Tomistominae

Last updated

Tomistominae
Temporal range: Eocene - Recent, 55–0  Ma
Tomistoma schlegelii (2).jpg
False gharial, Tomistoma schlegelii
Scientific classification OOjs UI icon edit-ltr.svg
(disputed)
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Clade: Longirostres
Superfamily: Gavialoidea
Family: Gavialidae
Subfamily: Tomistominae
Kälin, 1955
Genera

Tomistominae is a subfamily of crocodylians that includes one living species, the false gharial. Many more extinct species are known, extending the range of the subfamily back to the Eocene epoch. In contrast to the false gharial, which is a freshwater species that lives only in southeast Asia, extinct tomistomines had a global distribution and lived in estuaries and along coastlines.

Contents

The classification of tomistomines among Crocodylia has been in flux; while traditionally thought to be within Crocodyloidea, molecular evidence indicates that they are more closely related to true gharials as members of Gavialoidea.

Description

Tomistomines have narrow or longirostrine snouts like gharials. The living false gharial lives in fresh water and uses its long snout and sharp teeth to catch fish, although true gharials are more adapted toward piscivory, or fish-eating. Despite the similarity with gharials, the shapes of bones in tomistomine skulls link them with crocodiles. For example, both tomistomines and crocodiles have thin postorbital bars behind the eye sockets and a large socket for the fifth maxillary tooth. The splenial bone of the lower jaw is long and slender, forming a distinctive "V" shape not seen in gharials.

Evolutionary history

Skull of Kentisuchus toliapicus. Kentisuchus.jpg
Skull of Kentisuchus toliapicus.

Tomistomines first appeared in the Eocene in Europe and North Africa. The oldest known tomistomine is Kentisuchus spenceri from England, although a possible tomistomine fossil from the Paleocene of Spain is even older. [1] Other early tomistomines include Maroccosuchus zennaroi from Morocco and Dollosuchus dixoni from Belgium. These early tomistomines inhabited the Tethys Ocean, which covered much of Europe and North Africa during the Paleogene. Several early tomistomines are found in coastal marine deposits, suggesting that they lived along the shoreline or in estuaries. Extinct gavialoids are also thought to have been coastal animals. The marine lifestyles of these early forms likely allowed tomistomines to spread around the Tethys, forming a northern population in Europe and a southern in North Africa. [1]

Later in the Eocene and Oligocene, tomistomines spread across Asia. The middle Eocene species Ferganosuchus planus and Dollosuchus zajsanicus are known from Kazakhstan and Kyrgyzstan. Tomistomines reached China and Taiwan with the late Eocene species Maomingosuchus petrolica and the Miocene species Penghusuchus pani . [2] One species, "Tomistoma" tandoni, lived in India during the middle Eocene. During this time, the Indian subcontinent was separated from mainland Asia, creating a barrier to species that could not tolerate salt water. The Obik Sea, which separated Europe from Asia, also impeded travel. Tomistomines were able to cross these areas, indicating that they had tolerance to salt water. [1]

Rhamphosuchus crassidens, a giant tomistomine from India. Rhamphosuchus crassidens.jpg
Rhamphosuchus crassidens , a giant tomistomine from India.

Tomistomines crossed the Atlantic Ocean and spread into the Americas in the Oligocene, Miocene, and Pliocene. The earliest known neotropical tomistomine is Charactosuchus kuleri from Jamaica. A close relationship has been proposed between C. kuleri and D. zajsanicus from Belgium, suggesting that tomistomines migrated from Europe to the Americas through the De Geer land bridge connecting Norway to Greenland and the North American mainland or the Thule land bridge connecting Scotland, Iceland, Greenland, and the North American mainland. The genus Thecachampsa was present along the eastern coast of North America during the Oligocene, Miocene, and Pliocene. [1]

Tomistomines disappeared from Europe during the Oligocene but returned by the end of the epoch. They diversified and became common in the middle Miocene. One tomistomine, Tomistoma coppensi, is known from the late Miocene of Uganda. The appearance of tomistomines in central Africa is unusual because there is little evidence of late Miocene species in North Africa, an area where they must have traveled through from Europe. [1]

Tomistomines may have traveled from Africa into Asia when Arabia collided with the Eurasian continent in the Early Miocene. However, Asian Miocene tomistomines may also have descended from the Eocene tomistomines that were already present in eastern Asia. Tomistomines spread throughout the Indian subcontinent during this time. One species, Rhamphosuchus crassidens , was one of the largest crocodilians that ever lived, growing to an estimated 8 to 11 metres (26 to 36 ft). New species such as Toyotamaphimeia machikanensis were present in Japan in the Pleistocene. In southeast Asia however, there is little fossil evidence of the tomistomines that preceded the false gharial. Therefore, its relation with extinct species is unclear. [1]

Phylogeny

Tomistominae is cladistically defined as Tomistoma schlegelii (the false gharial) and all species closer to it than to Gavialis gangeticus (the gharial) or Crocodylus rhombifer (the Cuban crocodile). [3] [4] This is a stem-based definition for tomistominae, and means that it includes more basal extinct tomistomine ancestors that are more closely related to the false gharial than to the gharial or crocodiles.

Hypotheses of tomistomine phylogeny
Morphological
Crocodylia  

Gavialidae 395153358 a3b38c70f2.jpg

Alligatoridae Spectacled Caiman.JPG

  Crocodylidae  

Crocodylinae Neuguinea-krokodil-0272.jpg

Tomistominae Tomistoma schlegelii.jpg

Molecular
Crocodylia  

Alligatoridae Spectacled Caiman.JPG

  Gavialoidea  

Gavialis 395153358 a3b38c70f2.jpg

Tomistominae Tomistoma schlegelii.jpg

Crocodylidae Neuguinea-krokodil-0272.jpg

Below is a cladogram based morphological studies comparing skeletal features that shows the members of Tomistominae as belonging to Crocodylidae: [5]

Crocodylidae

Crocodylinae

Tomistominae

Xaymacachampsa

Megadontosuchus

Kentisuchus

Maroccosuchus

Dollosuchoides

Thecachampsa

Penghusuchus

Toyotamaphimeia

Tomistoma cairense

Maomingosuchus

Tomistoma schlegelii False gharial

Gavialosuchus

Tomistoma lusitanicum

Paratomistoma

Tomistoma coppensi


Based on morphological studies of extinct taxa, the tomistomines (including the living false gharial) were long thought to be classified as crocodiles and not closely related to gavialoids. [6] However, recent molecular studies using DNA sequencing have consistently indicated that the false gharial (Tomistoma) (and by inference other related extinct forms in Tomistominae) actually belong to Gavialoidea (and Gavialidae). [7] [4] [8] [9] [10] [11] [12]

Below is a cladogram from a 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data that shows the tomistomines belonging to Gavialidae, and that the members traditionally belonging to Tomistominae may in fact be paraphyletic with respect to the gharial: [11]

Longirostres

Crocodyloidea/Crocodylidae

Gavialoidea
Gavialidae
( Gavialinae ?)

Gavialis gangeticus Gharial

Gavialis bengawanicus

Gavialis browni

Gryposuchus colombianus

Ikanogavialis

Gryposuchus pachakamue

Piscogavialis

Harpacochampsa

Toyotamaphimeia

Penghusuchus

Gavialosuchus

(stem-based group)
(Tomistominae?)

Tomistoma lusitanicum

Tomistoma schlegelii False gharial

(stem-based group)
(crown group)

Tomistoma cairense

Dollosuchoides

Maroccosuchus

Paratomistoma

Kentisuchus

(stem-based group)
Traditional Tomistominae
(crown group)

Related Research Articles

<span class="mw-page-title-main">Gavialinae</span> Subfamily of gharial crocodylians

Gavialinae is a subfamily of large semiaquatic crocodilian reptiles, resembling crocodiles, but with much thinner snouts. Gavialinae is one of the two major subfamilies within the family Gavialidae - the other being the subfamily Tomistominae, which contains the false gharial and extinct relatives.

<span class="mw-page-title-main">Gavialidae</span> Family of gharial crocodylians

Gavialidae is a family of large semiaquatic crocodilians with elongated, narrow snouts. Gavialidae consists of two living species, the gharial and the false gharial, both occurring in Asia. Many extinct members are known from a broader range, including the recently extinct Hanyusuchus. Gavialids are generally regarded as lacking the jaw strength to capture the large mammalian prey favoured by crocodiles and alligators of similar size so their thin snout is best used to catch fish, however the false gharial has been found to have a generalist diet with mature adults preying upon larger vertebrates, such as ungulates.

<span class="mw-page-title-main">False gharial</span> Species of crocodilian

The false gharial, also known by the names Malayan gharial,Sunda gharial and tomistoma is a freshwater crocodilian of the family Gavialidae native to Peninsular Malaysia, Borneo, Sumatra and Java. It is listed as Vulnerable on the IUCN Red List, as the global population is estimated at around 2,500 to 10,000 mature individuals.

<i>Tomistoma</i> Genus of crocodilians

Tomistoma is a genus of gavialid crocodilians. They are noted for their long narrow snouts used to catch fish, similar to the gharial. Tomistoma contains one extant (living) member, the false gharial, as well as potentially several extinct species: T. cairense, T. lusitanicumT. coppensi, and T. dowsoni. However, these species may need to be reclassified to different genera as studies have shown them to be paraphyletic, for example: previously assigned species T. taiwanicus from Taiwan, is reclassified to the genus Toyotamaphimeia, and T. dowsoni should be excluded from Tomistoma based on phylogenetic analysis.

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

Boverisuchus is an extinct genus of planocraniid crocodyliforms known from the middle Eocene of Germany and western North America. It was a relatively small crocodyliform with an estimated total length of approximately 2.2–3.6 metres (7.2–11.8 ft).

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

Toyotamaphimeia is a genus of extinct gavialid crocodylian which lived in Japan and Taiwan during the Pleistocene. A specimen recovered in 1964 at Osaka University during the construction of a new science building has been dated to around 430–380 thousand years old based on the stratum in which it was found. Toyotamaphimeia was a fairly large crocodylian measuring approximately 6.3–7.3 metres (21–24 ft) long. Two species are named, T. machikanensis from Japan and T. taiwanica from Taiwan, both originally described as members of the genus Tomistoma.

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

Gavialosuchus is an extinct genus of gavialoid crocodylian from the early Miocene of Europe. Currently only one species is recognized, as a few other species of Gavialosuchus have since been reclassified to other genera.

Dollosuchoides, colloquially known as the Crocodile of Maransart, is an extinct monospecific genus of gavialoid crocodilian, traditionally regarded as a member of the subfamily Tomistominae. Fossils have been found in the Brussel Formation of Maransart, Belgium and date back to the middle Eocene.

Eogavialis is an extinct genus of eusuchian crocodylomorph, usually regarded as a gavialoid crocodylian. It superficially resembles Tomistoma schlegelii, the extant false gharial, and consequently material from the genus was originally referred to Tomistoma. Indeed, it was not until 1982 that the name Eogavialis was constructed after it was realised that the specimens were from a more basal form.

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

Kentisuchus is an extinct genus of gavialoid crocodylian, traditionally regarded as a member of the subfamily Tomistominae. Fossils have been found from England and France that date back to the early Eocene. The genus has also been recorded from Ukraine, but it unclear whether specimens from Ukraine are referable to Kentisuchus.

Maroccosuchus zennaroi is an extinct gavialoid crocodylian from the Early Eocene of Morocco, traditionally regarded as a member of the subfamily Tomistominae.

Paratomistoma is an extinct monospecific genus of gavialoid crocodylian. It is based on the holotype specimen CGM 42188, a partial posterior skull and lower jaw discovered at Wadi Hitan, Egypt, in Middle Eocene-age rocks of the Gehannam Formation. The skull is unfused but considered morphologically mature. Paratomistoma was named in 2000 by Christopher Brochu and Philip Gingerich; the type species is P. courti in honor of Nicholas Court, who found CGM 42188. They performed a phylogenetic analysis and found Paratomistoma to be a derived member of Tomistominae, related to the false gharial. It may have been a marine or coastal crocodilian.

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

Penghusuchus is an extinct genus of gavialid crocodylian. It is known from a skeleton found in Middle to Upper Miocene rocks of Penghu Island, off Taiwan. The taxon was described in 2009 by Shan and colleagues; the type species is P. pani. It may be related to two other fossil Asian gavialids: Toyotamaphimeia machikanensis of Japan and Hanyusuchus sinensis of South China. It was a medium-sized gavialid with an estimated total length of 4.5 metres (15 ft).

<span class="mw-page-title-main">Crocodyloidea</span> Superfamily of crocodiles

Crocodyloidea is one of three superfamilies of crocodilians, the other two being Alligatoroidea and Gavialoidea, and it includes the crocodiles. Crocodyloidea may also include the extinct Mekosuchinae, native to Australasia from the Eocene to the Holocene, although this is disputed.

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

Thecachampsa is an extinct genus of gavialoid crocodylian, traditionally regarded as a member of the subfamily Tomistominae. Fossils have been found from the eastern United States in deposits of Miocene age. Those named in the 19th century were distinguished primarily by the shape of their teeth, and have since been combined with T. antiquus. More recently erected species were reassigned from other genera, although their assignment to Thecachampsa has since been questioned.

Gryposuchinae is an extinct subfamily of gavialid crocodylians. Gryposuchines lived mainly in the Miocene of South America. However, "Ikanogavialis" papuensis may have survived more recently, into the Late Pleistocene/Holocene. Most were long-snouted coastal forms. The group was named in 2007 and includes genera such as Gryposuchus and Aktiogavialis, although a 2018 study indicates that the group might be paraphyletic and rather an evolutionary grade towards the gharial.

<span class="mw-page-title-main">Gavialoidea</span> Superfamily of large reptiles

Gavialoidea is one of three superfamilies of crocodylians, the other two being Alligatoroidea and Crocodyloidea. Although many extinct species are known, only the gharial Gavialis gangeticus and the false gharial Tomistoma schlegelii are alive today, with Hanyusuchus having become extinct in the last few centuries.

<span class="mw-page-title-main">Brevirostres</span> Taxon of reptiles

Brevirostres is a paraphyletic group of crocodilians that included alligatoroids and crocodyloids. Brevirostres are crocodilians with small snouts, and are distinguished from the long-snouted gharials. It is defined phylogenetically as the last common ancestor of Alligator mississippiensis and Crocodylus niloticus and all of its descendants. This classification was based on morphological studies primarily focused on analyzing skeletal traits of living and extinct fossil species, and placed the gharials outside the group due to their unique skull structure, and can be shown in the simplified cladogram below:

Tomistoma cairense is an extinct species of gavialoid crocodilian from the Lutetian stage of the Eocene era. It lived in North East Africa, especially Egypt. Remains of T. cairense have been found in the Mokattam Formation, in Mokattam, Egypt. Tomistoma cairense did not have a Maxilla process within their lacrimal gland, whereas all extant (living) crocodilians do.

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

Maomingosuchus is an extinct genus of gavialoid crocodylian from Late Eocene of Southeast Asia. It was discovered in Priabonian-aged deposits of China and possibly also Thailand. The type species, originally Tomistoma petrolica, was named in 1958 and was redescribed as Maomingosuchus in 2017. A second species, Maomingosuchus acutirostris, was described in 2022 from middle-upper Eocence deposits of the Na Duong Basin in northern Vietnam. It is proposed to be a basal member of Gavialoidea, or alternatively within the family Tomistominae. It was a relatively small gavialoid with an estimated total length of 3–3.5 metres (9.8–11.5 ft).

References

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