Orientalosuchina

{{Automatic taxobox

| taxon = Orientalosuchina

| image = Protoalligator huiningensis (Paleozoological Museum of China, May 23, 2008).jpg

| image_caption = Partial skull and jaw of Protoalligator huiningensis, on display at the Paleozoological Museum of China

| fossil_range = Maastrichtian-Eocene, {{fossil range|72|34}}

| authority = Massonne et al., 2019

| display_parents = 2

| subdivision_ranks = Genera

| subdivision =

{{extinct}}Dongnanosuchus
{{extinct}}Eoalligator
{{extinct}}Eurycephalosuchus
{{extinct}}Jiangxisuchus?
{{extinct}}Krabisuchus
{{extinct}}Orientalosuchus
{{extinct}}Protoalligator

}}

Orientalosuchina is an extinct clade of alligatoroid crocodylians from Southeast and East Asia that lived between Maastrichtian and Eocene.

The clade was named as the result of a 2019 study by Massonne et al. that included several extinct alligatoroid taxa from Asia and found that they were all closely related and together formed a monophyletic clade as basal members of Alligatoroidea. They defined this clade as "the most inclusive clade containing Orientalosuchus naduongensis, Krabisuchus siamogallicus, Eoalligator chunyii, Jiangxisuchus nankangensis and Protoalligator huiningensis, but not Brachychampsa montana, Stangerochampsa mccabei, Leidyosuchus canadensis, Diplocynodon darwini, Bottosaurus harlani, or any species of recent Crocodylia".

History of discovery

While Orientalosuchina have only been recognized as a clade relatively recently, the first discoveries assigned to this clade date back to 1964 when Yang Zhongjian (also known as C.C. Young) discovered crocodilian remains in the Guangdong Province of China. While much of the material discovered by Young was fragmentary, he nevertheless established two species based on it, the crocodyloid Asiatosuchus nanlingensis and the alligatoroid Eoalligator chunyii. Shortly after this discovery more material was uncovered in the Anhui Province, though these fossils would remain undescribed for close to 20 years before Young eventually coined the name Eoalligator huiningensis on the basis of skull remains.{{Cite book|last1=Young|first1=C. C.|year=1982|title=Selected Works of Yang Zhongjian|chapter=A Cenozoic crocodile from Huaining, Anhui.|publisher=Academia Sinica; China|pages=47-48}}

Resesarch on what are now recognized as orientalosuchines would pick up again in the 2010s, beginning with the description of Krabisuchus siamogallicus. The fossil material of Krabisuchus had been collected by the joint efforts of Thai and French paleontologists under Varavudh Suteethorn and Eric Buffetaut during the late 80s and early 90s from lignite pits within the Krabi Basin of Thailand. While preliminary observations had regarded the Krabi material as a species of Allognathosuchus, by 2010 the genus was regarded as a wastebasket taxon with several former species placed in their own genera. Due to this Jeremy E. Martin and Komsorn Lauprasert established the genus Krabisuchus.. In 2014 Pavel P. Skutschas and colleagues reported the discovery of another broad-snouted crocodilian, this time from the Maoming Basin of southern China. While the initial findings were too incomplete for a detailed description, the team noted that the fossil appeared to represent an alligatoroid, simply referred to as the "Maoming alligator" at the time.{{Cite journal|last1=Skutschas|first1=P. P.|last2=Danilov|first2=I. G.|last3=Kodrul|first3=T. M.|last4=Jin|first4=J.|year=2014|title=The first discovery of an alligatorid (Crocodylia, Alligatoroidea, Alligatoridae) in the Eocene of China|journal=Journal of Vertebrate Paleontology|volume=34|issue=2|pages=471–476|doi=10.1080/02724634.2013.809725}}

In 2016 a revision of Eoalligator was published by Yan-Yin Wang, Corwin Sullivan and Jun Liu, who took note of sevearl issues with Young's description of it and Asiatosuchus nanlingensis. The team highlighted that Young did not provide a detailed description for many of the specimen he referred to Eoalligator, nor fully prepared all the fossil material. One of their main points however was the fact that Young never properly distinguished his two taxa, which they argued share some key features in their anatomy. Wang and colleagues came to the conclusion that Eoalligator chunyii was actually a junior synonym of Asiatosuchus nanlingensis while Eoalligator huiningensis should be placed in its own genus which they dubbed Protoalligator. This further had the side effect that the team regarded Eoalligator chunyii to represent a crocodyloid, while Protoalligator remained an alligatoroid. While the distinction between Eoalligator and Protoalligator was readily accepted, Wang eventually contributed to a second study published in 2018 that reinstated Eoalligator as a valid genus after continued study revealed anatomical differences between it and Asiatosuchus nanlingensis.{{cite journal |author1=Xiao-Chun Wu |author2=Chun Li |author3=Yan-Yin Wang |year=2018 |title=Taxonomic reassessment and phylogenetic test of Asiatosuchus nanlingensis Young, 1964 and Eoalligator chunyii Young, 1964 |journal=Vertebrata PalAsiatica |volume=56 |issue=2 |pages=137–146 |url=https://www.researchgate.net/publication/324584171}}

Two major studies were published in 2019, first among these the description of Jiangxisuchus nankangensis from the Late Cretaceous of China, which was interpreted as a crocodyloid closely related to Eoalligator. The second major study was the description of Orientalosuchus naduongensis, which was based on a plethora of specimen including multiple skulls, lower jaws and even postcranial material, discovered in the late 2000s and early 2010s in the Na Duong Basin in Northeastern Vietnam, close to the border with China. The description of Orientalosuchus allowed Tobias Massonne and colleagues to furthermore establish a monophyletic clade consisting of multiple South-East Asian crocodilians. This clade, which they dubbed Orientalosuchina, was defined as the most inclusive clade to contain to contain Orientalosuchus, Krabisuchus, Jiangxisuchus, Protoalligator and Eoalligator but not Brachychampsa, Stangerochampsa, Bottosaurus, Diplocynodon, Leidyosuchus or any modern crocodilian.

While some subsequent studies would come to question Massonne's interpretation of Orientalosuchina, especially the reported alligatoroid affinities, others would expand on it. In 2021 Hsi-yin Shan and colleagues would describe additional material from the Maoming Basin, allowing them to describe the short-snouted crocodilian from these sediments as Dongnanosuchus hsui. Only a year later a team lead by Xiao-Chun Wu described yet another orientalosuchin, the incredibly short snouted Eurycephalosuchus gannanensis from the Maastrichtian Hekou Formation of China.

Species

class="wikitable"

!Genus

!Species

!Age

!Location

!Notes

!Image

Dongnanosuchus{{Cite journal|last1=Shan|first1=Hsi-yin|last2=Wu|first2=Xiao-Chun|last3=Sato|first3=Tamaki|last4=Cheng|first4=Yen-nien|last5=Rufolo|first5=Scott|title=A new alligatoroid (Eusuchia, Crocodylia) from the Eocene of China and its implications for the relationships of Orientalosuchina|url=https://www.cambridge.org/core/journals/journal-of-paleontology/article/abs/new-alligatoroid-eusuchia-crocodylia-from-the-eocene-of-china-and-its-implications-for-the-relationships-of-orientalosuchina/3E35C6F6E6467E46E87E94DF62DF70AE|journal=Journal of Paleontology|year=2021|volume=95 |issue=6 |language=en|pages=1–19|doi=10.1017/jpa.2021.69|bibcode=2021JPal...95.1321S |s2cid=238650207 |issn=0022-3360|url-access=subscription}}

|D. hsui

|Eocene

|{{flag|China}}

|Dongnanosuchus is the youngest orientalosuchin from China and known from fossil remains recovered from the oil shale beds of the Maoming Basin (Youganwo Formation).

|frameless

Eoalligator{{cite journal|last=Young|first=C.-C.|year=1964|title=New fossil crocodiles from China|journal=Vertebrata PalAsiatica|volume=8|issue=2|pages=189–208|language=zh-cn,en| url=http://www.ivpp.cas.cn/cbw/gjzdwxb/xbwzxz/201001/P020100104370758259553.pdf}}

|E. chunyii

|Maastrichtian - Paleocene

|{{flag|China}}

|Eoalligator was the first orientalosuchin to be named, having been described by Yang Zhongjian in 1964. Fossils have been recovered from the Late Cretaceous Zhenshui Formation as well as the Paleocene Shanghu Formation, suggesting that Eoalligator survived the meteor impact that was responsible for the extinction of the dinosaurs. Eoalligator was once thought to be synonymous with Asiatosuchus nanlingensis, but research has since then rejected this hypothesis.

|frameless

Eurycephalosuchus{{cite journal |last1= Wu| first1=X.C.|last2=Wang|first2=Y.C.|last3=You|first3=H.L.|last4=Zhang|first4=Y.Q.|last5=Yi|first5=L.P.|year=2022| title = New brevirostrines (Crocodylia, Brevirostres) from the Upper Cretaceous of China |journal=Cretaceous Research|at=105450 |doi=10.1016/j.cretres.2022.105450 }}

|E. gannanensis

|Maastrichtian

|{{flag|China}}

|Eurycephalosuchus from the Late Cretaceous Hekou Formation is regarded as one of the most unusually proportioned orientalosuchins. While most members of the clade have a snout described as short and blunt, that of Eurycephalosuchus is extreme even by these standards. It is also possibly the smallest member of Orientalosuchina.

Jiangxisuchus{{cite journal |last1=Li |first1=C. |last2=Wu |first2=X. C. |last3=Rufolo |first3=S. J. |year=2019 |title=A new crocodyloid (Eusuchia: Crocodylia) from the upper cretaceous of China |journal=Cretaceous Research |volume=94 |pages=25–39 |doi=10.1016/j.cretres.2018.09.015 |s2cid=133661294 }}

|J. nankangensis

|Maastrichtian

|{{flag|China}}

|Jiangxisuchus is among the more debated members of Orientalosuchina, having originally been classified as a crocodyloid closely related to Eoalligator. Some subsequent research has continued to argue for it being more closely related to modern crocodiles than to alligators, but even studies placing it within Orientalosuchina generally do so as a close relative to Eoalligator. Fossils of Jiangxisuchus were initially described to have come from the Late Cretaceous Nanxiong Formation, though later papers have attributed the specific sediments to the Hekou Formation.

|frameless

Krabisuchus{{cite journal |author1=Jeremy A Martin |author2=K. Lauprasert |year=2010 |title=A new primitive alligatorine from the Eocene of Thailand: relevance of Asiatic members to the radiation of the group |journal=Zoological Journal of the Linnean Society |volume=158 |issue=3 |pages=608–628 |doi=10.1111/j.1096-3642.2009.00582.x}}

|K. siamogallicus

|Eocene (Priabonian)

|{{flag|Thailand}}

|Krabisuchus is exclusively known from the Krabi Basin of southern Thailand, where it lived during the latest Eocene. It was initially interpreted as a relative of Allognathosuchus before being placed in the clade Orientalosuchina.

Orientalosuchus{{cite journal |author1=Tobias Massonne |author2=Davit Vasilyan |author3=Márton Rabi |author4=Madelaine Böhme |year=2019 |title=A new alligatoroid from the Eocene of Vietnam highlights an extinct Asian clade independent from extant Alligator sinensis |journal=PeerJ |volume=7 |pages=e7562 |doi=10.7717/peerj.7562 |pmid=31720094 |pmc=6839522 |doi-access=free }}

|O. naduongensis

|Eocene (Late Bartonian - Priabonian)

|{{flag|Vietnam}}

|Orientalosuchus is the namesake of the clade Orientalosuchina and was described in 2019 from several specimen recovered from the Na Duong Basin of northern Vietnam. Due to its broad skull and blunt posterior teeth, it has been interpreted as a generalist who's diet might have included turtles.

|frameless

Protoalligator{{cite journal |author1=Yan-Yin Wang |author2=Corwin Sullivan |author3=Jun Liu |title=Taxonomic revision of Eoalligator (Crocodylia, Brevirostres) and the paleogeographic origins of the Chinese alligatoroids |journal=PeerJ |year=2016 |volume=4 |pages=e2356 |doi=10.7717/peerj.2356 |pmid=27635329 |pmc=5012266 |doi-access=free}}

|P. huiningensis

|Middle Paleocene

|{{flag|China}}

|Protoalligator was originally named Eoalligator huiningensis, but moved to its own genus in 2016 after Eoalligator was briefly synonymized with the crocodyloid Asiatosuchus nanlingensis. Since Protoalligator was still regarded as an alligatoroid, its name was specifically chosen to carry on the meaning of Eoalligator, though now both are considered to be valid species and potential relatives. The fossils are known from the Paleocene Wanghudun Formation.

|frameless

Phylogeny

=External relationships=

The precise relationship between orientalosuchins and other crocodilians is a disputed subject with several different interpretations of how they would fit into the group. Traditionally, orientalosuchins have been interpreted as part of the Alligatoroidea clade, most commonly thought to consist of some basal taxa like Deinosuchus and Diplocynodon as well as the derived alligatorids, which are split into Alligatorinae and Caimaninae. Even prior to the recognition of Orientalosuchina as a clade, several members included in this group were thought to be closely related to alligatorids. For instance, Eoalligator, as the name would suggest, was originally classified as an alligatoroid, as was Protoalligator (formerly a species of Eoalligator).{{Cite journal|last1=Wang|first1=Y.-Q.|last2=Li|first2=C.K.|last3=Li|first3=Q.|last4=Li|first4=D.-S.|year=2016|title=A synopsis of Paleocene stratigraphy and vertebrate paleontology in the Qianshan Basin, Anhui, China.|journal=Vertebrata PalAsiatica|volume=54|issue=2|pages=89-120}} Similarily, Dongnanosuchus was initially known as the "Maoming alligator" and early phylogenies featuring Krabisuchus generally regarded the taxon as having a possible connection to the early alligatoroid Allognathosuchus among others.

These largely separate results would eventually be used by Tobias Massonne and colleagues to erect the clade Orientalosuchina, which the team recovered as the earliest branch of Globidonta. Following this interpretation, orientalosuchins would have split from the alligatoroid lineage after taxa such as Deinosuchus, Leidyosuchus and Diplocynodon but before the split into caimans and alligators. This hypothesis is notably favored by studies following Massonne in recovering a monophyletic Orientalosuchina, such as Shan et al. (2021) and Wu et al. (2022). A similar topology was also recovered by Jules D. Walter and colleagues in 2025, with the only major difference being that their study argued that Deinosuchus, Leidyosuchus and Diplocynodon are all non-crocodilians, therefore rendering Globidonta redundant and leaving Orientalosuchina as the basalmost branch of Alligatoroidea. However the team notes that the position of Orientalosuchina is an unstable one and not well supported.{{Cite journal |last1=Walter |first1=J. D. |last2=Massonne |first2=T. |last3=Paiva |first3=A. L. S. |last4=Martin |first4=J. E. |last5=Delfino |first5=M. |last6=Rabi |first6=M. |title=Expanded phylogeny elucidates Deinosuchus relationships, crocodylian osmoregulation and body-size evolution |year=2025 |journal=Communications Biology |volume=8 |at=611 |doi=10.1038/s42003-025-07653-4 |doi-access=free |pmc=12018936 }}

Shown below are the phylogenetic results of Shan et al. (2021) as well as Walter et al. (2025).

- valign="top"

| align="left" width="50%" |

{{clade| style=font-size:85%;line-height:85%

|label1=Crocodylia

|1={{clade

|1=Gavialoidea

|2={{clade

|1=†Borealosuchus

|2={{clade

|1=†Planocraniidae

|label2=Brevirostres

|2={{clade

|1=Crocodyloidea

|label2=Alligatoroidea

|2={{clade

|1=†Leidyosuchus

|2={{clade

|1=†Diplocynodon

|2={{clade

|1=†Deinosuchus

|label2=Globidonta

|2={{clade

|1=†Orientalosuchina

|label2=Alligatoridae

|2={{clade

|1=Alligatorinae

|2=Caimaninae

}}}}}}}}}}}}}}}}}}}}

| align="left" width="50%"|

{{clade| style=font-size:85%;line-height:85%

|1={{clade

|1=†Borealosuchus

|2=†Diplocynodon

}}

|2={{clade

|1=†Leidyosuchus

|2={{clade

|1=†Deinosuchus

|2={{clade

|1=†Planocraniidae

|label2=Crocodilia

|2={{clade

|1=Longirostres (including Crocodyloidea and Gavialoidea)

|label2=Alligatoroidea

|2={{clade

|1=†Orientalosuchina

|2={{clade

|1=Alligatorinae

|2=Caimaninae

}}}}}}}}}}}}}}}}

| align="right" width="50%" |

A similar objection to that of Walter et al. has been raised by Nils Chabrol and colleagues in 2024, who note the conflicting anatomical features of orientalosuchins. In this study two different results were recovered, with Orientalosuchina generally being less inclusive than established by Massonne. The result that recovers a select few orientalosuchins as closer to alligators, achieved through implied weighting of phylogenetic characters, has them form a clade at the base of Alligatoroidea. Both analysis feature Protoalligator as an unrelated alligatoroid. Under equal weighting of characters the results suggest a closer relationship with Longirostres, the clade formed by crocodyloids and gavialoids, with Orientalosuchina splitting off before these two clades diverged from one-another. Much like how Protoalligator was found as an alligatoroid regardless of the used method, both results find Jiangxisuchus to be a member of Longirostres independent of Orientalosuchina. The reason for these strongly conflicting results is the mosaic of anatomical features seen in members of Orientalosuchina. For instance, many members of the clade possess bulbous, globular teeth towards the back of the jaw, a feature associated with early alligatoroids (hence the clade name Globidonta). However, several orientalosuchins also feature a prominent notch between the premaxilla and maxilla which receives the enlarged fourth dentary tooth, a feature not seen in modern alligators but still well developed in crocodylids. The way the teeth interlock on the other hand strikes a middle ground between the two clades, not forming the same overbite as observed in most alligatoroids but also not fully interlocking as is traditional for Longirostres. Chabrol and colleagues argue that this mix of characters could be tied to the early divergence of orientalosuchins, having split off before some of these features became ingrained in their respective lineages.{{Cite journal|last1=Chabrol |first1=N. |last2=Jukar |first2=A. M. |last3=Patnaik |first3=R. |last4=Mannion |first4=P. D. |year=2024 |title=Osteology of Crocodylus palaeindicus from the late Miocene–Pleistocene of South Asia and the phylogenetic relationships of crocodyloids |journal=Journal of Systematic Palaeontology |volume=22 |issue=1 |at=2313133 |doi=10.1080/14772019.2024.2313133 |bibcode=2024JSPal..2213133C }}

- valign="top"

| align="left" width="50%" |

{{clade| style=font-size:85%;line-height:85%

|1={{clade

|1=Longirostres

|2={{clade

|1={{clade

|1=†Qianshanosuchus

|2=†Asiatosuchus depressifrons

}}

|2={{clade

|1=†Crocodylus affinis

|2=†Asiatosuchus germanicus

}}}}

|2={{clade

|1=†Planocraniidae

|label2=Alligatoroidea

|2={{clade

|1=†Orientalosuchina

|2=other alligatoroids

}}}}}}}}}}

| align="left" width="50%"|

{{clade| style=font-size:85%;line-height:85%

|1={{clade

|1=†Planocraniidae

|2={{clade

|1=†Asiatosuchus germanicus

|2={{clade

|1={{clade

|1=†Asiatosuchus depressifrons

|2=†Crocodylus affinis

}}

|2={{clade

|1=†Qianshanosuchus

|2={{clade

|1=†Jiangxisuchus

|2={{clade

|1=†Quinkana

|2={{clade

|1=†Australosuchus

|2={{clade

|1=†Orientalosuchina

|2={{clade

|1=Gavialoidea

|2=Crocodyloidea

}}}}}}}}}}}}}}}}}}}}

| align="right" width="50%" |

The results of Chabrol and colleagues in part reflect previous results concerning Jiangxisuchus. While most orientalosuchins had been regarded as alligatoroids prior to the clade being named, Jiangxisuchus was initially described as a crocodyloid, a placement also recovered in 2021.{{cite journal |last1=Rio |first1=Jonathan P. |last2=Mannion |first2=Philip D. |date=6 September 2021 |title=Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem |journal=PeerJ |volume=9 |pages=e12094 |pmid=34567843| doi=10.7717/peerj.12094|pmc=8428266 |doi-access=free}} Eoalligator, though initially described as an alligatoroid, has also been frequently recovered as a crocodyloid. This includes as a synonym of Asiatosuchus nanlingensis in 2016{{cite journal |author1=Yan-Yin Wang |author2=Corwin Sullivan |author3=Jun Liu |title=Taxonomic revision of Eoalligator (Crocodylia, Brevirostres) and the paleogeographic origins of the Chinese alligatoroids |journal=PeerJ |year=2016 |volume=4 |pages=e2356 |doi=10.7717/peerj.2356 |pmid=27635329 |pmc=5012266 |doi-access=free}}, as part of a large polytomy in 2018 and as the sister taxon to Jiangxisuchus in 2019. However in all those cases the two taxa are isolated from other orientalosuchins, rather than shifting the entire groups position within Crocodilia.

A hypothesis that would place Orientalosuchina as a whole outside of Alligatoroidea has been proposed by Jorgo Ristevski and colleagues in a 2023, with some of their results suggesting that orientalosuchins could have been part of the clade Mekosuchinae. While most of their phylogenies recover mekosuchines and orientalosuchins as being unrelated to one-another, two trees find orientalosuchins to be deeply nested within Mekosuchinae. More specifically, these two trees show orientalosuchins to be closely related to dwarf forms like Trilophosuchus and Mekosuchus, whereas large-bodied mekosuchines like Baru and Paludirex are more basal. Within the broader context of Crocodilia, this would suggest that orientalosuchins are actually part of an early off-shoot of the branch that includes Longirostres. However even in this study the position of Orientalosuchina is not without doubt. For one this topology was only recovered in two out of eight analysis, with the remaining six all suggesting more traditional topologies. Furthermore, the features that could be used to argue for a close relationship between mekosuchines and orientalosuchins are either not present in all genera within their respective clades or more widespread across crocodilia.{{Cite journal|last1= Ristevski|first1=J.| last2=Willis|first2=P.M.A.|last3=Yates |first3=A.M.|last4=White|first4=M.A.|last5=Hart |first5=L.J.|last6=Stein|first6=M.D.|last7=Price|first7=G.J. |last8=Salisbury |first8=S.W.|year=2023|title=Migrations, diversifications and extinctions: the evolutionary history of crocodyliforms in Australasia|journal=Alcheringa: An Australasian Journal of Palaeontology|pages=1–46 |doi=10.1080/03115518.2023.2201319|s2cid=258878554 |doi-access=free|hdl=1959.4/104056|hdl-access=free}}

- valign="top"

| align="left" width="50%" |

{{clade| style=font-size:85%;line-height:85%

|label1=Crocodylia

|1={{clade

|1=Alligatoroidea

|2={{clade

|1=†Planocraniidae{{extinct}}

|2={{clade

|1={{clade

|1=†Asiatosuchus germanicus{{extinct}}

|2=†Mekosuchinae (including Orientalosuchina){{extinct}}

}}

|2={{clade

|1=†Prodiplocynodon{{extinct}}

|2={{clade

|1={{clade

|1=†"Crocodylus" affinis{{extinct}}

|2=†"Crocodylus" depressifrons{{extinct}}

}}

|2={{clade

|1=†"Crocodylus" acer{{extinct}}

|2=†Brachyuranochampsa{{extinct}}

}}

|label3=Longirostres

|3={{clade

|1=Gavialoidea

|2=Crocodyloidea

}}}}}}}}}}}}}}

| align="left" width="50%"|

{{clade| style=font-size:85%;line-height:85%

|label1=Mekosuchinae

|1={{clade

|1=†Kalthifrons

|2={{clade

|1={{clade

|1=†Quinkana meboldi

|2={{clade

|1=†Quinkana fortirostrum

|2=†Quinkana timara

}}}}

|2={{clade

|1={{clade

|1=†Paludirex gracilis

|2=†Paludirex vincenti

}}

|2={{clade

|1=†Baru wickeni

|2=†Baru darrowi

}}}}}}}}

|2={{clade

|label1=Orientalosuchina

|1={{clade

|1=†Krabisuchus

|2={{clade

|1=†Orientalosuchus

|2={{clade

|1=†Jiangxisuchus

|2=†Eoalligator

}}}}}}

|2={{clade

|1=†Dongnanosuchus

|2={{clade

|1=†"Baru" huberi

|2={{clade

|1=†Volia

|2=†Trilophosuchus

|3={{clade

|1=†Mekosuchus sanderi

|2=†Mekosuchus whitehunterensis

|3=†Mekosuchus inexpectatus

}}}}}}}}}}}}}}

| align="right" width="50%" |

=Internal relationships=

When Orientalosuchina was described in 2019 it was specifically defined based on the inclusion of five species: Orientalosuchus naduongensis, Krabisuchus siamogallicus, Eoalligator chunyii, Jiangxisuchus nankangensis and Protoalligator huiningensis. However, the internal topology of this clade was initially poorly resolved, with most of these species being placed in a large polytomy and only Orientalosuchus and Krabisuchus being found to have a closer relationship to each other than to other orientalosuchins. Additional research in subsequent years also saw the description and inclusion of Dongnanosuchus hsui and Eurycephalosuchus gannanensis within Orientalosuchina. In both instances, the authors maintained the monophyly of the group, continuing to include all five of Massonne's defining species within the clade, but with a better resolved internal relationships. Both studies place Krabisuchus as the earliest diverging orientalosuchin, followed by Protoalligator as the next basalmost genus within the clade. In both studies Jiangxisuchus and Eoalligator are sister taxa. The close relationship between the two animals from Cretaceous China has previously also been found by Li and colleagues in 2019, though in said case they were regarded as crocodyloids. Orientalosuchus, Dongnanosuchus and Eurycephalosuchus are all part of a polytomy that further includes the Jiangxisuchus - Eoalligator clade following the results of Wu et al. (2022). Walter and colleagues present another alternative, finding Protoalligator as the basalmost genus in place of Krabisuchus, lending further support for the Jiangxisuchus - Eoalligator clade and recovering Dongnanosuchus as the sister taxon to Krabisuchus and Orientalosuchus.

- valign="top"

| align="left" width="50%" |

{{clade| style=font-size:85%;line-height:85%

|label1=Orientalosuchina

|1={{clade

|1=†Krabisuchus siamogallicus

|2={{clade

|1=†Protoalligator huiningensis

|2={{clade

|1=†Orientalosuchus naduongenis

|2=†Dongnanosuchus hsui

|3=†Eurycephalosuchus gannanensis

|4={{clade

|1=†Jiangxisuchus nankangensis

|2=†Eoalligator chunyii

}}}}}}}}}}

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{{clade| style=font-size:85%;line-height:85%

|label1=Orientalosuchina

|1={{clade

|1=†Protoalligator huiningensis

|2={{clade

|1={{clade

|1=†Jiangxisuchus nankangensis

|2=†Eoalligator chunyii

}}

|2={{clade

|1=†Dongnanosuchus hsui

|2={{clade

|1=†Orientalosuchus naduongenis

|2=†Krabisuchus siamogallicus

}}}}}}}}}}

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While originally defined around the presence of five specific taxa, some later studies could only recover significantly less inclusive versions of the clade. In the study that recovered Orientalosuchina within Mekosuchinae, the core monophyletic group is only formed by Orientalosuchus, Krabisuchus, Jiangxisuchus and Eoalligator, with the latter two once again each others closest relatives. Protoalligator was recovered as part of a polytomy at the base of Crocodilia and though Dongnanosuchus was still closely allied with orientalosuchins in the study, it was found to be phylogenetically closer to small-bodied mekosuchines, splitting off after the divergence of the other traditional forms. Chabrol and colleagues were likewise unable to place all members originally used in the definition of Orientalosuchina within a monophyletic group. Both in the scenario that orientalosuchins were alligatoroids and the scenario that they were closer to Longirostres, the group was found to consist of only Orientalosuchus, Dongnanosuchus, Krabisuchus and Eurycephalosuchus. In both scenarios Dongnanosuchus and Orientalosuchus were found to be sister taxa, with the key difference being whether Krabisuchus and Eurycephalosuchus formed their own clade or were successively branching species of the clade.