Biogeographic Histories and Chronologies of Derived Iguanodontians

Asociación Paleontológica Argentina. Publicación Especial 7 ISSN 0328-347X VII International Symposium on Mesozoic Terrestrial Ecosystems: 107-111.Buenos Aires, 30-6-2001 Biogeographic histories and chronologies of derived iguanodontians Jason J. HEADl and Yoshitsugu KOBAYASHp.2 Abstract. The geographic distributions, chronology, and phylogenetic relationships of derived iguanodontians describe a biogeographic history of active intercontinental dispersal, which is tested via comparison with eustatic sea level fluctuations. A revised phylogeny of derived iguanodontians does not support a monophyletic Iguanodontidae, and produces a lineage culminating Hadrosauridae that is first recorded in the early Late Cretaceous of both Asia and North America. This distributions suggests dispersal between Asia and North America during the Late Cretaceous. Biogeographic hypotheses describ- ing isolation of North America during the Early Cretaceous are not supported by sea level data. Dispersal patterns among Late Cretaceous taxa are corroborated by short term regressive phases in sea levels, but no distinction can be made between hypotheses of dispersal in both directions, and repeated immigration of Asian taxa into North America. Keywords. Cretaceous. Biogeography. Dispersa!. Sea levels. Iguanodontia. Hadrosauridae. Introduction Sea level histories can be used as an independent test of biogeographic hypotheses. On a geologic The purpose of this analysis is to incorporate a re- timescale, trans-continental distributions of taxa are vised phylogeny of derived iguanodontian di- contro11edby tectonic processes, induding resultant nosaurs (Hadrosauriformes sensu Sereno, 1999)into sea level fluctuations, which affect areas of emer- a biogeographic and chronological history, and to gence. Eustatic transgressive and regressive events test this history against concurrent sea level fluctua- altemately prohibit and facilitate active dispersal tions. Specifically,we: (1) construct a phylogeny of across seaways and landbridges. A11else being derived iguanodontians; (2) use that phylogeny to equal, pattems of distribution should be correlated augment biogeographic histories, and; (3) test both to sea level changes. First occurrences of hypotheti- previous and new hypotheses of Early and Late cal immigrants should be preceded by short- or long- Cretaceous biogeography by comparison with sea term regressive events, and periods of isolation levels as an indicator of potential for dispersal. should coincide with transgressions. Iguanodontians are Laurasian in origin, with active dispersal and local extinctions driving trans-continental distributions (Brett-Surman, 1979; Norman Materials and methods 1998a). Iguanodontians dispersed into North Africa A phylogeny of derived iguanodontians (figure 1) at least once prior to the mid-Aptian (Taquet and was constructed from 12 taxa and 24 characters (ap- Russell, 1999),but our analysis focuses on Laurasian pendix 1). Critical assumptions of our phylogeny are biogeography. Timing and direction of dispersals are monophyly of Hadrosaurinae and Lambeosaurinae not well resolved for a11higher order taxa, but phy- (Weishampel and Homer, 1990). Claosaurus and logenetic relationships and first occurrences suggest Tanius are poorly known, but their geographic and both an ancestral center of origin and a minimum temporal distributions are significant. They were timing of immigration for a lineage. Currently, how- manua11yplaced in our phylogeny, and their posi- ever, no additional test of dispersal biogeography tions are more tentative than other taxa. The phy- has been proposed. logeny was placed in a geographic and chronological context, and the Cretaceous eustatic sea level curves 'Department of Geological Sciences and Shuler Museum of of Haq et al., 1987(figure 2) were used to test the re- Paleonlology, Soulhern Melhodisl Ul\iv~rsity, Dallas TX 75275, sultant biogeographic hypotheses. We use the USA. 'Fukui Prefectural Dinosaur Museum, 51-11 Terao, Muroko, Westem Interior Seaway as the indicator of potential Katsuyama, Fukui 911-8601 [apan. dispersal and isolation because: (1) transgressive ©Asociación Paleontológica Argentina 0328-347X/01$00.00+50 108 J.J. Head and Y.Kobayashi events including initial completion of the Seaway lguanodon (102Ma) are temporally constrained, and can be correlated to global sea levels to provide a measure of Ouranosaurus sea level required to isolate dispersal routes, and; (2) it is correlated to a well-sampled terrestrial fauna Fukui form (Jacobs and Winkler, 1998). Altirhinus Phylogeny and biogeography Probactrosaurus Our phylogeny is generally consistent with pub- Eolambia lished studies, with two exceptions: Our study does L...- Protohadros not support a monophyletic Iguanodontidae (Norman, 1998a), and Eolambia forms an unresolved Telmatosaurus trichotomy with Probactrosaurus and more derived L...- taxa, as opposed to being a basal lambeosaurine Gilmoreosaurus (Kirkland, 1998).We have achieved only limited res- L...- olution of the interrelationships among some taxa ------- Claosaurus due, in part, to both the small number of characters used in our analysis and missing data. However, this - ---- Tanius lack of resolution also mirrors controversy among more exhaustive analysis (e.g., Norman 1998a, "--- Bactrosaurus Sereno, 1999). A new taxon, the Fukui form, from [apan (?Berriasian-?Aptian) is significant because it ~L[Hadrosaurinae represents the first occurrence of characteristics pre- Lambeosaurinae viously considered diagnostic of more derived clades (Kobayashi and Azuma, 1999), and because it in- Figure 1. Strict consensus of 13 trees (tree length = 37 steps, Cl. = creases the diversity of Early Cretaceous iguanodon- .70, and R.l. = .65) of ingroup relationships determined via a tians. The low resolution of interrelationships of heuristic search in PAUP 3.1 (Swofford, 1993),exclusive of Tanius Iguanodon, Ouranosaurus, Altirhinus, and the Fukui and Claosaurus (dashed lines). Camptosaurus, Dryosaurus, and Tenontosaurus were used as successive outgroups. form limit biogeographic reconstructions. However, the phylogenetic polytomy of these taxa does not sig- These distributions suggest a biogeographic pat- nificantly alter current biogeographic hypotheses. tern of alternating intervals of dispersal between Norman (1998a) described a history of Laurasiatic North America and Asia from the beginning of the dispersal of Iguanodon prior to the Hauterivian, fol- Late Cretaceous to the Turonian, but the directions of lowed by North American isolation and European- dispersal are not constrained. Intervals of dispersal Asian connection by the Aptian. Isolation of North are separated by periods of endemism and in situ America is considered to have persisted until the lat- evolution. Hypotheses of in situ evolution are sup- est Albian (Kirkland et al., 1997), based on North ported by short phylogenetic distances that are re- American faunal endemicity. stricted to brief periods of time, and geographic con- Systematic relationships of more derived taxa currence shared between Eolambia and Protohadros placed in a chronological and biogeographic frame- (and possibly Claosaurus) and between work represent a progressive transition series culmi- Gilmoreosaurus, Bactrosaurus, and Tanius. nating in Hadrosauridae (sensu Forster, 1997). This Geographic distributions indica te a late Early grade begins with Probactrosaurus in the Early Cretaceous dispersal of Eolambia into North America, Cretaceous of Asia, and with early-middle Late with subsequent divergence of Protohadros and Cretaceous Eolambia and Protohadros lin North Claosaurus, and a second migration into Asia prior to America, and with a series of Asian hadrosauroids the Turonian, with subsequent divergence of (Godefroit et al., 1998)approximately coeval with the hadrosauroids, followed by Hadrosauridae. The first occurrences of Hadrosauridae in the Turonian of phylogenetic status of Telmatosaurus requires an ad- North America and Asia (Weishampel and Horner, ditional dispersal back into Asia, between the first oc- 1990;Pasch, 1995). Ages of Asian hadrosauriods are currences of Protohadros and Claosaurus. The system- ambiguous, but the first occurrence of atic status of Claosaurus is tentative, however, and the Hadrosauridae minimally constrains divergence necessity of additional dispersal into Asia can only be times (MDTs Weishampel et al., 1993) of successive determined once the relative positions of sister taxa to the base of the Turonian. Telmatosaurus and Claosaurus are resolved. A.P.A. PublicaciónEspecial7,2001 Biogeography of derived iguanodontians 109 Distributions of hadrosaurids indicate Laurasian dis- dispersal routes, resulting in intercontinental faunal persals by the Turonian, followed by migration into similarity. There are six intervals in the Late South America by the Campanian, and Antarctica by Cretaceous when sea levels fall below completion of the Maastrichtian (Brett-Surman, 1977; Case et al., the WIS, presumably reflecting intervals of greater 1998). likelihood for intercontinental dispersal, and fauna s should represent alternating periods of endemicity Comparison with sea levels and immigration. Lowered Early Cretaceous sea levels are inconsis- Long- and short term trends in Cretaceous sea tent with hypotheses of isolation and endemicity levels are described in figure 2. Sea levels increased during the Early Cretaceous. We offer two alternate during the Albian, with a maximum transgressive explanations: (1)

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