def reduce_to_contemporaneous(ts):
    """
    Simplify the ts to only the contemporaneous samples, and return the new ts + node map
    """
    samples = ts.samples()
    contmpr_samples = samples[ts.tables.nodes.time[samples] == 0]
    return ts.simplify(
        contmpr_samples, map_nodes=True, keep_unary=True, filter_populations=False,
        filter_sites=False, record_provenance=False, filter_individuals=False)