介形类系统分类与起源演化的形态、分子和化石证据

介形类(Ostracoda)因其丰富的化石记录和广布的海陆现生代表类群,而被认为是进化生物学中研究生物多样性产生机制和演变历程的颇具潜力的重要模式生物。介形类在甲壳亚门中的谱系发生位置、起源及其内部各类群间的系统关系还存在诸多争议。基于其体制构造的形态学特征,介形类被归入甲壳亚门下的颚足纲(Maxillopoda),但来自18S rDNA序列数据分析却显示Maxillopoda不是单系群。基于化石记录和壳体形态特征,高肌虫(Bradoriida)长期以来被认为是介形类的一个祖先类群,但保存有软躯体的早寒武世化石的研究表明,Bradoriida不是介形类甚至可能也不属于甲壳类。不同的研究者所强调的壳体和肢体形态特征各异,导致介形类最大的现生类群速足目(Podocopida)的四个超科之间的关系也存在诸多推测。壳体和肢体特征在系统演化意义上的不兼容,需要分子生物学等证据的介入。分子、形态和化石证据的积累及各种信息整合是系统演化研究的必然趋势。     

MOLECULAR PHYLOGENY OF THE GENUS CAULERPA (CAULERPALES,CHLOROPHYTA) INFERRED FROM CHLOROPLAST tufA GENE1

The genus Caulerpa consists of about 75 species of tropical to subtropical siphonous green algae. To better understand the evolutionary history of the genus, a molecular phylogeny was inferred from chloroplast tufA sequences of 23 taxa. A sequence of Caulerpella ambigua was included as a potential outgroup. Results reveal that the latter taxon is, indeed, sister to all ingroup sequences. Caulerpa itself consists of a series of relatively ancient and species‐poor lineages and a relatively modern and rapidly diversifying clade, containing most of the diversity. The molecular phylogeny conflicts with the intrageneric sectional classification based on morphological characters and an evolutionary scheme based on chloroplast ultrastructure. High bootstrap values support monophyly of C. mexicana, C. sertularioides, C. taxifolia, C. webbiana, and C. prolifera, whereas most other Caulerpa species show para‐ or polyphyly.     

PHYLOGENETIC SYSTEMATICS OF THE ULVACEAE (ULVALES,ULVOPHYCEAE) USING CHLOROPLAST AND NUCLEAR DNA SEQUENCES1

Systematic hypotheses for the Ulvaceae were tested using phylogenetic analysis of sequences for the gene encoding the large subunit of RUBISCO, small subunit rDNA and a combined data matrix. Representatives of eight putative ulvaceous genera and twelve additional taxa from the Ulvophyceae and Trebouxiophyceae were included in analyses using maximum parsimony and maximum likelihood criteria. Molecular data supported hypotheses for the Ulvaceae that are based on the early development of vegetative thalli and motile cell ultrastructure. Ulvaceae sensu Floyd and O'Kelly, including Percursaria Bory de Saint‐Vincent, Ulvaria Ruprecht and a complex of closely related species of Chloropelta Tanner, Enteromorpha Link and Ulva L. was supported; however, monophyly of Enteromorpha and Ulva was not supported. The Ulvales and Ulotrichales sensu Floyd and O'Kelly were monophyletic. Blidingia Kylin and Kornmannia Bliding were allied with the former and Capsosiphon Gobi with the latter, although relationships among these and other taxa in these orders remain uncertain. The Ulvales are characterized by an isomorphic life history pattern, gametangia and sporangia that are identical in structure and development, motile cells with bilobed terminal caps and proximal sheaths consisting of two equal subunits. Method of motile cell release and the gross morphology of vegetative thalli are not systematically reliable characters.     

A phylogeny of the flowering plant family Apiaceae based on chloroplast DNA rpl16 and rpoC1 intron sequences: towards a suprageneric classification of subfamily Apioideae

The higher level relationships within Apiaceae (Umbelliferae) subfamily Apioideae are controversial, with no widely acceptable modern classification available. Comparative sequencing of the intron in chloroplast ribosomal protein gene rpl16 was carried out in order to examine evolutionary relationships among 119 species (99 genera) of subfamily Apioideae and 28 species from Apiaceae subfamilies Saniculoideae and Hydrocotyloideae, and putatively allied families Araliaceae and Pittosporaceae. Phylogenetic analyses of these intron sequences alone, or in conjunction with plastid rpoC1 intron sequences for a subset of the taxa, using maximum parsimony and neighbor-joining methods, reveal a pattern of relationships within Apioideae consistent with previously published chloroplast DNA and nuclear ribosomal DNA ITS based phylogenies. Based on consensus of relationship, seven major lineages within the subfamily are recognized at the tribal level. These are referred to as tribes Heteromorpheae M. F. Watson & S. R. Downie Trib. Nov., Bupleureae Spreng. (1820), Oenantheae Dumort. (1827), Pleurospermeae M. F. Watson & S. R. Downie Trib. Nov., Smyrnieae Spreng. (1820), Aciphylleae M. F. Watson & S. R. Downie Trib. Nov., and Scandiceae Spreng. (1820). Scandiceae comprises subtribes Daucinae Dumort. (1827), Scandicinae Tausch (1834), and Torilidinae Dumort. (1827). Rpl16 intron sequences provide valuable characters for inferring high-level relationships within Apiaceae but, like the rpoC1 intron, are insufficient to resolve relationships among closely related taxa.     

INTRON REVEALED BY NUCLEOTIDE SEQUENCE OF LARGE SUBUNIT OF RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE/OXYGENASE FROM CODIUM FRAGILE (CHLOROPHYTA): PHYLOGENETIC ANALYSIS1

The coding sequence for the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) from Codium fragile (Suringar) Hariot chloroplast DNA is 1428 bp in length and contains a 1813-bp group II intron. The only other organisms in which introns have been found in the rbcL gene are Euglena and Astasia. The Codium intron likely had a separate origin from the Euglena and Astasia introns, based on comparisons of intron sizes and sequences. Phylogenetic analyses of rbcL nucleotide and amino acid sequences place Codium between Chlorella and two Chlamydomonas spp., indicating that the Chlorophyceae may be polyphyletic.     

CLOSTERIUM MONILIFERUM-EHRENBERGII (CHAROPHYCEAE, CHLOROPHYTA) SPECIES COMPLEX VIEWED FROM THE 1506 GROUP I INTRON AND ITS2 OF NUCLEAR rDNA

To assess phylogenetic relationships and speciation modes in Closterium , we sequenced two noncoding regions of the nuclear ribosomal cistron, the 1506 group I intron in small subunit and the internal transcribed spacer 2, for a total of 58 strains of the Closterium moniliferum-ehrenbergii species complex. These include both homothallic and heterothallic C. moniliferum Erenberg ex Ralfs v. moniliferum , heterothallic C. moniliferum v. submoniliferum (Woronichin) Krieger, and heterothallic C. ehrenbergii Meneghini ex Ralfs that can be divided into several mating groups. We found no or very little sequence divergence within single mating groups of C. ehrenbergii and among all heterothallic strains of C. moniliferum v. moniliferum or C. moniliferum v. submoniliferum. Nevertheless, sequence divergence was much greater between those mating groups of C. ehrenbergii and also among the three traditional taxa . Maximum parsimony and maximum likelihood analyses showed that the taxon C. ehrenbergii was not monophyletic. The two varieties of C. moniliferum appeared as a sister clade to certain mating groups of C. ehrenbergii . Among the clades that were recovered in different trees by maximum parsimony and maximum likelihood analyses, we consistently found two large conspicuous clades: clade I consisted of mating groups A, B, C, H, K, and L of C. ehrenbergii whose zygospores have smooth-walls, and clade II contained the mating groups D, E, I, J, and S whose zygospores are scrobiculate. Phylogenetic incongruences observed are discussed from the viewpoints of the different molecular nature of the group I intron and internal transcribed spacer 2, as well as putative rapid diversification of the mating groups and probable ancient ancestral hybridization.     

MOLECULAR AND PHYLOGENETIC CHARACTERIZATION OF PHORMIDIUM SPECIES (CYANOPROKARYOTA) USING THE CPCB‐IGS‐CPCA LOCUS1

The accurate determination of species of Cyanoprokaryota/Cyanophyceae has many important applications. These include the assessment of risk with regard to blooms in water reservoirs as well as the identification of species capable of producing valuable bioactive compounds. Commonly, Cyanoprokaryota are classified based on their morphology. However, morphological criteria are not always reliable because they may change, for example, due to environmental factors. Thus, genetic and molecular analyses are a promising additional approach, but their application has so far been limited to relatively few genera. In light of this, we present here the first characterization of species and strains of the genus Phormidium Kütz. based on the cpcB‐IGS‐cpcA locus of the phycocyanin operon. In phylogenetic analyses using deduced amino acid sequences of the cpcB‐cpcA regions, Phormidium was found to be polyphyletic. This analysis appeared to be dominated by the cpcB region, which is characterized by a relatively high percentage of informative substitutions. The percentage of variable positions within the cpcB‐IGS‐cpcA locus overall was 16.5%, thereby indicating a level of divergence remarkably higher than that reported for Nodularia and Arthrospira in previous studies relying on cpcB‐IGS‐cpcA. Further, alignment of informative nucleotide substitutions in the cpcB‐IGS‐cpcA sequences revealed a mosaic distribution, which may be indicative of genetic recombination events. Finally, the length and sequences of the IGS region alone proved useful as markers to differentiate the cyanobacterial genus Phormidium. However, whether the IGS region per se is sufficiently discriminatory to differentiate between Phormidium species or even strains requires further investigation using newly identified Phormidium sequence data.     

活化石植物－－苏铁树叶绿体DNA分子中的核糖核苷酸

随着分子生物学的深入发展,科学工作者对脱氧核糖核酸(DNA)的研究也更加深入。近年来发现一些植物叶绿体DNA(cpDNA)、动物线粒体DNA(mtDNA)分子中含有少数核糖核苷酸。其中对豌豆,菠菜和莴苣叶绿体DNA分子中的核糖核苷酸研究较多,而且比较详细。研究这个问题,使用的方法是碱(KOH)或核糖核酸酶(RNase)处理cpDNA。如果DNA分     

ORIGINS OF GENOTYPIC VARIATION IN NORTH AMERICAN DANDELIONS INFERRED FROM RIBOSOMAL DNA AND CHLOROPLAST DNA RESTRICTION ENZYME ANALYSIS

Restriction enzyme analysis of ribosomal DNA (rDNA) and chloroplast DNA (cpDNA) is used to assess the relative contribution of hybridization and mutation as sources of genotypic variation in weedy asexual dandelions, with focus on the dandelion flora of North America. Of 318 North American dandelions surveyed, 145 rDNA-cpDNA clones are detected. The combined rDNA-cpDNA genotypes show that most of the polymorphic rDNA and cpDNA restriction sites or lengths in these plants are also present in weedy asexual dandelions collected from natural populations in Europe and in asexual and diploid taxa (microspecies) chosen to represent diverse Eurasian members of the genus. However, of 222 combined rDNA-cpDNA genotypes found in 427 asexual plants surveyed, only 9 genotypes are found in both North American and Eurasian dandelions. Two rDNA and three cpDNA characters are unique to individual plants in North America and are consistent with mutational origins of genotypic variation in asexual lineages. But the array of genotypic diversity, characterized by different combinations of the rDNA and cpDNA characters, show that multiple hybridization events are a more important source of genotypic variation than mutation in the asexual polyploids. The rDNA and cpDNA data also indicate polyphyletic origin of several asexual Taraxacum taxa.     

RECONSTRUCTION OF THE EVOLUTION OF REPRODUCTIVE CHARACTERS IN PONTEDERIACEAE USING PHYLOGENETIC EVIDENCE FROM CHLOROPLAST DNA RESTRICTION-SITE VARIATION

We reconstructed the phylogenetic history of Pontederiaceae using chloroplast DNA restriction-site variation from approximately two-thirds of the species in this family of aquatic monocotyledons. The molecular phylogeny was used to evaluate hypotheses concerning the evolution of reproductive characters associated with the breeding system. The family has four main genera, two of which (Eichhornia and Pontederia) have tristylous, predominantly outcrossing species, while two (Monochoria and Heteranthera) have enantiostylous taxa. Self-incompatibility is restricted to some but not all tristylous species. In Eichhornia and Pontederia, predominantly selfing species with small monomorphic flowers (homostyly) have been hypothesized to result from the multiple breakdown of tristyly. Restriction-site variation provided a well supported phylogeny of ingroup taxa, enabling the mapping of reproductive characters onto trees. Two contrasting optimization schemes were assessed, differing in the relative weights assigned to shifts in character states. The reconstructed sequence of floral character-state change was used to assess competing hypotheses concerning the origin and breakdown of tristyly, and the relationships between tristylous and enantiostylous syndromes. Our results indicate that the class of optimization scheme used was the most critical factor in reconstructing character evolution. Despite some topological uncertainties and difficulty in reconstructing the primitive floral form in the family, several broad conclusions were possible when an unordered, unequally-weighted optimization scheme was used: (1) tristyly originated either once or twice, while the occurrence of enantiostyly in Monochoria and Heteranthera was always found to have independent origins; (2) tristyly has repeatedly broken down leading to selfing, homostylous taxa; and (3) self-incompatibility probably arose after the origin of floral trimorphism, a sequence of events that conflicts with some evolutionary models.     

THE EVOLUTION OF DIAPAUSE IN THE KILLIFISH FAMILY RIVULIDAE (ATHERINOMORPHA,CYPRINODONTIFORMES): A MOLECULAR PHYLOGENETIC AND BIOGEOGRAPHIC PERSPECTIVE

Phylogenetic relationships within the family Rivulidae (order Cyprinodontiformes) are investigated using 1972 aligned base pairs of mitochondrial DNA (mtDNA) for samples representing 66 species. Genes analyzed include those encoding the 12S ribosomal RNA; transfer RNAs for valine, glutamine, methionine, tryptophan, alanine, asparagine, cysteine, and tyrosine; complete NADH dehydrogenase subunit II; and part of cytochrome oxidase I. Parsimony analysis of the aligned mtDNA sequences results in a single most parsimonious tree. The phylogeny reveals two independent origins of developmental diapause within the family Rivulidae. It is unlikely that diapause evolved de novo in each group, suggesting that the presence or absence of diapause is the result of developmental switches between alternative stabilized pathways. Phylogeny of the family Rivulidae shows high concordance with predictions derived from the geological history of South America and Central America. Basal lineages in the rivulid phylogeny are distributed primarily on geologically old areas, whereas more nested lineages occur in geologically younger areas. However, there is little concordance between the molecular phylogeny and currently available morphological hypotheses and existing taxonomies. Based on the mtDNA phylogeny, the genera Pterolebias, Rivulus, Pituna, and Plesiolebias are considered nonmonophyletic and warrant taxonomic reassessment.     

BIOCHEMICAL TAXONOMY AND MOLECULAR PHYLOGENY OF THE GENUS CHLORELLA SENSU LATO (CHLOROPHYTA)

A multimethod approach was used to characterize unicellular green algae that were traditionally assigned to the genus Chlorella Beijerinck and to resolve their phylogenetic relationships within the Chlorophyta. Biochemical, physiological, and ultrastructural characters, together with molecular data such as DNA base composition and DNA hybridization values, were compared with a molecular phylogeny based on complete 18S rRNA sequences. Our results show that Chlorella taxa are dispersed over two classes of chlorophytes, the Trebouxiophyceae and the Chlorophyceae. We propose that only four species should be kept in the genus Chlorella (Chlorophyta, Trebouxiophyceae): C. vulgaris Beijerinck, C. lobophora Andreyeva, C. sorokiniana Shih. et Krauss, and C. kessleri Fott et Nováková. Common characteristics of these taxa are glucosamine as a dominant cell wall component and the presence of a double thylakoid bisecting the pyrenoid matrix. Norspermine, norspermidine, and secondary carotenoids are never produced. Other "Chlorella" species belong to different taxa within the Trebouxiophyceae ( "C." protothecoides = Auxenochlorella protothecoides [Krüger] Kalina et Punčochářová, "C." ellipsoidea, "C." mirabilis, "C." saccharophila, and "C." luteoviridis ) and Chlorophyceae ( "C." zofingiensis and "C." homosphaera = Mychonastes homosphaera Kalina et Punčochářová). The latter taxa can easily be recognized by the production of secondary carotenoids under nitrogen-deficient conditions.     

MOLECULAR SYSTEMATICS OF THE FLORIDEOPHYCEAE (RHODOPHYTA) USING NUCLEAR LARGE AND SMALL SUBUNIT rDNA SEQUENCE DATA

Sequence data are presented for approximately 85% of the nuclear large subunit (LSU) rDNA gene for one member of the Bangiophyceae and 47 members of the Florideophyceae, the latter representing all but one of the currently recognized florideophyte orders. Distance, parsimony, and maximum likelihood analyses of these data were used to generate phylogenetic trees, and bootstrap resampling was implemented to infer robustness for distance and parsimony results. LSU phylogenies were congruent with published nuclear small subunit (SSU) rDNA results in that four higher level florideophyte lineages were resolved: lineage 1, containing the order Hildenbrandiales; lineage 2, recovered only under distance analysis, composed of the orders Acrochaetiales, Balliales, Batrachospermales, Corallinales, Nemaliales, Palmariales, and Rhodogorgonales; lineage 3, containing the Ahnfeltiales; and lineage 4, composed of the orders Bonnemaisoniales, Ceramiales, Gelidiales, Gigartinales, Gracilariales, Halymeniales, Plocamiales, and Rhodymeniales. Analyses were also performed on a combined LSU–SSU data set and an SSU-only data set to account for differences in taxon sampling relative to published studies using this latter gene. Combined LSU–SSU analyses resulted in phylogenetic trees of similar topology and support to those obtained from LSU-only analyses. Phylogenetic trees produced from SSU-only analyses differed somewhat in particulars of branching within lineages 2 and 4 but overall were congruent with the LSU-only and combined LSU–SSU results. We close with a discussion of the phylogenetic potential that the LSU has displayed thus far for resolving relationships within the Florideophyceae.     

MOLECULAR DELINEATION OF SPECIES AND SPECIES RELATIONSHIPS IN THE RED ALGAL AGAROPHYTES GRACILARIOPSIS AND GRACILARIA (GRACILARIALES)1

Delineation of species in the economically important agarophyte genera Gracilaria and Gracilariopsis has proven extremely difficult using available morphological characteristics. In this study, we examine the usefulness of two transcribed spacers for molecular systematic studies of these genera. The polymerase chain reaction was used to amplify the internal transcribed spacers (ITSs) and the intervening 5.8S ribosomal DNA of the nuclear ribosomal repeat region. In addition, a plastid spacer region and flanking regions of coding genes were amplified from the RUBISCO operon. Both regions were sequenced for individuals and populations of Gracilariopsis lemaneiformis (Bory) Dawson, Acleto, et Foldvik to determine the usefulness of these spacers in delimiting populations. These studies reveal that there is as much variation among individuals of a population as there is between individuals of geographically separate populations. In addition, the ITS spacer regions were compared between different species of Gracilariopsis and Gracilaria. The nuclear ITS spacer region is conserved at a species level in both genera and provides phylogenetically informative characters that can be used to examine species interrelationships among relatively closely related taxa. However, because of the difficulties of aligning this entire region among species from the two genera, the ITS region is not useful for examining intergenera relationships. ITS interspecies sequence comparisons indicate that Gracilariopsis lemaneiformis from California is significantly different from G. lemaneiformis from China and that a species of Gracilariopsis from Peru is more closely related to G. lemaneiformis from North Carolina than it is to the other Gracilariopsis species examined. In addition, these studies indicate that Gracilaria chilensis Bird, McLachlan, et Oliveira from New Zealand and Gracilaria tenuistipitata Chang et Xia from southeast Asia are as closely related as are Gracilaria verrucosa (Hudson) Papenfuss, G. pacifica Abbott, and Gracilaria robusta Kylin. Phylogenetic analysis of aligned plastid spacer sequences from Gracilaria and Gracilariopsis taxa provide similar conclusions about species relationships.     

PARSIMONY,MOLECULAR EVOLUTION,AND BIOGEOGRAPHY: THE CASE OF THE NORTH AMERICAN GIANT SALAMANDER

To draw biogeographic conclusions about the Central Highlands region of the United States, we reconstructed the phylogeny of hellbender (Cryptobranchus alleganiensis) populations from restriction-site variation in mtDNA. We were unable to root the phylogeny using an outgroup and therefore could not weight restriction-site gains more heavily than site losses. As a result, maximum parsimony results in low phylogenetic resolution because of high levels of homoplasy in the data set. Use of a recently published algorithm based on an explicit model of molecular evolution yielded much greater resolution of the mtDNA relationships. This phylogeny indicates the two subspecies of hellbenders are paraphyletic with respect to one another. Hellbenders found in the southern Ozarks (C. a. bishopi) are either most closely related to populations of C. a. alleganiensis inhabiting the Tennessee River drainage or are so divergent that phylogenetic affinities are undetectable. Extremely low levels of divergence among mtDNA haplotypes found in populations from Pennsylvania, Indiana, Illinois, and the northern Missouri Ozarks suggest a recent, probably post-Pleistocene, invasion of this region from a refugium in one of these areas. Biogeographic hypotheses of the causes and timing of hellbender distributions differ significantly from those postulated from analyses of fish species relationships. Possible reasons for the discrepancy are discussed.     

A SPECIATIONAL HISTORY OF “LIVING FOSSILS”: MOLECULAR EVOLUTIONARY PATTERNS IN HORSESHOE CRABS

Horseshoe crabs' exceptional morphological conservatism over the past 150 My has led to their reputation as “living fossils,” but also has served to obscure phylogenetic relationships within the complex. Here we employ nucleotide sequences from two mitochondrial genes to assess molecular evolutionary rates and patterns among all extant horseshoe crab species. The American species Limulus polyphemus proved to be the sister taxon to a clade composed of the Asiatic species Tachypleus gigas, T. tridentatus, and Carcinoscorpius rotundicauda, whose relationships inter se were not resolved definitively. Both absolute and relative rate tests suggest a moderate slowdown in sequence evolution in horseshoe crabs. Nonetheless, dates of the lineage separations remain uncertain primarily because of reservations about molecular-clock calibrations resulting from large rate variances at examined loci across Arthropods and other animal lineages, as inferred in this and prior studies. Thus, ironically, separation dates as estimated by molecular evidence in general may remain most insecure in taxonomic groups for which such information is needed most—those lacking strong biogeographic or fossil benchmarks for internal-clock calibrations. In any event, the current results show that large numbers of molecular characters distinguish even these most morphologically conservative of organisms. Furthermore, comparisons against previously published mitochondrial sequence data in the morphologically dynamic hermit crab–king crab complex demonstrates that striking heterogeneity in levels of morphotypic differentiation can characterize Arthropod lineages at similar magnitudes of molecular divergence.     

麂属(Muntiacus)动物MDR-1基因序列分析及其分子进化关系

对麂属（Muntiacus)中的3种动物：赤麂（M.muntjak)(2n-6♀,7♂）,小麂（M.reevesi)(2n=46),黑麂（M.crinifrons(2n=8♀,9♂）MDR－1基因（multidrug resistance,多药耐药基因）726bp左右的片段进行了序列分析并根据序列信息建立分子系统树,同时探讨了这3种动物的起源,分类地位及进化关系。     

中国化石两栖类和有鳞类研究进展:过去15年回顾

过去15年中,我国的化石两柄类和有鳞类研究取得了加速进展。共报道了16种两栖类和22种有鳞类,其中15种两栖类和11种有鳞类为新种,包括我国最古老的四足动物宁夏晚泥盆世的潘氏中国螈,湖北中三叠世的大型全椎两栖类宽头远安鲵,东北晚侏罗世/早白垩世的多种滑体两栖类(如无尾类三燕丽蟾和北票中蟾,有尾类奇异热河螈和东方塘螈),华北占近纪的蜥蜴类(如淅川短齿蜥和垣曲响蜥),以及内蒙古晚白垩世的多种蜥蜴类等。部分旧属种被修订,多与热河生物群的种类有关,如细小矢部龙过去依据幼年个体被认为是一种小型细弱的蜥蜴,新材料显示它实为大型强壮的种类。一批新的两栖类和有鳞类重要化石点被发现,如辽宁北票市四合屯、陆家屯和葫芦岛市水口子,河北丰宁县炮仗沟以及内蒙古宁城县道虎沟和乌拉特后旗巴彦满达呼。我国晚侏罗世/早白垩世两栖类和有鳞类对研究滑体两栖类和有鳞类相关类群的起源和早期演化提供了重要信息,但系统发育研究工作尚处于初级阶段。     

A LONG-SNOUTED DYROSAURID (CROCODYLIFORMES, MESOEUCROCODYLIA) FROM THE PALEOCENE OF MOROCCO: PHYLOGENETIC AND PALAEOBIOGEOGRAPHIC IMPLICATIONS

Abstract:  New material of a long-snouted dyrosaurid has been discovered in the Paleocene of Morocco. It consists of a well-preserved skull with embedded mandible and four dorsal vertebrae. The particularly elongate snout, proportionally the longest of all known dyrosaurids, allows precise identification of this material as Atlantosuchus coupatezi Buffetaut, 1979 a , and presentation of an emended diagnosis for this species previously known only from a mandibular symphysis. A phylogenetic analysis of the dyrosaurids indicates a close relationship between A. coupatezi and Rhabdognathus . It also confirms a previous hypothesis that Congosaurus is distinct from Hyposaurus . It is more closely related to Atlantosuchus than Hyposaurus . The analysis also allows palaeobiogeographic interpretations to be made. Dyrosaurids ranged from North Africa to other areas. They were rare during the Maastrichtian and endemic to each continent at this time. Competition with large marine reptiles, such as mosasaurs, limited their dispersal during the Late Cretaceous. The disappearance of these rivals during the 'K-T crisis' enabled their diversification and widespread dispersal during the Paleocene, with the same genera present on several continents.