Chrysochampsa Temporal range: Eocene | |
---|---|
The holotype skull of Chrysochampsa | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | Archosauromorpha |
Clade: | Archosauriformes |
Order: | Crocodilia |
Family: | Alligatoridae |
Subfamily: | Caimaninae |
Genus: | † Chrysochampsa Estes, 1988 |
Species | |
|
Chrysochampsa is an extinct monospecific genus of caiman of the clade Brachychampsini. Fossils have been found from the Golden Valley Formation of North Dakota and date back to the Wasatchian regional North American faunal stage of the early Eocene. During this time North Dakota experienced the Early Eocene Climatic Optimum, creating lush forests, swamps and meandering rivers that were the home to at least four distinct crocodilians. Unlike the contemporary Ahdeskatanka , which was a small animal with crushing teeth, Chrysochampsa would have been a generalist and due to its size and lack of significant mammalian carnivores the apex predator of the region. The genus had been proposed to be synonymous with Allognathosuchus in 2004s, but this claim has since then been repeatedly refuted. A 2024 study has recovered it as an early branching member of the Caimaninae, forming a clade with Cretaceous forms such as Brachychampsa . Chrysochampsa is a monotypic genus, containing only the type species, Chrysochampsa mlynarskii.
Chrysochampsa was described by Richard Estes in 1988 based on a fairly complete skull and assorted other fossils recovered from the Turtle Valley site of the Golden Valley Formation of North Dakota. However, Estes diagnosis of the new taxon was rather simple, the only distinguishing feature cited being the proportions of the fronal bone. [1] In a 2004 Spencer Lucas and Robert M. Sullivan published a study in which they proposed that Chrysochampsa was simply a species of Allognathosuchus , with an earlier abstract version of the study going as far as suggesting it was synonymous with Allognathosuchus mooki [2] (though Lucas and Sullivan did not go as far in the finalized publication). [3] Their conclusion was criticized by Christopher A. Brochu that same year, who argued that the features used to link Allognathosuchus and Chrysochampsa were universally present among early Cenozoic alligatoroids. [4] It wasn't until 20 years later that another study explicitly dealt with Chrysochampsa again with Adam P. Cossette and David A. Tarailo publishing a full redescription of the genus alongside their description of its smaller contemporary Ahdeskatanka . Not only did their study reaffirm the validity of Chrysochampsa and back it up with an improved diagnosis, they further shed light on the taxon's previously uncertain relationship with other alligatoroids, determining it to be a caiman rather than an alligatorid. [5]
The name Chrysochampsa roughly translates to "golden crocodile" from the Greek "chrysos" and "champsa", a name chosen in reference to the name of the Golden Valley Formation. The species name is a patronym and references polish paleontologist Marian Mlynarski, who Estes chose to honor for his contributions to paleoherpetology. [5]
Chryochampsa was a relatively large crocodilian for its time with a broad snout (approximately a third longer than wide) similar to Albertochampsa and Brachychampsa. The surface of the skull is described as plain, lacking any prominent bosses, ridges or other major structures to adorn it. Looking at the skull from above shows that its edges are not straight, but somewhat sinuous, with a notable expansion in the region of the first six maxillary teeth. There's also a second expansion, tho the compression and deformation that affects the holotype skull makes it unclear where exactly. Like modern alligators and unlike true crocodiles, Chrysochampsa had an overbite, as revealed by the fact that the teeth of the lower jaw left occlusal marks on the lingual side of the toothrow. [5]
The nares of Chrysochampsa are keyhole-shaped and their edges are level with the rest of the surrounding skull surface. Most of the edge of the nares is formed by the premaxillae, with the only exception being the posterior-most edge where the nasal bones contact the opening. In this regard Chrysochampsa bears a resemblance to Stangerochampsa , although the amount of the nasals that extends into the nares is even smaller than in the Cretaceous taxon. On its underside the premaxillae preserve the incisive foramen, though it is largely obscured. Based on what is visible, it appears to have been teardrop-shaped and possibly intersected the lower premaxillary-maxillary suture. When viewed from above, the premaxillae form a long and thin posterior process that extends back to the position of the fourth maxillary tooth. The maxillae are proportionally longer than in other members of Brachychampsini and broadly contact the premaxillae and nasal bones. Like in Brachychampsa montana, the maxillae form a small V-shaped process that extends in-between the prefrontal bone and the lacrimal bone. [5]
One of the first diagnostic traits recognizd for Chrysochampsa was the particular shape of the frontal bone. Ever since the original description by Estes, it has been noted for the fact that the region between the eyes was incredibly narrow, yet widened significantly once entering the skull table. There, the frontal contacts the parietal bone and the postorbitals, forming a three-way suture that briefly contacts the large, semicircular supratemporal fenestrae. This means that the frontal. Unlike in other forms, where the postorbitals play a part in forming the margins of the eyesockets, this rolle is entirely filled by the frontal in Chrysochampsa. This is in part due to the shape, as in Chrysochampsa the postorbitals are more rectangular, while they are boomerang-shaped in the animal's closest relatives. The parietal is hourglass-shaped and the squamosals, which form the back corners of the skull table, are boomerang-shaped. Like in Brachychampsa but different from Albertochampsa and Stangerochampsa, the supraoccipital bone actually makes a visible contribution to the dorsal surface of the skull table, appearing as a wider than long and crescent-shaped element at the very back of the structure. [5]
The lower jaw of Chrysochampsa is described as U-shaped and robust. The mandibular symphysis, the region where the two halves of the lower jaw meet, is formed mostly by the dentary bone and to a lesser extent by the splenial. The symphysis ends at approximately the level of the fourth dentary alveolous, which would house the largest tooth in the lower jaw. [5]
Each premaxilla of Chrysochampsa contained five teeth of varying size. Based on the alveoli, the first two teeth were small, followed by a larger third tooth and a fourth that was the largest and a fifth that resembled the first two in size. The maxillary toothrow begins small but the size of the individual teeth grows rapidly leading up to the fourth maxillary tooth before they decrease in size again. The lower jaw contains 19 dentary teeth per hemimandible, with the individual tooth sockets circular to ovoid in appearance. The teeth themselves bear slight carinae (cutting edges) and striations. The early teeth of the lower jaw, like those in the premaxillae, show a size increase from the first to the fourth, with the fourth being the largest of the entire lower jaw as is common in crocodilians. After this the teeth grow smaller and then larger again, reaching their peak with the 12th tooth (which is the second largest tooth of the entire lower jaw) before reducing in size once more. [5]
Relatively few postcranial elements of Chrysochampsa are described, including the unkeeled osteoderms and the intercentrum of the atlas, the first neck vertebrae. The osteoderms are described as squared and similar to those of other members of the Alligatoridae, yet differing from the closely related Brachychampsa. The intercentrum of the atlas is plate shaped owing to the fact that it is naturally dorsoventrally (top to bottom) compressed, anatomy that is also common in alligatorids. [5]
The relationship between Chrysochampsa and other alligatoroids has long remained elusive. Though it was originally described as an alligatorid by Estes, [1] Christopher Brochu did not include it in his 1999 study on alligatoroid phylogenetics as he considered the taxon a wildcard, appearing in so many possible positions that it caused the collapse of the strict consensus trees. [6] The next attempt to resolve the position of Chrysochampsa was conducted by Jessica Miller-Camp in 2016 and did prove fruitfull. This thesis recovered it as the basalmost member of Globidonta, diverging from other alligatoroids after Deinosuchus and Diplocynodon but before Brachychampsa , Albertochampsa , Stangerochampsa and the split between alligatorines and caimanines. [7]
The most thorough examination of the phylogenetic position of Chrysochampsa stems from the 2024 study by Cossette and Tarailo, who provided a redescription and amended diagnosis for the animal. Their study found that Chrysochampsa formed a clade with multiple Cretaceous forms, namely Brachychampsa montana, Brachychampsa sealyi, Albertochampsa langstoni and Stangerochampsa mccabei. This clade, which was found to be the earliest-diverging branch of caimans, was dubbed Brachychampsini. [5]
Alligatoroidea |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Chrysochampsa lived during the Early Eocene Climatic Optimum in what is now the Golden Valley Formation of North Dakota. During this time of increased global temperatures, faunal turnover and plant diversification, North Dakota was warm and humid, with mean annual temperature being 18.5° Celsius. The environment inhabited by Chrysochampsa consisted of lowland swamps, meandering rivers and streams and subtropical to tropical forests that grew along their banks. At least 41 species of macroflora have been identified from the formation including both terrestrial forms like ferns, conifers, and dicots and also floating and rooted aquatic plants. One common plant from the formation was the floating fern Salvinia preauriculata . [5]
Various mammals have been recovered from the Golden Valley Formation, consisting of ungulates like Homogalax and Hyopsodus , early primates like Pelycodus and Teilhardina and even a multituberculate, Parectypodus . Carnivorous mammals are rarer and often on the smaller scale, but also present. Among these are teeth tentatively assigned to the hyaenodont Sinopa and fossils of the carnivorans Miacis and Didymictis . [5]
In addition to the crocodiles of the formation, these swamps and streams were inhabited by a wide range of aquatic and semi-aquatic animals. Fish are represented in part by bowfins and gars and amphibians by frogs and salamanders (including the genera Batrachosauroides and Chrysoriton ). A number of freshwater turtles are also known, including Baptemys , Echmatemys and Plastomenus , as well as softshell turtles of the genus Trionyx . [5]
Crocodilian remains are especially abundant in the sediments of the Golden Valley Formation and are known to represent anywhere from four to five distinct forms. Two of these, Ahdeskatanka and an as of yet unnamed related form, are small-bodied alligatorines with blunt snouts and globular teeth that would be well suited for crushing hard shelled prey. A much larger crocodilian of the Golden Valley Formation is represented by an unnamed crocodyloid that exhibits a V-shaped lower jaw and pointed teeth. In many regards, this taxon may be similar to Borealosuchus, which was widespread across the United States during the Late Cretaceous and early Neogene. [5]
Chrysochampsa itself is similar to the unnamed crocodyloid in that it is among the large crocodilians of the formation. Unlike its Cretaceous relatives, Chrysochampsa had more conical teeth that, combined with its robust snout, draw comparison to modern American alligators. Like them and the contemporary crocodyloid, Chrysochampsa was likely a generalist predator capable of preying on almost anything that it could swallow. Given that the Golden Valley Formation was dominated by rivers and swamps, Chrysochampsa would have had a considerable advantage over the local mammal carnivorans, possibly explaining their relative rarity in the sediments. Notably, the fact that Chrysochampsa possessed conical rather than globular teeth, differentiating it from its closest relatives, might suggest that it had to adapt to such a generalist lifestyle due to increased competition with the small-bodied alligatoroids that possessed crushing dentition. [5]
Cossette and Tarailo do note that the recovery of the many crocodilians from the Golden Valley Formation may not necessarily represent true sympatry, as today many crocodilians overlap in range but are often separated by habitat preferences. For example, though Chrysochampsa and Ahdeskatanka could have inhabited the same environment, the fact alone that the latter was notably smaller meant that it could have more easily entered and navigated the forests that grew alongside the river banks and around the swamps, while Chrysochampsa, owing to its larger size, would have been more water-bound. At the same time, there is clear evidence for some niche partitioning among the forms, with their different sizes and morphologies allowing them to exploit different niches within the same biome. Again Chrysochampsa bears the hallmarks of being a generalist feeding on a wide range of prey including the local mammal fauna, whereas Ahdeskatanka had crushing dentition (though the degree of specialisation is uncertain). Further complexity is also added by the animal's growth cycles. Cossette and Tarailo highlight that only mature adults would be considered true apex predators, whereas younger individuals would fill the rolle of mesopredator instead. [5]
Ceratosuchus is an extinct genus of alligatorine crocodylian from latest Paleocene rocks of Colorado's Piceance Basin and earliest Eocene rocks of Wyoming's Bighorn Basin in North America, a slice of time known as the Clarkforkian North American Land Mammal Age. Like its modern relatives, Ceratosuchus was a swamp-dwelling predator. It is named for the pair of flattened, triangular bony plates that extend from the back of its head.
Wannaganosuchus is an extinct genus of small alligatorid crocodilian. It was found in Late Paleocene-age rocks of Billings County, North Dakota, United States.
Procaimanoidea is an extinct genus of alligatorid from the Eocene of North America. It was named posthumously in 1946 by Charles W. Gilmore; the type species is P. utahensis, from the Uintan of Utah. It is based on USNM 15996, a nearly complete skull and partial left hind leg. A second species, P. kayi, was named in 1941 by C.C. Mook as a species of Hassiacosuchus, for remains from the Bridgerian of Wyoming. It was reassigned to Procaimanoidea in 1967 by Wassersug and Hecht.
Harpacochampsa is a poorly known Early Miocene crocodilian from the Bullock Creek lagerstätte of the Northern Territory, Australia. The current specimen consists of a partial skull and fragments of a long, slender snout reminiscent of that of a false gharial, demonstrating that it was a piscivore in life.
Allognathosuchus is an extinct genus of alligatorine crocodylian with a complicated taxonomic history. It was named in 1921.
Navajosuchus is an extinct genus of alligatorine crocodylian. Its fossils have been found in the Paleocene-age Nacimiento Formation of the San Juan Basin, New Mexico. It was named in 1942 by Charles C. Mook, and the original type species was N. novomexicanus. N. novomexicanus was based on AMNH 5186, a partial skull collected in 1913. Later research showed that Navajosuchus novomexicanus was the same as the earlier-named Allognathosuchus mooki. However, A. mooki does not belong to the genus Allognathosuchus, and so the name of the crocodilian becomes Navajosuchus mooki. Under whichever name is used, this animal would have been a generalized predator of the Nacimiento floodplains. It was the most common Nacimiento Formation crocodilian, found in both the Puercan and Torrejonian faunal assemblages.
Asiatosuchus is an extinct genus of crocodyloid crocodilians that lived in Eurasia during the Paleogene. Many Paleogene crocodilians from Europe and Asia have been attributed to Asiatosuchus since the genus was named in 1940. These species have a generalized crocodilian morphology typified by flat, triangular skulls. The feature that traditionally united these species under the genus Asiatosuchus is a broad connection or symphysis between the two halves of the lower jaw. Recent studies of the evolutionary relationships of early crocodilians along with closer examinations of the morphology of fossil specimens suggest that only the first named species of Asiatosuchus, A. grangeri from the Eocene of Mongolia, belongs in the genus. Most species are now regarded as nomina dubia or "dubious names", meaning that their type specimens lack the unique anatomical features necessary to justify their classification as distinct species. Other species such as "A." germanicus and "A." depressifrons are still considered valid species, but they do not form an evolutionary grouping with A. grangeri that would warrant them being placed together in the genus Asiatosuchus.
Arambourgia is an extinct monotypic genus of alligatorine crocodylian from Europe. It was named in 1905 as Allognathosuchus gaudryi. It was made a separate genus Arambourgia in 1940. This was synonymized with Allognathosuchus haupti in 1990, but later reassigned as its own genus once again in 2004. Arambourgia was likely to have been part of an early dispersal event of alligatorines from North America to Europe during the Eocene epoch. Arambourgia had non-serrated teeth and a deep orienirostral snout, unlike the flatter snouts of most other alligatorids.
Brachychampsa is an extinct genus of alligatorid, possibly a basal caiman. Specimens have been reported from New Mexico, Colorado, Wyoming, Montana, North and South Dakota, New Jersey, and Saskatchewan, though only those from Montana, Utah, and New Mexico are based on material sufficient to justify the referral. Some specimens have been reported from the Campanian-aged deposits of Central Asia, although the species status is indeterminate for these fossils. The genus first appeared during the late Campanian stage of the Late Cretaceous and became extinct during the late Maastrichtian stage of the Cretaceous. Brachychampsa is distinguished by an enlarged fifth maxillary tooth in the upper jaw.
Orthogenysuchus is an extinct genus of caimanine alligatorids. Fossils have been found from the Wasatch Beds of the Willwood Formation of Wyoming, deposited during the early Eocene. The type species is O. olseni. The holotype, known as AMNH 5178, is the only known specimen belonging to the genus and consists of a skull lacking the lower jaws. The braincase is filled in by the matrix and most of the suture lines between bones are indiscernible, making comparisons with other eusuchian material difficult.
Prodiplocynodon is an extinct genus of basal crocodyloid crocodylian. It is one of the only crocodyloids known from the Cretaceous and existed during the Maastrichtian stage. The only species of Prodiplocynodon is the type species P. langi from the Lance Formation of Wyoming, known only from a single holotype skull lacking the lower jaw.
Stangerochampsa is an extinct genus of alligatorid, possibly an alligatorine or a stem-caiman, from the Late Cretaceous of Alberta. It is based on RTMP.86.61.1, a skull, partial lower jaws, and partial postcranial skeleton discovered in the late Campanian–early Maastrichtian-age Horseshoe Canyon Formation. Stangerochampsa was described in 1996 by Wu and colleagues. The type species is S. mccabei. The generic name honors the Stanger family, the owners of the ranch where the specimen was found, and the species name honors James Ross McCabe, who discovered, collected, and prepared it. Stangerochampsa is described as "small to medium–sized"; the type skull is 20.0 centimetres (7.9 in) long from the tip of the snout to the occipital condyle, and is 13.0 centimetres (5.1 in) wide at its greatest, while the thigh bone is 14.2 centimetres (5.6 in) long. It had heterodont dentition, with large crushing teeth at the rear of the jaws.
Alligator prenasalis is an extinct species of alligator from the Late Eocene period. It is well known, with many fossils having been collected from the Chadron and Brule Formations in South Dakota. The species was first named in 1904, but was originally classified as a crocodile in the genus Crocodilus. It was reassigned to the genus Alligator in 1918 on the basis of more complete material. It is the earliest known member of the genus Alligator.
Globidonta is a clade of alligatoroids that includes alligators, caimans, and closely related extinct forms. It is defined as a stem-based clade including Alligator mississippiensis and all forms more closely related to it than to Diplocynodon. The group's fossil range extends back into the Campanian stage of the Late Cretaceous with early alligatoroids such as Albertochampsa and Brachychampsa. Extinct globidontans were particularly common in North America and Eurasia, and their modern range also includes South America.
Culebrasuchus is an extinct, monotypic genus of caiman alligatorid known from the Early to Middle Miocene (Hemingfordian) of the Panama Canal Zone of Panama. It contains a single species, Culebrasuchus mesoamericanus.
Astorgosuchus is an extinct monospecific genus of crocodilian, closely related to true crocodiles, that lived in Pakistan during the late Oligocene period. This crocodile may have reached lengths of up to 7–8 m (23–26 ft) and is known to have preyed on many of the large mammals found in its environment. Bite marks of a large crocodile have been found on the bones of juvenile Paraceratherium, however if these were left by Astorgosuchus cannot be said with certainty. The genus contains a single species, Astorgosuchus bugtiensis, which was originally named as a species of Crocodylus in 1908 and was moved to its own genus in 2019.
Chinatichampsus is an extinct genus of crocodilian from the Devil's Graveyard Formation of Texas, specifically the Dalquest Desert Research Site. It is a monotypic genus, containing only the type species Chintanichampsus wilsonorum. A single specimen, TMM 45911–1, was first discovered in 2010. Chinatichampsus is the most basal Eocene caimanine, dating to between 42.8 and 41.5 million years ago, and is considered to be more basal than Protocaiman.
Qianshanosuchus is a genus of basal crocodyloid from the Paleocene of the Qianshan Basin, China. The fossil material, which includes an incomplete skull and parts of the lower jaw, show various features usually associated with juvenile crocodiles alongside various unique traits that were used to erect a new genus. It is the first and only basal crocodyloid currently known from the Paleocene of China, which had previously only yielded alligatoroids and planocraniids. Its presence in this part of the world and its basal position to species of the genus Asiatosuchus supports the idea that crocodyloids dispersed from Asia into Europe. Qianshanosuchus only includes a single species, Qianshanosuchus youngi.
Eurycephalosuchus is an extinct genus of orientalosuchine alligatoroid from the Late Cretaceous Jiangxi Province of China. Known from a well preserved skull and mandible alongside various postcranial remains, Eurycephalosuchus possessed a short and broad skull with a very short skulltable. Eurycephalosuchus lived with at least one other crocodilian, an indetermined member of the clade Brevirostres. The genus is monotypic, containing only the species Eurycephalosuchus gannanensis.
Ahdeskatanka is an extinct genus of alligator from the Early Eocene Golden Valley Formation of North Dakota, USA. Ahdeskatanka had a short, rounded snout with globular teeth that are well-suited for crushing hard-shelled prey, though its exact ecology is not known. Ahdeskatanka inhabited the vast wetlands that covered much of western North Dakota during the Early Eocene Climatic Optimum, an environment it shared with at least three other crocodilians. These include the large caiman Chrysochampsa and at least two unnamed forms, one a large crocodyloid and one more similar to Ahdeskatanka. Phylogenetic analysis suggests that it was an early diverging member of the Alligatorinae, possibly related to Allognathosuchus, though its position is not very stable. Only a single species, Ahdeskatanka russlanddeutsche, is placed in this genus.