Paleontology Research » Petalodus

Petalodus is by far the most interesting genus of vertebrate fossils found in Parks Township, Pennsylvania. These fossil “sharks” had jaws full of cutting serrated teeth, but are not “sharks” as we know them today. Sharks belong to the same class, Chondrichthyes, which is defined as “fishes having a cartilaginous skeleton.”

Their bodies did not preserve well because their skeletons are made of cartilage. Despite the large number of dental specimens found in the class, the genus is known only from its teeth. No fossilized body or jaw remains of the genus have been discovered worldwide. All current reconstructions of the creature are based on the body remains of sibling genera in its class, Chondrichthyes.

More about Petalodus ohioensis here

Kingdom	Animalia
Phylum	Chordata
Class	Chondrichthyes
Order	†Petalodontiformes
Family	†Petalodontidae
Genus	†Petalodus

Specimens from Parks Township

In 2019, I recovered four different teeth from the local limestone layer. A year later, I found ten more specimens, one from Pine Creek Limestone. All are the species Petalodus ohioensis, the default designation for the genus in North America.

Catalog ID	Specimen Name	Crown Height	Crown Width
CG-0015	Petalodus I	6mm	23mm
CG-0016	Petalodus II	9.5mm	24mm*
CG-0029	Petalodus III	8mm	28mm*
CG-0027	Petalodus IV	10.5mm	**
CG-0034	Petalodus V	14mm	27mm*
CG-0038	Petalodus VI	5.5mm***	**
CG-0045	Petalodus VII	10mm	25mm
CG-0047	Petalodus VIII	13mm	31mm
CG-0048	Petalodus IX	****	**
CG-0055	Petalodus X	11mm†	28mm
CG-0058	Petalodus XI	8mm†	27mm
CG-0070	Petalodus XII	****	**
CG-0087	Petalodus XIII	9mm	23mm
CG-0102	Petalodus XIV	Coming Soon	Coming Soon
CG-0107	Petalodus XV	Coming Soon	Coming Soon

Petalodus Tooth Anatomy

Below are three views of a Petalodus Tooth. Shown here are lingual, lateral, and labial views. The lingual view shows the tooth side facing inward toward the tongue. The labial view shows the side facing the outside of the mouth. The crown is convex, facing outward from the mouth.

The teeth of this genus are homodont, meaning that all teeth have the same morphology. Teeth toward the back appear flatter at the cutting edge, while those toward the front are taller. The side profile is sigmoid, or, more simply, S-shaped.

Named Petalodus Species

The online Paleobiological database lists sixteen (16) named species (2021). However, more than 30 exist (Harper 2018). Most species were named in the 1800s, but only a few, one or two (Harper 2018), were named in the 1900s.

Genus	Species	Year Described
Petalodus	acuminatus	1836 (Agassiz)
Petalodus	allegheniensis	1856 (Leidy)
Petalodus	arcuatus	1870 (St. John)
Petalodus	curtus	1870 (Newberry and Worthen)
Petalodus	davisii	1889 (Woodward)
Petalodus	flabellula	1889 (Woodward)
Petalodus	grandis	1883 (Davis)
Petalodus	hastingsiae	1840 (Owen)
Petalodus	hybridus	1875 (St. John and Worthen)
Petalodus	jewetti	1957 (Miller)
Petalodus	knappi	1879 (Newberry)
Petalodus	linearis	1838 (Agassiz)
Petalodus	linguifer	1866 (Newberry and Worthen)
Petalodus	ohioensis	1853 (Safford)
Petalodus	proximus	1875 (St. John and Worthen)
Petalodus	sagittatus	1843 (Agassiz)

Why so many different species?

One of the most challenging aspects of Petalodus is determining how newly named species relate to different parts of the animal’s mouth morphology. When researchers first found single specimens, the differences between them could be striking. There are two typical arrangements. One has a high crown, and the other has a lower, flat crown. These differences justified the creation of many new species. Several new species were also designated based on geological and geographical differences.

The two teeth on Plate 1 above greatly differ in crown height and appearance. In the late 1800s, morphometric differences were common enough to warrant the naming of two distinct species.

Petalodus Holotype Photographs

I am currently collecting holotype photographs. A type of a species is a specimen. A type of a genus is a species. The most prominent of several type variations is the holotype. Beyond holotypes, other designations exist. In searching for holotypes of Petalodus, these situations arise and need to be addressed.

Type Designation Descriptions

Holotype	The representative specimen in which to define the species. Typically these are the specimen in which the species was first defined.
Paratype	When the holotype is defined alongside other specimens in the same description, these specimens are Paratypes.
Allotype	Used to designate a specimen of the opposite sex of the holotype specimen. This specimen is from the group of paratypes. Also used if the specimen shows features not visible on the holotype.
Neotype	If the Holotype is lost or destroyed or not specified in the original description of a species, then a neotype specimen may be selected.
Syntype	One of many specimens originally described when a holotype isn’t selected. Typically it is best practice to later define a best-in-class specimen, which is called the Lectotype.
Lectotype	A specimen that is selected to serve as the single type specimen from a set of Syntypes.
Paralectotype	Once a Lectotype is defined, the remaining syntypes are re-designated as paralectotypes.
Hapantotype	When the type species specimen is two or more that represent different stages of life. A juvenile and adult for instance of a related specimen.
Iconotype	If a new species is designed from an illustration of a specimen, then the illustration is the iconotype. This does not appear to be in use in paleontology.

Petalodus allegheniensis

Described by Leidy in 1856, P. allegheniensis is often described as a junior synonym to P. ohioensis. Hay questioned the validity of P. ohioensis in writing as a senior synonym in 1895, but later in 1902, he listed it as such. As mentioned below, Hay later sent a high-quality cast of P. ohioensis to the Field Museum in Chicago, likely having examined it and made the determination.

This specimen was collected at the head of inclined plane No. 3 of the old Portage Railroad, in Blair County, Pennsylvania. This locality correlates with the Brush Creek limestone, which is located within the Glenshaw Formation. Digging the inclines that would carry railroad cars over the mountains in what is now known as the Allegheny Portage Railroad National Historic Site, exposed many layers of rock. While excavating space for the inclined plane No. 3, an engineer stumbled upon this specimen. It now resides as specimen ANSP 14541 at the Academy of Natural Sciences of Drexel University, in Philadelphia, PA, USA.

Original Description for P. allegheniensis

This species of Petalodus is established upon the specimen of a tooth, which Mr. Timothy Conrad borrowed from the cabinet of Charles A. Poulson, Esq., for mv inspection. It was presented to the latter gentleman by Townsend Ward, Esq., who, in a note, observes, it was given to him ” by the engineer of the stationary engine at the head of inclined plane number 3 of the old portage railroad,” which crossed the Alleghany [sic] Mountains from Hollidaysburg, in Blair County, Pennsylvania. Mr. Ward further states, “it was obtained from a stratum about one foot thick, black, carboniferous, and calcareous, which was exposed by the excavation for the buildings to accommodate the stationary engine.”

Joseph Leidy, 1856

Petalodus ohioensis

In July 2020, I learned of a much better cast discovered by Wayne Itano and Kenneth Carpenter through correspondence with the Field Museum of Chicago. Specimen FMNH PF 673. This specimen is a set of three casts. One is labial, one is lingual, and one is of the whole. They are much higher resolution than the ones at Yale. O.P. Hay had sent them to the museum in 1896. William Simpson, the Vertebrate Collections Manager, provided the researchers with photographs.

J. M. Safford, the original describer of Petalodus ohioensis, continued to work as a professor until 1900. He likely sent these casts to Hay in 1895. Hay described P. securinger in 1895 and likely requested the specimen for comparison.

Petalodus acuminatus

Louis Agassiz, a Swiss geologist and biologist, originally described this species in 1836. The holotype is specimen MHNN-FOS 171, currently in the Muséum d’histoire naturelle de Neuchâtel, Switzerland. SM E 4291 is listed as a holotype and identified as P. acuminatus; however, it is the holotype of P. rhombus. Eventually, P. rhombus was synonymized with P. acuminatus.

The specimen appears to be slightly more than half of a full tooth. The center of the crown consists of a piece of enamel that is adhered to the matrix. The holotype shows a cutting-edge impression.

Petalodus rhombus

P. rhombus is a legacy species that has been replaced by P. acuminatus. The holotype of P. rhombus is specimen SM E 4291 housed in the Sedgwick Museum of Earth Sciences at the University of Cambridge. As part of the BG3D Type Fossils project, the specimen photo is the best I’ll likely get. It was later designated as a junior synonym of P. acuminatus. McCoy originally described this specimen as Petalodus rhombus in 1848, a new species.

Petalodus curtus

First described in 1870 from a specimen in Illinois. The original plate illustration from his description is shown below. I am still searching for the holotype of this species, which is likely what is illustrated below.

TEETH of moderate size, thin and light in crown and root; crown broadly arched, twice as wide as high, concavo-convex laterally and vertically ; superior margin serrated or roughened by the termini of the calcigerous tubes ; anterior face of crown without imbricating enamel folds, half as high as posterior face; posterior face elliptical in outline, basal enamel folds 5-6, broad and strong ; root relatively short and thin, on posterior face two-thirds the height of the crown, in breadth two-thirds that of the crown, sides nearly straight, bottom arched and somewhat three-lobed, strongly beveled off so as to form a blunt edge on the anterior and longer side.

In general aspect this tooth resembles most P. linguifer, N. and W., from the Chester limestone, but it is thinner, and has a much shorter root, of which the lower edge is characteristically beveled. There is no other species for which it is likely to be mistaken.

Formation and locality : Keokuk limestone; Otter creek, Jersey county, Illinois.

J. S. Newberry, A.H. Worthen, Geological Survey of Illinois, Vol 4 Geology and Paleontology, Section 1 Descriptions of Vertebrates, 1870.

Petalodus grandis

The tooth this species was described from was said to be 2.5 inches across. I believe an inch from Dublin in 1883 is probably the same as an inch in the United States today. Davis named it a new species based on its large size.

The described specimen was assigned an identification number, and I am currently trying to obtain current photographs of the specimen.

Petalodus hastingsii

Sir Philip Egerton provided the tooth described by Sir Richard Owen in 1840. Owen later described the tooth as having a thin layer of dense enamel and a smooth, shining surface. The holotype does exist, along with a neotype. They are NHMUK PV P613 (Holotype) and NHMUK PV P75414 in the Natural History Museum, London. We don’t currently have photos, so for now the illustrations will do.

One important point is that the illustration is mirrored from the actual specimen. The specimen consists of only 30-40% of the original crown.

Petalodus hybridus

Described in 1875 by St. John and Worthen, this specimen came from Sir William Cornelius Van Horne’s collection. Van Horne served as president of the Canadian Railroad Company and was later knighted. The specimen was originally considered to be P. linguifer, and P. curtus. The authors state that the tooth may be an intermediate evolutionary form stuck between the two species. Under this assumption, and given its uniqueness, it should be named a new species. The fossil collection of Sir William was eventually transferred to the University of Chicago. We are still searching for the specimens.

Petalodus jewetti

The holotype of this species comes from the University of Kansas Biodiversity Institute, Division of Vertebrate Paleontology. This specimen was first described by Halsey W. Miller (Jr.) in 1957. The specimen catalog ID is KUVP 6672. It appears to have been glued back together in several places. The photos, as described in the original, appear to show the same silhouette.

John Mark Jewett originally found the described specimen in October 1956. It was the first Petalodus tooth ever recorded as found in the Pennsylvanian rocks of Kansas. It was found in what was called the Plattsmouth limestone, Oread formation, Virgilian, upper Pennsylvanian, in a quarry in northwestern Franklin County, Kansas. The anterior crown face height measured 25 mm, and the width was 40 mm. The posterior crown face height is 35mm.

Halsey W. Miller’s Arguments

Miller argued that the tooth’s morphometric distinctions and its occurrence in a geographically separate area from other species warranted naming a new species. Miller was aware that teeth from different parts of the jaw could indeed be different but held that it would be for certain until someone found a Petalodus jaw with embedded teeth.

A. J. Robb III (2003) considers P. jewetti a junior synonym of P. ohioensis, but he cited the same precautions Miller did. Miller also noted that many species in the genus have been erroneously given unique species names for the same reasons as Robb, but he still named this a new species based on a combination of morphology and geography.

Petalodus linearis

Of all the teeth I have researched and examined via photographs, this species highly likely does not belong to the genus Petalodus. Louis Agassiz observed that these teeth were very long, specifically six times as long as they were wide. The collection included a mix of teeth, originally described and illustrated by Agassiz as Psammodus linearis. One syntype is a rounded-top specimen that lacks the classic spade shape of Petalodus teeth. The rest are present as very long teeth. The illustration is shown below.

The longest of these teeth are six times longer than wide;

Louis Agassiz

Petalodus linguifer

The type specimen, X-521, comes from the Prairie Research Institute Center for Paleontology at the University of Illinois. There are two other specimens, VPF-199 and VPF-201, at the Museum of Comparative Zoology at Harvard University. The first illustrated specimen below was described as a perfect specimen from Pope County.

Petalodus proximus

In 1875, this was described alongside P. hybridus. This tooth was compared to P. allegheniensis; however, its uniqueness also designated it as a new species. Dr. Leidy also apparently provided two original specimens of P. allegheniensis to compare this specimen with. So the duo had more to go on than simply illustrations. The following is part of their description.

These fragments exhibit a uniformity of characters which has led provisionally to their recognition as a distinct form. From Petalodus Alleghaniensis, Leidy, with which they are associated, they are distinguished by the regularly arched crest, the comparatively horizontal direction of the basal border of the concave face, relatively low convex face, and apparently short, broadly rounded base, which is produced downward in nearly the same vertical plane as the convex crown-face, comparatively slight antero-posterior diameter, and about two-thirds the lateral diameter of the crown.

St. John and Worthen, 1875 Geological Survey of Illinois, Vol 6, Geology and Paleontology

Petalodus sagittatus

Originally grouped with the genus Chomatodus, Agassiz wrote in his Recherhes sur les poissons fossiles 1833-1843 (Research of the fossil fish) that his Chomatodus acuminatus is now part of a new genus Petalodus from M. Owen. He said it now belongs to another family, other than that of Cestraciontes, because of its sharp teeth. Agassiz then listed species of the new genus, Petalodus. Agassiz named the following species: Hastingsiae (now corrected as Hastingsii), psittacinus, laevissimus, rectus, radicans, marginalis, and sagittatus.

Frederick McCoy illustrated this species in a book in 1855, based on a specimen in the Geological Museum of the University of Cambridge.

Digital References

The following are website references for information used in this article.

• Fossils of Parks Township – Catalog – Petalodus
• Fossilworks – Taxon Page
• YPM 2861 Collections Page – Yale Peabody Museum of Natural History
• Google Books – The annals and magazine of natural history, zoology, botany and geology: incorporating the journal of botany, Volume 2, Taylor & Francis, 1848
• GB3D Type Fossils – SM E 4291 – Fossil specimen : SM E 4291 – Holotype

References

• Agassiz, L. 1838. Recherches Sur Les Poissons Fossiles. Tome III (livr. 11). Imprimérie de Petitpierre, Neuchatel 73-14
• Bruner, J.C., 1992, A catalogue of type specimens of fossil fishes in the Field Museum of Natural History: Fieldiana Geology, v. 23, pp. 1–54.
• Harper, J.A., 2018, Reflections on Petalodus, a Common Late Paleozoic “Shark”1 Tooth Found in Western Pennsylvania’s Rocks, Pennsylvania Geology V. 48 No 2, pp. 3-11
• Hay, O.P., 1895, Description of a new species of Petalodus (P. Securiger) from the Carboniferous of Illinois, The Journal of Geology, pp. 561-564
• Hay, O.P. 1902 Bibliography and catalogue of the fossil Vertebrata of North America. U.S. Geological Survey, Bulletin 179, 868 p.
• Itano, W., Carpenter, K, 2020, High-quality Casts of the Missing Holotype of Petalodus ohioensis Safford 1853 (Chondrichthyes, Petalodontidae) at the Field Museum of Natural History and their Bearing on the Validity and Priority of the Species, Geology of the Intermountain West, V. 7, pp. 197-203
• Itano, W., 2020, “Petalous Ohioensis, the Most Common Shark Tooth Found at McCoy, Colorado, and the Search for Its Lost Holotype: Part 1: History of Petalodus Ohioensis from Its Discovery to the Early Twentieth Century.” Trilobite Tales 38, no. 2, pp. 22–26.
• Knowles, V., 2010, William C. Van Horne: Railway Titan, p 25
• Leidy, J. 1856. Descriptions of some remains of fishes from the Carboniferous and Devonian formations of the United States. Journal of the Academy of Natural Science of Philadelphia, 2nd Series, 3, p. 159-165.
• Miller, H. W., Jr., 1957, Transactions of the Kansas Academy of Science, Vol. 60, No. 1, Petalodus jewetti, a New Species of Fossil Bradyodont Fish From Kansas, pp. 82-85
• Owen, R., 1840, Odontography; or, A treatise on the comparative anatomy of the teeth
• Robb, A. J., III, 2003, Notes on the occurrence of some petalodont shark fossils from the Upper Pennsylvanian rocks of northeastern Kansas: Transactions of the Kansas Academy of Science, v. 106, no. 1/2, pp. 71–80, https://doi.org/10.1660/0022-8443(2003)106[0071:NOTOOS]2.0.CO;2
• Safford, J.M., 1853, Tooth of Getalodus [sic] ohioensis, American Journal of Science and Arts, V. 16, No. 46, p. 142.
• Sedgwick, A., McCoy, F, 1850-1855, A synopsis of the classification of the British Palæozoic rocks; With a systematic description of the British Palæozoic fossils in the Geological museum of the University of Cambridge.
• Woodward, A.S., 1889, Catalogue of the Fossil Fishes in the British Museum (Natural History) Part 1, pp. 1-613
• Worthen, A.H., Newbery, J.S., 1866, Geological Survey of Illinois, Vol 2, Paleontology.
• Zangerl, R., Winter, H.F., Hansen, M.C., 1993, Comparative microscopic dental anatomy in the Petalodontida (Chondrichthyes, Elasmobranchii), pp. 16-23