Leptostyrax was a genus of prehistoric sand tiger shark measuring an impressive 20 feet long which lived in the oceans around North America, Europe, Africa, and Australia during the Cretaceous Period approximately 125-75 million years ago.
Leptostyrax has a long history of paleontological study, and it has gone through numerous name-changes over the years. Its fossilized teeth were first officially named and described in 1875 based upon specimens recovered from Kansas, USA. However, these teeth were not exclusive to North America. In fact, this shark appears to have had a worldwide distribution during the middle Cretaceous, similar to sand tigers today. This has led paleontologists to ascribe different names to these teeth depending on what region they were found in, and it was only in the 1980s that it was understood that these teeth all belonged to the same animal.
In 1875, the famous American paleontologist Edward D. Cope coined the name Lamna macrorhiza to refer to four fossilized shark teeth found within Ellis County, Kansas and two others from Rooks County, Kansas. These teeth were dated to the “Niobrara epoch” (Cope 1875, page 297; plate XLII), now known as the Niobrara Formation, which dates to approximately 87-82 MYA. During this time, the whole central third of North America was covered by the Western Interior Sea, and was home to numerous famous marine creatures such as the giant sea turtle Archelon and the 40 foot long mosasaur Tylosaurus. These shark teeth are similar in appearance to those belonging to the modern-day Sand Tiger Shark (Carcharias taurus), being tricuspid in form, with a large central cusp which possesses a wavy S-shaped curve in sideways view and a smaller pointy cusp on either side at the base, and possessing a strongly bi-forked root.
Sand Tiger Shark (Carcharias taurus). Photo by D. Ross Robertson of the Smithsonian Institution (November 11, 2016). Public domain image, Wikimedia Commons.
https://commons.wikimedia.org/wiki/File:Carcharias_taurus_SI.jpg.
In 1889, the British paleontologist Arthur S. Woodward noted that several fossil shark teeth which were in the collections of the British Museum of Natural History bore a resemblance to those ascribed to Lamna macrorhiza. These included thirteen teeth which had been uncovered from Albian-aged deposits in Folkestone, Kent, England and another five specimens which had been acquired in 1888 from Cenomanian-aged deposits in Saratov, Russia. All of these specimens were ascribed the name Lamna macrorhiza (Woodward 1889, pages 399-400). In 1894, Woodward wrote a follow-up article on Cretaceous shark teeth found within Britain, stating that numerous teeth belonging to Lamna macrorhiza have been found within England (Woodward 1894, page 198). Later, more tooth specimens were uncovered from late Albian strata by the town of Speeton in northeastern England (Underwood and Mitchell 1999, pages 37-38).
In 1900, the American paleontologist Samuel W. Williston ascribed the name Leptostyrax bicuspidatus to teeth found within the Cretaceous-aged Mentor Beds (named in 1895 by F. W. Cragin after the village of Mentor, Saline County, Kansas), located 4.5 miles southwest of Marquette, Kansas (Jones 1897, pages 111-112; Williston 1900, pages 28, 42; plate VI). The name Leptostyrax means “thin spike” in ancient Greek (λεπτός, leptos = “thin”; στύραξ, styrax = “spike”). The teeth were similar to those of sand tigers except they were bicuspid rather than tricuspid, with one large central point and a single smaller point located on only one side.
Multiple teeth belonging to this animal have been found within Kiowa Shale of Kansas, which is dated to the later part of the Albian Stage of the middle Cretaceous Period (Scott 1970, pages 9-12; Schultze et al 1982, page 10; Frederickson et al 2015: e0127162). Additionally, teeth belonging to Leptostyrax have been found within Glen Rose Formation of northern Texas (early Albian Stage, 113-108 MYA) (Barck 1992, pages 3-24), late Albian strata in Texas (Cappetta and Case 1999, pages 5, 24), and also possibly within the Turonian-aged Eagle Ford Group near Dallas, Texas (Schultze et al 1982, page 9). It has been noted that the marine ecosystems within both Kansas and Texas during the middle of the Cretaceous Period were similar (St. John 1887, pages 132-152; Cobban and Reeside Jr. 1952, pages 1,011-1,044). Fossilized shells belonging to the prehistoric oyster Inoceramus comancheanus are found within the middle part of the Kiowa Shale and the lower part of the Duck Creek Formation of Texas, indicating that those strata are of the same age. Both of these strata have been dated to the later part of the Albian Stage of the middle Cretaceous Period, approximately 105 MYA (Scott 1970, pages 9-12; Frederickson et al 2015: e0127162).
In 1902, the French paleontologist Maurice Leriche wrote of finding teeth belonging to Lamna macrorhiza within Cenomanian-aged deposits near the town of Bavay, France (located near the France-Belgium border), and also within “Senonian-aged” (an outdated term which encompasses the final third of the Cretaceous Period, including the Coniacian, Santonian, Campanian, and Maastrichtian Stages; Oxford Reference “Senonian”) strata within the departments of Aisne and Somme in the Picardy region of northern France. However, Leriche gave all of these teeth a new name – Odontaspis macrorhiza (Leriche 1902, pages 109-110) – in reference to their similarity to those of sand tiger sharks. There are three extant species of sand tigers: two of which are included under the genus Odontaspis, and one under the genus Carcharias. Leriche’s report is the first recorded acknowledgment in the scientific literature that these teeth belong to this type of shark. In 1906, Leriche wrote a follow-up article on fish fossils found within northern France, and again stated that Odontaspis macrorhiza was found within Cenomanian and “Senonian” strata. Within the latter stage, the fossils were recovered specifically within those strata which also contained fossils of the belemnite Actinocamax quadratus (a.k.a. Gonioteuthis quadrata) and Belemnitella mucronata (Leriche 1906, page 348). Both of these species date to the middle of the Campanian Stage, approximately 80-75 MYA (Cobban and Scott 1964, page 6; Christensen 1998, pages 97, 99, 102). In 1927, Leriche mentioned that fossilized teeth belonging to Odontaspis macrorhiza (formerly classified as a separate species, O. rochebrunei) were found within clay deposits dated to the later part of the Cenomanian Stage near the city of Charente in west-central France, as well as from Santonian-aged deposits in Lonzée, Namur Province, Belgium and Turonian deposits in Autreppe, Hainaut Province, Belgium (Leriche 1927, pages 239-240). Fossil shark teeth belonging to this species have also been recovered from the cliffs near the port-town of Le Havre in Normandy (Maury 1960, pages 32-37), near the town of Gargas within the Provence region of southeastern France (Cappetta 1975, pages 122-123), and within lower and middle Albian strata near the town of Saint-Dizier within the upper Marne River Valley (Biddle 1993, pages 208-209).
In 1935, a report was published on fossilized shark teeth which were found within chalk deposits in Lithuania dated to the latter half of the Cretaceous Period. Odontaspis macrorhiza was one of the species identified (Dalinkevicius 1935, pages 243-305). A single partial tooth ascribed to Leptostyrax (species unknown) was found at Ullstorp, Sweden, which was believed to date to the Santonian Stage of the late Cretaceous (Siverson 1992, pages 525, 532-533, 535). Teeth belonging to this animal have also been found in the region of Kaniv, Ukraine within strata dated to the Aptian, Albian, Cenomanian, and Turonian Stages of the Cretaceous (Popova et al 2015, page 12).
In 1977, Odontaspis macrorhiza was re-named to the genus Plicatolamna. The following year, it was re-named once again to Megarhizodon. In 1982, it was re-named yet again to Leptostyrax macrorhiza, using the genus name which had been given by Sam Williston in 1900 and the species name given by Edward D. Cope in 1875 (Schultze et al 1982, pages 9-10). This assessment was confirmed in 1993 (Biddle 1993, pages 208-209), and has stuck since then. However, considering the numerous taxonomic name-changes which have occurred, I wouldn’t be a bit surprised if this animal was re-named yet again in the future.
So far, fossils of this animal have been confined to the prehistoric northern region of Laurasia. However, fossil teeth belonging to Leptostyrax macrorhiza have been found in southern Tunisia (Contessi 2013, pages 23, 26, 33, 36), in Egypt (Slaughter and Thurmond 1974, pages 25-40), and in Angola (Antunes and Cappetta 2002, pages 85-146), all of which would have formed part of the prehistoric southern region of Gondwana. This indicates that Leptostyrax had a worldwide range. Additionally, fossil teeth have also been found in the lower part of the Gearle Siltstone of the Southern Carnarvon Basin of western Australia, which dates to the mid-to-late Albian Stage (Siverson 1997, pages 453-465). All of this shows that Leptostyrax had a worldwide distribution, similar to how sand tigers are found today in coastal waters around the world.
Up to now, all we have discussed are fossilized teeth. However, body fossils are also known…perhaps. Three vertebrae belonging to a lamniform shark (collection ID code: OMNH 68860) were found within the upper part of the Duck Creek Formation within Tarrant County, Texas, a few miles northwest of the city of Fort Worth. The Duck Creek Formation is divided into four sub-units based upon the presence of distinctive species of invertebrates. These are, arranged from lowest/oldest to highest/newest: the Desmoceras zone, the Schloenbachia zone, the Scaphites zone, and the Kingeria zone. The rocks in which the vertebrae were found in belong to the Scaphites zone, and therefore date to the later part of the Albian Stage of the middle Cretaceous Period approximately 105 MYA. Although the exact identity of these vertebrae is uncertain, a 2015 report proposed that they could belong to Leptostyrax (Frederickson et al 2015: e0127162). By comparing the size of the vertebrae found in northern Texas to those belonging to a modern-day sand tiger, it has been suggested that Leptostyrax grew to be 6.3-6.6 meters (20.6-21.6 feet) long and that the individual which the vertebrae belonged to was 18 years old when it died (Frederickson et al 2015: e0127162; Frederickson et al 2016, pages 272-277). The size of this animal is comparable with a modern-day Great White Shark.
In 2010, another species, Leptostyrax stychi (named after Mr. Tobias Stych who found the fossils) was named based upon teeth found in Sarstedt, Germany (located about 20 km southeast of the city of Hannover) within rocks dated to the early Barremian Stage of the early Cretaceous Period, approximately 128-125 MYA. This species pre-dates L. macrorhiza by a substantial timespan (Schmitz et al 2010, pages 283, 285-287), and consequently indicates that there might be another intermediate species of Leptostyrax which hasn’t been discovered yet. These teeth, too, were similar in appearance to the teeth of the modern-day Sand Tiger Shark (Carcharias taurus).
Map of where fossils of Leptostyrax (L. macrorhiza, L. stychi, and L. sp.) have been found. Map derived from “World Map Blank – with blue sea” (public domain image, Wikimedia Commons).
https://en.wikipedia.org/wiki/File:World_Map_Blank_-_with_blue_sea.svg.
Leptostyrax was stated in the past to be a close relative of Cretoxyrhina, commonly known as the Ginsu Shark, which lived in the Western Interior Sea during the late Cretaceous Period (Barck 1992, pages 3-24). However, Leptostyrax has subsequently been placed within the family Eoptolamnidae along with the genera Eoptolamna and Protolamna due to their similarity in tooth shape (Kriwet et al 2008, pages 278-290; Schmitz et al 2010, page 287).
As big as Leptostyrax was, it might not have been the biggest shark in its ecosystem. In 1997, the Japanese paleontologist Kenshu Shimada described a single large incomplete vertebral centrum which was recovered from the Kiowa Shale of Kansas (collection ID code: KUVP 16343). This partial vertebra was declared to belong to a species of lamniform shark, and it was claimed that the animal it belonged to measured 8.3-9.8 meters (27-32 feet) long. However, because this vertebra is incomplete, and since there were no other associated remains, this size estimate needs to be taken with a great amount of caution as it could be exaggerated. It’s possible that this vertebra fossil is another specimen of either Leptostyrax, but this cannot be certain (Shimada 1997, pages 522-524; Frederickson et al 2015: e0127162).
Below is an illustration of what Leptostyrax might have looked like, based upon the modern-day Sand Tiger Shark. This drawing was made with No.2, No.3, and colored pencils on printer paper.
Leptostyrax. © Jason R. Abdale (December 13, 2023).
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