DOI: 10.5061/dryad.51j0j
title: Data from: Anatomy, systematics, paleoenvironment, growth, and age of the sauropod dinosaur Sonorasaurus thompsoni from the Cretaceous of Arizona, USA

description: Sauropod dinosaurs are rare in the Cretaceous North American fossil record
 in general and are absent from that record for most of the Late
 Cretaceous. Sonorasaurus thompsoni from the Turney Ranch Formation of the
 Bisbee Group of Arizona, USA, potentially represents one of the youngest
 sauropods before their ca. 30-million-year-long hiatus from the record.
 The anatomy of Sonorasaurus has only been briefly described, its taxonomic
 validity has been questioned, several hypotheses have been proposed
 regarding its phylogenetic relationships, and its life history, geologic
 age, and reported paleoenvironment are ambiguous. Herein we assess the
 systematics, paleoenvironment, life history, and geologic age of
 Sonorasaurus based on firsthand observation, bone histology, and fieldwork
 in the holotypic quarry and environs. The validity of S. thompsoni is
 substantiated by autapomorphies. Cladistic analysis firmly places it
 within the Brachiosauridae, in contrast to results of some recent
 analyses. Bone histology suggests that the only known exemplar of
 Sonorasaurus grew slowly and sporadically compared to other sauropods and
 was approaching its adult size. In contrast with previous assessments of a
 coastal/estuarine paleoenvironment for the Turney Ranch Formation, our
 sedimentological and plant macrofossil data indicate that Sonorasaurus
 lived in a semiarid, low relief evergreen woodland that received highly
 variable (perhaps seasonal) precipitation. We obtained detrital zircons
 from the holotypic quarry for U-Pb dating, which only yielded
 Barremian-aged and older grains, whereas other radiometric and
 biostratigraphic data suggest that the sediments at the quarry were
 deposited near the Albian-Cenomanian boundary. Sonorasaurus is
 taxonomically valid, represents one of the geologically youngest
 brachiosaurid sauropods, and inhabited a harsh inland evergreen-dominated
 woodland environment that limited its growth. A review of other Bisbee
 Group dinosaurs suggests that its fauna, although poorly sampled, exhibits
 broad similarity to those from coeval North American horizons, reinforcing
 the apparent faunal homogeneity at the time.
description: FileS1_AgeDataSupplemental Data 1. Microsoft Excel file containing age data from U/Pb detritral zircon dating. Two samples were analyzed: SONO–MS from a site near the quarry, which yielded a youngest single–grain age of 149.3 +/– 4 Ma and SONO–CA from the Sonorasaurus holotype quarry, which yielded a youngest single–grain age of 129.2 +/– 9.9 Ma.FileS2_DorsalRibSupplemental Data 2. Dorsal rib of a titanosauriform sauropod dinosaur (ASDM 807) in posterior view, found in the ‘middle’ Cretaceous Turney Ranch Formation approximately 0.6 km from the holotypic Sonorasaurus quarry, Arizona, USA. Cross sections along the shaft are indicated.FileS3_maxillaSupplemental Data 3. Skin of exterior bone belonging to a sauropod maxilla from the Turney Ranch Formation.FileS4_TheropodFemurSupplemental Data 4. Theropod femur (ASDM 2111) found in the ‘middle’ Cretaceous Turney Ranch Formation approximately 300 m from the holotypic Sonorasaurus quarry, Arizona, USA: 1, medial; 2, posterior; 3, lateral; 4, anterior views. Abbreviation: ftr=fourth trochanter.File S5 Sonorasaurus matrixSupplemental Data 5. Nexus file containing character-taxon matrix used in the cladistic analysis.FileS5_DEmicSonorasaurusMatrix