Bathysuchus

Last updated

Bathysuchus
Temporal range: Kimmeridgian, 155–150  Ma
O
S
D
C
P
T
J
K
Pg
N
Bathysuchus megarhinus holotype.png
Holotype rostrum
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauria
Clade: Pseudosuchia
Clade: Crocodylomorpha
Clade: Crocodyliformes
Suborder: Thalattosuchia
Family: Teleosauridae
Subfamily: Aeolodontinae
Genus: Bathysuchus
Foffa et al., 2019
Species:
B. megarhinus
Binomial name
Bathysuchus megarhinus
(Hulke, 1871)

Bathysuchus ("deep water crocodile") is an extinct genus of teleosaurid thalattosuchian from Late Jurassic (Kimmeridgian) deep water marine deposits in England and France. Bathysuchus displays features that suggest it was more pelagic than other teleosaurids (along with its close relatives within the Aeolodontinae), including smoother skull bones and reduced armour plating, similar to the fully marine metriorhynchids. This was possibly an adaptation to rising sea levels during the Kimmeridgian, as its earlier relatives such as Teleosaurus were suited for shallow coasts and lagoon environments.

Contents

Description

Assigned tooth Bathysuchus tooth.png
Assigned tooth

Bathysuchus is a very long-snouted (longirostrine) teleosaurid, currently known only from several snouts, the back of the skull, teeth, and a few osteoderms. It is distinguished from other derived teleosaurids in the following characteristics: strongly ventrally deflected anterior margin of the premaxilla; five premaxillary alveoli, the caudal-most being considerably reduced in size; anterodorsally oriented external nares; conical teeth bearing carinae which are only visible on the apical third of the crown. Other salient diagnostic characters can be found in the tooth count, shape of external nares (which is roughly '8'-shaped) and strong deflection of the premaxilla down and outwards. [1] [2]

The osteoderms of Bathysuchus are unlike those of other teleosaurids. Teleosaurid osteoderms are typically heavily ornamented with irregular or tear-drop shaped pits radiating in a starburst pattern, while those of Bathysuchus have small circular pits arranged in alternating rows (shared with Aeolodon). All but the single caudal osteoderm also lack keels. The osteoderms are also generally smaller and thinner than typical of teleosaurids. [2]

Discovery

Bathysuchus was originally described as a new species of Teleosaurus, T. megarhinus, by John Whitaker Hulke in 1871 on the basis of NHMUK PV OR 43086, an incomplete snout from the Kimmeridge Clay Formation of Kimmeridge Bay in Dorset, England. [3] In his 1888 catalog of extinct reptiles and amphibians preserved in the Natural History Museum, Richard Lydekker referred it to Steneosaurus , as S. megarhinus. [4] Delair (1958) did not accept the attribution of T. megarhinus to Steneosaurus, [5] and a 2005 cladistic recovered the species as closer to Teleosaurus than to other species traditionally assigned to Steneosaurus. [6] A preliminary report from 2015 indicated that "Steneosaurus" megarhinus is distinct from all other Middle-Late Jurassic teleosaurids and deserved its own genus. [1] This study was followed up in 2019 by a re-description of all the specimens attributed to the species, which were assigned to a new distinct genus, Bathysuchus megarhinus. [2]

The generic name Bathysuchus comes from the Ancient Greek βαθύς (bathus) for 'deep' and tσoῦχος (soûkhos) for 'crocodile', with the intended translation of "deep water crocodile", referring to its inferred lifestyle. [2]

Three specimens are known for Bathysuchus: the holotype, NHMUK PV OR 43086, and DORCM G..5067i-v are both incomplete snouts from Kimmeridge Bay, Dorset, part of the deep water Kimmeridge Clay Formation. An additional skull from the slightly older Aulacostephanus eudoxus Sub-Boreal ammonite Zone of “La Crouzette”, Francoulès, is known from Quercy, France. [1]

Classification

Bathysuchus has consistently been recognised as a teleosauroid thalattosuchian, although its affinities to Teleosaurus and Steneosaurus were only based on superficial features of the skull. The anatomical distinctiveness of Bathysuchus was recognised in 2019 by Foffa and colleagues through a thorough re-description of the known specimens. This also allowed them to include it in an updated phylogenetic analysis of thalattosuchians incorporating the newly recognised traits. Their analysis found Teleosauroidea to be split into two major groups, one containing Teleosaurus and other generally long-snouted genera that they referred to as 'clade T' (now Aeolodontinae), and another of Steneosaurus edwardsi, the durophagous Machimosaurini, and their closest relatives that they called 'clade S' (now Machimosaurini, Teleosauroidea and Teleosaurinae). Bathysuchus was found to be a member of 'clade T' most closely related to Sericodon , its sister taxon, and then Aeolodon ; Foffa et al. (2019) initially believed that Bathysuchus was more closely related to Aeolodon than to Sericodon, but Johnson et al. (2020) have proven otherwise. [7] Their results are shown simplified below: [2]

Assigned osteoderms Bathysuchus osteoderms.png
Assigned osteoderms
Thalattosuchia

This simplified cladogram by Johnson et al. (2020) shows the updated location of Bathysuchus within Teleosauridae and Aeolodontinae: [7]


Thalattosuchia

Palaeobiology

Stratigraphic and palaeogeographic distribution of Bathysuchus. Bathysuchus distribution.png
Stratigraphic and palaeogeographic distribution of Bathysuchus.

Bathysuchus was identified as sharing several characteristics with Aeolodon and metriorhynchids that suggest it was more pelagic than other teleosaurids. Anatomically, Bathysuchus shares with them the reduced ornamentation of the skull, as well as smaller, less sculpted osteoderms. It is unknown if it also had proportionately smaller limb bones, as known from its close relative Aeolodon. The reduction of the osteoderms in size and complexity is suggested to be related to thermoregulation, as the vascularised osteoderms of crocodylomorphs are thought to radiate heat into the body. In pelagic marine reptiles basking is not as necessary as the ambient water temperatures fluctuate less, and a similar shift may have occurred in the lineage leading to Bathysuchus and its relative Aeolodon that allowed them to reduce their osteoderm coverage. [2]

The presence of Bathysuchus fossils in the Kimmeridge Clay is also significant, as this represents a deep water environment on the outer shelf with depths estimated to be around 150—200 metres, and was associated with deep water fauna including large pliosaurs, geosaurine metriorhynchids and ophthalmosaurid ichthyosaurs. This environment was part of the Jurassic Sub-Boreal Seaway, which was noted to show a decline in teleosaurid diversity across the Middle—Late Jurassic boundary as global sea levels rose. It's possible then that Bathysuchus and Aeolodon represent an attempt at shallow-water teleosaurids to adapt to a more pelagic lifestyle as the local environment changed, while other teleosaurids became restricted to the Tethys Ocean and the margins of continental Europe. [2]

Related Research Articles

<span class="mw-page-title-main">Kimmeridge Clay</span> Geological formation in England

The Kimmeridge Clay is a sedimentary deposit of fossiliferous marine clay which is of Late Jurassic to lowermost Cretaceous age and occurs in southern and eastern England and in the North Sea. This rock formation is the major source rock for North Sea oil. The fossil fauna of the Kimmeridge Clay includes turtles, crocodiles, sauropods, plesiosaurs, pliosaurs and ichthyosaurs, as well as a number of invertebrate species.

<i>Machimosaurus</i> Genus of reptiles

Machimosaurus is an extinct genus of machimosaurid crocodyliform from the Late Jurassic and Early Cretaceous. The type species, Machimosaurus hugii, was found in Switzerland. Other fossils have been found in England, France, Germany, Portugal, Switzerland and Tunisia. Machimosaurus rex is the largest named teleosauroid and thalattosuchian, with an estimated length of up to 7.15 m (23.5 ft). Machimosaurus is the largest known crocodyliform of the Jurassic.

<span class="mw-page-title-main">Thalattosuchia</span> Clade of marine crocodylomorphs

Thalattosuchia is a clade of mostly marine crocodylomorphs from the Early Jurassic to the Early Cretaceous that had a cosmopolitan distribution. They are colloquially referred to as marine crocodiles or sea crocodiles, though they are not members of Crocodilia and records from Thailand and China suggest that some members lived in freshwater. The clade contains two major subgroupings, the Teleosauroidea and Metriorhynchoidea. Teleosauroids are not greatly specialised for oceanic life, with back osteoderms similar to other crocodyliformes. Within Metriorhynchoidea, the Metriorhynchidae displayed extreme adaptions for life in the open ocean, including the transformation of limbs into flippers, the development of a tail fluke, and smooth, scaleless skin, and probably gave live birth, seemingly uniquely among archosaurs.

<span class="mw-page-title-main">Teleosauridae</span> Extinct family of reptiles

Teleosauridae is a family of extinct typically marine crocodylomorphs similar to the modern gharial that lived during the Jurassic period. Teleosaurids were thalattosuchians closely related to the fully aquatic metriorhynchoids, but were less adapted to an open-ocean, pelagic lifestyle. The family was originally coined to include all the semi-aquatic thalattosuchians and was equivalent to the modern superfamily Teleosauroidea. However, as teleosauroid relationships and diversity was better studied in the 21st century, the division of teleosauroids into two distinct evolutionary lineages led to the establishment of Teleosauridae as a more restrictive family within the group, together with its sister family Machimosauridae.

<i>Plesiosuchus</i> Extinct genus of reptiles

Plesiosuchus is an extinct genus of geosaurine metriorhynchid crocodyliform known from the Late Jurassic of Dorset, England and possibly also Spain. It contains a single species, Plesiosuchus manselii.

<i>Pelagosaurus</i> Extinct genus of reptiles

Pelagosaurus is an extinct genus of thalattosuchian crocodyliform that lived during the Toarcian stage of the Lower Jurassic, around 183 Ma to 176 Ma, in shallow epicontinental seas that covered much of what is now Western Europe. The systematic taxonomy of Pelagosaurus has been fiercely disputed over the years, and was assigned to Thalattosuchia after its systematics within Teleosauridae were disputed. Pelagosaurus measured 2–3 m (6.6–9.8 ft) long.

Cricosaurus is an extinct genus of marine crocodyliforms of the Late Jurassic. belonging to the family Metriorhynchidae. The genus was established by Johann Andreas Wagner in 1858 for three skulls from the Tithonian of Germany. The name Cricosaurus means "Ring lizard", and is derived from the Greek Krikos- ("ring") and σαῦρος -sauros ("lizard"). It was a relatively small reptile, with C. suevicus and C. araucanensis measuring 2 m (6.6 ft) and 3.2 m (10 ft) in total body length, respectively.

<i>Steneosaurus</i> Extinct genus of reptiles

Steneosaurus is a dubious genus of teleosaurid crocodyliform from the Middle or Late Jurassic of France. The genus has been used as a wastebasket taxon for thalattosuchian fossils for over two centuries, and almost all known historical species of teleosauroid have been included within it at one point. The genus has remained a wastebasket, with numerous species still included under the label ‘Steneosaurus’, many of which are unrelated to each other.

<i>Mycterosuchus</i> Extinct genus of reptiles

Mycterosuchus is an extinct genus of teleosaurid crocodyliform from the Middle Jurassic (Callovian) of England. Although previously synonymized with Steneosaurus, recent cladistic analysis considers it distantly related to the Steneosaurus type species.

<i>Sericodon</i> Extinct genus of reptiles

Sericodon is an extinct genus of teleosaurid crocodyliform from the Late Jurassic (Tithonian) of Germany and Switzerland. The genus contains a single species, S. jugleri. Sericodon was placed in 'Clade T' (Aeolodontinae) and was found to be the sister taxon to Bathysuchus, another teleosaurid.

<span class="mw-page-title-main">Metriorhynchoidea</span> Extinct superfamily of reptiles

Metriorhynchoidea is an extinct superfamily of thalattosuchian crocodyliforms from the Early Jurassic to the Early Cretaceous of Europe, North America and South America. Metriorhynchids are fully aquatic crocodyliforms. Named by Fitzinger, in 1843, it contains the basal taxa like Teleidosaurus, Zoneait and Eoneustes and the family Metriorhynchidae. An unnamed taxon is known from Chile.

<i>Torvoneustes</i> Extinct genus of reptiles

Torvoneustes is an extinct genus of metriorhynchid thalattosuchian. It is known from skull and postcranial remains found in the Kimmeridge Clay Formation of Dorset and Wiltshire, England, the Virgula Marls of Switzerland and also from Oaxaca, Mexico . The holotype skull of the type species was initially assigned to the species Metriorhynchus superciliosus. Postcranial remains were later discovered from the same quarry as the skull, and then these specimens were recognised as belonging to a new species of Dakosaurus, as D. carpenteri. The species was named to honour Simon Carpenter, an amateur geologist from Frome in Somerset, who discovered the fossils.

<i>Macrospondylus</i> Extinct genus of reptiles

Macrospondylus is an extinct genus of machimosaurid teleosauroid crocodyliform from the Early Jurassic (Toarcian) of Europe. Fossils are known from the Posidonia Shale of Germany, the Whitby Mudstone of the United Kingdom, and the "schistes bitumineux" of Luxembourg.

<i>Lemmysuchus</i> Extinct genus of reptiles

Lemmysuchus is a genus of machimosaurid thalattosuchian from the Middle Jurassic Callovian of England and France. Like many other teleosauroids from Europe, it has had a convoluted taxonomic history.

<i>Indosinosuchus</i> Extinct genus of reptiles

Indosinosuchus is a genus of teleosaurid neosuchian that lived during the Late Jurassic or Early Cretaceous in what is now Thailand. It contains two species, the type species I. potamosiamensis and I. kalasinensis, both recovered from the lower Phu Kradung Formation. It is unique among teleosauroids as it is the only named genus known from a freshwater environment, while most other members of the group are marine. Indosinosuchus is placed in the family Teleosauridae, but has a relatively robust skull that bears resemblance to members of the Machimosauridae. Biomechanical analysis of its mandible and teeth suggest that it would have had a substantial bite force comparable to animals like Lemmysuchus. The two Indosinosuchus species however differ in the speed at which they could open and close their jaws, impacting their respective ecology and possibly explaining how they coexisted in the same environment. All known specimens of this genus were recovered from a single locality, which has been interpreted as a mass death site, possibly caused by a drought or flash flood. The precise age of Indosinosuchus is unclear, as the vertebrate fossils of the Phu Kradung Formation support a Late Jurassic age, while palynological data suggests an Early Cretaceous (Berriasian) age.

<i>Deslongchampsina</i> Extinct genus of marine crocodilians

Deslongchampsina is an extinct genus of machimosaurid crocodyliform from the Middle Jurassic (Bathonian) Cornbrash Formation of England and France, possibly from the Calcaire de Caen. The type and only known species is D. larteti, which was variously referred to Teleosaurus and the wastebasket taxon Steneosaurus before its distinction was formally recognised in 2019. Its snout was not as elongated as some other teleosauroids (mesorostrine), and the shape of its jaws and teeth suggest that it was a generalist predator, unlike the more powerful contemporary machimosaurin Yvridiosuchus.

<i>Plagiophthalmosuchus</i> Genus of reptiles (fossil)

Plagiophthalmosuchus is a genus of teleosauroid, known form the Early Jurassic Whitby Mudstone Formation of Whitby, Yorkshire, UK, and Dudelange, Luxembourg. The type species, P. gracilirostris, was originally named as a species of Teleosaurus in 1836, but then it was moved to Steneosaurus in 1961, but it was again moved to its own genus in 2020.

<span class="mw-page-title-main">Machimosauridae</span> Extinct family of reptiles

Machimosauridae is an extinct family of teleosauroid thalattosuchian crocodyliforms. The family was first identified in 2016, when fossils of teleosauroid thalattosuchians, including an indeterminate close relative of Lemmysuchus and Machimosaurus, were described from the Middle Jurassic (Bathonian) of Morocco. The family was largely expanded in 2020 when the systematics of Teleosauroidea were re-reviewed. Members of this family generally were larger than the teleosaurids.

<i>Andrianavoay</i> Extinct genus of reptiles

Andrianavoay is an extinct genus of teleosauroid from the Bathonian Kandreho Formation of Madagascar.

<i>Turnersuchus</i> Extinct genus of reptiles

Turnersuchus is an extinct genus of thalattosuchian, a group of marine crocodylomorphs, from the Pliensbachian of the United Kingdom. It is the oldest diagnostic member of Thalattosuchia and was also found to be the group's most basal member, being situated outside the two major groups Metriorhynchoidea and Teleosauroidea. Subsequently, this genus is considered to be of great importance to understanding the relationship between thalattosuchians and other crocodylomorphs as well as their rapid diversification during the early Jurassic. Turnersuchus is a monotypic genus, meaning it includes only a single species, Turnersuchus hingleyae.

References

  1. 1 2 3 Foffa D, Young MT, Brusatte SL, Steel L. (2015) New specimen and revision of the late Jurassic teleosaurid 'Steneosaurus’ megarhinus. PeerJ PrePrints 3:e1351v1 https://doi.org/10.7287/peerj.preprints.1351v1
  2. 1 2 3 4 5 6 7 Foffa, D.; Johnson, M.M.; Young, M.T.; Steel, L.; Brusatte, S.L. (2019). "Revision of the Late Jurassic deep-water teleosauroid crocodylomorph Teleosaurus megarhinus Hulke, 1871 and evidence of pelagic adaptations in Teleosauroidea" (PDF). PeerJ . 7: e6646. doi: 10.7717/peerj.6646 . PMC   6450380 . PMID   30972249.
  3. Hulke, J. W., 1871, Note on a Fragment of a Teleosaurian snout from Kimmeridige Bay, Dorset: Quarterly Journal of the Geological Society of London, v. 17, p. 442-443.
  4. Lydekker, R. (1888). Catalogue of the Fossil Reptilia and Amphibia in the British Museum (Natural History). Part I. Containing the Orders Ornithosauria, Crocodilia, Dinosauria, Squamata, Rhynchocephalia, and Proterosauria. British Museum (Natural History):London, 1-309.
  5. J. B. Delair. 1958. The Mesozoic reptiles of Dorset. Part one. Proceedings of the Dorset Natural History and Archaeological Society 79:47-72.
  6. Mueller-Töwe, I. J. 2005. Phylogenetic relationships of the Thalattosuchia. Zitteliana A45: 211-213.
  7. 1 2 Johnson, Michela M.; Young, Mark T.; Brusatte, Stephen L. (2020). "The phylogenetics of Teleosauroidea (Crocodylomorpha, Thalattosuchia) and implications for their ecology and evolution". PeerJ. 8: e9808. doi: 10.7717/peerj.9808 . PMC   7548081 . PMID   33083104.