Halisaurinae

Halisaurinae Temporal range: Late Cretaceous 86.3–66  Ma PreꞒ Ꞓ O S D C P T J K Pg N
Skeleton of Halisaurus arambourgi .
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Clade:	†Mosasauria
Superfamily:	†Mosasauroidea
Family:	†Mosasauridae
Subfamily:	†Halisaurinae Bardet et al., 2005
Genera
†Halisaurini †Eonatator †Halisaurus †Phosphorosaurus †Pluridensini †Pluridens

The Halisaurinae are a subfamily of mosasaurs, a group of Late Cretaceous marine lizards. They were small to medium-sized, ranging from just under 3 meters in Eonatator sternbergi to as much as 8 or 9 meters in Pluridens serpentis.^[1] They tended to have relatively slender jaws and small, numerous teeth, suggesting a diet of small fish and other prey. Although the skeleton is primitive compared to other Mosasauridae in many respects, halisaurines had the distinctive hypocercal tail of other mosasaurids^[2] suggesting good swimming ability, and they persisted alongside other mosasaurs until the end of the Cretaceous. The earliest known remains of halisaurines occur in rocks of Santonian age and the subfamily persists until the latest Maastrichtian. Halisaurines are known from North and South America, Europe, Asia and Africa,^[3] indicating a more or less global distribution in the Late Cretaceous. Four genera are currently recognized: Eonatator, Halisaurus, Phosphorosaurus and Pluridens.

Description

The Halisaurinae exhibit several characteristics that suggest they are more primitive than mosasaurs of more derived subfamilies. In particular, their flippers are poorly differentiated, meaning that while better adapted to life in oceans than plesiopedal mosasaur genera like Dallasaurus and Tethysaurus, they were poor swimmers compared to many of their contemporaries. Lacking swimming capabilities are quite surprising considering that most other small mosasaurs were adapted to be fast and nimble. The description of Phosphorosaurus ponpetelegans revealed that Phosphorosaurus was highly specialized to compensate for its lack of hydrophalangy.^[4]

Despite their shortcomings, the Halisaurinae had diversified and reached a global distribution by the end of the Maastrichtian whilst other subfamilies, particularly the Plioplatecarpinae and Tylosaurinae, appear to have been in decline.^[5] There is also evidence supporting that they were accomplished intercontinental migrators, with a known large-scale migration event involving Eonatator during the Campanian from the Western Interior Seaway of North America to what today is southern Sweden.^[6]

Bardet et al. (2005, p. 464

Phylogeny

Designation of this subfamily followed many decades of confusion surrounding the

Several discoveries throughout the 1980s and 1990s helped shed light on Halisaurus, with more complete specimens of the type species H. platyspondylus being discovered and Phosphorosaurus ortliebi being momentarily reassigned to the genus by Lingham-Soliar (1996).^[12] In 2005, the species Halisaurus sternbergii was reassigned to its own genus, Eonatator, along with the description of the new species Halisaurus arambourgi by Nathalie Bardet and colleagues. With the description of Eonatator as a closely related genus to Halisaurus, the two genera were grouped into the new subfamily Halisaurinae. Their study supported the model that the group was a sister-group to more advanced mosasaurs.^[7] Since the description of Eonatator, two more species of Halisaurus, H. ortliebi and H. walkeri were recognised as separate genera; Phosphorosaurus and Pluridens respectively.

The recentmost major phylogenetic analysis of mosasaurs, conducted by Tiago R. Simões and colleagues in May

The following cladogram is modified from Longrich et al. (2021),[14] with placement of higher taxa based on Madzia & Cau (2017).^[15]

In their 2023 description of the new

• Halisaurus
  • H. platyspondylus
  • H. arambourgi
  • H. onchognathus (nomen dubium; holotype destroyed during World War II)
• Phosphorosaurus
  • P. ortliebi
  • P. ponpetelegans
• Eonatator
  • E. sternbergii
  • E. coellensis
• Pluridens
  • P. walkeri
  • P. calabaria
  • P. serpentis

References