Lepisosteus occidentalis – the Western Gar

Introduction

The Hell Creek Formation of the western United States is understandably known for its dinosaur fossils, including Tyrannosaurus and Triceratops. However, in terms of sheer physical numbers, there are other species found here which surpass them by far. One of these is a prehistoric fish – a gar called Lepisosteus occidentalis, “the Western Gar”. Hundreds of fossils of this freshwater fish have been found in the Hell Creek Formation and in other geological formations elsewhere within western North America. Although the Western Gar is extinct, the gar genus Lepisosteus is still around today, divided into four extant species, and all of them are native exclusively to North America.

Discovery

During the 1850s, as the United States expanded westward, a few fossilized fish scales were collected by a certain F. V. Hayden near the Judith River in what was then the Territory of Nebraska. These fossil scales were sent back east to be examined by Joseph Leidy of the Philadelphia Academy of Natural Sciences, who was regarded as the greatest anatomist and biologist of his time. Professor Leidy believed that the fossils belonged to the fish genus Lepidotes, since this fish was known to have thick scales covered with enamel, and these scales which had been found in Nebraska looked very similar. In 1856, he officially named this particular species Lepidotes occidentalis (1).

However, over twenty years later in 1877, Edward D. Cope of the Philadelphia Academy of Natural Sciences re-examined these fossil fish scales, and he realized that they actually belonged to a prehistoric gar. In a way, it was an easy mistake to make. Lepidotes and its relatives such as Semionotus were close relatives of gars, despite not looking like them. Like gars, they had rows of interlocking thick diamond-shaped scales. The genus Lepisosteus, meaning “boney scales” in reference to the thick scales which covered the body, had been established in 1803 to refer to modern-day gars. Since this fossil animal was evidently a gar itself, Cope reclassified it as Lepisosteus occidentalis, “the Western Gar”. The holotype consists of the original five scales which were found in Nebraska, and they are held in the collections of the Academy of Natural Sciences of Drexel University (formerly known as the Philadelphia Academy of Natural Sciences) (2).

Description

Traditionally, any fossil gar material which has been found within western North America dating to the end of the Cretaceous Period has been ascribed to the Western Gar, including fossils from the Hell Creek Formation, the Judith River Formation, and the Lance Formation. However in 1976, Edward Wiley proposed that these fossils did not belong to the genus Lepisosteus, but instead belonged to Atractosteus, which is the genus of the modern-day Alligator Gar (Atractosteus spatula). However, Wiley is very much in the minority, as most sources which I have looked at still classify it as a species of Lepisosteus (3).

While the Hell Creek Formation is occasionally divided into “early” and “late” stages, with different species inhabiting different sections, the gar Lepisosteus occidentalis is found throughout the entire rock series of the Hell Creek Formation. Not only was Lepisosteus occidentalis found within all of the rock layers of the Hell Creek Formation, but it was evidently extremely common as well. According to a survey of Hell Creek fossils within North and South Dakota which was conducted in 2002, 938 specimens have been assigned to this species, which is a remarkable number indeed, and accounts for 9.23% of all fossils found within the formation. Over one-third of all Hell Creek Formation localities within the Dakotas contained gar fossils (4).

The geological range of this species is from the Judithian to the Torrejonian Stages of the late Cretaceous Period and into the Tertiary Period, from approximately 85-60 million years ago. This makes the Western Gar one of the few species which are confirmed to have survived the mass extinction at the end of the Mesozoic Era (5).

Below is an illustration of what the Western Gar (Lepisosteus occidentalis) would have looked like, based upon how modern-day Lepisosteous species appear. The drawing was made with No.2 pencil and colored pencils.

Western Gar (Lepisosteus occidentalis). © Jason R. Abdale (March 2, 2022)

Source citations

  1. Bryant, Laurie J. (1989). “Non-Dinosaurian lower vertebrates across the Cretaceous–Tertiary boundary in northeast Montana”. University of California Publications in Geological Sciences, volume 134 (October 1989). Page 23.
  2. Bryant, Laurie J. (1989). “Non-Dinosaurian lower vertebrates across the Cretaceous–Tertiary boundary in northeast Montana”. University of California Publications in Geological Sciences, volume 134 (October 1989). Page 23.
  3. Bryant, Laurie J. (1989). “Non-Dinosaurian lower vertebrates across the Cretaceous–Tertiary boundary in northeast Montana”. University of California Publications in Geological Sciences, volume 134 (October 1989). Pages 23-24; Pearson, Dean A.; Schaefer, Terry; Johnson, Kirk R.; Nichols, Douglas J.; Hunter, John P. (2002). “Vertebrate biostratigraphy of the Hell Creek Formation in southwestern North Dakota and northwestern South Dakota”. Geological Society of America, Special Paper 361 (2002). Page 154.
  4. Pearson, Dean A.; Schaefer, Terry; Johnson, Kirk R.; Nichols, Douglas J.; Hunter, John P. (2002). “Vertebrate biostratigraphy of the Hell Creek Formation in southwestern North Dakota and northwestern South Dakota”. Geological Society of America, Special Paper 361 (2002). Pages 156, 158; Seattle Community Network. “Cretaceous ‘Hell Creek Faunal Facies’; Late Maastrichtian”, by Phillip Bigelow (November 3, 1997; last revised July 20, 2010). http://www.scn.org/~bh162/hellcreek2.html. Accessed on January 11, 2014.
  5. Bryant, Laurie J. (1989). “Non-Dinosaurian lower vertebrates across the Cretaceous–Tertiary boundary in northeast Montana”. University of California Publications in Geological Sciences, volume 134 (October 1989). Page 23.; Fossilworks. “Lepisosteus occidentalis Leidy 1856 (gar)”. http://www.fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=63033. Accessed on March 2, 2022.

Bibliography

Bryant, Laurie J. (1989). “Non-Dinosaurian lower vertebrates across the Cretaceous–Tertiary boundary in northeast Montana”. University of California Publications in Geological Sciences, volume 134 (October 1989). Pages 1-107.
https://books.google.com/books/about/Non_dinosaurian_Lower_Vertebrates_Across.html?id=YgpMDwkS6yIC.

Pearson, Dean A.; Schaefer, Terry; Johnson, Kirk R.; Nichols, Douglas J.; Hunter, John P. (2002). “Vertebrate biostratigraphy of the Hell Creek Formation in southwestern North Dakota and northwestern South Dakota”. Geological Society of America, Special Paper 361 (2002). Pages 145-167.
https://www.researchgate.net/profile/John-Hunter-10/publication/236153389_Vertebrate_biostratigraphy_of_the_Hell_Creek_Formation_in_southwestern_North_Dakota/links/00b4951672208f03d4000000/Vertebrate-biostratigraphy-of-the-Hell-Creek-Formation-in-southwestern-North-Dakota.pdf.

Seattle Community Network. “Cretaceous ‘Hell Creek Faunal Facies’; Late Maastrichtian”, by Phillip Bigelow (November 3, 1997; last revised July 20, 2010). http://www.scn.org/~bh162/hellcreek2.html. Accessed on January 11, 2014. NOTE: This website is no longer active.

Fossilworks. “Lepisosteus occidentalis Leidy 1856 (gar)”. http://www.fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=63033. Accessed on March 2, 2022.



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