Megalolamna is an extinct genus of large mackerel shark that lived approximately 23.5 to 15 million years ago (Mya), from the Late Oligocene to the Middle Miocene epochs.

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.

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 Japanese paleontologist Kensu Shimada and his colleagues in 2016 from five isolated fossil teeth having been discovered in the United States, Japan and Peru.

[1] 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.

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.

[2] The same year, German paleontologist Jürgen Pollerspöck and Shimada describe several additional specimens having been discovered in Europe, more precisely in Austria, France, Germany and Italy.

[3] 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] as Otodus serotinus.

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.

[3] 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.

This dentition therefore indicates that the animal should have monognathic heterodonty,[1] i.e. differently shaped mesial (the most forward) and distal (the furthest behind) teeth along the upper or lower jaws.

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.

[3] A large majority of the geological formations from which Megalolamna is documented would have been shallow marine environments,[1][7][3] although some fossils also suggest that the animal also lived in cold, subtropical waters.