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DINOSAUR SUCCESS in the TRIASSIC: a NONCOMPETITIVE ECOLOGICAL MODEL This Content Downloaded from 137.222.248.217 on Sat, 17

DINOSAUR SUCCESS in the TRIASSIC: a NONCOMPETITIVE ECOLOGICAL MODEL This Content Downloaded from 137.222.248.217 on Sat, 17

VOLUME 58, No. 1 THE QUARTERLY REVIEW OF BIOLOGY MARCH 1983

DINOSAUR SUCCESS IN THE : A NONCOMPETITIVE ECOLOGICAL MODEL

MICHAEL J. BENTON

University Museum, Parks Road, Oxford OX] 3PW, England, UK

ABSTRACT

The initial radiation of the in the Triassic period (about 200 million ago) has been generally regarded as a result of successful competition with the previously dominant - like . A detailed review of major terrestrial of the Permo- Triassic, including estimates of relative abundance, gives a different picture of the pattern of faunal replacements. Dinosaurs only appeared as dominant faunal elements in the latest Triassic after the disappear- ance of several groups qf mammal-like reptiles, thecondontians (ancestors of dinosaurs and other ), and (medium-sized ). The concepts of differential survival ("competitive") and opportunistic ecological replacement of higher taxonomic categories are contrasted (the latter involves chance radiation to fill adaptive zones that are already empty), and they are applied to the record. There is no evidence that either thecodontians or dinosaurs demonstrated their superiority over mammal-like reptiles in massive competitive take-overs. Thecodontians arose as medium-sized after the of certain mammal-like reptiles (opportunism, latest ). Throughout most of the Triassic, the thecodontians shared adaptive zones with advanced mammal-like reptiles () until the latter became extinct (random processes, early to ). Among herbivores, the mammal-like reptiles were largely replaced by diademodontoid mammal-like reptiles and rhynchosaurs (differential survival, middle to late Triassic). These groups then became extinct and dinosaurs replaced them and radiated rapidly (opportunism, latest Triassic). The late Triassic may be linked with floral and climatic changes. Explanations of success based on the competitive superiority of their thermoregulation or locomotory capability are unnecessary in this model.

INTRODUCTION achieved large size very early in the radia- tion and ruled on land for the next 120 JHE TRIASSIC period (225 to 190 mil- million years. lion years ago) is one of the most im- The pattern of transition from mammal- portant in the history of terrestrial like reptiles to dinosaurs has been described life. Throughout most of the Triassic, the by many authors (e.g., Cox, 1967, 1973a; mammal-like reptiles () dominated Crompton, 1968; Robinson, 1971; Romer, as small to large-sized herbivores and carni- 1972; Colbert, 1973; Bakker, 1975a,b, 1977, vores, but towards the end of the period they 1980; Halstead, 1975; Charig, 1980). These virtually disappeared. Within an apparently authors have assumed that the mammal-like short space of time, dinosaurs radiated from reptiles declined gradually in importance being at first rather rare unimportant during the middle and late Triassic, and that to occupying nearly all terrestrial dinosaurs and their ancestors, the thecodon- niches at the end of the Triassic. They tians, rose to dominance at the same time.

?) 1983 by the Stony Brook Foundation, Inc. All rights reserved.

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Conflict between mammal-like reptiles and complex and unsatisfactory. The Triassic is dinosaurs is the usual cause proposed for divided into several stages on the basis of this. Dinosaur and thecodontian superiority marine molluscs (ammonites), and there are has been traced to their improved locomo- clearly major problems in trying to assign tory capability (Bakker, 1968, 1971; Ostrom, terrestrial deposits to these stages, since 1969; Charig, 1972, 1979, 1980; Sill, 1974; Triassic ammonites and reptiles are rarely Hotton, 1980), or to an advanced thermoregu- found associated. Attempts are now being latory physiology, either a "warm-blooded" en- made, however, to correlate the standard dothermy(Bakker, 1971, 1972, 1975a,b, 1977, ammonite stages with zones based on spores 1980) or a "cold-blooded" inertial homeother- and pollen (Anderson, 1980; Schopf and my (Spotila, Lommen, Bakken, and Gates, Askin, 1980). A summary of the main reptile 1973; Halstead, 1975; Benton, 1979a,b; beds of the Triassic, based on the work of Hotton, 1980). None of these explanations Cox (1967, 1973b), Sill (1969), Colbert has gained universal approval, and they are (1975), Olsen and Galton (1977), Anderson all untestable speculations. Nevertheless, and Cruickshank (1978), Bonaparte (1978), this "competitive model" is presented in all Cooper (1982) and many others, is given in current textbooks and popular works dealing Fig. 1. The terms "Formation," "Series," and with the subject. "Zone" are used for the different reptile beds In to examine this transition in de- according to local custom, and they may be tail, it is necessary to distinguish the pattern regardedof as roughly equivalent. A "Group" historical events, which may be assessed on includes several Formations, and a "Mem- the basis of the known fossil record, from the ber" is a subdivision of a Formation. process by which we seek to explain the pat- There has been some controversy over the tern. It is my intention, first, to present the correct placement of the Santa Maria For- basic data on the relative abundance of dif- mation and the , ferent reptile groups through the Triassic which are assigned here to the or and to analyze the data, with clear state- stages of the Upper Triassic. Romer ments of their limitations. Second, I will test (1970, 1975) argued that these were Middle against the data the fit of different models for Triassic in age, but the close resemblance of the replacement of synapsids by thecodon- elements in their faunas to those of the Ger- tians and dinosaurs. The currently accepted man Mittelkeuper, the Sand- model involves direct competition between stone Formation of Scotland, parts of the an individual mammal-like reptile and of the and an individual thecodontian or dinosaur western , and the Maleri For- species, in which the latter tended to mation of now places them firmly in come off best. In the long term, then, the di- the Upper Triassic. Full details will be given nosaur genera, families, and orders became elsewhere. established and replaced the mammal-like reptile orders. We may term this the "dif- METHODS OF ANALYSIS ferential survival hypothesis." The alter- The basic approach in the present analysis native view, that which is presented here, is was to plot numbers of individuals within that the mammal-like reptiles as a group major faunas against time, rather than became extinct because of climatic and floral numbers of genera or families against time. changes, and the dinosaurs radiated initially The latter approach (diversity analysis) is into empty adaptive zones. This may be useful in the calculation of rates of . termed the "opportunistic replacement It says little, however, about the composition hypothesis." of faunas, and may give an erroneous im- A simple classification of the reptile pression of the importance of different groups involved is given in Table 1. groups. For example, according to diversity charts of Triassic reptiles (e.g., Colbert, OF THE 1966; Crompton, 1968; Robinson, 1971; TRIASSIC REPTILE BEDS Moody, 1977; Charig, 1979), thecodontians The relative dating (stratigraphy) of the were dominant in the late Triassic faunas of reptile beds within the Triassic period is (5-10 genera), whereas

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TABLE 1 Classtfication of the major terrestrial reptile groups of the late Permian and Triassic Modified from Romer (1966) and Anderson and Cruickshank (1978).

Subclass Anapsida (no openings behind eye) Infra-order Pareiasauria medium to large herbivores Subclass Synapsida ("mammal-like reptiles") ORDER THERAPSIDA (advanced mammal-like reptiles) Suborder Dinocephalia herbivores and carnivores Suborder Anomodontia Infra-order Endothiodontia medium to large herbivores Infra-order Dicynodontia small to large herbivores Suborder Theriodontia Infra-order Gorgonopsia small to medium carnivores Infra-order Scaloposauria small carnivores Infra-order Therocephalia small to medium carnivores Infra-order Cynodontia Superfamily Cynognathoidea small to medium carnivores Superfamily Diademodontoidea small to medium herbivores Superfamily Tritylodontoidea small to medium herbivores Infra-order Bauriamorpha small to medium herbivores Infra-order Ictidosauria small carnivores Subclass Diapsida (two skull openings behind eye) ORDER RHYNCHOSAURIA (beaked herbivores) small to medium herbivores ORDER (dinosaur ancestors) small to large carnivores Suborder Suborder Phytosauria Suborder Aetosauria (medium herbivores) Suborder ORDER CROCODYLIA () medium to large carnivores ORDER ("-hipped" dinosaurs) Suborder Infra-order Coelurosauria small to medium carnivores Infra-order Carnosauria medium to large carnivores Suborder Infra-order Prosauropoda medium to large herbivores ORDER ("-hipped" dinosaurs) Suborder small to medium herbivores

rhynchosaurs were not important (1 ). have been combined with close relatives for Abundance data show that the reverse was the purpose of the analysis. the case, however, for each thecodontian For the sake of clarity, and genus is represented by only a few speci- small "lizard-like" reptiles (e.g., procolopho- mens, and the single genus by nids, younginids, prolacertids, sphenodontids) several hundred. have generally been omitted because they Numbers of specimens have been ex- usually represent minute proportions of the tracted from many hundreds of descriptive total faunal count, are usually differentially taxonomic papers, from museum records, preserved and underrepresented, and enter and from correspondence with numerous into food chains (involving and in- local experts. Because of the novelty of these ) that cannot be considered here. numbers and because of their basic impor- Percentages have been calculated only for tance to an analysis of faunal change, they larger faunas (total numbers of individuals are listed, in summary form, in the Appen- ranging from 70 to 1000, and averaging 200) dix. The numbers have been then converted and these form the central part of the results to percentages of total faunal content, given below. However, some smaller faunas rounded to the nearest 10 per cent. Animals have been considered in comparison with represented by only one or two specimens better-known ones. Unfortunately, it was

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This content downloaded from 137.222.248.217 on Sat, 17 Jun 2017 14:36:56 UTC All use subject to http://about.jstor.org/terms MARCH 1983] DINOSA UR SUCCESS 33 not possible to obtain numerical data for the distinguished. These phases are roughly Russian and Chinese formations, nor for equivalent to some of the stratigraphic some of the German faunas. chronofaunas, or empires, established for Reptile footprint faunas are not con- the "middle" and late Permian, and the ear- sidered here because of a lack of published ly, middle, and late Triassic by various numerical data about them, and the difficul- authors (Olson, 1952, 1971; Romer, 1970, ty of obtaining such without extensive field- 1972, 1973, 1975; Bakker, 1977; Anderson work. They appear, however, to reveal the and Cruickshank, 1978). same story as the body (Haubold, The "middle" Permian Tapinocephalid 1971). Empire (Anderson and Cruickshank, 1978) The analysis suffers from certain limita- was dominated by small and tions of the data that are common to all medium-to-large dinocephalians and parei- paleoecological studies. The niche of a fossil asaurs as herbivores, and by dinocephalians, reptile is usually hard to define, since direct therocephalians, and gorgonopsians as small- evidence of diet and habits is rare. Also, the to-large carnivores. It is best represented by fossilized sample rarely corresponds to a true the Zone (=, Dinocephalian ecological community, and preservational Assemblage Zone + Pristerognathus/Diictodon bias clearly tends to emphasize medium-to- Assemblage Zone, Keyser and Smith, 1979) large water-side animals in the Triassic. Col- of South (Fig. 2). Closely comparable lector bias may lead to over-representation faunas occur on the Russian platform (Zones of the rarer animals from any particular for- I-III). mation. This will reduce the percentage of The late Permian Dicynodontid Empire commoner animals in the analysis, however, (Anderson and Cruickshank, 1978) was dom- and thus any major trends that are detected inated by small to large dicynodonts and will probably be real. "endothiodonts" as herbivores, with a few re- The results are presented in the form of maining . Carnivores were medi- relative abundance polygons for major taxa, um to-large gorgonopsians and small-to-medi- based on the main faunas. Small drawings um scaloposaurians, therocephalians, and show the relative sizes and shapes of the ani- early cynodonts. The dinocephalians were mals for selected faunas. The text is re- all extinct, and dicynodonts represented 80 stricted to a brief outline of major faunal to 90 per cent of all animals present. The changes and to comments on relevant, less best-known representatives of this empire well-known faunas that are not shown in the are in the Cistecephalus Zone (= Tropidostoma figures. It was considered desirable to indi- microtrema Assemblage Zone + Aulacephalo- cate the pre-Triassic situation, and this has don baini Assemblage Zone) and been done by offering histograms of the well- Zone (= lacerticeps Assemblage known middle to late Permian Zone) of (Figs. 2, 3). Com- faunas of South Africa, which immediately parable faunas occur in Scotland (Hopeman predate the Assemblage Zone Formation of Elgin), the Russian faunas. platform (Zone IV, with the oldest thecodon- tian, Archosaurus), and and India FAUNAL ANALYSES (Anderson and Cruickshank, 1978, p. 44). /South America AreaThe Permian ended with decreasing faunal (including , China, India diversity (part), and the extinction of many groups of , marine , and reptiles, ) possibly in response to the global reduction The combined area of southern Africa and in marginal seas as united (Newell, South America presents the best sequence of 1967; Schopf, 1974). reptile faunas from the late Permian to the The Triassic Period opened with the Ly- earliest . It is best to start by sum- strosaurid Empire (Anderson and Cruick- marizing events there first. Five important shank, 1978). The dominant medium-to- phases of faunal replacement, each of which large was the dicynodont Lystrosau- ended with major extinctions, may be rus, and carnivores were small-to-medium

This content downloaded from 137.222.248.217 on Sat, 17 Jun 2017 14:36:56 UTC All use subject to http://about.jstor.org/terms TIME (million years ago) 230 220 210 200 190 140 x PERMIAN TRIASSIC JURASSIC MIDDLE UPPER LOWER MIDDLE < UPPER .5 LOWER UPPER

Scythian | o I Norian Faunas 1 2 3 45 6 7 8 9 10 11 12 (13)

Pareiasauria (M-L) relative Dinocephalia Herbivores abundance (Tapinocephalidae) % (M-L) 100

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Tarity modontoides

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(Sauropodomorpha) Thecyodontia W Others Lo1?

Ornithisc hia (S -M ) <- n L/J/L i

lDinocephalia (Titanlosuchidae, etc.) .:-:::: . .. . (M-L) -\Carnivores Gorgonopsia ... (S-M)

Therocephalia .:: .'.::U (S-M) Scaloposauria ......

(S-)

Saurischia (Theropoda) (S-M) TAPINO- DICYNO- LYSTROSAURID RHYNCHOSAUR/ PRO- Lowland CEPHALiD DONTID: EMPIRE / DJADEMODONTOID /SAUROPOD reptiles EMPIRE EMPIRE / EMPIRE_ EMPIRE

GLOSOPTERIS "TRANSITiONAL"/ /CONIFER Lowland Il FLORA FLORA / FLORA / FLORA floras

FIG. 2. THE RELATIVE ABUNDANCE OF THE MAJOR GROUPS OF TERRESTRIAL REPTILES IN THE LATE PERMIAN AND TRIASSIC OF SOUTHERN AFRICA, SOUTH AMERICA, AND RELATED AREAS The time-scale (upper horizontal ) is drawn to scale for the late Permian and Triassic, and stratigraphic assignments of faunas are based on Fig. 1. Faunas come from the following formations: 1,

This content downloaded from 137.222.248.217 on Sat, 17 Jun 2017 14:36:56 UTC All use subject to http://about.jstor.org/terms MARCH 1983] DINOSAUR SUCCESS 35 therocephalians and cynodonts, and the first Norian. Other less well-known faunas that well-known thecodontian, fit in here are the N'tawere Formation of (Chasmatosaurus). The example of this (intermediate between the Cynogna- empire is the Lystrosaurus Assemblage Zone thus Zone and ), the of South Africa (Figs. 2, 3), and nearly iden- Puesto Viejo and Rio Mendoza Formations tical faunas occur in Russia, China, India of Argentina (like the Zone), the (Panchet Formation), (?Rewan of India (like the Man- Formation), and Antarctica (Fremouw For- da Formation), and Zones V and VI of mation). Russia (like the Cynognathus Zone). The The subsequent Cynognathus Zone ( = Kan- Maleri Formation of India and Lossiemouth nemeyeria Assemblage Zone) was transitional Sandstone Formation of Scotland share the to the next phase of ecological replacement dominance of a rhynchosaur with these (see Fig. 2). Medium-sized and large dicyno- southern faunas, but they have other in- donts were still important herbivores, but fluences and will be discussed later as part of small-to-medium herbivorous cynodonts the northern area. (diademodontoids) became abundant. The- The Prosauropod Empire (= Melanoro- codontians were beginning to diversify, and saurid/Plateosaurid Empire, Anderson and they include the rare , the first Cruickshank, of 1978) was dominated by a series of massive carnivores, which did not dinosaurs as medium-to-large herbivores oust the mammal-like reptiles, however, and carnivores. They appeared abundantly since advanced cynodonts (e.g., Cynognathus) first in the and earliest Jurassic in had radiated as medium-sized predators. the southern hemisphere [South Africa The Rhynchosaur/Diademodontoid (Elliot, Clarens Formations, Figs. 2, 3), Empire ( = Kannemeyeriid/Diademodontid (), South Amer- Empire, Anderson and Cruickshank, 1978) ica (upper , El lasted from the Anisian to the Norian. The Tranquilo Formation), India (Dharmaram main characteristic of the faunas [Manda Formation), and China (Lower Lufeng (sensu stricto), Santa Maria, Ischigualasto; Series)] at the same time, where some Figs. 2, 3] is the remarkable dominance of achieved vast size ( from the each by a medium-sized rhynchosaur , 12 m long). Early or- (40-60 % of all individuals). When rhyncho- nithischians (e.g., , Heterodon- saurs were absent (e.g., Chafiares Forma- tosaurus) probably fed on low plants. The tion, Fig. 2), their place was taken by diade- coelurosaurs were small carnivores, but modontoids. Some large dicynodonts were larger predator niches were not filled until present, and the carnivores consisted of somewhat later-so-called carnosaurs from cynodonts and thecodontians, the latter fi- the late-Norian and Rhaetian of nally taking over completely in, the Norian and England are represented by a and faunas. The Norian faunas also had rare di- isolated teeth (, Palaeosauriscus). nosaurs and "paracrocodiles." Thus, by a A typical late Jurassic (Tendaguru slow process, thecodontians had finally re- Formation, ) is shown on the ex- placed mammal-like reptiles as carnivores by treme right of Fig. 2 in order to indicate later late Triassic times, in all but a few small in- developments (data from Russell, Beland, sectivore adaptive zones but nevertheless and McIntosh, 1980). The main changes are both groups were extinct by the end of the the replacement of palaeopods by giant

"Tapinocephalus Zone," South Africa; 2, "Cistecephalus Zone," South Africa; 3, "Daptocephalus Zone," South Africa; 4, "Lystrosaurus Zone," South Africa; 5, , Antarctica; 6, "Cynognathus Zone," South Africa; 7, Manda Formation, Tanzania; 8, Chaniares Formation, Argentina; 9, , ; 10, Ischigualasto Formation, Argentina; 11, Elliot Formation, South Africa; 12, Lower Lufeng Series, China. Original data are given in the Appendix. The Tendaguru Formation fauna from Tanzania (Upper Jurassic, 13) is added for comparison (data from Russell et al., 1980). The lowland floras (Anderson and Anderson, 1970; Retallack, 1977) and corresponding faunal empires (Anderson and Cruickshank, 1978; this work) are given at the foot of the chart. L, large; M, medium; S, small.

This content downloaded from 137.222.248.217 on Sat, 17 Jun 2017 14:36:56 UTC All use subject to http://about.jstor.org/terms PROSAUROPOD

123456 ~~~~~~~~~~~~~~~~~EMPIRE

12 64 56 + 2 3 4 6

ELLIOT FORMATION, S AFRICA (?.Rhaetian) U U Triassic- ..,++. L Jurassic

RHYNCHOSAUR/ 123 0 _4 0 1 l 2 3 IADEMODONTO ... ~~~~~~~~~~~~~~~EMPIRE ...... SANTA MARIA FORMATION, BRAZIL (Carnian/Norian)

4 1 2 3 4

CHANARES FORMATION, ARGENTINA (Ladinian) M/U Triassic

LYSTROSAURID EMPIRE

1 23456 1 2 3 4 5 6

LYSTROSAURUS ZONE, S AFRICA (Scythian) L Triassic

3 4 DICYNODONTID EMPIRE

23~~~~~~~ ~ ~~ ~ ~ ~~~~~~~~~ metre 78 CISTECEPHALUS ZONE, S AFRICA 1 metre U Permian

FIG. 3. REPRESENTATIVE FAUNAS OF THE FOUR LOWLAND REPTILE EMPIRES OF THE LATE PERMIAN AND TRIASSIC OF SOUTHERN AFRICA, SOUTH AMERICA, AND RELATED AREAS The histograms show the relative abundance of each genus or group of related genera (data in Ap- pendix). Histogram shading scheme, same as in Fig. 2. Sketches show the appearance and size of the animals in question (all drawn to scale). Cistecephalus Zone [Herbivores: (1), endothiodont (2), dicynodonts Diictodon, Emydops, Pristerodon (3), Cistecephalus (4), Tropidostoma (5), Aulacephalodon (6); carnivores: gorgonopsians (7), scaloposaurians and therocephalians (8)]. Lystrosaurus Zone [Herbivores: dicynodonts Lystrosaurus (1), Myosaurus (2); carnivores: therocephalian Moschorhinus (3), cynodonts (4), (5), thecodontian Chasmatosaurus (6)]. Chaiiares Formation [Herbivores: dicynodont Dinodontosaurus (1), diademodont (2); carnivores: Probelesodon (3), thecodontians (4)]. Santa Maria Formation [Herbivores: dicynodonts Stahleckeria, Dinodontosaurus (1), diademodont (2), rhynchosaur Scaphonyx (3); carnivores: thecodontians (4)].

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sauropods and the relative increase in impor- The Carnian to mid-Norian for- tance of diverse ornithischian dinosaurs. mations of Germany (Gipskeuper, Schilf- sandstein, Lehrbergstufe, Blasensandstein) and are dominated by the The sequence of Empires that is so well and the fresh-water fish-eating developed in South Africa, South America, (, , Palaeorhinus), and we and many other areas, breaks down when we may identify this as a fresh-water and low- try to classify the faunas from the middle to land Metoposaur/ Empire. Other late Triassic of the United States and parts of faunas that are dominated by these two forms Europe. The differences do not indicate sep- are the early Norian of arate areas of faunal development (e.g., Wyoming (see Figs. 4, 5; rarer elements: Gondwanaland and Laurasia, Colbert, large thecodontian, large dicynodont: Dawley, 197 1) because many elements are shared Zawiskie, and Cosgriff, 1979), the early to between north and south (Romer, 1970; middle Norian Dockum Group (see Figs. 4, Charig, 1971; Cox, 1973a). Many of the 5; rarer elements: peculiarly northern animals indicate more and , obscure , un- aquatic faunas. named rhynchosaur), and the early to mid- The Scythian Buntsandstein of Germany dle Norian Chinle Formation lower fauna and the lower Moenkopi Formation of Ari- (see Figs. 4, 5; rarer elements: aetosaurs zona are dominated by amphibians and Desmatosuchus and Typothorax, dicynodont Chirotherium trackways, probably produced , Colbert, 1972b). The thecodon- by carnivorous thecodontians. Other ani- tians, dicynodonts, and rhynchosaurs are mals include small procolophonids, eosuch- probably southern influences, but the aeto- ians, and rhynchocephalians (Schmidt, saurs appear to be more important. They are 1928) (Figs. 4, 5). The early Ladinian upper present mainly in the northern hemisphere Moenkopi Formation of and the late (a few specimens in the Ischigualasto and Ladinian Lettenkohle of Germany are also Los Colorados Formations of Argentina) dominated by amphibians, together with a and are restricted to the Norian and Rhae- few obscure thecodontians. Some of the am- tian. They occur in the Metoposaur/Phyto- phibians are present also in the typical em- saur Empire and subsequently in some pro- pires already described, and some occur only sauropod faunas of the latest Triassic. here (e.g., ). We may name a The early Norian Maleri Formation of In- freshwater Scythian-Ladinian Capitosaurid/ dia (Fig. 6) contains a perfect mix of ele- Mastodonsaurid Empire for these Euro- ments of the Rhynchosaur/Diademodontid pean and American faunas, although capito- Empire and the Metoposaur/Phytosaur Em- saurs also occur as rare elements in the Lys- pire. The reptiles and ostracods clearly point trosaurid Empire. These amphibians are to strong northern affinities, although India present also in the early Ladinian Broms- is normally assumed to have been joined to grove Sandstone Formation of the English Africa in the Triassic (Sohn and Chatterjee, Midlands, but it also has a small rhyncho- 1979). The early Norian Lossiemouth Sand- saur and elements of the marine Nothosau- stone Formation of Elgin (see Fig. 6) has no rid/Mixosaurid Empire (Anderson and mammal-like reptiles, but the rhynchosaur Cruickshank, 1978) of the German Muschel- and the thecodontian Or- kalk (nothosaur, macrocnemid, Walker, nithosuchus are closely comparable to South 1969). The late Ladinian Sol'lletsk Series American forms. The Elgin fauna shows no (Zone VII) of Russia has similar amphib- particular affinities with the then neighbor- ians, but also some dicynodonts (Battail, ing German and North American faunas ex- 1980). cept for cosmopolitan forms. These transi-

Elliot Formation [Herbivores: tritylodont (1), prosauropod dinosaurs (4), (5), ornithischian dinosaurs Fabrosaurus, (6); carnivores: "crocodiles" (2), coelurosaur dinosaur Syntarsus (3)].

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tmya) 220 210 200 190 tional faunas link the quite different contem- TRIAS SIC porary faunas of the Norian of Germany and LOWER MIDDLE tPUPPER ER South America. Scythian Anisian | Carnian| Norian loX Dinosaur-dominated faunas appear first Faunas 1 2345 6 7 in Germany and North America just before

relative the typical Prosauropod Empire of Gond- abundance % Dicynodontia wanaland described above. The German 100 (M-L) Stubensandstein (middle Norian) contains various saurischians: small carnivorous coe-

Aetosauria lurosaurs () and larger - ~~~~~~(M-~L) herbivorous palaeopods like , as Rhynchosauria 4 well as remnant amphibians (), phytosaurs and aetosaurs (). The Trilophosauria A fM) succeeding late Norian Knollenmergel also has amphibians, and abundant Plateosaurus

Prosauropoda (see Figs. 4, 5). Equivalent faunas occur in Herbivores f(-L) France and England (Bristol), and in the Rhaetian of the same countries. The upper part of the Chinle Formation (middle Norian) has abundant specimens of the coe- lurosaur , as well as remaining Metoposaurus, phytosaurs, and aetosaurs (see Figs. 4, 5: Colbert, 1974a). The succeeding Glen Canyon Group yields a few dinosaurs Amphibia (S-M) and the earliest Jurassic (?) Portland Forma- tion of the eastern United States contains medium-large herbivorous prosauropods, Thecodontia (gen) phytosaurs, and "paracrocodiles." These (S-M) German and United States formations may be included in the Prosauropod Empire, al- though they lack the giant Melanorosaurus and (M-L) have a few hangovers from the Metoposaur/ Phytosaur Empire.

DISCUSSION

Carnivores C;irnitOres Coelurosauria ~(S-M) 4 Triassic Ecological Replacements: Faunal Dynamics CAPITOSAUJRID/f CAP .SARID I SAUR/ SAURO- METOPO- PRO- MASTODONSAURID PHYTOSAUR POD The data from northern and southern EMPIRE I EMPIRE I EMPIRE Lowland reptiles faunas are summarized in Fig. 7. We may now assess various explanations that have FIG. 4. THE RELATIVE ABUNDANCE OF THE been given for the following events in the MAJOR GROUPS OF TERRESTRIAL REPTILES IN THE Triassic: TRIASSIC OF NORTH AMERICA AND EUROPE (a) a replacement of gorgonopsian mam- The time-scale is the same as in Fig. 3 (mya = millions of years ago), and stratigraphic assign- mal-like reptiles by thecodontians as ments of faunas are based on Fig. 1. Thecodontia medium to large carnivores (late Per- (gen) includes all thecodontians except phytosaurs mian to earliest Scythian) (Fig. 2); and aetosaurs. Faunas come from the following (b) a replacement of cynodont mammal- formations: 1, Buntsandstein, Germany; 2, Popo like reptiles by thecodontians as carni- Agie Formation, Wyoming; 3, Dockum Forma- vores (early Norian); tion, , New Mexico; 4, Chinle Formation (lower fauna), Arizona; 5, Chinle Formation (up- per fauna), Arizona; 6, Knollenmergel, Ger- mated from less accurate counts than the others. many; 7, Rhaetian, Germany. Original data, in The new lowland reptile empires established here Appendix. Figures for faunas 1 and 7 are esti- are given at the foot of the chart.

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PROSAUROPOD EMPIRE

2/3 ~~~~~~~~U U Triassic- 1 2 34 L Jurassic

r 20%KNOLLENMERGEL. GERMANY (U Norian)

1234~~~~~~~~~~~~~~~~~~

CHINLE FORMATION (UPPER), ARIZONA (M Norian) METOPOSAUR/ PHYTOSAUR

1 2 3 4 s 5

_ DO CKUM FORMATION, TE XA S (L Norian)

1234~~~~~~

1 U Triassic POPO AGIE FORMATION, WYOMING (L Norian)

CAPITOSAURID/ 2 MASTODON- SAURID EMPIRE 12 3 BUNTSANDSTEIN, GERMANY (U Scythian) 1 mer L -M Triassic

FIG. 5. REPRESENTATIVE FAUNAS OF THE THREE LOWLAND REPTILE EMPIRES OF THE TRIASSIC OF NORTH AMERICA AND EUROPE Conventions as in Fig. 3. Buntsandstein [Herbivore: procolophonid Sclerosaurus (2); fish-eaters: am- phibians Mastodonsaurus, Parotosaurus (1); carnivores: thecodontians (3)]. Popo Agie Formation [Herbivore: dicynodont Placerias (2); fish-eater: amphibian Metoposaurus (1); carnivores: thecodontian (3), phytosaurs Palaeorhinus, (4)]. Dockum Formation [Herbivores: Trilophosaurus (2), rhynchosaur (3), aetosaurs Desmatosuchus, Typo- thorax (4); fish-eater: amphibian Metoposaurus (1); carnivores: phytosaurs Phytosaurus, (5)]. Chinle Formation (upper fauna) [Herbivore: Typothorax (3); fish-eater: amphibian Meto- posaurus (1); carnivores: phytosaur Phytosaurus (2), coelurosaur dinosaur Coelophysis (4)]. Knollenmergel [Herbivores: prosauropod dinosaurs Plateosaurus (2), Gresslyosaurus (3); fish-eater: am- phibian Cyclotosaurus (1); carnivore: coelurosaur dinosaur Halticosaurus (4)].

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p S g4X, ~~~~~~~~~~~~~~~~1 metre

++ ...... EM PIRE ?

++ 1 2 3 4 1 2 ++ LOSSIEMOUTH FORMATION, ELGIN (Norian)

RHYNCHOSAUR/ 5 6 7 ~~~~~~~~~~~IADEMODONTOID + + ~~~~~~~~~~~~~~METOPOSAUR/ ++ PHYTOSAUR

1 2 3 4 5 6 7 1 2 3 4 EMPIRE

MALERI FORMATION, INDIA (Norian)

FIG. 6. THE FAUNAS OF THE FORMATION (SCOTLAND) AND MALERI FORMATION (INDIA) Conventions as in Fig. 3. Lossiemouth Sandstone Formation [Herbivores: rhynchosaur Hypero- dapedon (1), aetosaur (2); carnivores: thecodontian (3), coelurosaur dinosaur (4)]. Maleri Formation [Herbivores: diademodont (2), rhynchosaur Paradapedon (3), aetosaur Typothorax (4), prosauropod dinosaur (7); fish-eater: amphibian Metoposaurus (1); carnivores: phytosaur (5), coelurosaur dinosaur (6)].

(c) a replacement of dicynodont mam- scale replacements. In such cases, it has been mal-like reptiles by rhynchosaurs, dia- argued (e.g., Schopf, 1979) that we should demodontoids, and aetosaurs as the adopt a stochastic point of view, in which dominant herbivores (Anisian to early origination and extinction are considered to Norian); be random with respect to taxonomic group. (d) a replacement of thecodontians, di- Nevertheless, I believe that it is still worth- cynodonts, rhynchosaurs and dia- while to seek particular explanations for cer- demodontoids by dinosaurs (middle to tain large-scale replacement events in the late Norian). past, and that the fossil record contains the There are problems in scaling up ecological data to test these explanations. concepts of competition between individuals A fauna in equilibrium may be perturbed, and species to explain large-scale replacements and individual species become extinct as a in the past. At the level of individual result of the influx of new forms or by envi- organisms, the outcome of each interaction ronmental change. These possible outcomes may be explained by a particular cause. Fur- are termed differential survival ("competi- ther, if members of one species repeatedly tive") ecological replacement and opportu- replace those of another, the former species nistic ecological replacement, respectively. can be said to have positive differential sur- (1) Differential survival ('competitive) replace- vival when compared with the one it is ment may result when a group of native ani- replacing. Individuals and species may be mals and a group of invaders occupy similar subject to selection at different levels in a adaptive zones. If they compete, the invader hierarchy of evolution (microevolution and may succeed and the native become extinct, macroevolution respectively: Eldredge and and this fact could be recorded in the fossil Gould, 1972; Stanley, 1975), and reasons for record. If, however, the native repulses the each extinction and replacement may be invader, this is unlikely to be recorded (Mar- found. This deterministic approach may not shall, 1981). be valid in seeking explanations for larger- (2) Opportunistic replacement arises when ex-

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tinction is caused by some factors uncon- associated with climatic or floral nected with the new incumbents of the adap- change. tive zone who just "happened along" at the An opportunistic hypothesis for the replace- appropriate time. This has been termed ment of group A by group B would be sug- "passive replacement" by Marshall (1981, gested by the following pattern: p. 146). (1) B will appear or radiate only after the Whole families or orders of animals may extinction of A; become extinct and others may become es- (2) the rate of replacement should be tablished in their place by a summation of rapid (in paleontological terms, this interspecific interactions in three ways: would imply a time span of less than (1) positive differential survival of all one million years, and possibly a few species in a particular group, giving the pre- thousands or tens of thousands of decessor group a high extinction rate and the years, if such stratigraphic accuracy successor group a high origination rate; were possible); (2) opportunistic replacement displayed (3) A and B will not be found together, or by all species in a group after the extinction- B may be unobtrusively present when of another group; A is dominant; and (3) a random mixture of (1) and (2). (4) the replacement will be associated When put in these terms, it seems most un- with climatic or floral change. likely that examples of pure differential sur- With these criteria in mind, we may ex- vival of a family or order based on interspe- amine events (a) through (d) mentioned cific competition could be demonstrated in above: the fossil record. Such explanations are nor- (a) The appearance and radiation of the- mally adduced in cases of the long-term codontians as medium to large carnivores at dwindling of one taxon, and the concomitant the end of the Permian and the beginning of rise of another that occupied similar adaptive the Triassic was sudden and followed the ex- zones. It would be hard to prove that ran- tinction of mammal-like reptiles such as the dom effects and external factors were not in- Gorgonopsia. This was in part opportunistic volved. On the other hand, sudden world- replacement. Cynodonts arose in late Per- wide extinctions of whole families or orders, mian times and their radiation and that of which are potentially demonstrable in the the thecodontians was matched by decreas- fossil record, do point to some environmen- ing abundance of therocephalians and scalo- tal change or other external cause. posaurians, so that competition may have We may attempt to distinguish purely dif- been involved between carnivores of small to ferential survival replacement from purely medium size. opportunistic replacement in the fossil rec- (b) The supposed replacement of cyno- ord by an examination of the relative abun- donts by thecodontians in the early Norian dance over time of the groups in question. A may be more apparent than real. The two differential survival hypothesis for the groups arose in the late Permian and evolved replacement of group A by group B would be side by side for thirty million years. suggested by the following pattern: Members of both groups are found together (1) A will tend to decrease in abundance, in similar proportions in many faunas, and and B will increase in abundance over they must have occupied rather different time; adaptive zones. The cynodonts became ex- (2) the rate of replacement should be tinct in the middle Norian, and the gradual (in paleontological terms, this thecodontians survived a little longer. We would imply a time span of more than can hardly link the extinction of the cyno- one million years, say, and often more donts with the rise of the thecodontians, and than 10 to 20 million years); neither differential survival nor opportunism (3) A and B will be found together, and can be proposed as an explanation. either could be dominant in any par- (c) The replacement of dicynodonts by ticular formation; and rhynchosaurs, diademodontoids, and aeto- (4) the replacement will not necessarily be saurs was never quite completed. The rhyn-

This content downloaded from 137.222.248.217 on Sat, 17 Jun 2017 14:36:56 UTC All use subject to http://about.jstor.org/terms MARCH 1983] DINOSAUR SUCCESS 43 chosaurs and diademodontoids achieved which. . . were not yet 'fully improved' in dominance first in various their locomotor adaptations" (p. 209). faunas, but the dicynodonts did not become There is no question that thecodontians extinct. Aetosaurs were important herbi- and dinosaurs had a semi-erect or erect limb vores in certain late Triassic faunas, but they pose that was better adapted for supporting were often present with dicynodonts. All weight than was the sprawling limb pose of four groups became extinct about the same the early synapsids. It can be argued that it time in the middle Norian. We are evidently was also better adapted for fast locoffiotion. dealing with partial replacement by differen- Middle and late Triassic cynodonts were high- tial survival. The rhynchosaurs will be fur- ly advanced in their dentition, however, and ther discussed below. they also had an obligatory erect hindlimb (d) The rise of the dinosaurs was rapid in gait (Kemp, 1980). It is also more likely that middle-late Norian times. It followed the ex- these middle and late Triassic synapsids tinction of thecodontians, dicynodonts, were endothermic than that the thecodon- rhynchosaurs and diademodontoids, and ap- tians and dinosaurs of that time were (Brink, pears to have been associated with climatic 1956; McNab, 1978; Benton, 1979a; Baur and floral changes. These will be discussed and Friedl, 1980). The middle and late below. It is suggested here that the initial ra- Triassic rhynchosaurs, normally classed with diation of dinosaurs was an opportunistic oc- the synapsids as losers in the competition cupation of empty adaptive zones. with archosaurs, had a semi-erect hindlimb Most,.if not all, previous authors have im- gait (Benton, 1981). Scenarios that attempt plicitly accepted that the replacement of to explain complex replacement processes by mammal-like reptiles by thecodontians, and reference to single characters are likely to be then by dinosaurs, was a competitive process gross oversimplifications. The differential throughout. It has been assumed that archo- survival hypotheses for dinosaur success tend saur characters were superior to those of the to be intangible and they are untestable in synapsids. For example: "In the competition their present form. with Triassic archosaurs, the retention of As a preliminary to the development of an sprawling locomotion, and possibly the lack opportunistic replacement hypothesis for the of efficient heat-loss mechanisms in therap- achievement of dominance by the dinosaurs, sids caused their extinction" (Bakker, 1971, we must consider briefly the climatic changes p. 656). in the Triassic, the Triassic floras, the role of Charig (1980) has given the best account the rhynchosaurs, and the evidence for the of how the competitive model is supposed to earliest dinosaurs. have operated. He has described the faunal Environments of Triassic Reptiles replacement of carnivorous mammal-like reptiles by thecodontians as accelerating rap- In the Triassic, all continents were united idly up to the beginning of the late Triassic, as the "super-continent" Pangaea, and when the latter group triumphed. Synapsids worldwide faunal similarities existed during and rhynchosaurs, however, were dominant this time. There were apparently no polar ice as herbivores until the middle of the late caps, the surface temperatures of the earth Triassic. Then, selection pressure on com- were generally higher, and climates around peting thecodontian carnivores caused some the world were more uniform than today. of them to adapt to a herbivorous diet Fluviatile, lacustrine, and aeolian deposi- (aetosaurs). "The more intense competition tional environments were dominant, and in between the many carnivorous archosaurs in the middle Triassic, thick evaporite (halite) the late Triassic and the greater selection sequences filled basins in northeastern North pressure which it engendered led to the per- America, western Europe, and north Africa fection of the 'fully improved' limb posture in (Frakes, 1979). Pangaea drifted north dur- the sauropodomorph line [see Table 1].... ing the Triassic (Smith and Briden, 1977), These had a great advantage over the few and the combined area of South Africa and surviving herbivorous , the rhyn- South America, for example, moved from chosaurs and the other groups of archosaurs latitudes 60-70? to 40-50?. The northward

This content downloaded from 137.222.248.217 on Sat, 17 Jun 2017 14:36:56 UTC All use subject to http://about.jstor.org/terms 44 THE QUARTERLY REVIEW OF BIOLOGY [VOLUME 58 drift moved this continental mass into The Dicroidium Flora dominated lowland warmer, more arid climatic zones during the environments of the southern hemisphere course of the Triassic (Kremp, 1977), and from late Scythian to late Norian times this shift must have influenced the faunas. (Schopf and Askin, 1980). Representatives Northern areas (Europe, North America) come from various localities in Australia, did not move so far in latitude because of ro- New Zealand, India, South Africa, Zim- tations occurring near the equator, and their babwe, Argentina, and Brazil (Anderson climates probably did not change so much and Anderson, 1970; Retallack, 1977). during the Triassic. Dicroidium and its relatives (e.g., Xylopteris, An analysis of the sedimentology of im- Johnstonia) were abundant in a range of habi- portant Triassic reptile sites (Tucker and tats from broadleaf forest and heath to xero- Benton, in press) shows that nearly all are phytic woodland. Other elements of the Di- from lowland situations, and these may be croidium Flora include equisetaleans (e.g., classified into three groups: Neocalamites), filicaleans (ferns, e.g., Clado- (1) moist, warm, equable lakeside and phlebis), "cycadophytes" (e. g., Taeniopteris), riverside; Ginkgoales (e.g., Baiera), and conifers (e.g., (2) seasonal (monsoon?) with Podozamites) (Anderson, 1974; Retallack, waterside vegetation and dry sandy or 1977). savannah-like interchannel areas; Northern hemisphere floras of the middle (3) largely semi-arid to arid aeolian envi- to late Triassic are generally dominated by ronments with transitory and "cycadophytes," ferns, and conifers, and con- pools. tain no seed ferns. Examples occur in En- Most reptile beds may be gland, Germany, Russia, and the Carnian- classed as forming in environment no. 1. Norian Chinle Formation of Arizona (in- There was increasing aridity in the late cluding the petrified forest - with 50 species Scythian and middle Triassic in many areas, of macroplants, including fungi, lycopods, but in the early late Triassic most reptile sphenopsids, ferns, conifers, ginkgos, beds appear to belong to the humid mon- , and bennettitaleans; Ash, 1980). soonal environment no. 2. Finally, there was Dicroidium and its relatives disappeared by a major arid to semi-arid phase at the end of the end of the Norian, except for a few locali- the Triassic, and many reptile faunas of that ties in the Rhaetian of Queensland (de time experienced environment no. 3. Jersey, 1975; Retallack, 1977). It did not survive into the Jurassic, although some Triassic Floras other seed ferns (e. g., Lepidopteris, Pachyp- Triassic megaplants are even more spo- teris) continued through the Era. A radic in occurrence than are the reptiles, and new worldwide flora, dominated by diverse they are very rarely associated with them. conifers and bennettitaleans, took over in the However, some patterns of floral replace- Rhaetian and Jurassic (Anderson and ment do emerge, and it is argued here that Anderson, 1970; Barnard, 1973; Hughes, they were very important in influencing rep- 1976; Miller, 1977), with well-known tile faunal change. representatives in Argentina, Yorkshire The widespread Flora of Gond- (England), Greenland, and Germany. wanaland disappeared towards the end of the The Role of the Rhynchosaurs Permian, and was replaced initially by a "transitional flora" (Anderson and Anderson, The importance of the rhynchosaurs in 1970) in the latest Permian and early Triassic faunas was stressed by Romer Scythian. Representative floras come from (1960, 1963, 1970, 1972, 1975) and this sig- various localities in India, Australia, and nificance has also been emphasized here. In New Zealand. During this time, such groups view of recent disagreement about the diets as psilopsids, lycopods, and equisetaleans of rhynchosaurs and because of the impor- (horsetails) became less abundant, and the tance attached to them in this analysis, in in- pteridosperm (seed fern) Dicroidium and its fluencing the early radiation of dinosaurs, relatives rose in importance. they will now be discussed further.

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___ > 025 cm

b X

FIG. 8. RHYNCHOSAURS (a) Reconstruction of the South American rhynochosaur Scaphonyx; (b) side view of the skull of the Scottish rhynchosaur Hyperodapedon; (c) palatal view.

Rhynchosaurs probably derived from the have become extinct throughout the world at stock during the Permian, and the same time, the middle Norian. This is an they share some thecodontian and some important point that was not evident when primitive eosuchian features (Cruickshank, the rhynchosaurs were considered to be 1972; Carroll, 1977). The earliest so-called mainly middle Triassic in age, with a few rhynchosaurs, Noteosuchus fKom the Lystro- late survivors in Scotland and India (Romer, saurus Assemblage Zone, and and 1975). from the Kannemyeria Assemblage Rhynchosaurs were squat quadrupedal Zone, are rare small lizard-like animals. The animals with sprawling limbs and large claws first ecologically important rhynchosaur is (Fig. 8a). Their heads were large and trian- from the Manda Formation, gular in top view. In side view (Fig. 8b), sev- and it appears in surprising abundance and eral characteristic points are evident: they is much advanced over its supposed had large eyes, curved, pointed bony "tusks," ancestors. The important Norian rhyn- a curved roller-like upper row, and a chosaurs are Scaphonyx from South America deep boat-shaped lower jaw. In palatal view (Argentina and Brazil), Paradapedon from In- (Fig. 8c), the small conical teeth are seen to dia, and Hyperodapedon from Elgin, Scotland. be arranged in dense rows on the , These approximately contemporary animals separated by a central groove. The lower jaw are all medium to large in size, they all dom- cut like a penknife blade upwards into the inate their respective faunas, they all display groove, but there was little back and for- identical adaptations, and they all appear to wards motion of the jaw and no sideways

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chewing movement. The deeply rooted teeth nated faunas. These dinosaurs (Stauriko- and the bone at the crest of the lower jaw saurus, , Ischisaurus, , were worn to a blade that fitted snugly into Saltopus) are represented by fragmentary re- the groove, and the upper teeth were worn mains (a total of less than 15 specimens) and only at the side of the groove. their exact relationships are uncertain It has been suggested that rhynchosaurs (Bonaparte, 1978; Galton, 1973). Many so- ate material (Huene, 1939; Romer, called dinosaurs of this age, and earlier, have 1960, 1963; Sill, 1971) or molluscs (Burck- been described (e.g., from hardt, 1900; Chatterjee, 1974, 1980). The Wyoming and elsewhere; Triassolestes from latter interpretation does not seem likely be- Argentina; Ornithosuchus from Elgin; Spon- cause of the lack of wear on the upper teeth dylosoma from Santa Maria), but these are in most specimens, and the inappropriate- now classified as advanced thecodontians ness of the shearing jaw action for dealing (Bonaparte, 1978; Galton, 1977; Galton and with hard-shelled animals. Also in favor of a Cluver, 1976). herbivorous diet is the barrel-shaped body It seems that dinosaurs became ecological- (that would accommodate a large gut for the ly important in the north in places where slow digestion of plants), the large numbers rhynchosaurs and Dicroidium were absent of these animals present in all faunas, and (Germany, North America). The extinction the absence of abundant fossil mollusc shells. of both rhynchosaurs and Dicroidium, and the The plant materials suggested by Romer worldwide extension of the conifer flora (1963) and Sill (1971) as forming the rhyn- thereafter permitted the new large dinosaurs chosaur diet include the "fruit" of lycopsids, to migrate south and radiate even more ex- sphenopsids, and ferns, artichoke-like ben- tensively. In all cases, it seems that they were nettitaleans, seed-ferns, and rhizomes. occupying empty adaptive zones that were Rhynchosaurs are rarely found with plant unsuitable for rhynchosaurs and synapsids. remains, but their rapid spread, massive The extinction of these two groups following local dominance, and subsequent apparently the floral changes were probably crucial fac- rapid extinction suggest that important ele- tors in the rapid rise to domination of the ments of their diet may have had a similar dinosaurs. history. The Triassic plant record suggests a parallel in the distribution of the Dicroidium A Model for Triassic Faunal Flora for the southern continents. Rhyn- Replacements, and Some Predictions Based on It chosaurs probably could not rear up on their The replacement of mammal-like reptiles hind legs, and would have had to feed at a by dinosaurs during the Triassic may be height no greater than 1 m. This limitation seen as a four-stage model: would have restricted their diet to Dicroidium, (1) Thecodontians replace gorgonopsians equisetaleans, ginkgos, and the fallen as medium-to-large predators at the or fruits of cycads and conifers. end of the Permian, following an ex- tinction event. Opportunism. The Rise of the Dinosaurs (2) Thecodontians and cynodonts radiate Dinosaurs are thought to have arisen from during the Triassic. Thecodontians three or more thecodontian lineages eventually take over after the cyno- (Charig, 1979). They are classified in two donts become extinct in the middle orders: the Saurischia and the Ornithischia. Norian. Random processes. Their early history is uncertain because of (3) Rhynchosaurs and diademodontoids their rarity until the late Norian (Cox, compete successfully with dicynodonts 1976). The oldest so-called dinosaur, Avipes, in the middle and late Triassic and are from the late Ladinian of Germany, is repre- dominant plant-eaters in most areas. sented by three incomplete metatarsals. The Their rise is matched by the rise of the earliest certain dinosaurs occur in the Ischi- Dicroidium Flora. Differential survival. gualasto and Santa Maria Formations, as (4) Dinosaurs radiate rapidly with the well as at Elgin, and in India, as very unim- new worldwide conifer and bennetti- portant elements of the rhynchosaur-domi- talean flora in the middle and late

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Norian after the extinction of the conifer floras, in the southern hemi- rhynchosaurs, diademodontoids, di- sphere. cynodonts, thecodontians, and aeto- saurs. Connected with climatic and floral changes. Opportunism. ACKNOWLEDGMENTS The following predictions may be made I thank the following for checking numbers for from the last part of this model, and they the graphs: J. M. Anderson, J. F. Bonaparte, S. may be tested by further fossil finds: Chatterjee, E. H. Colbert, A. R. I. Cruickshank, (1) Large synapsids or rhynchosaurs will J. W. Kitching and A. D. Walker. A. R. I. not be found associated with large di- Cruickshank, T. S. Kemp, A. L. Panchen, M. E. Tucker, R. M. Tucker, A. D. Walker, and W. A. nosaurs. Wimbledon kindly read and commented upon the (2) Large synapsids and rhynchosaurs manuscript at various stages. The artwork was will always be found to occur in older produced by Christine Cochrane and David deposits than those containing ecologi- Houghton, and I am extremely grateful to them. cally important dinosaurs. This study was carried out during tenure of (3) Rhynchosaurs will be associated with Natural Environment Research Council post- Dicroidium floras, and dinosaurs with graduate award GT4/78/GS/ 120.

LIST OF LITERATURE

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Appendix

The composition by genera of late Permian and Triassic reptile faunas. See Figs. 2-7. The faunas are arranged by geograplhie area and relative age. Numbers of specimens recorded (No.) for each genus are given. Thtese are summarized by combining similar genera and the percentage composition of well-represented faunas is calculated. Genera are grouped into families and orders. Abbreviations: AMPII, Amplhibia; BlAUR, Bauriamorpha; COEL, Coelurosauria; CROC, Crocodylia; CYNO, Cynodontia; DIAD, Diademodontoidea; DICY, Dicynodontia; DINO, Dinocephalia; END, Elndothiodontia; LOS, Eosuchia; GORG, Gorogonopsia; INC SED, Incertae sedis; MAMN, Mammalia; MESO, Mesosauria; MILL, Millerosauria; ORN, Ornithischia; PAR, Pareiasauria; PROC, ; PEROS, Prosauropoda; liYN, Rhynchosauria; SCAL, Scaloposauria; SQUAM, ; T11B, Thecodontia; TMIER, Therocephalia; TRIL, Trilophosauria; TRIT, ; YOUN, Younginidae. The taxonomic positions of the major groups may be found in Table 1.

No. +indet total % SOUTH AFRICA P.AR Pareiasauras 25 6 31 1 END Endothiodon 36 36 1 DICY Emydops, Pristerodon, TAPINOCEPHALUS ZONE Diictodon 66 +597 (+2000)2653 50 Cistecephalus 435 435 10 (=Dinocephalian Assemblage Zone + Pristergnatltis/Diictodon Tropidostoma, 230 +306 (c 150) 686 111 Asseniblage Zone) Karoo Basin, Sothtl Africa Rhachiceplhalus, Figtores based on Cox (1969 )and Kitching (1977, 1978, pers. Aulacephialodon 101 + 67 (+ 150) 318 7 comm.). G006 , (lorgonops, No. No. Cyonosauruis 93 + 74 167 4 AMIPiI Rhinesuchus 22 Riebeckosaurus I THER + SCAL 39 39 1 PAR Blradysatrus 72 Tapinocephalus 14 4375 Embrithosatirus 8 Keratoceplialus 8 INC S ID Eunotosatirus 11 PIhocasaurus fU MItLL Elliotsmoitlia 1 Mormosaurus 3 DAPTOCEPHALUS ZONE Broomia I DICY Dii todon c.400 INC SED Annitngia I GORG Aelurosaorus 5 (GDicynodon lacerticeg Assemblage Zone) Karoo Basin, S Africa DIO Anteosatirus 40 Aretognathlus 1 Feigures based on Gow (1975, 1977) and Kitching (1977, 1978, Paranteosatiroxs 1 Broomisatorus 1 pers. comm.). Jonkeria 35 Eoarretops 4 No. ao. Titanosuchus 44 Galesuchus 2 AMP16 1 ydekkerina 96 Aretognaibous 4 Struthiocepilalus 28 Gargonops C llranocentrodon 6 Aretops 2 Struthiocephaloides 3 Scylacognathus 1 Rhinesuchus 14 CyonosaLtruS 21 Strtitbiionops I Hipposatirus 3 PAR Pareiasaurus 15 Leontocep:alus 2 Taurocephalus I TIIER Plristerognathius 84 Auitlbodon 2 Lycaenops 6 osachops 17 Scymnosaurus 25 fPROC Owenetta 7 Plaragalerhinus 1 Delplbinognatlius 3 Alopecodoni 10 Spouldylolestes 1 Scylacognathus ?2 Crioceplialus 4 Lycosuchus G M .I LL Iilleretta 17 Broomicephalus 2 Avenantia I SCAIb lcticephalus 5 (4lillerIosaurus I Clelandina I Mlleropsis 8 Dinogorgon 2 SUIMMARY Y01N1 Youngina 15 Gorgognathus 52 No. IPalaeagama 1 Lycosaurus n PAR 80 10 Satirosternoin 1 ronubidgea Il I C S'eCD linnotosauus a I I DICY 1 'alemydops ?5 Rubidgea 9 1DNO Anteosaurus, Jankeria 76 9 "Daptoceplial 6us 4 S y osatnrus I Titanosucibus 44 5 Dicyn,odon ?150 Rubidgina 2 Struthliocephalus, , Diictodon ? IctidorhinaLs I Tapin ocephalus 89 10 Dinaniomodon 4 T'1EIR Moschorh i mtuns 19 DICY Diictodon c.400 47 Kingoria ?2 Whaitsia 1 4 GORG Aeltirosaurus, Gorgonops, etc. 23 3 Otudenodon 734 SCAL lctidosuchop>s 23+ TIIER Pristerognattbus 84 10 Propel anomodoni 2 Tetracynodoni 10 Scymnosaurus, etc. 41 5 Pelanomodion 156 Cf'NO Cynosaurus 11 SCAL Icticephalus __ 0 G006 Aelurosaurus 2 Paratlirinaxodorn ?2 Cyonosaurus 21 25

CISTECEPHALUS ZONE SUMMARIY Note: litching (1977) does not enumexrate all specimeros of (GTropidostoma microtrena Assemblage Zone + Alaceplalodo thie extremely abundant dicynodonts. Numbers of inideterminate bai ii Assemblage Zone) Karoo Rasin, Sooith Africa slecimens (indet.) mentioined by him are added to the Figtires based on Cox (1964) and Kitciitig (1977, 1978, pers. appropriate groups, and a further adjustment is made in order comm. ) to bring the percentages close to those given by Keyser and No. No. Smith (1979). AMPH Rhinsesucihus 20 Ael uarosaurus 10+ No. +indet. total % IPAR Pareoiasaotrus 21 A etops 9 IAR P'areianaurus 17 2 2 19 1 Antlhodon 4 Arctognat hs 5 DICY Diietodoni, Palemydops, etc. 5 +600 605 43 MESO Noteosuchus 1 Cerdorb inus I Oudenodoni, etc. 91 100 1S91 14 YOUlN Galesphyrtis 1 Cyonosaurus 13+ Iinranomodon, Dicynodon, Releosatnrus I Gorgonops 13 "Daptoceplialus" 220 +1r0 520 23 END Endothiodon 36+ Lycaenops 14+ GORII Cyonosaurus, lrorubidgea, etc. 110 + 30 110 8 DICY Bracl7yuraniscus 5 Scylognatntis 4 TIlER Wh aitsia 73 + 17 90 6 Emydops 14+ Seylacops 4 SCAL Ictidosuchops 33 33 2 Palemydops 15+ Clelandina 2 CYN0 Procynosuchus 38 38 3 Pristerodon 20+ Dinogorgon 3 1406, Tropidlostoma 40+ Prorubidgea 1 Cistecephalus 435 Rubidgea 2+ Diietodon 12+ Lemurosaurus 2 Dicynodon 82+ Lyeaenodooi 3 LYSTROSAURUS ZONE Kingoria 4 T99ER Euchambersia 2 (GLystrosaurus Assemblage Zone) Karoo Basin, Sonttt Africa Oudenodon 190+ SCAI, llofmeyeria 4 Figures from Anderson and Anderson (1970) and Ktitching (1977, Rlhachicephlalus 26+ Ictidosuchioides 22 1978, pers. comm.). Aulacephalodon 75+ Tetracynodon 11 No. No. GOR8 Aelurognathus 7 AM4Pil Rhytidosteus 10 Kestrosaurus I SUMMARY Pneumatostega 2 PROC Procolophon 100? llranocentrodon 5 Owenetta 1 Note: Kitchling (1977) does alot enumerate all specimens of Lydekkerinia 189 EOS Prolacerta 7 the extremely abundanit dicynodooits. Numbers of indeterminate Broomulus I I specimens (indet.) mentioned by bim are added to the Putterillia 3 Noteosuchus I appropriate groups, atnd a furthier adjustment is made in order tN bring the percentages close to those given by Keyser and Limnoiketes I DICY Lystrosaurus c.1000 Smith (1979). 30 Mlyosaurus 10

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THER Moschorhinus 8 Thrinaxodon, etc. c.70 SCAL Oliviera 2 THEC Chasmatosaurus + ZAMBIA Rlegisaurus 1 Proterosuchus 13 Scaloposaurus 10 INC SED Aenigmasaurus 1 CYN Galesaurus 11 N'TAWERE FORMATION SUMMARY (Luangwa Valley, Zambia) No. % Figures from Brink (1963), Chernin (1974, 1977), Cox (1972), DICY Lystrosaurus 1000 90 Cruickshank (pers. comm.) and Kitching (pers. comm.). There THER Moschorhinus 8 1 are two faunas (lower and upper), but both are too small SCAL Scaloposaurus, etc. 13 1 (n=4, 7) for the calculation of percentages. CYN Thrinaxodon, etc. 81 7 Lower N'tawere Upper N tawere (Red Marl) THEC Chasmatosaurus 13 1 No. No. 1115 AMPH Batrachosuchus 1 AMPH Parotosaurus 2 labyrinthodonts 9 THEC undescribed 9 CYNOGNATHUS ZONE DICY Dolichuranus 1 DICY ?Sangusaurus 1 Kannemeyeria I ?Zambiasaurus 2 (GEannemeyeria Assemblage Zone) Karoo Basin, South Africa CYN Diademodon 1 CYN Luangwa 2 Figures from Grine and Hahn (1978), Kitching (1977, 1978, pers. comm.) and Krebs (1976, p. 71). No. No. AMPH 29 Kannemeyeria 21 Trematosuchus 3 BAUR 16 TANZANIA Microposaurus 2 Sesamodon 3 Batrachosuchus 7 CYN Tribolodon 2 MANDA FORMATION PROC Thelegnathus 8 Cynognathus 18 EOS Palacrodon 1 DIAD Diademodon 60 (Ruhuhu region, Tanzania) RIIYN Mesosuchus 3 Trirachodon 10 Figures from Anderson and Anderson (1970), Crompton (1955), Howesia 2 THEC Erythrosuchus 9 Cruickshank (pers. comm.), Huene (1939, 1942b, 1950) and DICY Kombuisia 2 13 Krebs (1976). No. No. SUMMARY AMPH Parotosaurus 3 undescribed 9 No. % metoposaur 1 CYN Aleodon 1 DICY Kannemeyeria, etc. 23 16 RIIYN Stenaulorhynchus C.55 Theropsodon 1 BAUR Bauria, etc. 19 12 TIIEC Parringtonia 1 DIAD Cricodon 2 CYN Cynognathus 18 12 Stagonosuchus 4 Scalenodon c.20 DIAD Diademodon 60 40 undescribed 12 undescriLbed 8 Trirachodon 10 6 DICY Tetragonias 10 THEC Erythrosuchus 9 6 SUMMARY Euparkeria 13 8 152 No. % RIIYN Stenaulorhynchus 55 45 TIIEC Stagonosuchus, etc. 17 14 ELLIOT FORMATION DICY Tetragonias 19 15 CYN Theropsodosi, etc. 2 2 (-Red Beds) Karoo Basin, South Africa DIAD Scalenodon, etc. 30 24 Figures based on Andersotn and Anderson (1970), Galtoni and 123 Cluver (1976), Haughton (1924), Kitching (pers. comm.), and Raath (1980). No. No. AMPII capitosaurs 9 Heterodontosaurus 2 CROC Erythrochampsa 1 1 ZIMBABWE Orthosuchus 1 Lanasaurus 1 Sphenosuclhus 1 2 FOREST SANDSTONE FORMATION COEL Syntarsus 9 CYN Trithelodon 1 PROS Euskelosaurus, etc. 10 6 (Zambezi Valley, Zimbabwe) Plateosauravus 3 TRIT Tritylodon c.60 Figures from Kitcliing (pers. comm.) and Raath (1969). 5 MAMM 1 No. D,l Massospondylus c.20 1 COEL Syntarsus 30 42 ORN Fabrosaurus 2 PROS Massospondylus 40 56 SUMMARY Euskelosaurus 2 2 T2- No. % CROC Erythrochampsa + undescr. 6 5 COEL Syntarsus 9 7 PROS Euskelosaurus, etc. 13 10 Massospondylus, etc. 25 19 ANTARCTICA ORN Fabrosaurus, etc. 8 6 CYN Pachygenelus, etc. 7 5 TRIT Tritylodon 60 46 FREMOUw FORMATION IMAMM Megazostrodon, etc. 2 2 (Beardmore Glacier, Antarctica) 130 Figures from Colbert (1972a, 1974b, pers. comm.), Colbert and Cosgriff (1974) and Colbert and Kitching (1975, 1977, 1981). No. No. AMPII Austrobrachyops 2 DICY Lystrosaurus 70+ (GCave Sandstone) Karoo Basin, South Africa Cryptobatrachus 9 Myosaurus 3 Figures based on Anderson and Anderson (1970), Galton and Cluver (1976), Hlaughton (1924) and Kitching (pers. comm.). temnospondyl 1 SCAL Ericiolacerta 2 EOS Prolacerta ?10 Pedaeosaurus I The vertebrates occur in the lower part of the formation. The PROC Procolophon 11 Rhigosaurus 1 total fauna is too small (n=27) for the calculation of percentages. THEC undescribed .3 CYN Thrinaxodon 14 No. No. SUMMARY CROC Notochampsa I Massospondylus 6 No. % Orthosuchus 1 Gryponyx 1? THEC undescribed 3? 2 Pedeticosaurus 1 ORN lleterodontosaurus 6 DICY Lystrosaurus, etc. (+100)173 89 COEL Syntarsus 1 CYN Pachygenelus 3 PROS 1 TRIT Tritylodon 1 SCAL Ericiolacerta, etc. 4 2 CYN Thrinaxodon 14 7 Aristosaurus 3 ICTID Diarthrognathus 2 194

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ARGENTINA EL TRANQUIILO FORMATION

(El Tranquilo Basin, Argentina) PUESTO VIEJo FORMATION Figures from Bonaparte (pers. comm.). The total fauna is too small (n-12) for the calculation of percentages. (Iuesto V iejo Basin, Argentina) No. No. Figures from Bonapaite (1972, 1978, pers. comm.i). The total PfROS Plateosaurus c.5 Mussasaurus (young) 7 fauna is too small ( -10) for the calculation of percetntages. No. No. DICY Kannemeyeria 4 DIAD Ilascualgnathus 5 CYN Cynognathus I }RAZT L Rio MENDOZA FORMATION

(Caclieuta Basin, Argentina) SANTA MARIA FORMATION Figures from Bonaparte (1972, pers. comm.). The total fauna is too small (n=45) for the calculatioii of percentages. (Parana Basin, Brazil) No. No. Figures from Boiiaparte (pers. comm.), Coox (196,5), Galton Dl Y Viticeria 3 DIAD Aiidescynodoi c.40 (1977), Iluene (1942a), Krebs (1976) and Romer (1973 ). CYN Cromptodon 1 Rusconiodoii 1 No. No. PROC I DICY Barysoma I CACHEUTA FORMATION RIIYN Scaphonyx 150 Dlinodontosaurus 2h TiEC Hlopl itosuchus 1 Statbleckeria 6 (Caclicuta Basiii, Argentina) Prestosuclus C CYN Chiiiiquodon 3 Figures from Bonaparte (pers. comm.). The total fauna is too Procerosuchus 2) Belesodon 4 small (n=20) for the calctulation of percentages. Rauisuchus 7 I No. No. CROC Cerri tosaurtis 1DIIAD Massetognathus 1 AMPIII I'eloroceplialus c. 19 TIIE Cuyosuchius I Rhadino*uihus I Traversodon 9 C(OEIgIROS Staurikosaurus 1

CHAfARES FORMATION SUMMARN (lschigualasto Basin, Argentina) Figures from Bonaparte (1975, pers. comm.), Cox (196i8) and No. I Romer (1971, 1972). PROC Cdndelaria I 0 NYo. No. RHYN Scaplionyx 1130 68 TIIEC c.13 DICY Chaiiaria 1 THIE( Rauisuithus, etc. 15 7 Gracilisuchus 7 Diniodoiitosaurus 10 CROC Cerritosaurus, etc. 2 1 Gualosuchus 2 CYN c.5 (OEL/PROS S1 aur ikosaurus I 0 3 Probelesodon 15 DICI Dinodontosaurus, etc. 33 15 Lagosuchus 5 DIAD Massetogiiathuis 72-! CYN Belesodoni, etc. 8 4 1 blegagomphodon 4 DIAD Traversodoii, etc. 10 5 Luperosuchlus 220

SUMBMARY

No . { TIIEC Chaiiaresuchus, etc. 32 ' 3 DICY Dinodontosaurus, etc. 11 5 CYN Probelesodon, etc. 20 8 INDIA DIAD Massetognathus, etc. (flOO, Bonaparte,pers.comm,)170i 74 239 PANCHET FORMATION

(Damodar Valley, India) ISCHICGUALASTo FORMATION FPigures from Andersosl and Andersotn (1970), Colbert (1975), (Inschigualasto Basin, Argentiiia) Huene (1942c) and Robinson (1958). The total fauna is too Figures from Bonaparte (1972, 1978, pers. comm.), Cox (19165), small (n=34) for the calculation of percentages. Krebs (1976), Romer (1972, 1973 ) and Sill (1971). No. No. No. No. AMPII Goniioglyptus* 3 PROC undescribed I AMPII Pelorocephalus I COEL/ Herrerasaurus c.5 Pachygonia I THEC Chasmatosaurus 4 Promastodonsaurus 1 PBO Ischisaurus 2 Indobrachyops I DICY Lystrosaurus c.24 RHYN Scaphoiiyx 50 ORI Pisanosaurus I TIIEC Proterochiampsa 5 DIfCY Isciiigualastia 5 7 CYN 3 YERRAPALLI FORMATION Saurosuchus 7 DIAD Exaeretodon c.40 Triassolestes 2 Proexaeretodon 1 (Pranhita-Godavari Valley, India) Venaticosuchius I Ischignathits I Figures from Chatterjee (1980), Chowdhury (1970), atid Kutty and Chowdhury (1972). The total fauna is too small (ii-13) SUMMARN for the calculatioii of percentages. No. % No. No. RIIYN Scaplioiiyx 50+ 39 AMPII Parotosaurus 1 stagonolepid 91 THEC Aetosauroides, etc. 22 17 hracliyopid 91 DICI Rechnisaurus I COEL/PROS HIerrerasaurus, etc. 7 5 RIIYN Mesodapedon 2 Wadiasaurus 4 ORN Pisanosaurus 1 1 TIIEC erythrosuchid ?.1 DIAD triracihodont ?1 DICY lscliigualastia 5 4 rauisuchid I CYN Chiniquodon 3 2 DIAD Exaeretodon, etc. 42 32 13f) MALERI FORMATION Los COLORADos FORMATION (Pranliita-Godavari Valley, India) Figures from Chatterjee (1974, 1980, pers. comm.), Chatterjee (Ischigualasto Basin, Argentina) and Chowdliury (1974), Iluene (1940) and Kutty (1971). Figures from Bonaparte (1972, 1978, pers. comm.). All genera No. % are from the upper beds, except Jachialeria. The total fauna is AN1P11 M4etoposaiirus 18 19 too small (n=37) for the calculation of percentages. EOS Malerisaurus 2 2 No. No. RHYN Paradapedon 55 57 TIIEC 3 PROS Rlojasaurus c.20 THIEC Typothorax (?) 2 2 Biojasuchus 4 Coloradia I Parasuchus 14 15 Fascolosuchus 2 DICY Jachaleria I COEL podokesaur 2 2 CROC Hlemiprotosuchus I CYN Chaliminia 1 PROS anchisaur 1 1 Pseudhesperosuchus I TRIT cf. Tritylodon 2 DIAD Exaeretodon 2 2 COEL indet. I 9r6

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CH1INA CHINLE FORMATION (Arizona, USA) LYSTROSAURUS ZONE EQUIVALENT Figures from Colbert (1947, 1948, 1972b, 1974a, pers. comm.). There is a lower and an upper fauna. (Sinkiang, China) Lower fauna No.est. Upper fauna No. est. Figures from Charig and Sues (1976) and Huene (1959). The datc AMPH fletoposaurus ? 40 AMPII Metoposaurus 9 25 are not sufficient for the calculation of percentages. TIIEC Typothorax c.10 10 THEC Typothorax ? 10 No. No. Desmatosuchus 10 Phytosaurus 9 15 PROC Santaisaurus 1 DICY Llstrosaurus 20+ THiEC Proterosuceaus 4 Rutiodon ? 30 COEL Coelophysis 100+ 50 Phytosaurus ? Jlesperosuchus 1 5 LOWER LUFENG SERIES DICY Placerias c.45 15 (Yunnan, China) Figures from Huene (1959) and Simmons (1965). GLEN CANYON GROUP No. No. (Aripona, USA) SQUAW Fulengia 1 PROS c.100 Figures from Colbert (pers. comm.) and Galton (1976). The THEC ?Pachysuchus I ?Sinosaurus 2 faunas are too small (n=8, c.20, 4) for the calculation of ?Strigosuchus 1 ORN Tatisaurus I percentages. ?Dihothrosuchus 1 TRIT Bienotherium c.10 CROC 9Platyognathus t Lufengia I MOENAVE FORMATION 9 icrochampsa I MAidS c.6 No. COEL Lukousaurus 2 CROC Protosuclius 8 indet. 3

SUMMARY KAYENTA FORMATION No THEC cf. Desmatosuclhus c.2 ORN Scutellosaurus 2 No. COEL? Dilophosaurus 2 TRIT cf. Tritylodon 10+ 9TI{EC Dibothlrosuchus, etc. 3 2 CROC ?Microchampsa, etc. 2 1 NAVAJO FORMATION COEL Lukousaurus, etc. 5 4 CROC 1 iPROS Ammosaurus 2 PROS Lufengosaurus, etc. 100 82 COEL Segisaurus 1 ORN Tatisaurus 1 1 TRIT Bienotherium, etc. 11 10 122 NEWARK GROUP (PORTLAND FORMATION)

(Atlantic States, USA) Figures from Colbert (1970, pers. comm.) and Galton (1976). The fauna is too small (n=9) for the calculation of NORTHI AMERICA percentages.

MOENKOP I FORMAT ION No. No. PROC procoloplhonid 1 P'ROS Anchisaurus 2 (Ari/'ona, USA) TUEC Stegomus 2 Ammosaurus 2 Figures from Wielles (1947). There are two faunas (lower, CROC Stegomosuclius I itidet. 1 upper), but neither iS large enough (ni1+, 210) for the Laliulation of percetitages. No. INo. Lower Fauiia (Wupatki Menber) AMPII Stanocephalosaurus I f Upper Fauna (biolbrook Member) SCOTIUND AMPR Iiadrokkosaurus c.14 TRIL Anisodontosaurus Cyclotosaurus 3 TIIEC Arivonasaurus 2 Loss I EMOU-TH FORMATI ON Rhadalpgnathus 1 indet. 9 (Elgin, NE Scotland) Figures from Walker (1961, 1964, pers. coma.) and Benton (1977, 1981). PoPo AGIE FORMATION No. No. (Wlyoming, USA) iROC Leptopleuron c.30 Ornithosuchus 12 Figures from Dawley et al. (1979) and oueoie (1926). EOS Brachyrhinodon c.10 9 No. est. % RUIYN Hyperodapedoii 35 7 AMPII Metoposaurus ? 40+ THEC Stagonolepis 30 COEL Saltopus 1 TIIEC Paleorhlinus 1' SUMMARY A igistorhlinus ? 40+ 9Rutiodon I No. 1+ Poposaurus 2 5 RIYN Ilyperodapedoii 35 40 1leptasuchus 1 5 TIIEC Stagonolepis 30 35 DICY Placerias 2 10 Ornitliosuchus, etc. 21 24 COEL Sal topus I 1 DOCKUM FORMATION 837 (Texas, New Mexico, USA) Figures from Case (1932), Colbert (pers. comm.), Sawin (1947), and Westplial (1976). The Dockum Formation is divided into a lower, middle and upper fauna, btit detailed information on the GERMANY composition of each is not readily available, and the figures are combined. KNOLLENMERGEL No. est. % AMPII Metoposaurus 25+ 35 (Germany, France) TRIL Trilophosaurus ? 10 Figures from Iluene (1908, 1932). RIuYN undescribed 4 2 No. est. TI1EC Desmatosuchus 5+ 2 AMPII Cyclotosaurus c.15 20 Typothorax 15+ 22 Plagiosaurus ? 3 COEL Iirocompsognathus 4 5 Angistorii nus 30 P'ROS Plateosaurus 50+ 60 Poposatirus 1 1 Gresslyosaurus 10+ 15

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