Megalolamna

Megalolamna; Temporal range: Late Oligocene to Middle Miocene ; ~24–15 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Fossil teeth from the Dos Bocas Formation, Ecuador
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Order:	Lamniformes
Family:	† Otodontidae
Genus:	† Megalolamna ; Shimada et al., 2016
Species:	†M. serotinus
Binomial name
	†Megalolamna serotinus; (Probst, 1879)
Synonyms
	List Otodus serotinusProbst, 1879; Lamna bassaniiAlessandri, 1897 ; Odontaspis taurus obliquaCaretto, 1972 ; Megalolamna paradoxodonShimada et al., 2016; ;

Last updated November 11, 2024

Megalolamna is an extinct genus of large mackerel shark that lived from the Late Oligocene to the Middle Miocene. Fossils belonging to this genus are known from the Americas, Europe and Japan, and have been documented in scientific literature since the late 19th century. However, it was in 2016 that the fossils were described as belonging to the same distinct taxon called Megalolamna paradoxodon. However, a 2024 study reveals that the taxon was already described indirectly in 1879 under the name Otodus serotinus, the only known species of this genus then being renamed as Megalolamna serotinus. It is part of the Otodontidae, a family known to include the megalodon, of which this latter was also a contemporary. Although having a maximum length estimated at 5.1 m (17 ft), a measurement similar to that of the current great white shark, Megalolamna would have only fed on medium-sized prey. The front teeth of Megalolamna would have had the function of seizing the prey, before cutting it using the lateral teeth located at the corner of the mouth. Fossils proves that the genus had a cosmopolitan distribution and show that it inhabited mainly in shallow environments from tropical to mid-latitude areas.

Research history

During the 20th and 21st centuries, several fossil shark teeth dating from the Lower Miocene were discovered in the Americas and Japan. In the scientific literature, these same teeth were classified in different genus or are noted as having indeterminate generic position, but all authors recognized them as coming from the order Lamniformes. It is on the basis of many unifying common points that the new genus and species Megalolamna paradoxodon is described by Kensu Shimada and his colleagues in 2016 from five isolated fossil teeth having been discovered in the United States, Japan and Peru. The genus name Megalolamna derives from the Ancient Greek word μεγάλος (megálos, "big"), in combination with Lamna , type genus of Lamniformes. The specific name parodoxodon comes from the Latin paradoxum, "paradox", and the Ancient Greek ὀδούς (odoús, "tooth"), and refers to what the authors describe as "its paradoxical appearance of teeth".^[2] Shimada explains in more detail the etymological meaning of this scientific name in a press release accompanying the publication of the official description of the animal. The genus name Megalolamna is named because of its phylogenetic proximity to other large-toothed sharks such as the megalodon, but its combination with Lamna was chosen because of the superficial resemblance of its teeth to those of the salmon shark. The specific epithet refers to his still unresolved great temporal gap with Otodus.^[3] The designated holotype of the genus consists of a complete tooth cataloged as UCMP 112146, having been discovered in Kern County, California.^[2]

Earlier the same year, Jorge D. Carrillo-Briceño and colleagues described a set of teeth that had been discovered in the Guajira Peninsula, northern Colombia. Among these fossils is an isolated tooth which the authors attribute to an undetermined genus of lamniform sharks. They also refer to this same indeterminate taxon of teeth discovered in Austria, Switzerland, Germany, Sardinia, Peru, the East Coast of the United States and Maryland, where they are noted as very abundant.^[4] In notes added to their study, Shimada and his colleagues attribute the Colombian tooth to the taxon then erected, and also suggest that it is likely that the teeth discovered in the previously mentioned localities would then expand the geographical record of this taxon, although they are skeptical about the abundance of Maryland fossils.^[2]

In 2024, Jürgen Pollerspöck and Shimada describe several additional specimens having been discovered in Europe, more precisely in Austria, France, Germany and Italy, while also attributing teeth having been discovered in South Carolina, Maryland, Colombia, Peru and Ecuador.^[a] The dating of most of the teeth found extends its era of distribution from the Late Oligocene to the Middle Miocene. The authors also discover that two teeth discovered in Germany and Italy have already received their respective specific epithets in two works published at the end of the 19th century.^[1] The German syntype tooth having been discovered in the east of Baltringen, in the state of Baden-Württemberg, was the first to be named, being originally described in 1879 by Josef Probst [ de ] under the name Otodus serotinus.^[7]^{: 155–156} The Italian tooth discovered in Montferrat, in Piedmont, is described in 1897 by Giulio de Alessandri under the name Lamna bassanii. In the description, Alessandri named the taxon in honor of Francesco Bassani, who made a great contribution to the knowledge of Italian paleontology and stratigraphy.^[8]^: 38–39 These two names were recognized as valid in works published after 1899 and those up to 2006, but no researchers have visibly looked into the potential synonymy between them. The specific epithet serotinus being older than bassanii and parodoxodon, Pollerspöck and Shimada then moved this name to the genus Megalolamna, the taxon then being renamed Megalolamna serotinus according to the ICZN's principle of priority. The two other specific epithets erected since are then put into synonymy.^[1]

Description

The morphology of Megalolamna being completely unknown with the exception of its teeth, the measurements of the latter are used by Shimada et al. (2016) with those of several other lamniform sharks in order to calculate an overall estimate of its length. An expanded range gives a size ranging from 3.7 to 19.5 m (12 to 64 ft) long. This range of estimates is nevertheless considered highly exaggerated given that it is based on the common thresher shark, a shark whose tail is as long as its own body and has comparatively smaller teeth. A second, smaller range gives between 3.7 to 7.2 m (12 to 24 ft), calculating an average length of 5.1 m (17 ft) for the largest known specimen,^[2] which is a similar size to a typical great white shark.^[3]

The teeth of Megalolamna have the basic features of a lamniform, but are mainly distinguished by the presence of a pointed main cusp sometimes inclined laterally, lateral cusplets (small enameled cusps that appear at the base of the tooth's main crown) about equal in size and pointing upwards, and with a strongly bilobed root. The cusps and cusplets are both triangular in shape, and their cutting edges are smooth and razor-shaped.^[2]^[1] The largest known tooth measures 4.5 cm (1.8 in) in height,^[2] while the smallest documented measures 8.2 mm (0.32 in).^[1] Although it is very uncertain whether Megalolamna had one or more rows of teeth in the jaws, its teeth show an almost continuous series of dentition ranging from tall, symmetrical teeth to short, sloping teeth, with no notable differences that would indicate their location in the upper or lower jaw. This dentition therefore indicates that the animal should have monognathic heterodonty,^[2] i.e. differently shaped mesial (the most forward) and distal (the furthest behind) teeth along the upper or lower jaws.^[9]

Megalolamna's dentition is similar to those of most other large lamniform sharks, and its diet is expected to be specialized, having primarily fed on bony fish. However, where large lamniforms have a grasping and ripping type dentition, the lateral teeth of Megalolamna exhibit a cutting function. Thus, the animal probably seized its prey with the front teeth, before cutting it with the lateral teeth located at the corners of the mouth to an acceptable proportion for ingestion. The estimated body length of the animal also indicates that it fed on medium-sized fish, ranging from 0.5 to 1 m (1 ft 8 in to 3 ft 3 in).^[2]

Classification

Megalolamna is part of the family Otodontidae, a lineage of lamniform sharks known to notably include the megalodon.^[2]^[3] The phylogenetic analysis of Shimada et al. (2016) recovers it as the sister taxon of the type genus Otodus. In order to avoid making the genus Otodus paraphyletic, the authors transferred all of the species formerly classified in the genus Carcharocles to this latter. They then discovered that the species of the genus Otodus form an anagenetic sequence which represent different chronospecies. A similar case is also present for Cretalamna , because, being generally seen as an ancestral taxon to Otodus, it is also seen as paraphyletic. The discovery of Megalolamna, wicch presents dental characteristics similar to theses two genera, however allows Cretalamna and Otodus to remain monophyletic. For classification purposes, they maintain Cretalamna as distinct, but separate it into two lineages representing species dating from the Cretaceous and Cenozoic. The authors note, however, that the fact that Megalolamna and Otodus are related is not without problems, because there is a gap in appearance of about 43 million years each. This phylogenetic positioning then requires more in-depth research on Paleogene sharks as well as in the synapomorphies definable in the different genera of otodontids.^[2] The cladogram below is based after the results of Shimada et al. (2016),^[2] with the change of the specific epithet following Pollerspöck & Shimada (2024).^[1]

Otodontidae

Kenolamna gunsoni

Cretalamna spp.

	Megalolamna serotinus

	Otodus spp.

Paleoecology

Megalolamna fossils proves that the genus had a cosmopolitan distribution.^[4] Its distribution occupied in the eastern and western margins of the Pacific Ocean, in the western margin of the Atlantic Ocean, in the Caribbean Sea, in the Mediterranean Sea and the ancient Paratethys Sea. This shows that latitudinalally, Megalolamna occupied tropical to mid-latitude zones in the northern and southern hemispheres. This geographical distribution is quite similar to that of many current lamniforms such as the goblin shark, the megamouth shark or the Bigeye sand tiger. Based on this similarity, Pollerspöck & Shimada (2024) suggest that it is possible that fossils of Megalolamna might be found in the future in the Atlantic coasts of Africa and South America, along the Indian Ocean and Oceania.^[1] A large majority of the geological formations from which Megalolamna is documented would have been shallow marine environments,^[2]^[6]^[1] although some fossils also suggest that the animal also lived in cold, subtropical waters.^[4]

Notes

↑ The teeth from these last two countries were already described as those of Megalolamna in two works published respectively in 2019 and 2020.^[5]^[6]

Related Research Articles

The Lamniformes are an order of sharks commonly known as mackerel sharks. It includes some of the most familiar species of sharks, such as the great white as well as less familiar ones, such as the goblin shark and megamouth shark.

Carcharodon is a genus of sharks within the family Lamnidae, colloquially called the "white sharks." The only extant member is the great white shark. The extant species was preceded by a number of fossil (extinct) species including C. hubbelli and C. hastalis. The first appearance of the genus may have been as early as the Early Miocene or Late Oligocene. Carcharocles megalodon is still argued by some paleontologists to be a close relative of Carcharodon carcharias - as well as being in the same genus. The megalodon's scientific name was originally "Carcharodon" megalodon, but more recently, the giant shark has been assigned by most scientists to either the genus Carcharocles or Otodus.

Otodus megalodon, commonly known as megalodon, is an extinct species of giant mackerel shark that lived approximately 23 to 3.6 million years ago (Mya), from the Early Miocene to the Pliocene epochs. O. megalodon was formerly thought to be a member of the family Lamnidae and a close relative of the great white shark, but has been reclassified into the extinct family Otodontidae, which diverged from the great white shark during the Early Cretaceous.

Cretoxyrhina is an extinct genus of large mackerel shark that lived about 107 to 73 million years ago during the late Albian to late Campanian of the Late Cretaceous. The type species, C. mantelli, is more commonly referred to as the Ginsu shark, first popularized in reference to the Ginsu knife, as its theoretical feeding mechanism is often compared with the "slicing and dicing" when one uses the knife. Cretoxyrhina is traditionally classified as the likely sole member of the family Cretoxyrhinidae but other taxonomic placements have been proposed, such as within the Alopiidae and Lamnidae.

Otodus is an extinct, cosmopolitan genus of mackerel shark which lived from the Paleocene to the Pliocene epoch. The name Otodus comes from Ancient Greek ὠτ- and ὀδούς – thus, "ear-shaped tooth".

Otodus angustidens is an extinct species of prehistoric megatoothed sharks in the genus Otodus, which lived during the Late Eocene and Miocene epochs about 34 to 21 million years ago. The largest individuals were about 11–12 metres (36–39 ft) long. This shark is related to another extinct megatoothed shark, the famous Otodus megalodon.

Otodus chubutensis, meaning "ear-shaped tooth of Chubut", from Ancient Greek ὠτ and ὀδούς – thus, "ear-shaped tooth", is an extinct species of prehistoric megatoothed sharks in the genus Otodus, that lived during Oligocene, Miocene, and Pliocene, in ~28–5.3 milions years ago. The largest individuals were about 13.5 metres (44 ft) long. This shark is considered a close relative of the famous prehistoric megatoothed shark O. megalodon. However, as is the case with O. megalodon, the classification of this species is disputed.

Otodontidae is an extinct family of sharks belonging to the order Lamniformes. Its members have been described as megatoothed sharks. They lived from the Early Cretaceous to the Pliocene, and included genera such as Otodus, including the giant megalodon. Recent studies of the newly described genus Megalolamna indicate that the members of the genus Carcharocles should be reclassified as members of the genus Otodus. The genus Cretalamna which lived from the mid-Cretaceous-Paleogene is believed to be directly ancestral to Otodus, and thus to megalodon.

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<i>Otodus auriculatus</i> Extinct species of shark

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<i>Carcharodon hubbelli</i> Extinct species of shark

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References

1 2 3 4 5 6 7 8 Jürgen Pollerspöck; Kenshu Shimada (2024). "The first recognition of the enigmatic fossil shark genus Megalolamna (Lamniformes, Otodontidae) from the lower Miocene of Europe and M. serotinus (Probst, 1879) as the newly designated type species for the genus". Zitteliana. 98: 1–9. doi: 10.3897/zitteliana.98.e131387 . S2CID 273353972.
1 2 3 4 5 6 7 8 9 10 11 12 Kenshu Shimada; Richard E. Chandler; Otto Lok Tao Lam; Takeshi Tanaka; David J. Ward (2016). "A new elusive otodontid shark (Lamniformes: Otodontidae) from the lower Miocene, and comments on the taxonomy of otodontid genera, including the 'megatoothed' clade". Historical Biology . 29 (5): 704–714. doi:10.1080/08912963.2016.1236795. ISSN 0891-2963. S2CID 89080495.
1 2 3 DePaul University (October 3, 2016). "New large prehistoric shark discovered". ScienceDaily .
1 2 3 Jorge D. Carrillo-Briceño; Thodoris Argyriou; Vladimir Zatapa; René Kindlimann; Carlos Jaramillo (2016). "A New Early Miocene (Aquitanian) Elasmobranchii Assemblage from the la Guajira Peninsula, Colombia" (PDF). Ameghiniana . 53 (2): 77–99. doi:10.5710/AMGH.26.10.2015.2931. S2CID 10054825.
↑ Walter Landini; Alberto Collareta; Claudio Di Celma; Elisa Malinverno; Mario Urbina; Giovanni Bianucci (2019). "The early Miocene elasmobranch assemblage from Zamaca (Chilcatay Formation, Peru)". Journal of South American Earth Sciences . 91: 352–371. doi:10.1016/j.jsames.2018.08.004. S2CID 135097209.
1 2 Jorge D. Carrillo-Briceño; Jaime A. Villafaña; Carlos De Gracia; F. Fernando Flores-Alcívar; René Kindlimann; Juan Abella (2020). "Diversity and paleoenvironmental implications of an elasmobranch assemblage from the Oligocene–Miocene boundary of Ecuador". PeerJ . 8. e9051. doi: 10.7717/peerj.9051 . PMC 7195833 . PMID 32391203.
↑ Josef Probst (1879). "Beiträge zur Kenntniss der fossilen Fische aus der Molasse von Baltringen. Hayfische. (Schluss)" [Contributions to the knowledge of fossil fish from the Baltringen molasses. Hayfish. (Ending)]. Jahreshefte des Vereins für vaterländische Naturkunde in Württemberg (in German). 35: 127–191.
↑ Giulio de Alessandri (1897). "La pietra da cantoni di Rosignano e di Vignale (Basso Monferrato). Studi stratigrafici e paleontologici" [The stone from the cantons of Rosignano and Vignale (Basso Monferrato). Stratigraphic and paleontological studies.]. Museo Civico di Storia Naturale di Milano (in Italian). 6 (1): 1–98.
↑ Bruce J. Welton; Roger F. Farish (1993). "Shark and Ray Hard Parts". The collector’s guide to fossil sharks and rays from the Cretaceous of Texas (PDF). Lewisville: Before Time. pp. 15–16. ISBN 978-0-963-83940-4. Archived from the original (PDF) on July 2, 2024.

External links

Brian Clark Howard (October 4, 2016). "Extinct Car-Size Shark Discovered". National Geographic . Archived from the original on August 1, 2024.

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[7] The teeth from these last two countries were already described as those of Megalolamna in two works published respectively in 2019 and 2020.^[5]^[6]

[Pollerspöck&Shimada2024-1] 1 2 3 4 5 6 7 8 Jürgen Pollerspöck; Kenshu Shimada (2024). "The first recognition of the enigmatic fossil shark genus Megalolamna (Lamniformes, Otodontidae) from the lower Miocene of Europe and M. serotinus (Probst, 1879) as the newly designated type species for the genus". Zitteliana. 98: 1–9. doi: 10.3897/zitteliana.98.e131387 . S2CID 273353972.

[Shimadaetal2016-2] 1 2 3 4 5 6 7 8 9 10 11 12 Kenshu Shimada; Richard E. Chandler; Otto Lok Tao Lam; Takeshi Tanaka; David J. Ward (2016). "A new elusive otodontid shark (Lamniformes: Otodontidae) from the lower Miocene, and comments on the taxonomy of otodontid genera, including the 'megatoothed' clade". Historical Biology . 29 (5): 704–714. doi:10.1080/08912963.2016.1236795. ISSN 0891-2963. S2CID 89080495.

[ScienceDaily-3] 1 2 3 DePaul University (October 3, 2016). "New large prehistoric shark discovered". ScienceDaily .

[Carrillo-Briceñoetal2016-4] 1 2 3 Jorge D. Carrillo-Briceño; Thodoris Argyriou; Vladimir Zatapa; René Kindlimann; Carlos Jaramillo (2016). "A New Early Miocene (Aquitanian) Elasmobranchii Assemblage from the la Guajira Peninsula, Colombia" (PDF). Ameghiniana . 53 (2): 77–99. doi:10.5710/AMGH.26.10.2015.2931. S2CID 10054825.

[Landinietal2019-5] Walter Landini; Alberto Collareta; Claudio Di Celma; Elisa Malinverno; Mario Urbina; Giovanni Bianucci (2019). "The early Miocene elasmobranch assemblage from Zamaca (Chilcatay Formation, Peru)". Journal of South American Earth Sciences . 91: 352–371. doi:10.1016/j.jsames.2018.08.004. S2CID 135097209.

[Carrillo-Briceñoetal2020-6] 1 2 Jorge D. Carrillo-Briceño; Jaime A. Villafaña; Carlos De Gracia; F. Fernando Flores-Alcívar; René Kindlimann; Juan Abella (2020). "Diversity and paleoenvironmental implications of an elasmobranch assemblage from the Oligocene–Miocene boundary of Ecuador". PeerJ . 8. e9051. doi: 10.7717/peerj.9051 . PMC 7195833 . PMID 32391203.

[Probst1879-8] Josef Probst (1879). "Beiträge zur Kenntniss der fossilen Fische aus der Molasse von Baltringen. Hayfische. (Schluss)" [Contributions to the knowledge of fossil fish from the Baltringen molasses. Hayfish. (Ending)]. Jahreshefte des Vereins für vaterländische Naturkunde in Württemberg (in German). 35: 127–191.

[Alessandri1897-9] Giulio de Alessandri (1897). "La pietra da cantoni di Rosignano e di Vignale (Basso Monferrato). Studi stratigrafici e paleontologici" [The stone from the cantons of Rosignano and Vignale (Basso Monferrato). Stratigraphic and paleontological studies.]. Museo Civico di Storia Naturale di Milano (in Italian). 6 (1): 1–98.

[10] Bruce J. Welton; Roger F. Farish (1993). "Shark and Ray Hard Parts". The collector’s guide to fossil sharks and rays from the Cretaceous of Texas (PDF). Lewisville: Before Time. pp. 15–16. ISBN 978-0-963-83940-4. Archived from the original (PDF) on July 2, 2024.

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