texas Kendall County is a county located on the Edwards Plateau in the U.S. state of Texas. In 2020 United States Census, 2020 census, its population was 44,279. Its county seat is Boerne, Texas, Boerne. The county is named for George Wilkins Kendall ...

and

Natural Bridge Caverns The Natural Bridge Caverns are the largest known commercial caverns in the U.S. state of Texas. The name is derived from the 60 ft natural limestone slab bridge that spans the amphitheater setting of the cavern's entrance. The span was left ...

Comal County, Texas Comal County ( ) is a county located on the Edwards Plateau in the U.S. state of Texas. As of the 2020 census, its population was 161,501. Comal County is known for its rich German-Texan and European history. Its county seat is New Braunfels ...

, the lower parts of which are in the Glen Rose.

Fossil content

A variety of fossils are found in the Glen Rose, more abundantly in the lower Glen Rose than the upper, including numerous

gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. The ...

clams Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two she ...

and echinoids. Many species in the lower portion are not found in the upper portion.

Dinosaur tracks A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

have been found in many localities, as well as isolated vertebrate remains. Microfossils also are present, including one of the largest

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

ever found. *

Bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

. A variety of fossil bivalves have been found, usually preserved as internal molds, with the exception of oysters, scallops and

rudists Rudists are a group of extinct box-, tube- or ring-shaped marine heterodont bivalves belonging to the order Hippuritida that arose during the Late Jurassic and became so diverse during the Cretaceous that they were major reef-building organis ...

, which have their shells present although mineralized. Some of the clams are large and round and have been given the popular name "heart clams." Fossil bivalves include a number of rudists which form reefs in the lower Glen Rose. *

Gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. The ...

. Numerous gastropods are found in the Glen Rose, preserved as internal molds, the shells having dissolved away. Typical is ''Tylostoma'', illustrated below. *

Coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and se ...

s. Corals formed reefs in the lower Glen Rose and a number of species of such corals have been described. * Echinoids. A number of regular and irregular echinoids or "sea urchins" have been described from the Glen Rose. ''Salenia texana'' Credner and ''Heteraster obliquatus'' (Clark), illustrated below, are representative. * Crabs. Over 10 species of decapod crustaceans or "crabs" have been described from the Glen Rose, the remains consisting of isolated claws and

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...

s. *

Ammonites Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefis ...

. A number of ammonites have been reported from the Glen Rose, although they are rare. *

Foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

. A variety of fossil foraminifera occur in the Glen Rose, including ''Orbitolina texana'' (Roemer), a giant (for forams) shell over a centimeter in diameter. *

Vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...

. :Dinosaur footprints and trackways occur in a number of localities in the Glen Rose. See discussion below. Fossil remains of vertebrates, however, are rare and include the following isolated finds: :* '' Acrocanthosaurus'', an allosauroid theropod dinosaur (a few isolated bones). :* '' Pachycheilosuchus'', a mesoeucrocodylian or extinct crocodyle-like reptile. :* An indeterminate titanosauriform.Weishampel, D. B., Barrett, P. M., Coria, R. A., Le Loeuff, J., Xing, X., Xijin, Z., Sahni, A., Gomani, E. M. P., and Noto, C. (2004). "Dinosaur Distribution". in Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.). ''The Dinosauria'' (2nd ed.). Berkeley: University of California Press. p. 555. . :* '' Tenontosaurus'', an iguanodontid dinosaur :* '' Sauroposeidon'', a

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', ' lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their ...

dinosaur :* '' Radiodactylus'', an azhdarchoid

pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 ...

''An Azhdarchid Pterosaur Humerus from the Lower Cretaceous Glen Rose Formation of Texas'', Author(s): Phillip A. Murry, Dale A. Winkler and Louis L. Jacobs, Reviewed work(s): Source: Journal of Paleontology, Vol. 65, No. 1 (Jan., 1991), pp. 167-170 *

Plants Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...

Algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

. ''Porocystis globularis'' is the name given to a dimpled grape-shaped object common in the Glen Rose. Scientists have disagreed over its classification, but now believe it to be an algal fruiting body. :*

Cycads Cycads are seed plants that typically have a stout and woody ( ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male or ...

. Cycads have been found in the Glen Rose, primarily in the Paluxy Sands, and it has been stated that " e Trinity beds must be ranked as one of the five great cycad-yielding terraces of North America..."

Gallery of typical Glen Rose fossils

Image:Heteraster.jpg, ''Heteraster obliquatus'' (Clark), an irregular sea urchin Image:Salenia texana.jpg, ''Salenia texana'' Credner, a regular sea urchin Image:Tylostoma.jpg, ''Tylostoma'' sp., a gastropod Image:Arctica.jpg, ''Arctica gibbosa'' (Giebel), a "heart clam" (bivalve) Image:Porocystis.jpg, ''Porocystis globularis'' (Giebel), an algal fruiting body File:Orbitolina texana.jpg, ''Orbitolina texana'' (Roemer), a one-celled foramanifera

Dinosaur footprints and trackways

Dinosaur footprints and trackways are found in at least 50 localities in the Glen Rose, primarily at the top of the Upper Glen Rose and a smaller number at the top of the Lower Glen Rose. The most famous of these sites is the Paluxy River site in

near the town of Glen Rose, Texas, southwest of Fort Worth. In 1938, Roland T. Bird, assistant to

Barnum Brown Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. Named after the circus showman P. T. Barnum, he discovered the first documented remains of '' Tyrannosaurus'' during a career ...

of the

American Museum of Natural History The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 int ...

("AMNH") in New York, New York, discovered a dozen

and four

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

or carnosaur trackways all following the same general direction. Lockley, p. 186. These were the first sauropod footprints scientifically documented, and were designated a

National Natural Landmark The National Natural Landmarks (NNL) Program recognizes and encourages the conservation of outstanding examples of the natural history of the United States. It is the only national natural areas program that identifies and recognizes the best ...

in 1969. Some are as large as about 3 feet (1 m) across. The prints are thought to have been preserved originally in a tidal flat or a

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into '' coastal lagoons'' (or ''barrier lagoons ...

. Lockley, p. 191. Large slabs of the trackways were excavated and are on display at the AMNH and the Texas Memorial Museum in Austin, Texas, among other institutions. The sauropod tracks, now given the

ichnogenus An ichnotaxon (plural ichnotaxa) is "a taxon based on the fossilized work of an organism", i.e. the non-human equivalent of an artifact. ''Ichnotaxa'' comes from the Greek ίχνος, ''ichnos'' meaning ''track'' and ταξις, ''taxis'' meaning ...

name ''Brontopodus'', were made by an animal of 30 to 50 feet in length, perhaps a brachiosaurid such as ''

Pleurocoelus ''Astrodon'' (aster: star, odon: tooth) is a genus of large herbivorous sauropod dinosaur, measuring in length, in height and in body mass. It lived in what is now the eastern United States during the Early Cretaceous period, and fossils have ...

'', and the theropod tracks by an animal of 20 to 30 feet in length, perhaps an '' Acrocanthosaurus''. A variety of scenarios was proposed to explain the tracks. Some believed that they recorded a herd of sauropods, including young animals protected by their parents, being followed by a group of theropods and argued that the apparent disappearance of one of the sauropod trackways indicated a fatal attack by the theropods. Scientists today generally discount this explanation.

Martin Lockley Martin G. Lockley (born 1950) is a Welsh palaeontologist. He was educated in the United Kingdom where he obtained degrees (BSc and PhD) and post-doctoral experience in Geology in the 1970s. Since 1980 he has been a professor at the University ...

(1995) concludes that the tracks most likely represent twelve sauropods "probably as a herd, followed somewhat later by three theropods that may or may not have been stalking -- but that certainly were not attacking." Lockley notes that there are other similar group trackways and that the evidence sauropods moved in herds "in general, seems good." He takes issue, however, with Robert Bakker's theory that the Davenport Ranch trackway (another Glen Rose trackway) reflects large adults on the outside, protecting younger sauropods in the center, stating that the trackways merely show smaller animals following the larger ones. The fact that some of the Glen Rose trackways primarily include marks of the fore feet led Bird and others to suggest that the sauropods were semi-aquatic and made the tracks when partially swimming, a scenario that "has become deeply entrenched in the popular literature..." Lockley, p. 190. Again, Lockley discounts that theory, stating that the tracks were not well preserved or studied and that the view of sauropods as swimming "can not be supported using any convincing line of available evidence." Claims that human footprints have been found in the Glen Rose is discussed in the

article.

References

{{Reflist, 2

Bibliography

* Martin Lockley & Adrian P. Hunt, ''Dinosaur Tracks and Other Fossil Footprints of the Western United States,'' Columbia U. Press, New York (1995). *J. S. Nagle, ''Glen Rose Cycles and Facies, Paluxy River Valley, Somervell County, Texas.'' Texas Bureau of Economic Geology Geological Circular No. 68-1. 25 pp. (1968). *J. S. Nagle, ''Stepping Stair Hills.'' Texas Parks & Wildlife, vol. XXVI, No. 6, pp. 16-19. (June 1968). * E.H. Sellards, W.A. Adkins & F.B. Plummer, ''The Geology of Texas'', Univ. of Texas Bull. No. 3232 (1932 and many later reprints). * F. L. Stricklin, Jr., C. I. Smith, F.E. Lozo, ''Stratigraphy of Lower Cretaceous Trinity Deposits of Central Texas,' Bureau of Economic Geology, Univ. of Texas, Report of Investigations No. 71 (July 1971). *Marion Whitney, ''Some New Pelecypoda from the Glen Rose Formation of Texas,'' J. Paleontology, Vol. 26, p. 697 (Sept. 1952). * Keith Young, ''Lower Albian and Aptian (Cretaceous) Ammonites of Texas,'' Geoscience and Man, Vol. VIII (1974).

External links

Dinosaur Valley State Park
official site

from

talk.origins talk.origins (often capitalised to Talk.Origins or abbreviated as t.o.) is a moderated Usenet discussion forum concerning the origins of life, and evolution. It remains a major venue for debate in the creation–evolution controversy, and its of ...

Cretaceous geology of Texas Lower Cretaceous Series of North America Limestone formations of the United States Ichnofossiliferous formations Fossil trackways in the United States Paleontology in Texas Geography of Somervell County, Texas