PHALACROCORACIDAE, Reichenbach, 1849

Smith, ND & Ksepka, DT, 2015, Five well-supported fossil calibrations within the " Waterbird " assemblage (Tetrapoda, Aves), Palaeontologia Electronica 18 (1), pp. 1-21 : 11-12

STEM PHALACROCORACIDAE

Cormorants and Shags

Node Calibrated. This node represents the split between Phalacrocoracidae and their extant sister taxon, the Anhingidae . Phylogenetic analyses of both molecular ( Ericson et al., 2006; Hackett et al., 2008) and morphological ( Livezey and Zusi, 2006, 2007; Smith, 2010; Mayr, 2011b) data strongly support a sister-taxon relationship between Phalacrocoracidae and Anhingidae .

Fossil Taxa.? Borvocarbo stoeffelensis Mayr (2007)

Specimen. PW 2005/5022-LS (holotype). The holotype consists of a slightly dissociated, but still largely articulated, specimen, missing several vertebrae, the pelvis, and most of the left foot ( Mayr, 2007). The original description ( Mayr, 2007, p. 931) notes that while the specimen is currently reposited in Landesamt für Denkmalpflege Rheinland-Pfalz, Mainz, Germany, it will eventually be transferred to the Landessammlung für Naturkunde, Mainz, Germany.

Phylogenetic Justification. Phylogenetic justification is based on analyses of osteological data from Smith (2010). The analysis of Smith (2010) recovered three unambiguous synapomorphies of a? Borvocarbo stoeffelensis + Phalacrocoracidae clade, one of which exhibits no homoplasy on the most-parsimonious trees. Synapomorphies are represented in the mandible and pes of the skeleton. The synapomorphies supporting a? Borvocarbo stoeffelensis + Phalacrocoracidae clade, presented in the format: "Character(character state)", with boldface indicating no homoplasy in the character on the most-parsimonious trees, are: 91(1) Mandible, surangular, area at posteromedial attachment of M. adductus mandibulae externus profundus: presence of a single robust, knob-like tuberosity; 446(2) Pes, relative lengths of digits III and IV: digit IV significantly longer than digit III, often by nearly the entire distal phalanx of digit IV; 464(1) Pes, strong dorsoventral compression of phalanges of pes: present. In addition, there are two characters described by Mayr (2007) as suggestive of a close relationship between? Borvocarbo stoeffelensis and Phalacrocoracidae that were not included in the phylogenetic analysis of Smith (2010). These are a well-developed crista nuchalis sagittalis along the midline of the skull (absent in 'microcormorants') and an accessory transverse cranial crest present caudal to crista nuchalis transversa.

Minimum Age. 24.52 Ma

Soft Maximum Age. None specified.

Age Justification. The holotype of? Borvocarbo stoeffelensis was recovered from the fossil Lagerstätte Enspel, near Bad Marienberg in Westerwald, Rheinland-Pfalz, Germany. The Enspel deposits correspond to the upper Oligocene Mammal Paleogene reference level 28 ( Mertz et al., 2007). Laser fusion 40 Ar/ 39 Ar radiometric dating of volcanic feldspars from the lower and upper basaltic flows that bound the Enspel lacustrine deposits yielded ages of 24.56 ± 0.04 to 24.79 ± 0.05 Ma ( Mertz et al., 2007).

Phylogenetic position of total group Phalacrocoracidae and? Borvocarbo stoeffelensis . Mayr (2001) originally described a partial right foot, tarsometatarsus, and distal tibiotarsus to? Oligocorax sp. This specimen was later referred to? Borvocarbo stoeffelensis when this new taxon was erected by Mayr (2007). Although Mayr (2007, 2009b) has suggested that some of the characters supporting a? Borvocarbo stoeffelensis + Phalacrocoracidae could represent deeper synapomorphies of Phalacrocoracoidea ( Phalacrocoracidae + Anhingidae ) that are later lost in anhingas, the only phylogenetic analysis that has tested the relationships of? Borvocarbo stoeffelensis recovered it as the sister taxon to Phalacrocoracidae with fairly strong support (Smith 2010). Both morphological ( Cracraft, 1985; Bourdon et al., 2005; Livezey and Zusi, 2007; Smith, 2010) and molecular ( Ericson et al., 2006; Brown et al., 2008; Hackett et al., 2008) analyses have been consistent in recovering strong support for a Phalacrocoracidae + Anhingidae clade. The primary exceptions to this are the nuclear dataset based on intron 7 of the β-fibrinogen gene from Fain and Houde (2004) and the mitochondrial dataset of Kennedy et al. (2005), which both recover the aberrant grouping of Sulidae + Anhingidae , a result that may be due in part to long-branch attraction ( Kennedy et al., 2005).

Fossil record of total group Phalacrocoracidae and? Borvocarbo stoeffelensis . Potential older members of total group Phalacrocoracidae include Piscator tenuirostris , represented by a rostral section of the upper mandible and described by Harrison and Walker (1976b) as a cormorant; as well as a partial premaxilla from the early Oligocene Jebel Qatrani Formation of Egypt that was referred to the Phalacrocoracidae by Rasmussen et al. (1987). There are also undescribed cormorant-like specimens from the Eocene–Oligocene Quercy fissure fillings in France ( Mourer-Chauviré, 1982), and from the early Oligocene of Céreste, France ( Roux, 2002; Mayr, 2007), that have been suggested as representing the family. However, in most cases, these specimens are represented by extremely fragmentary material, and in all cases, their relationships have not been evaluated in a phylogenetic analysis.

The recently described Anhinga walterbolesi , a tarsometatarsus from the late Oligocene–early Miocene Etadunna Formation of South Australia, likely represents the oldest stem-member of Anhingidae (Worthy, 2012) . This specimen has the potential to be older than? Borvocarbo stoeffelensis . However, the referral of the type locality of Anhinga walterbolesi to the Etadunna Formation is based on the presence of the duck Pinpanetta tedfordi in these deposits, and the Etadunna Formation itself currently has an age range of 24–26 Ma, based on biostratigraphic and magnetostratigraphic data (Woodburne et al., 1994), making the minimum possible age younger than that for? Borvocarbo stoeffelensis . It is worth noting however, that this still suggests the oldest records for stem Phalacrocoracidae and close to the same time.

stem Anhingidae occur