A cladogram (from Greek clados "branch" and gramma "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to descendants, nor does it show how much they have changed, so many differing evolutionary trees can be consistent with the same cladogram. A cladogram uses lines that branch off in different directions ending at a clade , a group of organisms with a last common ancestor . There are many shapes of cladograms but they all have lines that branch off from other lines. The lines can be traced back to where they branch off. These branching off points represent a hypothetical ancestor (not an actual entity) which can be inferred to exhibit the traits shared among the terminal taxa above it. This hypothetical ancestor might then provide clues about the order of evolution of various features, adaptation, and other evolutionary narratives about ancestors. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational phylogenetics are now very commonly used in the generation of cladograms, either on their own or in combination with morphology.
58-514: Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction . Extinct crocodylomorphs were considerably more ecologically diverse than modern crocodillians. The earliest and most primitive crocodylomorphs are represented by " sphenosuchians ", a paraphyletic assemblage containing small-bodied, slender forms with elongated limbs that walked upright, which represents
116-446: A t e s {\displaystyle n.states} , c i occupies a range from 1 to ( n . s t a t e s − 1 ) / ( n . t a x a − ⌈ n . t a x a / n . s t a t e s ⌉ ) {\displaystyle (n.states-1)/(n.taxa-\lceil n.taxa/n.states\rceil )} . The retention index (RI)
174-445: A metric to measure how consistent a candidate cladogram is with the data. Most cladogram algorithms use the mathematical techniques of optimization and minimization. In general, cladogram generation algorithms must be implemented as computer programs, although some algorithms can be performed manually when the data sets are modest (for example, just a few species and a couple of characteristics). Some algorithms are useful only when
232-501: A branch-based clade, Pseudosuchia is the sister taxon of another branch-based clade, the Avemetatarsalia . Avemetatarsalians are bird-line archosaurs, including pterosaurs and dinosaurs (the latter including birds). A different definition was suggested by Benton and Clark, 1988: the node-based taxon including the last common ancestor of Rauisuchidae and aetosaurs and all of its descendants. Benton and Clark also named
290-540: A character in a phylogenetic analysis as they do not contribute anything to our understanding of relationships. However, homoplasy is often not evident from inspection of the character itself (as in DNA sequence, for example), and is then detected by its incongruence (unparsimonious distribution) on a most-parsimonious cladogram. Note that characters that are homoplastic may still contain phylogenetic signal . A well-known example of homoplasy due to convergent evolution would be
348-412: A cladogram can be roughly categorized as either morphological (synapsid skull, warm blooded, notochord , unicellular, etc.) or molecular (DNA, RNA, or other genetic information). Prior to the advent of DNA sequencing, cladistic analysis primarily used morphological data. Behavioral data (for animals) may also be used. As DNA sequencing has become cheaper and easier, molecular systematics has become
406-422: A dataset, the degree to which each character carries phylogenetic information, and the fashion in which additive characters are coded, rendering it unfit for purpose. c i occupies a range from 1 to 1/[ n.taxa /2] in binary characters with an even state distribution; its minimum value is larger when states are not evenly spread. In general, for a binary or non-binary character with n . s t
464-586: A diverse array of lifestyles during the Jurassic and Cretaceous periods, although only a single subset of crocodylomorphs, the Crocodilia, survive to the present day. Living crocodilians include crocodiles , alligators , caimans , and gavialids . The name Pseudosuchia was originally given to a group of superficially crocodile-like prehistoric reptiles from the Triassic period, but fell out of use in
522-513: A group called Crocodylotarsi, which includes most taxa now considered pseudosuchians. In 1990, Paul Sereno erected the clade Crurotarsi to supplant Pseudosuchia. However, Sereno defined Crurotarsi as a node-based clade, relying on the inclusion of groups such as Phytosauria , Aetosauria, and Crocodylomorpha . It is not equivalent to Pseudosuchia, which by definition must include all crocodilian-line archosaurs. For many years, Pseudosuchia and Crurotarsi have been considered partial synonyms because
580-457: A larger clade. The incongruence length difference test (ILD) is a measurement of how the combination of different datasets (e.g. morphological and molecular, plastid and nuclear genes) contributes to a longer tree. It is measured by first calculating the total tree length of each partition and summing them. Then replicates are made by making randomly assembled partitions consisting of the original partitions. The lengths are summed. A p value of 0.01
638-452: A more and more popular way to infer phylogenetic hypotheses. Using a parsimony criterion is only one of several methods to infer a phylogeny from molecular data. Approaches such as maximum likelihood , which incorporate explicit models of sequence evolution, are non-Hennigian ways to evaluate sequence data. Another powerful method of reconstructing phylogenies is the use of genomic retrotransposon markers , which are thought to be less prone to
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#1732773342998696-407: A similar definition, Crocodylotarsi, was named in 1988, possibly as a replacement for Pseudosuchia. The name Pseudosuchia, meaning "false crocodiles", has been used for over a century, and traditionally included only non-crocodilians, but when defined as a clade, Pseudosuchia came to include the group Eusuchia ("true crocodiles") as well. Crocodylotarsi may have been named to remove confusion, but as
754-410: A staggering diversity of reptiles with many different lifestyles. Early pseudosuchians were successful in the Triassic period. They included giant, quadrupedal apex predators such as Saurosuchus , Prestosuchus , and Fasolasuchus . Ornithosuchids were large scavengers, while erpetosuchids and gracilisuchids were small, light-footed predators. A few groups acquired herbivorous diets, such as
812-399: A stem-based clade, it is synonymous with Pseudosuchia. Because Pseudosuchia was named first, it has precedence. A third group, Crurotarsi , traditionally included the same archosaurs as Pseudosuchia, but as a node-based clade it is not synonymous. The scope of Crurotarsi has recently been changed by the phylogenetic placement of phytosaurs. In 2011, Sterling J. Nesbitt found phytosaurs to be
870-628: A subgroup of Neosuchia, emerged during the Late Cretaceous. Crocodylomorph diversity was severely reduced by the end-Cretaceous extinction event . The last group of terrestrially adapted crocodylomorphs was the Sebecidae , a group of large predatory notosuchians which persisted in South America until the middle Miocene around 12 million years ago. Historically, all known living and extinct crocodiles were indiscriminately lumped into
928-405: A subset of the group. The clade Pseudosuchia is potentially equivalent to Crurotarsi even though the latter has a different, node-based definition: "all taxa the least inclusive clade containing Rutiodon carolinensis (Emmons, 1856), and Crocodylus niloticus (Laurenti, 1768)." However, a major 2011 study of Triassic archosaur relations proposed that Rutiodon 's group, Phytosauria ,
986-636: A variety of forms, shapes, and sizes, which occupied a range of habitats. As with most amniotes , Crocodylomorphs were and are oviparous , laying eggs in a nest or mound, known from strata as old as the Late Jurassic. Adult size varies widely, from about 55 cm long in Knoetschkesuchus to much larger dimensions, as in Sarcosuchus . Most crocodylomorphs were carnivores , but many lineages evolved to be obligate piscivores , such as
1044-966: Is a cladogram modified from Nesbitt (2011) showing the new changes (bold terminal taxa are collapsed). † Proterosuchidae [REDACTED] † Erythrosuchus [REDACTED] † Vancleavea [REDACTED] † Proterochampsia [REDACTED] † Euparkeria [REDACTED] † Phytosauria [REDACTED] Avemetatarsalia (bird-lineage of archosaurs) [REDACTED] † Ornithosuchidae [REDACTED] † Gracilisuchus [REDACTED] † Turfanosuchus [REDACTED] † Revueltosaurus [REDACTED] † Aetosauria [REDACTED] † Ticinosuchus [REDACTED] † Poposauroidea [REDACTED] † Prestosuchus [REDACTED] † Saurosuchus [REDACTED] † Batrachotomus [REDACTED] † Fasolasuchus † Rauisuchidae [REDACTED] Crocodylomorpha [REDACTED] The following cladogram
1102-410: Is a character state that is shared by two or more taxa due to some cause other than common ancestry. The two main types of homoplasy are convergence (evolution of the "same" character in at least two distinct lineages) and reversion (the return to an ancestral character state). Characters that are obviously homoplastic, such as white fur in different lineages of Arctic mammals, should not be included as
1160-399: Is currently considered valid is Crocodilia in its present definition. Prehistoric crocodiles are represented by many taxa, but since few major groups of the ancient forms are distinguishable, a conclusion on how to define new order-level clades is not yet possible. (Benson & Clark, 1988). Crocodylomorpha in the modern sense, as defined by Paul Sereno in 2005, is phylogenetically defined as
1218-1043: Is from a slightly older study, Brusatte, Benton, Desojo and Langer (2010). Bold terminal taxa are collapsed. Several results of the study, such as the retention of a monophyletic Rauisuchia , the retention of phytosaurs within Pseudosuchia, and a close relation between aetosaurs and crocodylomorphs, replicate the results of older studies. However, the findings of Nesbitt (2011) have been more widely supported by pseudosuchian-focused analyses published since 2011. † Erythrosuchus [REDACTED] † Euparkeria [REDACTED] † Proterochampsidae [REDACTED] Avemetatarsalia [REDACTED] † Phytosauria [REDACTED] † Aetosauria [REDACTED] † Gracilisuchus [REDACTED] † Erpetosuchus [REDACTED] Crocodylomorpha [REDACTED] † Revueltosaurus [REDACTED] † Ornithosuchidae [REDACTED] Cladogram The characteristics used to create
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#17327733429981276-411: Is obtained for 100 replicates if 99 replicates have longer combined tree lengths. Some measures attempt to measure the amount of homoplasy in a dataset with reference to a tree, though it is not necessarily clear precisely what property these measures aim to quantify The consistency index (CI) measures the consistency of a tree to a set of data – a measure of the minimum amount of homoplasy implied by
1334-589: Is one of the two primary "daughter" clades of the Archosauria . The skull is often massively built, especially in contrast to ornithodires ; the snout is narrow and tends to be elongated, the neck is short and strong, and the limb posture ranges from a typical reptilian sprawl to an erect stance like dinosaurs ' or mammals ', although achieving it a different way. The body is often protected by two or more rows of armored plates. Many crurotarsans reached lengths of three meters or more. Pseudosuchians appeared during
1392-404: Is one of two major divisions of Archosauria , including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs", in contrast to the "bird-line archosaurs" or Avemetatarsalia . Despite Pseudosuchia meaning "false crocodiles", the name is a misnomer as true crocodilians are now defined as
1450-526: Is usually done by comparison to the character states of one or more outgroups . States shared between the outgroup and some members of the in-group are symplesiomorphies; states that are present only in a subset of the in-group are synapomorphies. Note that character states unique to a single terminal (autapomorphies) do not provide evidence of grouping. The choice of an outgroup is a crucial step in cladistic analysis because different outgroups can produce trees with profoundly different topologies. A homoplasy
1508-572: The Miocene . The earliest lineages of Crocodylomorpha are placed into the paraphyletic " Sphenosuchia ", which are characterized by slender bodies with elongate legs. The oldest known crocodylomorph is Trialestes , known from the Late Triassic (Carnian-Norian) of Argentina, around 231–225 million years ago, the last groups of "sphenosuchians" persisted until the end of the Jurassic. During
1566-459: The order Crocodilia. However, beginning in the late 1980s, many scientists began restricting the order Crocodilia to the living species and close extinct relatives such as Mekosuchus . The various other groups that had previously been known as Crocodilia were moved to Crocodylomorpha and the slightly more restrictive Crocodyliformes . Crocodylomorpha has been given the rank of superorder in some 20th and 21st century studies. The old Crocodilia
1624-635: The Jurassic, crocodylomorphs diversified, including the emergence of herbivorous and omnivorous forms, as well as the aquatically adapted Neosuchia and Thalattosuchia , with Thalattosuchia and several groups of neosuchians becoming adapted to a marine lifestyle over the Jurassic and Cretaceous During the Cretaceous, the Notosuchia were a diverse group across the Southern Hemisphere occupying many diverse ecologies. Modern crocodilians ,
1682-497: The ancestral morphology of Crocodylomorpha. These forms persisted until the end of the Jurassic. During the Jurassic, crocodylomorphs morphologically diversified into numerous niches, with the subgroups Neosuchia (which includes modern crocodilians) and the extinct Thalattosuchia adapting to aquatic life, while some terrestrial groups adopted herbivorous and omnivorous lifestyles. Terrestrial crocodylomorphs would continue to co-exist alongside aquatic forms until becoming extinct during
1740-577: The birds, while the crocodilians continued with little change. Today, the crocodiles , alligators , and gharials are the surviving representatives of this lineage. The Mesozoic range of cranial disparity is higher than the Triassic one, suggesting crocodylomorphs attained a high degree of diversification compared to Triassic pseudosuchians. Pseudosuchia was defined as a stem-based clade in 1985. It includes crocodiles and all archosaurs more closely related to crocodiles than to birds. A second clade with
1798-431: The character, "presence of wings". Although the wings of birds, bats , and insects serve the same function, each evolved independently, as can be seen by their anatomy . If a bird, bat, and a winged insect were scored for the character, "presence of wings", a homoplasy would be introduced into the dataset, and this could potentially confound the analysis, possibly resulting in a false hypothesis of relationships. Of course,
Crocodylomorpha - Misplaced Pages Continue
1856-434: The characteristic data are molecular (DNA, RNA); other algorithms are useful only when the characteristic data are morphological. Other algorithms can be used when the characteristic data includes both molecular and morphological data. Algorithms for cladograms or other types of phylogenetic trees include least squares , neighbor-joining , parsimony , maximum likelihood , and Bayesian inference . Biologists sometimes use
1914-691: The dataset). The rescaled consistency index (RC) is obtained by multiplying the CI by the RI; in effect this stretches the range of the CI such that its minimum theoretically attainable value is rescaled to 0, with its maximum remaining at 1. The homoplasy index (HI) is simply 1 − CI. This measures the amount of homoplasy observed on a tree relative to the maximum amount of homoplasy that could theoretically be present – 1 − (observed homoplasy excess) / (maximum homoplasy excess). A value of 1 indicates no homoplasy; 0 represents as much homoplasy as there would be in
1972-515: The dominant terrestrial carnivores and herbivores. As the Mesozoic progressed, the Protosuchia gave rise to more typically crocodile-like forms. While dinosaurs were the dominant animals on land, the crocodiles flourished in rivers, swamps, and the oceans, with far greater diversity than they have today. With the end-Cretaceous extinction , the dinosaurs became extinct, with the exception of
2030-468: The extant gharials. In some forms, like Hesperosuchus and Terrestrisuchus , metatarsal V still had one or two phalanges , but in Crocodyliformes all metatarsal V phalanges have been lost. [REDACTED] [REDACTED] [REDACTED] [REDACTED] Pseudosuchia Pseudosuchia (from Greek : ψεύδος (pseudos) , "false" and Greek : σούχος (souchos) , "crocodile")
2088-424: The extinction of all the pseudosuchians with the exception of Sphenosuchia and Crocodyliformes (both Crocodylomorpha ), the latter being the ancestors of modern-day crocodiles. A study published in 2010 postulates that there is significant evidence that volcanic eruptions changed the climate, causing a mass extinction that wiped out the dinosaurs' main competitors. This allowed the dinosaurs to succeed them as
2146-750: The first to establish the name Pseudosuchia in a phylogenetic context, using it as a branch-based taxon for all archosaurs more closely related to crocodilians than to birds. This made the name Pseudosuchia somewhat ironic because true crocodiles (i.e. members of Crocodylia) were now included in the group. Phylogenetic definitions of Pseudosuchia include "Crocodiles and all archosaurs closer to crocodiles than to birds" (Gauthier and Padian), "Extant crocodiles and all extinct archosaurs that are closer to crocodiles than they are to birds" (Gauthier, 1986), and more recently "the most inclusive clade within Archosauria that includes Crocodylia but not Aves" (Senter, 2005). As
2204-490: The heavily armored aetosaurs , and several were bipedal, such as Poposaurus and Postosuchus . The bizarre, ornithomimid -like shuvosaurids were both bipedal and herbivorous, with toothless beaks. Many of these Triassic pseudosuchian groups went extinct at or before the Triassic–Jurassic extinction event . However, one group, the crocodylomorphs , survived the major extinction. Crocodylomorphs themselves evolved
2262-540: The late Olenekian (early Triassic ); by the Ladinian (late Middle Triassic) they dominated the terrestrial carnivore niches. Their heyday was the Late Triassic, during which time their ranks included erect-limbed rauisuchians , herbivorous armored aetosaurs , the large predatory poposaurs , the small agile sphenosuchian crocodilians, and a few other assorted groups. The end-Triassic extinction caused
2320-399: The late 20th century, especially after the name Crurotarsi was established in 1990 to label the clade (evolutionary grouping) of archosaurs encompassing most reptiles previously identified as pseudosuchians. By this time, Pseudosuchia had also been defined as a clade , but it was not widely embraced until 2011. In 2011 paleontologist Sterling Nesbitt proposed that Crurotarsi, as it
2378-412: The latter clade encompasses all crocodilian-line archosaurs in most phylogenetic analyses. Sterling Nesbitt 's 2011 analysis places one crurotarsan group, Phytosauria, outside Pseudosuchia. Since the definition of Crurotarsi relies on phytosaurs, their placement outside Pseudosuchia (and thus Archosauria) means that the clade Crurotarsi includes both pseudosuchians and avemetatarsalians. Pseudosuchia
Crocodylomorpha - Misplaced Pages Continue
2436-476: The more derived Crocodyliformes . The basal crocodylomorph Saltoposuchidae was defined by Speikman, 2023 as the most inclusive clade containing Saltoposuchus connectens , but not Sphenosuchus acutus , Carnufex carolinensis , and Trialestes romeri . The clade Solidocrania was established by Alexander A. Ruebenstahl and colleagues in 2022 to unite crocodyliforms with their closest "sphenosuchian" relatives who both share similarly reinforced skulls. This clade
2494-471: The most inclusive clade containing Crocodylus niloticus (the Nile crocodile), but not Rauisuchus tiradentes , Poposaurus gracilis , Gracilisuchus stipanicicorum , Prestosuchus chiniquensis , or Aetosaurus ferratus . Below is a cladogram of most known crocodylomorphs from Stephan F. Speikeman in 2023. The modern consensus is that "sphenosuchians" form a paraphyletic assemblage leading towards
2552-518: The name "false crocodiles". In mid-20th century textbooks, like Alfred Sherwood Romer 's Vertebrate Paleontology and Edwin H. Colbert 's Evolution of the Vertebrates , Pseudosuchia constitutes one of the suborders of the now-abandoned order Thecodontia . Zittel's aetosaurs were placed in their own suborder, Aetosauria. Colbert considered small lightly built archosaurs, such as Ornithosuchus and Hesperosuchus — both of which were at
2610-705: The only reason a homoplasy is recognizable in the first place is because there are other characters that imply a pattern of relationships that reveal its homoplastic distribution. A cladogram is the diagrammatic result of an analysis, which groups taxa on the basis of synapomorphies alone. There are many other phylogenetic algorithms that treat data somewhat differently, and result in phylogenetic trees that look like cladograms but are not cladograms. For example, phenetic algorithms, such as UPGMA and Neighbor-Joining, group by overall similarity, and treat both synapomorphies and symplesiomorphies as evidence of grouping, The resulting diagrams are phenograms, not cladograms, Similarly,
2668-499: The problem of reversion that plagues sequence data. They are also generally assumed to have a low incidence of homoplasies because it was once thought that their integration into the genome was entirely random; this seems at least sometimes not to be the case, however. Researchers must decide which character states are "ancestral" ( plesiomorphies ) and which are derived ( synapomorphies ), because only synapomorphic character states provide evidence of grouping. This determination
2726-436: The program settles on a local minimum rather than the desired global minimum. To help solve this problem, many cladogram algorithms use a simulated annealing approach to increase the likelihood that the selected cladogram is the optimal one. The basal position is the direction of the base (or root) of a rooted phylogenetic tree or cladogram. A basal clade is the earliest clade (of a given taxonomic rank[a]) to branch within
2784-405: The results of model-based methods (Maximum Likelihood or Bayesian approaches) that take into account both branching order and "branch length," count both synapomorphies and autapomorphies as evidence for or against grouping, The diagrams resulting from those sorts of analysis are not cladograms, either. There are several algorithms available to identify the "best" cladogram. Most algorithms use
2842-408: The sister taxon of Archosauria, and therefore not crocodile-line archosaurs. Because phytosaurs are included in the definition of Crurotarsi, crurotarsans are not solely crocodile-line archosaurs, but also bird-line archosaurs and phytosaurs. Under this phylogeny, Crurotarsi includes phytosaurs, crocodiles, pterosaurs, and dinosaurs, while Pseudosuchia still contains only crocodile-line archosaurs. Below
2900-460: The term parsimony for a specific kind of cladogram generation algorithm and sometimes as an umbrella term for all phylogenetic algorithms. Algorithms that perform optimization tasks (such as building cladograms) can be sensitive to the order in which the input data (the list of species and their characteristics) is presented. Inputting the data in various orders can cause the same algorithm to produce different "best" cladograms. In these situations,
2958-523: The time reconstructed as theropod dinosaur-like bipeds — to be typical pseudosuchians. These small forms were assumed to be the ancestors of all later archosaurs. The name Pseudosuchia became a wastebasket taxon into which all thecodonts that did not fit in the other three suborders could be placed. Even Sharovipteryx and Longisquama , two enigmatic Triassic reptiles that bear little resemblance to archosaurs, have been regarded as pseudosuchians. Gauthier and Padian (1985) and Gauthier (1986) became
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#17327733429983016-406: The tree. It is calculated by counting the minimum number of changes in a dataset and dividing it by the actual number of changes needed for the cladogram. A consistency index can also be calculated for an individual character i , denoted c i . Besides reflecting the amount of homoplasy, the metric also reflects the number of taxa in the dataset, (to a lesser extent) the number of characters in
3074-423: The user should input the data in various orders and compare the results. Using different algorithms on a single data set can sometimes yield different "best" cladograms, because each algorithm may have a unique definition of what is "best". Because of the astronomical number of possible cladograms, algorithms cannot guarantee that the solution is the overall best solution. A nonoptimal cladogram will be selected if
3132-464: Was defined as the least inclusive clade including Junggarsuchus sloani , Almadasuchus figarii , and Macelognathus vagans . Erpetosuchus [REDACTED] Redondavenator Carnufex CM 73372 Trialestes Pseudohesperosuchus Litargosuchus Hesperosuchus [REDACTED] Kayentasuchus Dromicosuchus Sphenosuchus Junggarsuchus Almadasuchus Macelognathus The Crocodylomorpha comprise
3190-404: Was not closely related to other traditional "crurotarsans", at least compared to avemetatarsalians such as pterosaurs and dinosaurs . As a result, Crurotarsi could be a much broader clade than Pseudosuchia. Other recent studies support a more traditional phylogeny. Contrary to popular belief, crocodilians differ significantly from their ancestors and distant relatives, as Pseudosuchia contains
3248-399: Was proposed as an improvement of the CI "for certain applications" This metric also purports to measure of the amount of homoplasy, but also measures how well synapomorphies explain the tree. It is calculated taking the (maximum number of changes on a tree minus the number of changes on the tree), and dividing by the (maximum number of changes on the tree minus the minimum number of changes in
3306-479: Was subdivided into the suborders: Mesosuchia is a paraphyletic group as it does not include eusuchians (which nest within Mesosuchia). Mesoeucrocodylia was the name given to the clade that contains mesosuchians and eusuchians (Whetstone and Whybrow, 1983). The previous definitions of Crocodilia and Eusuchia did not accurately convey evolutionary relationships within the group. The only order-level taxon that
3364-568: Was then defined, must include not only crocodilian-line archosaurs, but all other archosaurs including birds, non-avian dinosaurs , and pterosaurs . The clade Pseudosuchia as originally defined could still be used to identify crocodilian-line archosaurs, and since many recent studies support Nesbitt's findings, Pseudosuchia is again commonly used. The name Pseudosuchia was coined by Karl Alfred von Zittel in 1887–1890 to include three taxa (two aetosaurs and Dyoplax ) that were superficially crocodilian-like, but were not actually crocodilian. Hence
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