Fossils of Howard County, Texas: Triassic Gems

By J. R. Tamsitt, Ph.D.

Koskinodon (Buettneria) perfectus, a pre-historic denizen of Howard County, Texas.

  

From 1939 through 1942 efforts by governmental project

workers (WPA) provided a wealth of fossil materials from

many localities in Texas, and one of the most complete

collections of about 11,000 specimens of vertebrates was from

the Chinle (Dockum) formation of the Late Triassic in Howard

County. Remains were deposited in floodplains, ponds, lakes,

and rivers confined to a large basin that received sand, silt and

clay sediments from adjacent highlands (Fig. 1). Most quarries

were located on the ranch of Mrs. Sarah Mina Hyman and

daughters, Mrs. Otis Chalk and Mrs. Dora Roberts, 3 miles

north of Otis Chalk, Texas (Fig.2, 3).

      Although paleobotanical specimens have not been reported

from the Otis Chalk quarries, of invertebrates unionid bivalves

(freshwater molluscs) were abundant (Elder, 1987). A small

crustacean of unknown affinity was found in a coprolite (fossil

feces) (Murry, 1986).

       Vertebrate fossil collections from the Otis Chalk area were

initially made by E. C. Case of the University of Michigan in

1927 and by J. W. Stovall for the University of Oklahoma in

1931 (Gregory, 1972). Elder (1978) described the paleontology

and processes of fossilization in these quarries. Several hundred

acres of eroded land provided a rich source for these fossils,

which are from the Otischalkian (Carnian) land vertebrate

faunachron (Desojo and Heckert, 2004). The collection includes

fish, a small shark, small dinosaurs, dinosaur- and crocodile-

like reptiles, and amphibians (Fig.4) (Lucas et al., 1993;

Lehman and Chatterjee, 2005; Murry, 1986, 1989; Wilson,

1948). An important fish site not far from the reptile quarries

was excavated by Bob Schaeffer of the American Museum of

Natural History, New York, in 1954 and 1962. Many of these

fossils are discussed here, and a list from Lucas et al. (1993) is

 given in Appendix I.

      Fish faunas include both freshwater sharks and bony fish,

including lung fish and a lobe-finned fish or coelocanth

(reviewed by Huber et al., 1993; Schaeffer, 1967). Hybodontoid

(“humped tooth”) sharks (Lonchiodion humblei) were small,

reaching a length of about 6 inches (15.2 cm), and inhabited

freshwater. Lungfish (Arganodus) were 3 feet (1 m) in length

and weighed to 70 pounds (32 kg). Their comb-shaped teeth

were used as crushing plates for clams. They were probably

similar to modern lungfish and lived in underwater burrows

during dry periods until monsoons occurred. The lobe finned

fish was not determined but likely similar to the related species

from New Mexico, Chinlea sp. (Fig. 5). Among fossilized fish

was the carnivorous Turseodus, which fed on invertebrates and

other fish. Also present was the omnivore Ceratodus, which fed

on aquatic plants, worms, other invertebrates, and fish. Several

"ganoid" fishes (with armor-like scales consisting of bony

plates covered with layers of dentine and enamel) —

Lasalichthys, Cionichthys, and Synorichthys — were found in

Howard County (Gregory, 1972; Murry, 1986). Few articulated

or complete fish specimens have been found (Milner et al.,

2006), although Schaeffer (1967) described several articulated

specimens, including the type specimen of the ganoid fish

Cionichthys greeni (complete skull).

      More than a dozen skulls and much of the remainder of the

skeleton of a new species of an amphibian swamp predator

were unearthed by H. J. Sawin from the Otis Chalk site.

Buettneria howardensis was described by Sawin (1944) and is

considered to be a synonym of Koskinonodon perfectus. About 2

meters long, K. perfectus was an impressive amphibian (Fig. 6).

It possessed sharp, conical teeth and most likely fed on fish and

other small aquatic life. Upward facing eye sockets (Fig. 7)

suggest that Koskinonodon was an ambush predator, waiting in

the soft mud at the bottom of ponds and attacking prey

suddenly from below. Koskinonodon represents one of the last

of the labyrinthodont amphibians, which were common

worldwide during the late Paleozoic Era but became extinct at

the end of the Triassic Period. A much smaller amphibian,

Latiscopus disjunctus, with a high, narrow cranium, was

described by Wilson (1948) and is known only from Howard

County.

      Fossils discovered in Howard County and New Mexico

document for the first time that dinosaurs and their non-

dinosaur ancestors lived side by side for tens of millions of

years. Chindesaurus bryansmalli (Fig. 8) was a small, bipedal

carnivore about 3 m (10’) long and weighed 200 pounds (91 kg).

Described in 1995 by Long and Murry, a fragment of a thigh

bone (femur) was found in Howard County. Examples of Late

Triassic reptiles from Howard County are Coahomasuchus

kahleorum, Longosuchus meadi, Lucasuchus hunti, unspecified

species of the semi-aquartic Phytosauridae, and Archosauria

indet. (See complete list of fossils from the Otis Chalk quarries

in the Paleobiology Database; Lucas et al., 1993).

Coahomasuchus, Lucasuchus, and Longosuchus (Fig. 9) are

similar genera in the Family Stagonolepididae. They were

heavily armored, small to medium-sized herbivores. The head

was small relative to the large body, and distinctive in shape,

flat and blunt at the front, like the snout of a pig. Chisel-shaped

teeth were small and leaf-like. Longosuchus was found in the

Dockum Group and Coahomasuchus in the Colorado City

Formation in Howard County, north of the abandoned town of

Otis Chalk.

       Among fossils recovered from the Otis Chalk quarries were

remains of Trilophosaurus buettneri (Fig. 10), described by Case

(1928) as a new species. This reptile was a herbivore and to 2.5

meters long. It had a short, unusual, heavily-built skull,

equipped with massive, broad flattened cheek teeth with sharp

shearing surfaces for cutting up tough plant material. Teeth

were absent from the premaxilla and front of the lower jaw,

which in life were probably covered with a horny beak. Elder

(1978, 1987) noted the presence of abundant coprolites at the

Trilophosaurus quarry. Trilophosaurs are known only from the

Late Triassic of North America and Europe.

      Poposaurus gracilis (Fig. 11), represented by numerous

fossil remains in the Otis Chalk Quarries, belongs to an

unusualgroup of crocodile-like reptiles that includes sail-

backed, beaked, and aquatic carnivores. Fossils have been

found in Wyoming, Utah, Arizona, and Texas. Poposaurus was

an obligate biped, that is, it walked on two legs rather than

four, as in theropod dinosaurs. But as a pseudosuchian

(“false crocodile”), it is more closely related to living

crocodilians than to dinosaurs.

      After excavation of the Howard County quarries 50-60

years ago, a small portion of the specimens were prepared,

studied, and published, and an even smaller number were put

on display in museums around the country, including Texas

Memorial Museum in Austin, Texas. Most were stored in

jackets (Fig. 12) at The University of Texas Vertebrate

Paleontology Laboratory in north Austin (Airhart, 2011). Now

young paleontologists are opening and studying these jacketed

specimens as part of their research, and new discoveries will

undoubtedly result from this treasure trove of Triassic life.

I am grateful to Doyle Phillips for encouraging me to write these data for Howard County and to Dr. Timothy Rowe for critically reviewing the manuscript. – July 22, 2012, Austin, Texas.

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Fig.1. Map of the Permian Basin. Howard County is indicated by the letter “H.”

 

 

Fig. 2. Yahoo map of the Otis Chalk area [1] of Howard County, Texas.

 

 

Fig. 3. Google Earth relief map of the Otis Chalk (small yellow triangle) area of Howard County. Most cleared areas are sites of producing oil wells.

 

 

 

Fig. 4. Triassic mural, Dinosaur Hall, Smithsonian Institution, Washington, D. C.

 

Fig. 5. Artist’s rendition of the coelacanth Chinlea sp., Wickipedia.

 

Fig. 6. Artist's rendition of Koskinodon (Buettneria) perfectus and size comparison to a human, Wilipedia.

Fig. 7. Dorsal surface of cranium of Kiskinodon  (Buettneria) perfectus, American Museum of Natural History, New York.

 

Fig. 8. The small dinosaur Chindesaurus bryansmalli was a large predator for Triassic times (Finsley, 1999).

 

 

 

 

 

 

Fig. 9. Mounted specimen of Longosuchus meadi, Texas Memorial

Museum, Austin, and artist’s rendition (below).

 

Fig. 10. Mounted specimen of Trilophosaurus buettneri, Wikipedia.

 

Fig. 11. Artist rendition of Poposaurus, a crocodile-like predator, and size comparison to human, Wikipedia.

 

Fig. 12. WPA jackets stored at The University of Texas Vertebrate Paleontology Laboratory, Austin (Airhart, 2011).

 

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REFERENCES

Airhart, M. 2011. Jackson School of Geosciences, The University of Texas at Austin, News. Fossil time capsules: Unwrapping depression era fossil stashes yields new discoveries, February.

Case E. C. 1928. A cotylosaur from the Upper Triassic of western Texas. Journal of Washington Academy of Science 18:177-178.

Desojo, J.B., and A. B. Heckert. 2004. New information On the braincase and mandible of Coahomasuchus (Archosauria: Aetosauria) from the Otischalkian (Carnian) of Texas. Neues Jahrbuch für Ecologie und Palaontologie Monatscheft, pp. 605-616.

Elder, R. L. 1978. Paleontology and paleoecology of the Dockum Group, Upper Triassic, Howard County, Texas. M.S. thesis, University of Texas, Austin, Texas, 205 pp.

----------. 1987. Taphonomy and paleoecology of the Dockum Group, Howard County, Texas. Journal of the Arizona-Nevada Academy of Science, 22(1):85-94.

Finsley, C. E. 1999. Discover Texas dinosaurs. Gulf Publishing Co, Houston. x + 150 pp. Gregory, J. T. 1945. Osteology and relationships of Trilophosaurus. University of Texas Publication 4401: 273-359.

-----------. 1953. Typothorax and Desmatosuchus. Postilla, 16:1–27.

----------. 1972. Vertebrate faunas of the Dockum Group, Triassic, Eastern New Mexico and west Texas. New Mexico Geological Society, Guidebook of East-Central New Mexico. In Twenty-third Field Conference, September 1972, V. C. Kelley and F. D. Trauger, eds. Pp. 120-123.

  Heckert, A.B. 2004. Late Triassic microvertebrates from the lower Chinle Group (Otischalkan-Adaminian: Carnian), southwestern U.S.A. New Mexico Museum of Natural History and Science, Bulletin 2, 170 pp.

---------- and S. G. Lucas. 1999. A new aetosaur (Reptilia: Archosauria) from the Upper Triassic of Texas and the phylogeny of aetosaurs. Journal of Vertebrate Paleontology, 19:50–68.

---------- and ----------. 2000. Taxonomy, phylogeny, biostratigraphy, biochronology, paleobiogeography, and evolution of the Late Triassic Aetosauria (Archosauria: Crurotarsi). Zentralblatt für Geologie und Paläontologie, I (11–12):1539–1587.

----------, -----------, L. F. Rinehart , M. D. Celeskey, J. A. Spielmann, and A. P. Hunt. 2010. Articulated skeletons of the aetosaur Typothorax coccinarum Cope (Archosauria: Stagonolepididae) from the Upper Triassic Bull Canyon Formation (Revueltian: early-mid Norian), eastern New Mexico, USA. Journal of Vertebrate Paleontology, 30:619-642.

Huber, P., Lucas, S. G., and Hunt, A. P., 1993, Late Triassic fish assemblages of the North American Western Interior. Museum of Northern Arizona Bulletin, 59: 51-66.

Hunt, A. P., and S. G. Lucas. 1990. Re-evaluation of “Typothorax” meadei, a Late Triassic aetosaur from the United States. Paläontologische Zeitschrift, 64:317–328.

Jacobs, L. 1995. Lone Star dinosaurs. Texas A & M University Press, College Station. xi + 160 pp.

Lehman, T., and S. Chatterjee. 2005. Depositional setting and vertebrate biostratigraphy of the Triassic Dockum Group of Texas. J. Earth Syst. Sci., 114 (3): 325–351.

Long, R. A., and P. A. Murry. 1995. Late Triassic (Carnian and Norian) tetrapods from the Southwestern United States. New Mexico Museum of Natural History and Science Bulletin, 4: 1-254.

Lucas, S. G., A. P. Hunt and R. Kahle. 1993. Late Triassic Vertebrates from the Dockum Formation near Otis Chalk, Howard County, Texas. New Mexico Geological Society Guidebook, 44th Field Conference, Carlsbad Region, New Mexico and West Texas, pp. 237-244.

---------- and A. B. Heckert. 1996. Late Triassic aetosaur biochronology. Albertiana, 17:57–64. Milner, A. R. C., J. I. Kirkland and T. A. Birthisel. 2006. The geographic distribution and biostratigraphy of Late Triassic-Early Jurassic freshwater fish faunas of the southwestern United States. Pp. 522-529. In Harris et al., eds, The Triassic-Jurassic Terrestrial Transition. New Mexico Museum of Natural History and Science Bulletin 37.

Murry, P. A. 1986. Geology and paleontology of the Dockum Formation (Upper Triassic), West Texas and eastern New Mexico. Pp. 109-137. In K.Padian (ed.), The beginning of the age of dinosaurs; Faunal change across the Triassic-Jurassic boundary. Cambridge University Press, Cambridge, England.

----------. 1989. Geology and paleontology of the Dockum Formation (Upper Triassic), West Texas and eastern New Mexico, in Lucas, S. G., and Hunt, A. P., eds. Dawn of the Age of Dinosaurs in the American Southwest. New Mexico Museum of Natural History, p. 102-148.

----------. 1989a. Paleoecology and vertebrate faunal relationships of the Upper Triassic Dockum and Chinle Formations, southwestern United States. Pp. 375-400. In A.P. Hunt & S.G. Lucas (eds.) Dawn of the Age of Dinosaurs in the American Southwest , New Mexico Museum of Natural History.

----------. 1989b. Geology and paleontology of the Dockum Formation (Upper Triassic), West Texas and eastern New Mexico. Pp. 102-148. In A. P. Hunt & S. G. Lucas (eds.) Dawn of the Age of Dinosaurs in the American Southwest. New Mexico Museum of Natural History.

----------, J. A. Spielmann, A. B. Heckert, and A. P. Hunt. 2007. Topotypes of Typothorax coccinarum, a Late Triassic aetosaur from the American Southwest. New Mexico Museum of Natural History and Science Bulletin 41:241–247.

Paleobiology Database. Otis Chalk Quarry 1, SMU 122, TMM 31025 (Triassic of the United States).

----------. Otis Chalk Quarry 3, TMM 31100 (Triassic of the United States).

----------. Otis Chalk Quarry 3A (Triassic of the United States).

Parker, W. G., and J. W. Martz. 2010. Using positional homology in Aetosaur (Arachosauria: Pseudosuchia) osteoderms to evaluate the taxonomic status of Lucasuchus hunti. Journal of Vertebrate Paleontology, 30(4):1100–1108.

  Sawin, H. J. 1944. Amphibians from of the Dockum Triassic Howard County, Texas. Contributions to Geology, The University of Texas, 4401: 361-399.

----------. 1947. The pseudosuchian reptile Typothorax meadei. Journal of Paleontology, 21: 201–238.

Schaeffer, B. 1967. Late Triassic fishes from the western United States. Bulletin of the American Museum of Natural History, 135: 285-342.

Small, B. J. 1989. Aetosaurs from the Upper Triassic Dockum Formation, Post Quarry, West Texas. Pp. 301–308. In S. G. Lucas and A. P. Hunt (eds.), Dawn of the Age of Dinosaurs in the American Southwest. New Mexico Museum of Natural History, Albuquerque, New Mexico.

Spielmann, J. A., Lucas, S. G., Rinehart, L. F. and A. B. Heckert. 2008. The Late Triassic archosauromorph Trilophosaurus. New Mexico Museum of Natural History and Science Bulletin, 43: 1–177.

Wilson, J. A. (1948). "A small amphibian from the Triassic of Howard County, Texas". Journal of Paleontology 22: 359–361.

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Appendix I. Vertebrate Fauna from the Dockum Formation near Otis Chalk, Howard County, Texas (from Lucas et al., 1993).

Class Chondrichthyes
Lissodus sp.—One tooth.

Class Osteichthyes
Arganodus sp.—Toothplates of this lungfish.
Colobodontidae—Unidentified tooth plates cf. Turseodus sp.; corrugated scales.
Cionichthys greeni—Several partial skeletons.
Lasalichthys hillsi—One specimen.
Sinorichthys stewarti—Several partial skulls and isolated bones.

Class Amphibia
Latiscopus disjunctus—Is known only from a skull.
Buettneria perfecta—Several skulls and other bones. Apachesaurus sp.—Isolated intercentra.

Class Reptilia
Otischalkia elderae— Limb and upper jaw elements.
Trilophosaurus buettneria—More than two-thirds of the vertebrate fossils from the WPA quarries 1 and 2. Two sizes of individuals are present, and it is not certain whether the two morphs are ontogenetic members of the same species or represent distinct taxa.
Malerisaurus langstoni— a partial but poorly preserved skeleton.
Procolophonidae—Reported by Murry (1989).
"Primitive reptiles"—Jaw elements with rows of teeth. It is suspected that they are contaminants to the Otis Chalk fauna.
Poposaurus gracilis—All rauisuchian (Triassioc archosaurs) specimens from Otis Chalk probably pertain to this taxon.
Longosuchus meadei--One of the best-known aetosaurs from North America because of the abundant specimens from Otis Chalk.
New aetosaur genus—An articulated skeleton from Otis Chalk pertains to a new genus of aetosaurs , which is distinguished by its very wide dorsal paramedian scutes with radial ornamentation. This specimen exhibits a waisted carapace anterior to the pelvis and lacks raised bosses on the dorsal paramedian scutes.
Paleorhinus bransoni--at least five skulls.
Angistorhinus alticephalus—Represented by skulls and other bones.
Brachysuchus megalodon—Known from skulls, lower jaws, and other bones.